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BEGIN:VEVENT
SUMMARY:Progress toward simulating binary black holes with SpECTRE
DTSTART;VALUE=DATE-TIME:20220727T100000Z
DTEND;VALUE=DATE-TIME:20220727T101500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-711@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Geoffrey Lovelace (California State University\, Ful
lerton)\nhttps://indico.tpi.uni-jena.de/event/224/contributions/711/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/711/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What happened this week?
DTSTART;VALUE=DATE-TIME:20220729T104500Z
DTEND;VALUE=DATE-TIME:20220729T110000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-535@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Sebastiano Bernuzzi (Jena FSU)\nhttps://indico.tpi.u
ni-jena.de/event/224/contributions/535/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/535/
END:VEVENT
BEGIN:VEVENT
SUMMARY:What is Numerical Relativity
DTSTART;VALUE=DATE-TIME:20220725T123000Z
DTEND;VALUE=DATE-TIME:20220725T130000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-534@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Bernd Bruegmann ()\nhttps://indico.tpi.uni-jena.de/e
vent/224/contributions/534/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/534/
END:VEVENT
BEGIN:VEVENT
SUMMARY:UV completions\, fixing the equations\, and nonlinearities in k-es
sence
DTSTART;VALUE=DATE-TIME:20220729T090000Z
DTEND;VALUE=DATE-TIME:20220729T091500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-562@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Guillermo Lara (SISSA)\nScalar-tensor theories with
first-derivative self interactions\, known as k-essence\, may provide inte
resting phenomenology on cosmological scales. On smaller scales\, however\
, initial value evolutions (which are crucial for predicting the behavior
of astrophysical systems\, such as binaries of compact objects) may run in
to instabilities related to the Cauchy problem becoming potentially ill-po
sed. Moreover\, on local scales the dynamics may enter in the nonlinear re
gime\, which may lie beyond the range of validity of the infrared theory.
Completions of k-essence in the ultraviolet\, when they are known to exist
\, mitigate these problems\, as they both render Cauchy evolutions well-po
sed at all times\, and allow for checking the relation between nonlinearit
ies and the low energy theory's range of validity. In this talk\, I will p
resent an exploration of these issues explicitly by considering an ultravi
olet completion to k-essence and performing vacuum 1+1 dynamical evolution
s within it. I will argue that these results are consistent with the low-e
nergy theory\, and will compare with evolutions obtained with the low-ener
gy theory suitably deformed with a phenomenological "fixing the equations"
approach.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/562/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/562/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nonlinear evolution of black holes in Quadratic Gravity
DTSTART;VALUE=DATE-TIME:20220729T084500Z
DTEND;VALUE=DATE-TIME:20220729T090000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-558@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Aaron Held (Jena University and The Princeton Gravit
y Initiative)\nI present the first numerical-relativity simulations for bl
ack holes in Quadratic Gravity\, i.e.\, including the leading-order (quadr
atic) curvature corrections to General Relativity. I review the nonlinear
degrees of freedom and discuss a well-posed initial value formulation for
Quadratic Gravity\, both in spherical symmetry and in (3+1) dimensions. In
spherical symmetry\, self-convergence tests and decaying constraint viola
tions confirm numerically stable evolution of perturbations on Minkowski a
s well as Schwarzschild spacetime. For the first time\, I will also presen
t full (3+1) simulations of black-hole initial data\, which enable ongoing
work to simulate black-hole binary systems in Quadratic Gravity.\n\nhttps
://indico.tpi.uni-jena.de/event/224/contributions/558/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/558/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Core collapse in scalar-tensor theory with massive fields
DTSTART;VALUE=DATE-TIME:20220729T083000Z
DTEND;VALUE=DATE-TIME:20220729T084500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-574@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Roxana Rosca-Mead (TPI\, University of Jena)\nThough
General Relativity has been successfully tested so far\, concepts such as
dark energy and string theory suggest the need of modifying it. Scalar-te
nsor theory is one of the most popular alternatives discussed. We produce
studies of stellar core collapse in spherical symmetry that were performed
by adapting the numerical code GR1D to the case of massive scalar-tensor
gravity. We systematically explore the parameter space that characterizes
the progenitor stars\, the equation of state and the scalar-tensor theory
of the core collapse events. We identify a remarkably simple and straightf
orward classification scheme of the resulting collapse events. For any giv
en set of parameters\, the collapse leads to one of three end states\, a w
eakly scalarized neutron star\, a strongly scalarized neutron star or a bl
ack hole\, possibly formed in multiple stages. The latter two end states c
an lead to strong gravitational-wave signals that may be detectable in pre
sent continuous-wave searches with ground-based detectors. We identify a v
ery sharp boundary in the parameter space that separates events with stron
g gravitational-wave emission from those with negligible radiation.\n\nhtt
ps://indico.tpi.uni-jena.de/event/224/contributions/574/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/574/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dynamical descalarization with a jump during black hole merger
DTSTART;VALUE=DATE-TIME:20220729T074500Z
DTEND;VALUE=DATE-TIME:20220729T080000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-551@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Daniela Doneva (University of Tuebingen)\nThe black
hole merger in scalar-Gauss-Bonnet gravity can lead to dynamical descalari
zation this is a spontaneous release of the scalar hair of the newly forme
d black hole. Depending on the exact form of the Gauss-Bonnet coupling fun
ction\, the stable scalarized solutions can be either continuously connect
ed to the Schwarzschild black hole\, or the transitions between the two ca
n happen with a jump. In the present talk we will discuss the black hole h
ead-on collisions in scalar-Gauss-Bonnet gravity prone to dynamical descal
ization and the gravitational wave manifestation of such a jump. The disti
nct signature in the gravitational wave signal will share similarities wit
h the effects expected from first order matter phase transitions happening
during neutron star binary mergers.\n\nhttps://indico.tpi.uni-jena.de/eve
nt/224/contributions/551/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/551/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Evolution of binary black holes in Einstein scalar Gauss Bonnet
DTSTART;VALUE=DATE-TIME:20220729T073000Z
DTEND;VALUE=DATE-TIME:20220729T074500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-547@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Maxence Corman (Perimeter Institute)\nIn recent year
s\, gravitational wave observation of black holes have furnished new oppor
tunities to test our understanding of gravity in the strong field\, highly
dynamical regime. However\, in order to perform model dependent tests of
General Relativity with these observations one needs accurate waveforms fo
r modified gravity theories which is still an outstanding theoretical prob
lem. In this talk\, we will discuss some recent progress in this regard\,
in particular the use of the modified harmonic formulation of Horndeski th
eories of gravity to numerically solve for the dynamics of binary black ho
les systems in such theories\, including the merger phase. We will focus o
n the particular case of Einstein-Scalar-Gauss-Bonnet gravity as it is not
only motivated by effective field theory but also admits scalar hairy bla
ck hole solutions.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributio
ns/547/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/547/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Binary black hole coalescence in scalar-Gauss-Bonnet gravity
DTSTART;VALUE=DATE-TIME:20220729T071500Z
DTEND;VALUE=DATE-TIME:20220729T073000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-568@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Hector Okada da Silva (Max Planck Institute for Grav
itational Physics (Albert Einstein Institute))\nIt was recently shown that
a broad class of gravity theories that couples a dynamical scalar field t
o the Gauss-Bonnet invariant can lead to spontaneous scalarization of blac
k holes\, allowing these objects to grow "scalar hair" once certain condit
ions are met and to remain "bald" otherwise. While most works on the topic
