We will explain the construction of the euclidean vacuum state for linearized gravity on de Sitter spacetime by a rigorous version of Wick rotation. We will discuss issues related to gauge invariance, positivity and invariance under de Sitter isometries.

The analysis of quantum states in non-smooth spacetimes has two main motivations. First, there are several models of physical phenomena that require spacetime metrics with finite regularity. These include models of gravitational collapse, astrophysical objects and general relativistic fluids. Second, the well-posedness of Einstein’s equations, viewed as a system of hyperbolic PDE requires...

Motivated by a long-standing aim to understand the emergence of spacetime and its relation to entanglement in the context of gauge/gravity duality, we study the relations between subsystem entanglement entropies. These quantities are delimited by the so-called holographic entropy cone, characterized conveniently by holographic entropy inequalities or alternately by certain extreme states. ...

It is well known that the expectation value of the stress-energy tensor for a quantum field must be renormalized. While there exists a well-understood formal resolution to the renormalization problem, the practical implementation is technically difficult in black hole spacetimes. The first successful computation of the renormalized stress-energy tensor in a black hole spacetime dates back to...

In order to study physical effects of quantum fields on curved spacetimes, one needs appropriate

Hadamard states to describe the fields. In this talk, we present a rigorous construction, including

the proof of the Hadamard property, of the Unruh state for the free scalar field on slowly rotating

Kerr-de Sitter spacetimes. We sketch how this state can be used to compute the stress-energy...

We show that if a massive body is put in a quantum superposition of spatially separated states, the mere presence of a black hole in the vicinity of the body will eventually destroy the coherence of the superposition. This occurs because, in effect, the gravitational field of the body radiates soft gravitons into the black hole, allowing the black hole to harvest "which path'' information...

A long-standing problem in QFT and quantum gravity is the construction of an “IR-finite" S-matrix. In the gravitational case, the existence of these “infrared divergences” is intimately tied to the “memory effect” (i.e. the permanent displacement of test masses due to the passage of a gravitational wave). In this talk, I shall explain the origin of these connections and illustrate that the...

What are the essential aspects of quantum theory needed in order to understand compact relativistic objects? Relying solely on universal properties of QFTs at high energies, we show that as a star contracts towards its Buchdahl radius the effects of the trace anomaly become macroscopic at densities much below the Planck scale. As a consequence the unstable modes of scalar fields disappear,...