Physik-Combo

29 Mar 2022, 10:00 → 31 Mar 2022, 16:30 Europe/Berlin

Abbeanum/Ground floor-HS1 - Hörsaal 1 (TPI, FSU Jena)

The Physik-Combo - a transregional training initiative of the RTG 2522 Jena Leipzig - provides in-depth research training in topical areas in the context of "Strong Dynamics and Criticality in Quantum and Gravitational Systems".

Its program consists of topical reviews delivered by invited experts in the field and project talks contributed by the RTG fellows and guests.

This spring's version is currently planned as a hybrid (face-to-face/online) meeting; because of the pandemic, the number of on-site participants is limited and essentially restricted to the members of the RTG. Friends and guests from neighboring universities are welcome to participate online.

The Physik-Combo continues the tradition of the Mitteldeutsche Physik-Combo. 

Tuesday 29 March

1 Welcome

Speaker: Holger Gies (TPI, FSU Jena)

2 Energy conditions and quantum energy inequalities

Speaker: Chris Fewster

3 Q&A

12:15 Lunch break

4 Functional methods for cosmic large-scale structure formation

Speaker: Alaric Erschfeld

15:30 Break

5 Phase Transitions in a Yukawa-QCD Model

Despite the standard model's great success at describing
particle physics phenomenology at currently accessible energies it is not considered to provide a fundamental description of nature. One problem of the SM is the so-called hierarchy problem.

In our study we employ the functional renormalization group to gain insights on the phase transition in a Yukawa-QCD toy model. We study the parameter-dependence of the second order phase transition, with particular emphasis on the dependence of the separation of Fermi scale
and QCD scale.

Speaker: Richard Schmieden

6 Background Effective Action with Nonlinear Massive Gauge Fixing

Non-Abelian gauge theories constitute fundamental building blocks in the description of elementary particle interactions and exhibit by construction invariance under local gauge transformations.
Quantization entails a breaking of such symmetry, which is generally restored by imposing a constraint equation (e.g. Zinn-Justin equation), as well as a natural emergence of a global symmetry called BRST symmetry.
In our study, we employ the background field method to construct an action which preserves both gauge and BRST invariance manifestly. The construction features BRST invariant mass parameters for the gluon and ghost fields.
In our formalism, we compute the running coupling and examine the implications of such a construction in the form and behavior of the one-loop effective action.

Speaker: Dimitrios Gkiatas

17:00 Discussion time

Wednesday 30 March

7 Geometry of rotating discs in Einstein-Maxwell theory and the Ehrenfest paradox

In 1909 Ehrenfest formulated a famous paradox concerning a rigidly rotating disc (or cylinder originally) within special relativity. It caused a lot of debate and there is no general agreement on its solution. Directly related to the paradox is the question of spatial geometry of rotating discs.
In this talk, I will discuss the charged rotating disc of dust which is a concrete, physically relevant solution of the Einstein-Maxwell equations in terms of a post-Newtonian expansion.
Based on the solution, the spatial geometry of the disc will be examined and a comparison to a standard disc within special relativity (described by Grøn) will be drawn in the Newtonian limit. Furthermore, I will show that new, interesting effects appear near the ultra-relativistic limit and for non-vanishing charge.

Speaker: David Rumler

8 Singularity theorems

Speaker: Chris Fewster

9 Q&A

10:45 Break

10 Characteristic Hadamard states and semi-classical gravitational collapse

To study the influence of quantum fields on the formation of a black hole, we show how locally covariant renormalization schemes for the stress-energy tensor for linear scalar fields can be adapted to a characteristic (i.e. null-cone) treatment of the semi-classical Einstein equations. Key to this approach is understanding the singularities of Hadamard parametrices restricted to null-cones. We show that for conformally coupled fields on spherically symmetric space-times the renormalization freedom of this stress-energy tensor can be reduced by conditions on the required initial data. Furthermore, we show how this approach provides hints that due to local quantum effects during gravitational collapse the (averaged) null energy condition may be violated, potentially implying that formation of a trapped surface (i.e. apparent horizon) need not lead to the formation of a black hole singularity.