have focused on isolated black holes\, progress has recently been made in
understanding this effect in binary black hole systems. I will present an
overview of what has been achieved so far in this context. I will discuss
new phenomena that takes place in black-hole binaries and explore some of
the potential observational consequences of these results.\n\nhttps://ind
ico.tpi.uni-jena.de/event/224/contributions/568/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/568/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fate of radiating black holes with minimum mass in Einstein-dilato
n-Gauss-Bonnet theory of gravity
DTSTART;VALUE=DATE-TIME:20220729T070000Z
DTEND;VALUE=DATE-TIME:20220729T071500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-546@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Fabrizio Corelli (Sapienza University of Rome)\nEins
tein-dilaton-Gauss-Bonnet is a theory of modified gravity in which a scala
r field\, called dilaton\, is nonminimally coupled to the metric via an ex
ponential function. Black holes (BHs) in this theory are particularly inte
resting since they possess a critical configuration with minimum mass and
finite Hawking temperature. This means that a critical BH loses mass due t
o Hawking's radiation\, but it is not clear what is its fate after this pr
ocess\, since it cannot reach a final configuration with lower mass. In a
recent work we studied this problem by means of fully nonlinear numerical
evolutions of spherically symetric BH spacetimes (Corelli\, De Amicis\, Ik
eda\, and Pani\, to appear on arXiv in the next few days). Specifically\,
by simulating the collapse of wave packets of a phantom scalar field we ha
ve been able to dynamically reduce the BH mass\, reproducing the effect of
the Hawking's evaporation process. In this talk I will present our result
s focusing on the case in which the BH mass falls below the critical value
. In particular I will show that in the formalism we used an elliptic regi
on with high curvature appears outside the apparent horizon\, and I will d
iscuss how this could possibly hint to a violation of the weak cosmic cens
orship conjecture.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributio
ns/546/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/546/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Merger dynamics of binary Boson stars
DTSTART;VALUE=DATE-TIME:20220728T164500Z
DTEND;VALUE=DATE-TIME:20220728T170000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-576@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Nils Siemonsen (Perimeter Institute)\nParticle physi
cs models of dark matter\, and extensions to the Standard Model\, predict
the existence of a large abundance of light scalar degrees of freedom in t
he universe. From a diffuse cloud\, these can form into clumps of energy -
boson stars. Additionally\, due to their high compactness\, close to that
of black holes\, these solutions serve as test beds to study the non-line
ar dynamics of a large class of ultra-compact objects. We outline a method
to obtain constraint satisfying binary Boson star initial data\, and disc
uss the dynamics of merging binaries\, focusing specifically on the format
ion of rotating Boson star remnants.\n\nhttps://indico.tpi.uni-jena.de/eve
nt/224/contributions/576/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/576/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The piercing of a boson star by a black hole
DTSTART;VALUE=DATE-TIME:20220728T163000Z
DTEND;VALUE=DATE-TIME:20220728T164500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-584@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Miguel Zilhao (Universidade de Aveiro)\nNew light fu
ndamental fields are natural candidates for all or a fraction of dark matt
er. Self-gravitating structures of such fields might be common objects in
the universe\, and could comprise even galactic haloes. These structures w
ould interact gravitationally with black holes\, process of the utmost imp
ortance\, since it dictates their lifetime\, the black hole motion and pos
sible gravitational radiation emission. I will present a study on the dyna
mics of a black hole piercing through a much larger fully relativistic bos
on star\, made of a complex minimally coupled massive scalar without self-
interactions. As the black hole pierces through the bosonic structure\, it
is slowed down by accretion and dynamical friction\, giving rise to gravi
tational wave emission. We find evidence of a "gravitational atom" left be
hind as a product of the process.\n\nhttps://indico.tpi.uni-jena.de/event/
224/contributions/584/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/584/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mergers of Exotic Compact Objects
DTSTART;VALUE=DATE-TIME:20220728T161500Z
DTEND;VALUE=DATE-TIME:20220728T163000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-540@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Miguel Bezares (SISSA)\nWe are in the era of gravita
tional wave (GW) astronomy\, with the rapidly growing catalogue of gravita
tional wave events detected by the LIGO-Virgo collaboration. These detecti
ons allow us to study the strong regime of gravity through GW signals prod
uced by the coalescence of compact objects. In this talk\, I will present
our numerical simulations on the coalescence of binary Exotic Compact Obje
cts\, considering two different types of binaries: boson stars and fermion
-boson stars (a model for neutron stars that contain a small fraction of d
ark matter). These binaries lead to different dynamics and gravitational s
ignatures during their coalescence respect to standard compact objects\, w
hich might be crucial to distinguish them from other binaries with current
/future detections by ground-based interferometers.\n\nhttps://indico.tpi.
uni-jena.de/event/224/contributions/540/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/540/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Initial data for unequal-mass boson star collisions
DTSTART;VALUE=DATE-TIME:20220728T160000Z
DTEND;VALUE=DATE-TIME:20220728T161500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-554@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Tamara Evstafyeva (University of Cambridge)\nInitial
data play a vital role in numerical simulations -- the ability to constru
ct constraint satisfying initial data closely representing the physical sy
stem determines the quality of the subsequent numerical evolution. It has
been shown by Helfer et. al. (arxiv:1802.06733) that plainly superposed in
itial data can lead to significant constraint violations that affect the p
hysics of the evolution of boson stars in the equal-mass case. In particul
ar\, plainly superposed initial data may lead to pre-mature collapse of th
e stars to a black hole and altered gravitational wave signals. However\,
the method proposed in Helfer et.al. is limited to the equal-mass case. In
this talk we develop a generalisation of their method to unequal-mass bin
aries that recovers the Helfer construction in the equal-mass limit. Whils
t a constraint solver is needed to obtain fully constraint satisfying init
ial data\, we can still significantly reduce constraint violations by usin
g our proposed construction. Furthermore\, the significant reductions in t
he constraint violations around the stars avoid unphysical features in the
boson star dynamics and the gravitational wave signals. We will present t
he methodology of the construction and show its applications to unequal-ma
ss boson star collisions.\n\nhttps://indico.tpi.uni-jena.de/event/224/cont
ributions/554/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/554/
END:VEVENT
BEGIN:VEVENT
SUMMARY:l-boson stars
DTSTART;VALUE=DATE-TIME:20220728T154500Z
DTEND;VALUE=DATE-TIME:20220728T160000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-585@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Olivier Sarbach (Universidad Michoacana de San Nicol
ás de Hidalgo)\nRecently\, a new class of fully nonlinear numerical solut
ions to the static\, spherically symmetric Einstein-Klein-Gordon system fo
r a collection of an arbitrary odd number of complex scalar fields with an
internal U(N) symmetry was found. These solutions are parametrized by an
angular momentum number l\, an excitation number n\, and a continuous para
meter representing the amplitude of the fields. They are regular at every
point\, possess a finite total mass\, and they generalize the standard sph
erically symmetric boson stars to arbitrary values of l. In this talk\, we
discuss the main properties of these l-boson stars\, including their stab
ility with respect to small perturbations\, their compactness\, the large
l limit\, their pressure anisotropy and some preliminary results regarding
their interpretation as a solution of the semi-classical Einstein-Klein-G
ordon equations.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions
/585/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/585/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Black hole binary mergers with light scalar fields: the impact of
initial data.
