Workshop Introduction

• Lionel London
• Sarben Sarkar (Department of Physics)

Workshop overview This workshop is funded by the EPSRC (UK) through a grant ''PT symmetric field theory'' held in the Physics Department of King's College London (with Sarben Sarkar as PI). Its role is to relate the study of non-Hermiticity in two areas, black hole physics and quantum optics

Input output formalism and other methods in quantum optics of much interest to the black hole community

• Almut Beige

Non-Hermitian Black Hole Physics I

• Lionel London

Non-Hermitian Black Hole Physics II

• Rodrigo Panosso Macedo

Non-hermitian quantum electrodynamics and photon localisation

• Almut Beige

Brainstorming session Review and questions and potential connections from the day's talks

The Input output formalism & developments involving nonMarkovian effects I

• Sarben Sarkar (Department of Physics)

Loss of coherence and coherence protection from a graviton bath

• Sougato Bose (UCL)

On the Green's-function approach to deriving balance laws in perturbation theory

• Adam Pound

Rotating black holes in the lab: ringdown and superradiance

• Sam Patrick

Wave phenomena around spinning black holes can be simulated using rotating draining fluid flows. These are inherently leaky systems due to the presence of a central sink, through which fluid and waves escape. Over the past decade, these simulators have been used to study black hole ringdown and superradiance in the gravity laboratory at the University of Nottingham. In this talk, I will summarise these experiments and the subsequent theoretical investigations they sparked.

Brainstorming

The Input output formalism & developments involving nonMarkovian effects II

• Sarben Sarkar (Department of Physics)

Quasi-normal mode expansions of black hole perturbations: a hyperboloidal Keldysh's approach

• Jerem Besson

We study asymptotic quasinormal mode expansions of linear fields propagating on a black hole background by adopting a Keldysh scheme for the spectral construction of the resonant expansions. This scheme requires to cast quasinormal modes in terms of a non-selfadjoint problem, something achieved by adopting a hyperboloidal scheme for black hole perturbations. The method provides a spectral version of Lax-Phillips resonant expansions, adapted to the hyperboloidal framework, and extends and generalises Ansorg & Macedo black hole quasinormal mode expansions beyond one-dimensional problems. We clarify the role of scalar product structures in the Keldysh construction that prove non-necessary to construct the resonant expansion, in particular providing a unique quasinormal mode time-series at null infinity, but are required to define constant coefficients in the bulk resonant expansion by introducing a notion of 'size' (norm). By (numerical) comparison with the time-domain signal for test-bed initial data, we demonstrate the efficiency and accuracy of the Keldysh spectral approach. Indeed, we are able to recover Schwarzschild black hole tails, something that goes beyond the a priori limits of validity of the method and constitutes one of the main results. We also demonstrate the critical role of highly-damped quasinormal mode overtones to accurately account for the early time behaviour. As a by-product of the analysis, Sobolev H^p pseudospectra are constructed and the convergence issues of the black hole quasinormal mode pseudospectra are clarified in agreement with Warnick’s theorem.

Biorthogonality in quantum mechanics

• Dorje Brody

Merger-ringdown in the self-force approach

• Adam Pound

A new approach in classical Klein-Gordon cosmology

• Eleni Kontou (KCL)

Brainstorming

Closing Remarks

• Sarben Sarkar (Department of Physics)
• Lionel London