Monday, December 8th, 2025
Workshop: Grigorios Fournodavlos
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: The initial boundary value problem for the Einstein vacuum equations with umbilic boundary
Speaker: Grigorios Fournodavlos
Abstract: In this talk, we will discuss the initial boundary value problem in general relativity from a mathematical point of view. We will first make the analogy to the classical Cauchy problem for the Einstein equations, first resolved by Yvonne Choquet-Bruhat in 1952, and highlight some desired properties that a potential treatment of timelike boundaries should have. Then, we will go over the various technical difficulties that arise in such an endeavor. The main result that we will present in the end concerns the local well-posedness of the problem for homogeneous Neumann conditions, in geometric terms, when the boundary is umbilic.
Title: The initial boundary value problem for the Einstein vacuum equations with umbilic boundary
Speaker: Grigorios Fournodavlos
Abstract: In this talk, we will discuss the initial boundary value problem in general relativity from a mathematical point of view. We will first make the analogy to the classical Cauchy problem for the Einstein equations, first resolved by Yvonne Choquet-Bruhat in 1952, and highlight some desired properties that a potential treatment of timelike boundaries should have. Then, we will go over the various technical difficulties that arise in such an endeavor. The main result that we will present in the end concerns the local well-posedness of the problem for homogeneous Neumann conditions, in geometric terms, when the boundary is umbilic.
Workshop: Batoul Banihashemi
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Thermodynamics of gravity at finite cutoff
Speaker: Batoul Banihashemi
Abstract: Defining thermodynamic ensembles for gravitational systems is tied to specifying boundary conditions. In this talk I'll first briefly review how introducing a Dirichlet timelike boundary clarifies thermodynamics of de Sitter space. Then I'll discuss geometries subjected to conformal boundary conditions, where the conformal class of the boundary metric and the trace of the extrinsic curvature K are held fixed. In the high temperature limit the series of subextensive terms in the free energy are compared to predictions from thermal effective field theory, and we observe agreement in all considered cases. Ensembles with negative K include solutions with cosmic-type horizons, where the system boundary is smaller than the horizon. In some regions of parameter space, these solutions are the dominant phase and are necessary for consistency with thermal effective field theory.
Title: Thermodynamics of gravity at finite cutoff
Speaker: Batoul Banihashemi
Abstract: Defining thermodynamic ensembles for gravitational systems is tied to specifying boundary conditions. In this talk I'll first briefly review how introducing a Dirichlet timelike boundary clarifies thermodynamics of de Sitter space. Then I'll discuss geometries subjected to conformal boundary conditions, where the conformal class of the boundary metric and the trace of the extrinsic curvature K are held fixed. In the high temperature limit the series of subextensive terms in the free energy are compared to predictions from thermal effective field theory, and we observe agreement in all considered cases. Ensembles with negative K include solutions with cosmic-type horizons, where the system boundary is smaller than the horizon. In some regions of parameter space, these solutions are the dominant phase and are necessary for consistency with thermal effective field theory.
Workshop: Don Marolf (Zoom)
Time: 2:30 PM - 3:30 PM
Location: SCGP 102/ZOOM
Title: Timelike Dirichlet Boundaries and the End of Time
Speaker: Don Marolf
Abstract: TBA
Title: Timelike Dirichlet Boundaries and the End of Time
Speaker: Don Marolf
Abstract: TBA
Workshop: Gonzalo Torroba (Discussion)
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Quantum aspects of time-like boundaries
Speaker: Gonzalo Torroba (Discussion)
Abstract: Timelike boundaries in gravitational systems provide a powerful framework for understanding quasilocal holography, cosmological horizons, and the microscopic structure of spacetime in the absence of asymptotic regions. This discussion session will focus on quantum aspects of timelike boundaries, including possible UV completions, lessons from holography, and effects from quantum fields. Participants are invited to share perspectives, open problems, and recent progress in this area.
Title: Quantum aspects of time-like boundaries
Speaker: Gonzalo Torroba (Discussion)
Abstract: Timelike boundaries in gravitational systems provide a powerful framework for understanding quasilocal holography, cosmological horizons, and the microscopic structure of spacetime in the absence of asymptotic regions. This discussion session will focus on quantum aspects of timelike boundaries, including possible UV completions, lessons from holography, and effects from quantum fields. Participants are invited to share perspectives, open problems, and recent progress in this area.