DTSTART;VALUE=DATE-TIME:20220728T110000Z
DTEND;VALUE=DATE-TIME:20220728T111500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-539@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Jamie Bamber (University of Oxford)\nScalar fields a
round compact objects are of interest for scalar-tensor theories of gravit
y and dark matter models consisting of a massive scalar\, e.g. axions. The
se fields can form long-lived clouds around black holes via superradiance
or simple gravitational accretion. Black hole binary mergers occuring insi
de such clouds\, or in dense scalar dark matter environments\, may modify
the gravitational wave signal compared to the vacuum case. I will discuss
our numerical relativity simulations of scalar field accretion\, and binar
y mergers in dense scalar field environments\, and the challenges we face
in producing realistic templates of such “dirty” binary black hole mer
gers for the next generation of gravitational wave observatories. In parti
cular I will explore the impact of the scalar field initial data.\n\nhttps
://indico.tpi.uni-jena.de/event/224/contributions/539/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/539/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Numerical Simulations of Dark Matter Admixed Neutron Star Binaries
DTSTART;VALUE=DATE-TIME:20220728T104500Z
DTEND;VALUE=DATE-TIME:20220728T110000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-553@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Mattia Emma (University of Potsdam)\nThe multi-messe
nger detection of GW170817\, GRB170817A\, and AT2017gfo originating from t
he merger of two neutron stars have been a scientific breakthrough. Under
the assumption that dark matter accumulates in and around neutron stars\,
multi-messenger observations of compact binary mergers will provide a new
way to search for and constrain the nature of dark matter. In this context
\, we extended the numerical-relativity code BAM to enable the simulation
of neutron stars that contain ordinary baryonic matter\, but also a mirror
dark matter component. We performed single star tests to verify our code
changes and perform the binary neutron star simulations using a two-fluid
approach. Despite the drawback that our simulations are based on superimpo
sed initial configurations\, we find that the presence of dark matter redu
ces noticeably the lifetime of the remnant and changes the amount of eject
ed material. Consequently\, electromagnetic signals that arise due to the
merger of binary neutron star mergers admixed with dark matter will be dif
ferent than those from `pure' neutron stars. Given the increasing sensitiv
ity of gravitational-wave interferometers and other observational faciliti
es\, our analysis gives a new perspective on how to probe the presence of
dark matter.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/553
/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/553/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dynamical friction from ultralight dark matter
DTSTART;VALUE=DATE-TIME:20220728T103000Z
DTEND;VALUE=DATE-TIME:20220728T104500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-579@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Dina Traykova (MPI for Gravitational Physics (AEI)\,
Potsdam)\nA promising way to study the properties and behaviour of dark m
atter on small scales is through the effects it may have on binary mergers
. In particular\, its presence around black holes may lead to a distinctiv
e dephasing of the signal due to dynamical friction. In this talk I will p
resent how we calculate this force numerically and discuss how our finding
s extend some already existing analytic results to the relativistic regime
\, where this effect can become detectable.\n\nhttps://indico.tpi.uni-jena
.de/event/224/contributions/579/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/579/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Parasite black holes: the swallowing of a fuzzy dark matter solito
n
DTSTART;VALUE=DATE-TIME:20220728T101500Z
DTEND;VALUE=DATE-TIME:20220728T103000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-559@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Taishi Ikeda (Sapienza University of Rome)\nFuzzy da
rk matter (FDM) is an exciting alternative to the standard cold dark matte
r (CDM) paradigm\, reproducing its many successful large scale predictions
\, but solving most of the existing tension with small scale (galactic) ob
servations. FDM models postulate that dark matter (DM) is constituted by l
ight bosons of mass~$m_\\psi\\sim 10^{-22}\\\,\\text{eV}$\, which behave l
ike CDM on scales larger than the de Broglie wavelength~$\\lambda_\\text{d
B}$ ($\\sim 1\\\, \\text{kpc}$\, in a typical galaxy)\, but are subjected
to a \\emph{wave pressure} on smaller scales. One of the most solid predic
tions from FDM cosmological numerical evolutions is the condensation of a
soliton core at the center of haloes. These solitons -- also known as boso
n stars (BSs) or oscillatons -- are stationary (or long-lived)\, self-grav
itating scalar field configurations supported by wave pressure. However\,
if these solitons host a \\emph{parasite} supermassive black hole (SMBH) t
hey will be swallowed by their guest\, as implied by the no-hair theorem.
It is thus crucial to understand in detail the accretion process and the t
imescales involved. Several works have assumed (based on crude estimates)
that the soliton remains largely unaltered by the presence of a central SM
BH and used then\, e.g.\, inner galactic rotation curves to put constraint
s on the mass~$m_\\psi$ of the FDM particles. In this work we use numerica
l relativity to self-consistently solve the problem of accretion of a BS b
y a central SMBH. We find the different stages of accretion\, estimate the
BS lifetime.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/55
9/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/559/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mergers of Dark-Matter admixed Neutron Stars
DTSTART;VALUE=DATE-TIME:20220728T100000Z
DTEND;VALUE=DATE-TIME:20220728T101500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-575@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Hannes Rüter (University of Coimbra)\nWe discuss th
e construction of quasi-equilibrium configurations of compact binaries\, i
n which each component of the binary is modeled as a mixture of two ideal
fluids. For the first fluid we use an ordinary baryonic-matter equation-of
-state and for the second fluid\, describing dark matter\, we trial differ
ent dark-matter equation-of-state. We use the obtained quasi-equilibrium c
onfigurations as the basis for numerical relativity merger simulations and
analyse the impact of the dark matter on the system's dynamical propertie
s and the waveforms of the emitted gravitational radiation.\n\nhttps://ind
ico.tpi.uni-jena.de/event/224/contributions/575/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/575/
END:VEVENT
BEGIN:VEVENT
SUMMARY:hp-Adaptive Mesh Refinement in bamps
DTSTART;VALUE=DATE-TIME:20220728T074500Z
DTEND;VALUE=DATE-TIME:20220728T080000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-573@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Sarah Renkhoff (TPI Jena)\nWe have implemented fully
adaptive hp mesh refinement into our pseudospectral NR code 'bamps'\, usi
ng heuristic indicators to drive dynamic refinement both in terms of cell
size and cell resolution\, while retaining both strong and weak scaling ac
ross several thousand processors. Because the mesh refinement infrastructu
re is independent of the evolved equations\, it can be applied to a variet
y of physics problems. Its first major application has been the study of c
ritical collapse of gravitational waves\, where it allowed tuning towards
criticality at a much higher efficiency compared to previous studies\, let
ting us examine several new families of initial data that had not previous
ly been studied.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions
/573/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/573/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Challenges and pitfalls in the development of a two moment GRRHD c
ode
DTSTART;VALUE=DATE-TIME:20220728T073000Z
DTEND;VALUE=DATE-TIME:20220728T074500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-567@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Carlo Musolino (Goethe Universität Frankfurt am Mai
n)\nSince the first general-relativistic simulation of a binary neutron-st
ar (BNS) merger less than a decade ago\, the numerical relativity communit
y has embraced increasingly sophisticated and accurate descriptions of the
physics of these systems\, most notably\, the gravitational-wave signal.
On the other hand\, the electromagnetic signals\, which are crucial to und
erstand in the novel context of multi-messenger astrophysics\, are signifi
cantly more challenging to predict. Indeed\, these signals stem from low-d
ensity expanding ejecta that must be captured in its dynamics and composit
ion for long timescales. Neutrinos play a prominent role in the cooling ph
ase of the merger remnant and during the expansion of the neutron-rich eje
cta\, thus affecting both dynamics and composition of the outflow. Therefo
re\, they are a key ingredient to achieve a realistic description of the m
erger phenomenon and its electromagnetic counterparts. In this talk\, I wi
ll present a new implementation of a gray two-moment (M1) radiation transp
ort scheme in full general relativity\, aiming to capture the neutrino phy
sics in BNS mergers. I will highlight the technical challenges involved in
the development of what is arguably a cutting edge tool for its modelling
capability in the context of BNS mergers\, while also presenting a compre
hensive set of tests that allow for cross-comparison and validation of suc
h codes in the research landscape.\n\nhttps://indico.tpi.uni-jena.de/event
/224/contributions/567/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/567/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Computational Quests: from Cactus to Simflowny and beyond
DTSTART;VALUE=DATE-TIME:20220728T070000Z
DTEND;VALUE=DATE-TIME:20220728T071500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-565@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Joan Masso (University of the Balearic Islands)\nWe
will quickly review the last 30 years of open general codes\, platforms\,
and frameworks for Numerical Relativity\, with special emphasis on the les
sons that we have learnt and the challenges that lie ahead. We will also d
escribe results and features of the last versions of different codes\, wit
h special emphasis on Simflowny: an open platform which automatically gene
rates efficient parallel AMR code of scientific dynamical models for diffe
rent simulation frameworks. It incorporates Finite-difference based method
s for both smooth and non-smooth solutions\, coupled with particle-based m
ethods. It allows for generic systems of PDEs\, and there are already impl
emented different formulations of the Einstein Equations\, the full relati
vistic MHD equations and both the leakage and the M1 approximation to mode
l the neutrino transport. Finally\, we will discuss the changes in develop
ment languages\, from Fortran and C++ legacy codes to Julia programming an
d GPUs.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/565/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/565/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Numerical evolution of Good-Bad-Ugly-F system as a toy model for h
yperboloidal numerical relativity
DTSTART;VALUE=DATE-TIME:20220728T071500Z
DTEND;VALUE=DATE-TIME:20220728T073000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-571@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Christian Peterson Borquez (Instituto Superior Tecni
co\, Lisbon)\nThe numerical solution of a system of hyperbolic PDEs all th
e way to future null infinity requires the knowledge of asymptotics. The G
ood-Bad-Ugly-F model is known to mimic the asymptotic properties of Einste
in equations in generalized harmonic gauge. In this talk I will present th
e results of numerical evolution of this system\, both in spherical symmet
ry and full 3D\, with the scope of using these ideas to incorporate the hy
perboloidal approach in numerical relativity simulations.\n\nhttps://indic
o.tpi.uni-jena.de/event/224/contributions/571/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/571/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Worldtube excision method for intermediate-mass-ratio inspirals: s
calar-field toy model in 3+1D
DTSTART;VALUE=DATE-TIME:20220727T104500Z
DTEND;VALUE=DATE-TIME:20220727T110000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-581@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Nikolas Wittek (Max-Planck-Institute for Gravitation
al Physics (AEI Potsdam))\nBinary black hole simulations become increasing
ly computationally expensive with smaller mass ratios because the Courant-
Friedrich-Lewy condition imposes smaller time steps by the need to resolve
the small black hole. Here we propose and explore a method for alleviatin
g the scale disparity in simulations with mass ratios in the intermediate
astrophysical range\, where purely perturbative methods may not be adequat
e. A region much larger than the smaller black hole is excised from the nu
merical domain\, and replaced with an analytical model approximating a tid
ally deformed black hole. We apply this idea to a toy model of a scalar ch
arge in a circular geodesic orbit around a Schwarzschild black hole\, solv
ing for the massless Klein-Gordon field in a 3+1D framework using SpECTRE\
, the new discontinuous Galerkin code of the SXS collaboration.\n\nhttps:/
/indico.tpi.uni-jena.de/event/224/contributions/581/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/581/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A task-based parallel elliptic solver based on discontinuous-Galer
kin methods
DTSTART;VALUE=DATE-TIME:20220727T103000Z
DTEND;VALUE=DATE-TIME:20220727T104500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-572@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Harald Pfeiffer (AEI Potsdam)\nThe solution of ellip
tic equations is an integral part of computational physics. This talk pres
ents a new elliptic solver which is based on a discontinuous Galerkin sche
me applicable to a wide class of elliptic partial differential equations.
