Calendar
All talks are the first workable Monday of the month at 4pm (GMT)
Calendar
All talks are the first workable Monday of the month at 4pm (GMT)
Please subscribe to our mailing list to receive the invitations!
Please subscribe to our mailing list to receive the invitations!
2026-1 series
February 2nd 2026: Albert Much (Leipzig, Germany), 'Generalizing Jacobson's derivation to QFT via modular theory.'
March 2nd 2026: Noa Zilberman (Princeton, USA) , 'The semiclassical energy outflux emerging from a collapsing shell'.
April 13th 2026: Ivette Fuentes (Southampton, UK), title TBA.
May 11th José Navarro-Salas (Valencia, Spain), title TBA.
Speaker: Ivette Fuentes
Title: TBA
Abstract: TBA
2025-2 series
September 8th 2025: Azadeh Maleknejad (Swansea, UK), 'Matter Creation by Cosmic Perturbations at 1-loop'.
October 6th 2025: Daniel Sudarsky (ICN-UNAM, Mexico), 'Semiclassical gravity and applications to Cosmology'.
November 3rd 2025: Jennie Traschen (Amherst, USA), 'Thermodynamics of KNdS Black Holes and Spin Systems Or, How I came to love negative temperature'
December 1st 2025: Panel discussion on black hole information paradox 2pm (UK time)
Speakers: Bernard Kay (York, UK), Suvrat Raju (ICTS, India), Carlo Rovelli (Marseille, France)
Moderator: Erik Curiel (Bonn, Germany)
2025-1 series
February 3rd 2025: Nicola Pinamonti (Genoa, Italy), 'Semiclassical Einstein equations. Theoretical aspects and some applications'.
March 3rd 2025: Erik Curiel (Bonn, Germany), 'Semi-Classical Gravity as Effective Field Theory and the Information-Loss Paradox'.
March 31st 2025: Silvia Pla (TUM, Germany), 'Low-energy states and CPT-invariance at the big bang '.
May 12th 2025: Christiane Klein (York, UK), 'The challenges of exploring quantum fields in rotating black holes'.
Speaker: Noa Zilberman
Title: The semiclassical energy outflux emerging from a collapsing shell
Abstract: When a compact object collapses to form a black hole, quantum field theory predicts the emission of an energy outflux to future null infinity, which later relaxes to Hawking radiation.
Within the semiclassical framework, we derive a simple, closed form, analytical expression for the energy outflux emitted from a spherical thin null shell collapsing to form a black hole (in 4D). In particular, this energy outflux vanishes (quadratically in r-2M) as the shell approaches the horizon. This result refutes claims that the Hawking energy outflux originates from the collapsing body, showing instead that it develops in a broad strong-field region. Additionally, this vanishing implies that semiclassical backreaction cannot prevent or significantly affect the classical process of gravitational collapse and horizon formation (as sometimes claimed). This talk is based on the joint work arXiv:2503.00622 with Amos Ori.
Speaker: Albert Much
Title: Generalizing Jacobson's Derivation to QFT via modular theory
Abstract: Jacobson showed that the Einstein equations follow from the thermodynamic relation \delta Q = T \delta S, where Q is the heat flux, T the temperature and S the entropy, applied to local Rindler horizons, using quantum field theoretic input such as the Unruh effect. This raises the question of whether gravity can be derived entirely within quantum field theory (QFT).
In this talk, I present a QFT-based extension of Jacobson’s argument formulated in terms of relative entropy, a well-defined and finite entropic quantity for local algebras in QFT. Approximating small spacetime regions by Minkowski space, we compute the relative entropy between the vacuum and coherent excitations of a Klein–Gordon field on a local Rindler horizon using modular theory. The resulting expression is governed by the stress–energy tensor and encodes the energy flux across the horizon. Identifying the variation of relative entropy with the area variation of the horizon then reproduces the semiclassical Einstein equations, providing a quantum-information-theoretic perspective on gravitational dynamics.
This talk is based on joint work with Philipp Dorau (https://arxiv.org/abs/2510.24491).
Title: Panel discussion on black hole information paradox
Participants: Bernard Kay, Suvrat Raju and Carlo Rovelli
Moderator: Erik Curiel
This is a specialists panel on the information loss paradox.