Speaker: Daan Janssen

11 Wedge-local observables in integrable models with bound states

Speaker: Karim Shedid

12:15 Lunch break

12 Black hole spectroscopy and fundamental physics implications of gravitational wave ringdown observations

Speaker: Gregorio Carullo

15:30 Break

13 GW190521: a dynamical capture of two black holes

Gravitational waves (GWs) represent a new channel to study the universe. They can lead to new --and at times unexpected-- discoveries about the nature of compact objects, such as black holes and neutron stars. However, our ability to extract the source properties from GW data crucially depends on the waveform models we employ to perform the analysis.
In this talk I will discuss the exemplary case of GW190521, the gravitational wave transient observed by LIGO and Virgo on 21 May 2019, whose astrophysical interpretation is strongly dependent on the model employed. After going over the possible interpretations that have been advanced, I will show that the data supports the first gravitational-wave detection from the dynamical capture of two stellar-mass black holes. This hypothesis is preferred over the more conservative scenario of two black holes coalescing along quasi-circular orbits.

Speaker: Rossella Gamba

14 Critical gravitational collapse with the code bamps

Critical phenomena emerges as we approach the threshold between gravitational collapse and dispersed fields. We study this phenomena associated to the gravitational field alone, in vacuum, by evolving gravitational waves. The axisymmetry of this setup allows us to verify critical phenomena beyond spherical symmetry. More importantly, widening the variety of initial data we can test the universality of these features. Our pseudo-spectral code bamps, with its new adaptive mesh refinement, has allowed us to tune six different one parameter families of initial data with the same resources that previously permitted us to tune one family. We present our results after evolving three prolate and three oblate, including two centred and four off-centred, families of Brill waves up to the threshold of critical collapse.

Speaker: Daniela Cors

17:00 PI / Fellow meeting

Thursday 31 March

15 Symmetry Breaking in Hydrodynamics and Holography

Symmetries are abundant in physical theories but often broken by Nature. In this talk I will discuss symmetry breaking and how is it incorporated into hydrodynamics -- an effective theory for the late time dynamics of conserved quantities. Such hydrodynamic frameworks may in turn be tested by the means of the holographic duality, the principles of which will be presented and some results shown.

Speaker: Seán Gray

16 Large charge expansion

Speaker: Susanne Reffert

17 Q&A

10:45 Break

18 Chiral symmetry for a gauge theory with one adjoint fermion on the lattice

In this talk, I will focus on how to implement chiral symmetry on the lattice through the overlap operator. We apply this approach to one flavour adjoint QCD to study whether an infra-red conformal behavior is observed or not. Our simulation shows that, quite deep in the infra-red regime, a natural length appears in terms of the chiral condensate, a strong numerical hint that the theory is not conformal, in contradiction to some previous results.

Speaker: Ivan Soler

19 One-Particle entanglement for one dimensional spinless fermions after an interaction quantum quench

Speaker: Matthias Thamm

12:15 Lunch break

20 New Evidence for Anyons: Collisions and Braiding

Fermions and bosons are fundamental realizations of quantum statistics, which governs both the symmetry of the wave function under the interchange of particle coordinates and the probability for two particles being close to each other spatially. Anyons in the fractional quantum Hall effect are an example for quantum statistics intermediate between bosons and fermions. Two recent experiments have provided evidence for such exotic anyonic statistics: the collision of anyons in a mesoscopic setup has demonstrated that anyons indeed have a reduced spatial exclusion as compared to fermions, and the symmetry of the quantum mechanical wave function for anyons has been measured directly by braiding anyons around each other in a Fabry-Perot interferometer. I will focus on the theoretical description of anyon collisions, which provides an interesting application of non-equilibrium bosonization.

Speaker: Bernd Rosenow

15:30 Discussion time