The solver is employing task-based parallelism and scales to a few thousan
d of compute cores. We show applications to the construction of initial da
ta for binary black holes and to the study of thermal noise in the mirrors
of interferometric gravitational wave detectors.\n\nhttps://indico.tpi.un
i-jena.de/event/224/contributions/572/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/572/
END:VEVENT
BEGIN:VEVENT
SUMMARY:FUKA: A public code for initial data of unequal-mass\, spinning co
mpact-object binaries
DTSTART;VALUE=DATE-TIME:20220727T101500Z
DTEND;VALUE=DATE-TIME:20220727T103000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-577@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Samuel Tootle (Goethe University)\nThe construction
of constraint-satisfying initial data is an essential element for the nume
rical exploration of the dynamics of compact-object binaries. While severa
l codes have been developed over the years to compute generic quasi-equili
brium configurations of binaries comprising either two black holes\, or tw
o neutron stars\, or a black hole and a neutron star\, these codes are oft
en not publicly available or they provide only a limited capability in ter
ms of mass ratios and spins of the components in the binary. We here prese
nt a new open-source collection of spectral elliptic solvers that are capa
ble of exploring the major parameter space of binary black holes (BBHs)\,
binary neutron stars (BNSs)\, and mixed binaries of black holes and neutro
n stars (BHNSs). Particularly important is the ability of the spectral-sol
ver library to handle neutron stars that are either irrotational or with a
n intrinsic spin angular momentum that is parallel to the orbital one. By
supporting both analytic and tabulated equations of state at zero or finit
e temperature\, the new infrastructure is particularly geared towards allo
wing for the construction of BHNS and BNS binaries. For the latter\, we sh
ow that the new solvers are able to reach the most extreme corners in the
physically plausible space of parameters\, including extreme mass ratios a
nd spin asymmetries\, thus representing the most extreme BNS computed to d
ate. Through a systematic series of examples\, we demonstrate that the sol
vers are able to construct quasi-equilibrium and eccentricity-reduced init
ial data for BBHs\, BNSs\, and BHNSs\, achieving spectral convergence in a
ll cases. Furthermore\, using such initial data\, we have carried out evol
utions of these systems from the inspiral to after the merger\, obtaining
evolutions with eccentricities ≲10−4−10−3\, and accurate gravitati
onal waveforms.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/
577/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/577/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Merger simulations of GW170817 with V-QCD EOS
DTSTART;VALUE=DATE-TIME:20220727T071500Z
DTEND;VALUE=DATE-TIME:20220727T073000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-578@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Konrad Topolski (Goethe University Frankfurt)\nIn my
talk\, I will present the latest results of general relativistic hydrodyn
amic simulations of binary neutron star mergers with the recently introduc
ed finite-temperature extension of the V-QCD equation of state. The V-QCD
model is based on the gauge/gravity duality and provides a consistent desc
ription of nuclear and quark matter at densities beyond nuclear saturation
which are realized in neutron stars. We simulate binaries that are consis
tent with GW170817 and study the imprint that a hadron-quark phase transit
ion may have in the gravitational-wave emission and in the thermodynamical
properties of the post-merger remnant.\n\nhttps://indico.tpi.uni-jena.de/
event/224/contributions/578/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/578/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Numerical relativity and the propagation of gravitational waves th
rough matter
DTSTART;VALUE=DATE-TIME:20220727T070000Z
DTEND;VALUE=DATE-TIME:20220727T071500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-541@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Nigel Bishop (Rhodes University)\nAuthors: Nigel T.
Bishop\, Monos Naidoo\, and Petrus J. van der Walt. Using linearized pertu
rbations within the Bondi-Sachs formalism\, we have considered the problem
of a gravitational wave (GW) source surrounded by a spherical dust shell.