Speaker: Jennie Traschen
Title: Thermodynamics of KNdS Black Holes and Spin Systems Or, How I came to love negative temperature
Abstract: Stephen Hawking pioneered the field of black hole thermodynamics, showing that black holes have thermodynamic properties analogous to a box of photons in thermal equilibrium. In contrast, the thermodynamic properties of Kerr-de Sitter (KdS) black holes, which are rotating black holes in a spacetime with positive cosmological constant, are similar to the thermodynamics of a set of non-interacting spins in a magnetic field. This spin system is characterized by bounded entropy S and energy E, with S(E) symmetric about its maximum due to a symmetry in the counting of states. As a result, the temperature is positive at lower energies and negative at higher energies.
The gravitational entropy and mass M of a black hole with positive cosmological constant are also bounded, unlike spacetimes with zero or negative cosmological constant. The entropy S(M) of a KdS black hole is symmetric about its maximum, due to a (less obvious) symmetry. This leads to positive and negative “system temperatures” of different black hole spacetimes. We show how the geometrical structure of a black hole horizon surrounded by a cosmological horizon, leads to these properties. These results provide evidence that the spacetimes have an underlying quantum structure of a finite dimensional Hilbert space. For example, the fact that the cosmological horizon has a negative temperature is seen to arise naturally when comparing KdS to constrained subsystems of spins.
Speaker: Daniel Sudarsky
Title: Semiclassical gravity and applications to Cosmology
Abstract: We review some conceptual problems in quantum theory and their repercussions in the way we treat the gravitation/quantum interface, emphasizing the manner in which they occur in the cosmological context. We will consider, in particular, issues arising in the discussion of inflation, such as the emergence of the seeds of cosmic structure, the predictions for generation of primordial gravity waves, and the problem of eternal inflation, where we find that the approach we advocate results in substantial departures from the findings obtained in the more traditional treatments.
Speaker: Azadeh Maleknejad
Title: Matter Creation by Cosmic Perturbations at 1-loop
Abstract: Conformal fields cannot be produced purely gravitationally in an expanding universe (4d FLRW geometry) at the tree level. However, this picture changes at the gravitational 1-loop level in the presence of cosmic perturbations, leading to a new and unavoidable mechanism for gravitational particle production. In this talk, I will explore the theory and cosmological implications of this effect.
Speaker: Christiane Klein
Title: The challenges of exploring quantum fields in rotating black holes
Abstract: In an era where the black holes in the universe become observationally accessible, it is increasingly important to have a good theoretical understanding of these objects. Since astrophysical black holes are usually rotating, this is the class of black holes one would like to understand, not only within the framework of GR, but also in extended frameworks such as semiclassical gravity. In this talk, I will discuss different features of rotating black holes and the challenges and opportunities they present for the study of free quantum theories on these spacetimes.
Speaker: Silvia Pla
Title: Low-energy states and CPT-invariance at the big bang
Abstract: In this talk, I will explain how to construct CPT-invariant quantum states in a radiation dominated-universe for scalars and spin ½ fields. I will show the explicit boundary conditions that these states must satisfy to become ultraviolet regular [Hadamard] and discuss the phenomenological consequences of the different choices (e.g., the impact on the predicted mass of a heavy right-handed neutrino). I will also discuss the motivation of this analysis and the role of the conformal anomaly (or the absence of it).
Speaker: Erik Curiel
Title: Semi-Classical Gravity as Effective Field Theory and the Information-Loss Paradox
Abstract: I examine several different formulations of the Information-Loss Paradox, discussing how they may and may not be related to each other. I then discuss what bearing a resolution of any of the formulations could have on attempts to formulate a theory of quantum gravity, in light of the fact that the framework of semi-classical gravity, in which the paradox is derived, is manifestly an effective field theory. I discuss two different ways one might treat semi-classical gravity as an effective field theory, and analyze the different possible consequences for each on the paradox. I conclude that the paradox is not necessarily problematic, though for reasons quite different from those of physicists such as Unruh and Wald and philosophers such as Maudlin, who come to a similar conclusion.
Speaker: Nicola Pinamonti
Title: Semiclassical Einstein equations. Theoretical aspects and some applications
Abstract: In this talk, we discuss properties of the semiclassical Einstein equation, which describes the backreaction of quantum matter on the geometry of classical backgrounds. After outlining general features of the equation and its solutions, we focus on backgrounds representing cosmological spacetimes. The matter is modeled as a quantum scalar field with a generic mass and arbitrary coupling to scalar curvature. We observe that the expectation value of the matter stress tensor, which sources gravity, contains a nonlocal term with higher-order derivatives. This term complicates a direct analysis of the solution of the system. We show how to address this issue by reformulating the semiclassical equation into a form suitable for analysis with Banach fixed-point methods.