It was shown that the shell causes the GWs to be modified both in magnitu
de and phase\; and that if the shell is viscous\, then the shear induced i
n the velocity field results in an energy transfer so damping the magnitud
e of the GWs. Both effects can be significant if the shell radius r is muc
h smaller than the GW wavelength λ\, and there are astrophysical scenario
s for which the modification to the GW signal is large enough to be measur
able. These scenarios include core collapse supernovae (CCSNe)\, quasinorm
al mode emission from the remnant of a binary neutron star (BNS) merger\,
and primordial GWs. In particular\, there are feasible values of the CCSNe
parameters for which viscous damping of the GW signal would be almost com
plete. In numerical relativity\, an evolution of the full Einstein and mat
ter field equations with GW extraction far from the source will properly i
nclude all effects described above. However\, in situations such as CCSNe
and BNS the complexity of the matter physics may necessitate an approximat
e treatment of the gravitational field or of the GW extraction. Results ob
tained in these cases may need to be corrected. The presentation builds on
our previous work: 1. N.T. Bishop\, M. Naidoo\, and P.J. van der Walt (20
20)\, Gen. Rel. Grav. 52:92\, https://doi.org/10.1007/s10714-020-02740-9 a
rXiv:1912.08289 2. M. Naidoo\, N.T. Bishop\, and P.J. van der Walt (2021)\
, Gen. Rel. Grav. 53:97\, https://doi.org/10.1007/s10714-021-02841-z arXiv
:2102.00060\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/541/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/541/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Towards the inclusion of bulk viscosity in numerical relativity si
mulations
DTSTART;VALUE=DATE-TIME:20220727T074500Z
DTEND;VALUE=DATE-TIME:20220727T080000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-544@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Michail Chabanov (Goethe University Frankfurt)\nBina
ry neutron star mergers provide the unique opportunity to study matter at
densities and temperatures unreachable in laboratories on earth. Its prope
rties are encoded in the equation of state whose influence on the graviati
onal wave signal of merging neutron stars can be used to constrain the phy
sics of the strong interaction. But it is not only the equation of state w
hich carries information about the underlying microphysics of neutron star
s. Transport effects such as bulk viscosity are hypothesized to influence
the dynamics binary neutron star mergers as well as opening another potent
ial window to study and constrain matter in such extrem conditions. In thi
s talk I will present the first steps towards the inclusion of transport e
ffects in fully general-relativistic numerical simulations. Here\, I will
introduce a conservative 3+1 formulation of the equations of dissipative g
eneral-relativistic hydrodynamics which enables the inclusion of dissipati
ve effects in numerical relativity codes. As a first application of this f
ormulation I will show standard tests in special relativity such as the sh
ock-tube problem. To further move on to general relativity\, the problem o
f stationary\, spherically symmetric black hole accretion including bulk v
iscosity is solved. Finally\, we present first results of oscillating neut
ron stars with bulk viscosity in a three-dimensional setup with a dynamica
lly evolved spacetime.\n\nhttps://indico.tpi.uni-jena.de/event/224/contrib
utions/544/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/544/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Universality of the turbulent magnetic field amplification in bina
ry neutron star mergers
DTSTART;VALUE=DATE-TIME:20220727T073000Z
DTEND;VALUE=DATE-TIME:20220727T074500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-536@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Ricard Aguilera-Miret (Universitat de les Illes Bale
ars)\nThe detection of a binary neutron star merger in 2017 through both g
ravitational waves and electromagnetic emission opened a new era of multim
essenger astronomy. During the merger\, several mechanisms like the Kelvin
-Helmholtz instability\, the winding up effect and the MRI\, can amplify t
he initial magnetic field in the remnant to be powerful enoguh for launchi
ng a jet\, with an associated short GRB. When performing simulations\, sim
plified assumptions arise for the initial magnetic field strength and topo
logy of the merging neutron stars. Here I will show convergent results by
using high-resolution\, large-eddy simulations of binary neutron star merg
ers\, following the newly formed remnant for up to 30 milliseconds. I will
specifically compare simulations with different initial magnetic field st
renghts and configurations\, going beyond the widespread-used aligned dipo
le confined within each star. I will show that the magnetic field is alway
s amplified up to ~10^16 G in the bulk region of the remnant\, while the i
nitial topology is quickly forgotten in a timescale of few miliseconds aft
er the merger due to the Kelvin-Helmholtz instability.\n\nhttps://indico.t
pi.uni-jena.de/event/224/contributions/536/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/536/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Towards Kokkos GR-Athena++: puncture evolutions on GPUs
DTSTART;VALUE=DATE-TIME:20220727T154500Z
DTEND;VALUE=DATE-TIME:20220727T160000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-582@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Francesco Zappa ()\nNumerical relativity plays a key
role in the study of the dynamical and strong-field gravity regime of bla
ck hole and neutron star binary systems. The accuracy required nowadays fo
r gravitational waves modeling and to investigate the outcome of compact b
inaries involving neutron stars and the matter and light emission can be o
btained only through high-resolution simulations. Such simulations can be
very costly and thus high-performance and scalable codes\, capable of effi
ciently making use of the modern massively-parallel architectures availabl
e nowadays\, are needed. It has become increasingly important to write cod
es that are portable\, i.e. able to run on several architectures while kee
ping a high parallel efficicency. A possibility to achieve this goal is of
fered by the Kokkos C++ library\, which allows one to easily write readabl
e codes that can be compiled on virtually any architecture\, included GPU
nodes. We present the first results of single puncture evolutions with a n
ew version of the oct-tree based code GR-Athena++\, rewritten with the Kok
kos paradigm. We compare CPUs and GPUs performance and we discuss the feas
ibility of binary black hole runs on GPUs\, which are challenging due to t
he small memory available on GPUs. We achieve a speed-up of $\\sim 50$ com
paring the new Kokkos-based code run on a GPU with respect to GR-Athena++
and we argue that it is possible to run a medium/high resolution binary bl
ack hole runs using $\\sim 4$ GPUs. These results demonstrate that a Kokko
s version of GR-Athena++ can in principle be used to perform binary black
hole evolution with a significant gain in speed\, providing a valid option
for exa-scale numerical relativity on the newest architectures.\n\nhttps:
//indico.tpi.uni-jena.de/event/224/contributions/582/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/582/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Entropy as shock indicator in neutron star merger simulations
DTSTART;VALUE=DATE-TIME:20220727T150000Z
DTEND;VALUE=DATE-TIME:20220727T151500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-552@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Georgios Doulis (TPI Jena)\nNumerical simulations ar
e the only way to calculate exact gravitational waveforms from binary neut
ron star mergers and to design templates for gravitational-wave astronomy.
Our knowledge about the physical properties of the inspiraling neutron st
ars\, the mechanisms inherent in the inspiral and the massive object produ
ced after the merger depends crucially on the accuracy of these numerical
simulations. In this talk\, I will present an entropy-based flux-limiting
scheme that can be used in high-order\, convergent simulations of neutron
star spacetimes. First\, I will demonstrate how the entropy produced durin
g the inspiral can be used to detect the presence of shocks and will incor
porate this idea into the design of a flux-limiter. Next\, it will be show
n that this entropy based flux-limiting scheme effectively tracks the stel
lar surface and the physical shocks during the inspiral. Finally\, I will
present the first neutron star merger simulations with such a method and w
ill demonstrate up to fourth-order convergence in the gravitational wavefo
rm phase. The observed convergence rates are two orders higher than the on
e achieved by state-of-the-art high-order characteristic schemes.\n\nhttps
://indico.tpi.uni-jena.de/event/224/contributions/552/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/552/
END:VEVENT
BEGIN:VEVENT
SUMMARY:GRHD simulations with GR-Athena++
DTSTART;VALUE=DATE-TIME:20220727T153000Z
DTEND;VALUE=DATE-TIME:20220727T154500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-545@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: William Cook (TPI)\nWe demonstrate the performance o
f the new code GR-Athena++ in evolving general relativistic hydrodynamics
(GRHD) in a dynamically evolving spacetime. GR-Athena++ utilises the task-
based parallelism and block based adaptive mesh refinement of the Athena++
code\, as well as its approach to solving GRHD problems in stationary spa
cetimes\; combined with new functionality to solve the Einstein equations
in the Z4c formulation. We demonstrate the performance of this new code by
simulating the evolution of Neutron Stars in GR-Athena++\, removing the C
owling approximation assumed in previous work\, presenting a fully dynamic
al spacetime evolution.\n\nhttps://indico.tpi.uni-jena.de/event/224/contri
butions/545/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/545/
END:VEVENT
BEGIN:VEVENT
SUMMARY:`GR-Athena++`: puncture evolutions on vertex-centered oct-tree AMR
DTSTART;VALUE=DATE-TIME:20220727T151500Z
DTEND;VALUE=DATE-TIME:20220727T153000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-550@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Boris Daszuta (Friedrich-Schiller-Universität Jena)
\n`GR-Athena++` is a general-relativistic\, high-order\, vertex-centered s
olver that extends the oct-tree\, adaptive mesh refinement capabilities of
the astrophysical (radiation) magnetohydrodynamics code `Athena++`. To si
mulate dynamical spacetimes `GR-Athena++` uses the Z4c evolution scheme of
numerical relativity coupled to the moving puncture gauge. Stable and acc
urate binary black hole merger evolutions are demonstrated in convergence
testing\, cross-code validation\, and verification against state-of-the-ar
t effective-one-body waveforms. `GR-Athena++` leverages the task-based par
allelism paradigm of `Athena++` to achieve excellent scalability. Strong s
caling efficiencies above 95% for up to 1.2×1e4 CPUs and excellent weak s
caling up to 1e5 CPUs in a production binary black hole setup with adaptiv
e mesh refinement are measured. `GR-Athena++` thus allows for the robust s
imulation of compact binary coalescences and and offers a viable path towa
rds numerical relativity at exascale.\n\nhttps://indico.tpi.uni-jena.de/ev
ent/224/contributions/550/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/550/
END:VEVENT
BEGIN:VEVENT
SUMMARY:High-order numerical methods for solving the M1 neutrino formalism
DTSTART;VALUE=DATE-TIME:20220726T161500Z
DTEND;VALUE=DATE-TIME:20220726T163000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-560@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Manuel R. Izquierdo (Universitat de les Illes Balear
es)\nModelling the transport of neutrinos is crucial for core-collapse sup
ernavoae and neutron star mergers. Evolving the complete Boltzmann equatio
ns for radiative transport is extremely expensive\, so several more effici
ent approximation formalisms have been developed to face such difficulty.
In this talk\, I will focus on the truncated-moment formalism\, considerin
g only the first two moments (M1) within the gray approximation\, which re
duces Boltzmann seven-dimensional equation to a system of 3+1 equations. J
ust the first two moments (radiation energy density and radiation flux) ar
e evolved\, while all the other higher-order moments are provided by an ap
proximate algebraic closure relation as a function of low-order moments. S
olving this approximated formalism is still mathematically challenging bec
ause it is necessary to model the interaction of radiation and matter in s
everal regimes where the evolution equations become stiff and behaves as a
n advection-diffusion problem. Here\, I will present different high-order
time integration schemes based on Implicit-Explicit Runge-Kutta (IMEX) met
hods designed to overcome the time-step restriction caused by such behavio
ur and analyze their performance in several numerical tests. Simulations w
ere carried out using Julia\, a high performance dynamic programming langu
age that allows the resulting code to be easily executed on GPUs.\n\nhttps
://indico.tpi.uni-jena.de/event/224/contributions/560/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/560/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Detectability of nuclear reactions in neutron star mergers through
gravitational waves
DTSTART;VALUE=DATE-TIME:20220726T160000Z
DTEND;VALUE=DATE-TIME:20220726T161500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-557@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Peter Hammond (University of Southampton)\nThe impac
t of nuclear reactions on observed signals from neutron star mergers is un
certain. We make a first attempt at quantifying that uncertainty by studyi
ng two cases that\, intuitively\, are the most extreme. In one case we ass
ume that the reactions happen instantaneously (on timescales much faster t
han can be resolved in simulations). In the other we assume reactions do n
ot happen (or occur on timescales much slower than the orbital\, or simula
tion\, timescale). We find that the resulting differences in the gravitati
onal wave signal are small\, but are potentially detectable by next genera
tion observatories. These differences will impact on parameter recovery ef
forts driven by matching to templates extracted from numerical relativity
simulations. Failure to take the effects discussed here into account may l
ead to systematic errors of unknown size being introduced into equation of
state parameters inferred from gravitation wave signals.\n\nhttps://indic
o.tpi.uni-jena.de/event/224/contributions/557/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/557/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Numerical relativity simulations of the neutron star merger GW1904
25: microphysics and mass ratio effects
DTSTART;VALUE=DATE-TIME:20220726T154500Z
DTEND;VALUE=DATE-TIME:20220726T160000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-543@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Alessandro Camilletti (University of Trento)\nGW1904
25 was the second gravitational wave (GW) signal compatible with a binary
neutron star (BNS) merger detected by the Advanced LIGO and Advanced Virgo
detectors. Despite intense follow-up campaigns\, no electromagnetic count
erpart was identified. Whether the associated kilonova was too dim or the
localisation area too broad is still an open question. We simulate 28 BNS
mergers with the chirp mass of GW190425 and spanning a mass ratio 1 ≤ q
≤ 1.67\, using numerical-relativity simulations with finite temperature\
, composition dependent nuclear equation of state (EOS) and neutrino radia
tion. The energy emitted in GWs is less than 0.083 Mo 𝑐^2\, where Mo is
the solar mass\, with a peak luminosity of 1.1 − 2.4 × 10 58 erg s^−
1 /(1 + q)^2 . Dynamical ejecta and disc mass are relatively small\, the f
ormer ranging between 5 × 10^−6 and 10^−3 solar masses and the latter
between 10^−5 and 0.1 solar masses . Asymmetric mergers\, especially in
the case of stiff EOSs\, are able to unbind more matter and to form heavi
er discs compared to equal mass binaries. The angular momentum of the disc
is 8 − 10 Mo the disc mass over three orders of magnitude in the disk m
ass. While the associated nucleosynthesis shows no peculiarity\, the simul
ated kilonovae are relatively dim compared with the GW170817 event. In par
ticular\, for distances compatible with GW190425\, we find AB magnitudes a
lways dimmer than 20 mag for the B\, r and K bands\, with brighter kilonov
ae associated to more asymmetric binaries and stiffer EOSs. We suggest tha
t\, even assuming a good coverage of GW190425’s sky location\, the kilon
ova signal could hardly have been detected by present wide-field surveys a
nd no firm constraints on the binary parameters or neutron star (NS) EOS c
an be argued from the lack of the detection.\n\nhttps://indico.tpi.uni-jen
a.de/event/224/contributions/543/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/543/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Primordial black hole formation during the QCD phase-transition
DTSTART;VALUE=DATE-TIME:20220726T103000Z
DTEND;VALUE=DATE-TIME:20220726T104500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-566@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Ilia Musco (INFN \, Sapienza University of Rome)\nTh
e formation of Primordial black holes is naturally enhanced during the QCD
phase transition\, because of the softening of the equation of state: at
a scale between 1 and 3 solar masses\, the threshold is reduced of about 1
0% with a corresponding abundance of primordial black holes increased by m
ore than 100 times. Such black holes could be an interesting source of gra
vitational waves emitted during black hole mergers\, detected by LIGO/VIRG
O.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/566/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/566/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Machine-Learning Gravitational-Wave Search Challenge 1: A summary
of results
DTSTART;VALUE=DATE-TIME:20220726T101500Z
DTEND;VALUE=DATE-TIME:20220726T103000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-583@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Ondřej Zelenka (TPI FSU Jena)\nCompact binary coale
scence waveforms generated by numerical relativity codes and associated ph
enomenological models are a critical part of gravitational-wave searches i
n detector data. However\, the computational cost of the conventional matc
hed-filtering searches is steeply rising as increased sensitivity of detec
tors expands the waveform parameter space. Lately\, machine-learning based
search algorithms have gained popularity as a potential efficient complem
ent to the conventional searches. The MLGWSC-1 has been created in order t
o build a unified testing network for these algorithms\, which rely on NR
and associated software. This contribution presents the idea\, organizatio
n and results of the challenge.\n\nhttps://indico.tpi.uni-jena.de/event/22
4/contributions/583/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/583/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Gravitational-wave data analysis with the Newman-Penrose scalar
DTSTART;VALUE=DATE-TIME:20220726T100000Z
DTEND;VALUE=DATE-TIME:20220726T101500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-542@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Juan Calderon Bustillo (University of Santiago de Co
mpostela)\nDetection and parameter inference of gravitational-wave signals
relies on the comparison of the incoming detector strain data to waveform
templates for the gravitational-wave strain $h(t)$ which ultimately rely
on the resolution of Einstein's equations via numerical relativity simulat
ions. These\, however\, commonly output a quantity known as the Newman-Pen
rose scalar $\\psi_4(t)$\, related to the strain by $\\psi_4(t)=\\mathrm{d
}^2h(t) / \\mathrm{d}t^2$. Therefore\, obtaining strain templates involves
a double time-integration that introduces artefacts that need to be eased
in a rather manual way. By taking second-order finite differences on the
detector data and inferring the corresponding noise distribution\, we deve
lop a framework to perform gravitational-wave data analysis directly using
$\\psi_4(t)$ templates. I will first demonstrate this formalism by recove
ring numerically simulated signals from head-on collisions of Proca stars
injected in Advanced LIGO noise. Next\, I will show a re-analysis of GW190
521 under the Proca-star merger scenario. Our framework removes the need t
o obtain the strain from numerical relativity simulations therefore avoidi
ng the associated systematic errors.\n\nhttps://indico.tpi.uni-jena.de/eve
nt/224/contributions/542/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/542/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Notes on the Asymptotics of near Kerr Initial Data by Evolutionary
Solvers
DTSTART;VALUE=DATE-TIME:20220726T074500Z
DTEND;VALUE=DATE-TIME:20220726T080000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-549@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Károly Csukás (University of Mississippi\, Wigner
RCP)\nWe studied the asymptotic behavior of perturbed Kerr initial data by
solving the evolutionary form of the vacuum Einstein constraint equations
. Unlike in the elliptic formulation\, solving the constraints in their ev
olutionary form\, we have direct control over the constrained data only on
a single 2-surface. This immediately raises the question of whether it ca
n guarantee asymptotic flatness of initial data. Previous works based on p
erturbed Schwarzschild initial data have already demonstrated that it is p
ossible to guarantee the asymptotic flatness of solutions. Integrating the
equations numerically\, we found that results on the modified parabolic-h
yperbolic system can be generalized to perturbed Kerr initial data. We hav
e also investigated a new\, more robust method for the algebraic-hyperboli
c system. Part of this work is funded by NSF CAREER Award PHY–2047382 an
d NKFIH Grant No. K-115434.\n\nhttps://indico.tpi.uni-jena.de/event/224/co
ntributions/549/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/549/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Critical phenomena in gravitational collapse with bamps
DTSTART;VALUE=DATE-TIME:20220726T073000Z
DTEND;VALUE=DATE-TIME:20220726T074500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-548@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Daniela Cors Agulló (TPI Jena)\nWe use our adapted
pseudo-spectral code bamps\, with its new hp adaptive mesh refinement\, to
tune close to the barrier between gravitational collapse and dispersed fi
elds\, in order to study the critical phenomena that emerges near that thr
eshold. In spherical symmetry\, we observe critical phenomena by evolving
massless scalar fields. This has allowed us to assess the adequate choice
of gauge source functions and damping parameters for collapse evolutions p
erformed with generalised harmonic gauge. On the other hand in axisymmetry
\, we evolve six one-parameter families of Brill wave initial data in vacu
um: three prolate and three oblate\, including two centred and four off-ce
ntred. In agreement with previous work we find two disjoint centres of col
lapse close to the threshold. We also found no evidence for strict DSS nor
universal power-law scaling of curvature quantities. Nevertheless\, appro
ximately universal strong curvature features and echoes were found within
all six families close to the threshold.\n\nhttps://indico.tpi.uni-jena.de
/event/224/contributions/548/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/548/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Axisymmetric critical collapse on a shoestring
DTSTART;VALUE=DATE-TIME:20220726T071500Z
DTEND;VALUE=DATE-TIME:20220726T073000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-561@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Anton khirnov (Institute of Theoretical Physics\, Ch
arles University\, Prague)\nThe study of vacuum critical collapse has acqu
ired an aura of unapproachability in its 30 years of existence. It is ofte
n thought that only highly sophisticated numerical methods together with i
mmense supercomputer clusters will suffice for treating this problem. In o
ur recent work we refute this folk lore by using only open-source code run
ning on single machines to discover universal echoing in near-critical axi
symmetric vacuum spacetimes. In this talk we discuss the technical aspects
of our work\, focusing on the implementation of our "quasi-maximal" slici
ng condition and tuning it to make the most of our limited computing resou
rces.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/561/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/561/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Modified CCZ4 formulation of Einstein-scalar-Gauss-Bonnet theory
DTSTART;VALUE=DATE-TIME:20220725T154500Z
DTEND;VALUE=DATE-TIME:20220725T160000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-538@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Llibert Aresté Saló (Queen Mary University of Lond
on)\nIn this talk I will present the equations of the Einstein-scalar-Gaus
s-Bonnet theory\, a modified theory of gravity\, in the 3+1 formulation wi
th a modified gauge that proves to be strongly hyperbolic. Then I'll show
some of the numerical results that we have obtained from the implementatio
n of these equations with GRChombo\, a numerical general relativity code w
ith fully adaptive mesh refinement.\n\nhttps://indico.tpi.uni-jena.de/even
t/224/contributions/538/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/538/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A new first-order formulation of the Einstein equations exploiting
analogies with electrodynamics
DTSTART;VALUE=DATE-TIME:20220725T153000Z
DTEND;VALUE=DATE-TIME:20220725T154500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-569@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Hector Olivares (Radboud University)\nThe Einstein a
nd Maxwell equations are both systems of hyperbolic equations which need t
o satisfy a set of elliptic constraints throughout evolution. However\, wh
ile electrodynamics and magnetohydrodynamics have benefited from a large n
umber of evolution schemes that are able to enforce these constraints and
are easily applicable to curvilinear coordinates\, unstructured meshes\, o
r N-body simulations\, many of these techniques cannot be straightforwardl
y applied to existing formulations of the Einstein equations. We develop a
3+1 a formulation of the Einstein equations which shows a striking resemb
lance to the equations of relativistic MHD and to EM in material media. Th
e fundamental variables of this formulation are the frame fields\, their e
xterior derivatives\, and the Nester-Witten and Sparling forms. These mirr
or the roles of the electromagnetic 4-potential\, the electromagnetic fiel
d strengths\, the field excitations and the electric current. The role of
the lapse function and shift vector\, corresponds exactly to that of the s
calar electric potential. The formulation is manifestly first order and fl
ux-conservative\, which makes it suitable for high-resolution shock captur
ing schemes and finite-element methods. Being derived as a system of equat
ions in exterior derivatives\, it is directly applicable to any coordinate
system and to unstructured meshes\, and leads to a natural discretisation
potentially suitable for the use of machine-precision constraint propagat
ion techniques such as the Yee algorithm and constrained transport. Due to
these properties\, we expect this new formulation to be beneficial in sim
ulations of many astrophysical systems\, such as binary compact objects an
d core-collapse supernovae as well as cosmological simulations of the earl
y universe.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/569/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/569/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Some ongoing Efforts for Evolving Einstein Field Equations on Hype
rboloidal Slices
DTSTART;VALUE=DATE-TIME:20220725T151500Z
DTEND;VALUE=DATE-TIME:20220725T153000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-555@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Shalabh Gautam (International Centre for Theoretical
Sciences (ICTS)\, Bengaluru\, India)\nOne of the challenges in numerical
relativity is to include future null infinity in the computational domain
with a well-posed formulation. Success will not only enable us to evolve a
ny system of astrophysical interest\, e.g. binary black holes and extracti
ng the gravitational wave signal at future null infinity\, with any desire
d accuracy\, but also help in studying various phenomena of fundamental in
terest. One proposal is to use hyperboloidal slices. In this talk\, I will
present our ongoing efforts for obtaining a well-posed formulation of the
Einstein Field Equations on hyperboloidal slices\, all in spherical symme
try. The natural extension will be to generalize these methods to full 3d.
\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/555/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/555/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Free hyperboloidal evolution using conformal compactification
DTSTART;VALUE=DATE-TIME:20220725T150000Z
DTEND;VALUE=DATE-TIME:20220725T151500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-580@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Alex Vano-Vinuales (CENTRA\, IST\, University of Lis
bon)\nGravitational wave radiation\, our window for probing the strong fie
ld and dynamical regime of gravity\, is unambiguously defined only at futu
re null infinity - the location in spacetime where light rays arrive and t
hus where signals and global properties of spacetimes can be measured. A c
onvenient way to reach it within numerical relativity simulations is by me
ans of hyperboloidal foliations\, smooth spacelike slices that reach futur
e null infinity. Among the approaches to the hyperboloidal problem\, here
I will focus on conformal compactification\, based on an idea by Nobel-lau
reate Roger Penrose. Our implementation uses the BSSN and Z4 formulations
of the Einstein equations and has provided some very promising numerical r
esults of a massless scalar field coupled to gravity in spherical symmetry
. I will give an update on the current ongoing work towards a 3D generaliz
ation\, as the final goal of this work is to provide a far-field numerical
framework that includes null infinity for simulations of compact object m
ergers with accurate gravitational wave extraction.\n\nhttps://indico.tpi.
uni-jena.de/event/224/contributions/580/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/580/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Boson-star binaries and gravitational waves
DTSTART;VALUE=DATE-TIME:20220728T150000Z
DTEND;VALUE=DATE-TIME:20220728T154500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-531@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Ulrich Sperhake (University of Cambridge)\nWe presen
t numerical simulations of boson-star binary systems and extract the gravi
tational waves emitted by these systems. We discuss numerical methods and
with particular focus on improved initial data and the spurious effects th
at may result from inappropriate choices for the construction of initial d
ata.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/531/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/531/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Black hole binaries in higher derivative theories of gravity
DTSTART;VALUE=DATE-TIME:20220728T134500Z
DTEND;VALUE=DATE-TIME:20220728T143000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-526@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Pau Figueras (Queen Mary University of London)\nIn t
his talk I will discuss recent progress on modelling black hole binaries i
n higher derivative theories of gravity. I shall consider first cubic Horn
deski theories for which the higher derivatives are in the scalar sector o
nly. In these theories in the weakly coupled regime\, even though the diff
erences with standard general relativity can be locally small\, they accum
ulate over the lifetime of a binary resulting in waveforms that significan
tly deviate from those in general relativity. In the second part of the ta
lk\, I will discuss binaries in a certain eight-derivative theory of gravi
ty. I will first discuss how such a theory can be rendered well-posed and
then will present results on binaries as well as pointing out generic issu
es that may arise when modelling black hole binaries in such theories.\n\n
https://indico.tpi.uni-jena.de/event/224/contributions/526/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/526/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Generalizations of Einstein theory by including a scalar field
DTSTART;VALUE=DATE-TIME:20220728T130000Z
DTEND;VALUE=DATE-TIME:20220728T134500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-530@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Carlos Palenzuela (Universitat de les Illes Baleares
)\nSupplementing General Relativity (GR) with an additional scalar degree
of freedom yields to a simple and popular class of gravitational theories
known as scalar-tensor theories. While scalar-tensor theories can produce
self-accelerated cosmic expansion without a cosmological constant\, they t
ypically produce also local deviations from GR on small scales. However\,
some theories possess “screening mechanisms” that locally produce a GR
-like phenomenology\, potentially passing existing constraints. Here we wi
ll study numerically the evolution of neutron star systems on two specific
scalar-tensor theories (i.e.\, one with this screening mechanism and the
other without). Both cases show a interesting non-linear dynamics which co
uld help to constrain these alternative theories by using current and near
future gravitational wave observations.\n\nhttps://indico.tpi.uni-jena.de
/event/224/contributions/530/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/530/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A high-order discontinuous Galerkin-finite-difference hybrid metho
d for numerical relativity
DTSTART;VALUE=DATE-TIME:20220727T130000Z
DTEND;VALUE=DATE-TIME:20220727T134500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-524@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Nils Deppe (California Institute of Technology)\nCon
servative finite difference methods have proven extremely robust and relia
ble for magnetohydrodynamics simulations of binary neutron star mergers. H
owever\, finite difference methods are generally less accurate and efficie
nt than spectral methods when the solution is smooth\, e.g. away from the
stellar surfaces. The attractiveness of spectral methods has been demonstr
ated by thousands of long and highly accurate binary black hole simulation
s. Discontinuous Galerkin methods seek to provide the accuracy of spectral
methods while also robustly capturing shocks in hydrodynamics simulations
. I will give an overview of a discontinuous Galerkin-finite-difference hy
brid method that inherits the best properties of both spectral and finite
difference methods. I will show longterm simulations of magnetized and rot
ating neutron stars\, as well as test problems to demonstrate the reliabil
ity and accuracy of the hybrid method.\n\nhttps://indico.tpi.uni-jena.de/e
vent/224/contributions/524/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/524/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Meeting Challenges at the Next Frontier in Numerical Relativity
DTSTART;VALUE=DATE-TIME:20220727T134500Z
DTEND;VALUE=DATE-TIME:20220727T143000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-529@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: David Neilsen (Brigham Young University)\nNumerical
relativity has been a frontier problem in computational science for over f
ifty years. The complexity of this research field spans multiple areas\, f
rom the properties of partial differential equations to high performance c
omputing. As gravitational wave detectors continually improve\, and new de
tectors come online\, a new challenge will be to compute waveforms with hi
gher fidelity and for a broader array of possible sources. We have develop
ed Dendro-GR\, a new computational platform for numerical relativity that
uses a highly scalable octree with sparse\, wavelet-based refinement. I wi
ll present some of initial results obtained with Dendro-GR for merging bla
ck hole binaries with different mass ratios. I will also talk about some p
ossible new directions\, including a new faster GPU-based extension of Den
dro-GR\, and some possible approaches to refine solutions in time as well
as space. Performance and scaling results for these codes will be presente
d.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/529/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/529/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Postmerger phase of neutron star coalescences
DTSTART;VALUE=DATE-TIME:20220726T150000Z
DTEND;VALUE=DATE-TIME:20220726T154500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-522@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Andreas Bauswein (GSI Helmholtzzentrum für Schwerio
nenforschung)\nWe discuss the postmerger stage of binary neutron star coal
escences. We present an analytic model of postmerger gravitational-wave em
ission\, which achieves an overall good description of the gravitational-w
ave signal. The physical parameters of the model are useful to understand
the dynamics of the system\, and we identify new mechanisms shaping the gr
avitational-wave spectrum. Moreover\, we address the deviations of individ
ual data points in quasi-universal relations of postmerger gravitational-w
ave features encoding the equation of state dependence. We also discuss th
e threshold for prompt black-hole formation and the impact of strong phase
transitions on postmerger properties.\n\nhttps://indico.tpi.uni-jena.de/e
vent/224/contributions/522/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/522/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Neutron star merger simulations to enable multi-messenger astronom
y studies
DTSTART;VALUE=DATE-TIME:20220726T134500Z
DTEND;VALUE=DATE-TIME:20220726T143000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-525@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Tim Dietrich (University of Potsdam)\nNumerical-rela
tivity simulations are prerequisites for a reliable interpretation of mult
i-messenger events such as binary neutron star or black hole neutron star
mergers. When using simulation results to interpret observational data\, i
t is of uttermost importance to also ensure a proper discussion of the unc
ertainties of the simulations. Keeping this in mind\, we show some of our
most recent results and identify how simulation uncertainties could affect
the development of gravitational-wave and electromagnetic models. Finally
\, we will discuss some of the most recent developments of our numerical-r
elativity code BAM and review its capability and shortcomings in simulatin
g compact binary mergers.\n\nhttps://indico.tpi.uni-jena.de/event/224/cont
ributions/525/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/525/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Self-consistent modeling of compact binary mergers in numerical re
lativity
DTSTART;VALUE=DATE-TIME:20220726T130000Z
DTEND;VALUE=DATE-TIME:20220726T134500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-528@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Kenta Kiuchi (Max Planck Institute for Gravitational
Physics)\nIn this talk\, I will present the recent progress of numerical
modeling of compact binary mergers\, which involves at least one neutron s
tar in numerical relativity. Our group develops self-consistent modelings
by performing a long-term numerical relativity neutrino-radiation magnetoh
ydrodynamic simulation. I will present the details of the simulation resul
ts and perspective.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributi
ons/528/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/528/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Numerical relativity in cosmological spacetimes
DTSTART;VALUE=DATE-TIME:20220725T134500Z
DTEND;VALUE=DATE-TIME:20220725T143000Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-523@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: Katy Clough (Queen Mary University of London)\nI wil
l review the use of numerical relativity to probe cosmological spacetimes\
, highlighting the particular challenges faced in such simulations compare
d to the asymptotically flat case associated with black holes. I will focu
s on its potential to inform the "inflation versus bounce" debate\, as an
illustration of these challenges.\n\nhttps://indico.tpi.uni-jena.de/event/
224/contributions/523/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/523/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dual-Frame Generalized Harmonic Gauge on Hyperboloidal Slices
DTSTART;VALUE=DATE-TIME:20220725T130000Z
DTEND;VALUE=DATE-TIME:20220725T134500Z
DTSTAMP;VALUE=DATE-TIME:20240918T080746Z
UID:indico-contribution-224-527@indico.tpi.uni-jena.de
DESCRIPTION:Speakers: David Hilditch (Instituto Superior Tecnico\, Lisbon)
\nBoth for studies of cosmic censorship and for practical purposes in grav
itational wave astronomy\, it is desirable to include future null-infinity
in the computational domain. Extending formulations of general relativity
known to behave well in the strong-field regime out to infinity with comp
actification is\, however\, a subtle game. In my presentation I will expla
in how the competition between decay of fields near infinity and growth of
coefficients (due to compactification) plays out in dual-frame generalize
d harmonic gauge. I will discuss the numerical implementation of the resul
ting PDEs.\n\nhttps://indico.tpi.uni-jena.de/event/224/contributions/527/
LOCATION:TPI\, FSU Jena Abbeanum/Ground floor-HS1 - Hörsaal 1
URL:https://indico.tpi.uni-jena.de/event/224/contributions/527/
END:VEVENT
END:VCALENDAR