Tuesday, December 9th, 2025
Workshop: Xiaoyi Liu
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: Euclidean well-posedness and Lorentzian ill-posedness of generalized conformal boundary conditions
Speaker: Xiaoyi Liu
Abstract: We study four-dimensional Einstein gravity with a finite boundary. We introduce a one-parameter family generalization of Anderson’s conformal boundary condition and show that these boundary conditions lead to a well-posed elliptic system in Euclidean signature. We further discuss the associated thermodynamic properties. In Lorentzian signature, we analyze the corresponding initial-boundary value problem (IBVP) and demonstrate that these boundary conditions render the system ill-posed at the linearized level.
Title: Euclidean well-posedness and Lorentzian ill-posedness of generalized conformal boundary conditions
Speaker: Xiaoyi Liu
Abstract: We study four-dimensional Einstein gravity with a finite boundary. We introduce a one-parameter family generalization of Anderson’s conformal boundary condition and show that these boundary conditions lead to a well-posed elliptic system in Euclidean signature. We further discuss the associated thermodynamic properties. In Lorentzian signature, we analyze the corresponding initial-boundary value problem (IBVP) and demonstrate that these boundary conditions render the system ill-posed at the linearized level.
Workshop: Gauri Batra
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: A theory of two-sided de Sitter space with matter and the cosmological future wedge
Speaker: Gauri Batra
Abstract: We show how to capture the states in the spectrum of two-sided de Sitter space with timelike boundaries, taking into account the causal connection between the two boundaries in states with matter. To do so, we review the construction of the theory describing one static patch with a timelike boundary via a deformation of AdS/CFT. We outline how this leads to a microstate count of the de Sitter horizon. We then study the two-sided theory by constructing the thermofield double for this system. We show how to consistently combine the one-sided theories to produce a theory of the two-sided system, where the two boundaries are in causal contact. This theory reproduces some expected properties of the two-sided system. We end with some exploration of bulk reconstruction in this framework, enabling us to study the cosmological future wedge
Title: A theory of two-sided de Sitter space with matter and the cosmological future wedge
Speaker: Gauri Batra
Abstract: We show how to capture the states in the spectrum of two-sided de Sitter space with timelike boundaries, taking into account the causal connection between the two boundaries in states with matter. To do so, we review the construction of the theory describing one static patch with a timelike boundary via a deformation of AdS/CFT. We outline how this leads to a microstate count of the de Sitter horizon. We then study the two-sided theory by constructing the thermofield double for this system. We show how to consistently combine the one-sided theories to produce a theory of the two-sided system, where the two boundaries are in causal contact. This theory reproduces some expected properties of the two-sided system. We end with some exploration of bulk reconstruction in this framework, enabling us to study the cosmological future wedge
Workshop: Kuroush Allameh
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: TBA
Speaker: Kuroush Allameh
Abstract: TBA
Title: TBA
Speaker: Kuroush Allameh
Abstract: TBA
Wednesday, December 10th, 2025
Workshop: Zhongshan An (Zoom)
Time: 9:30 AM - 10:30 AM
Location: SCGP 102/ZOOM
Title: Geometric boundary conditions for the IBVP of vacuum Einstein equations
Speaker: Zhongshan An
Abstract: In general relativity, it is of great interest to construct spacetimes satisfying the vacuum Einstein equations. While the Cauchy problem of vacuum Einstein equations has been well studied since the work of Choquet-Bruhat, the initial boundary value problem (IBVP) remains much less understood. To establish a well-posed IBVP, one needs to impose appropriate boundary conditions on the time-like boundary. However, due to the complexity of energy estimate and gauge issue, so far there has not been a canonical choice of boundary conditions. In this talk, I will discuss the local-in-time well-posedness of various choices of geometric boundary conditions for the IBVP based on a series of works joint with Michael Anderson
Title: Geometric boundary conditions for the IBVP of vacuum Einstein equations
Speaker: Zhongshan An
Abstract: In general relativity, it is of great interest to construct spacetimes satisfying the vacuum Einstein equations. While the Cauchy problem of vacuum Einstein equations has been well studied since the work of Choquet-Bruhat, the initial boundary value problem (IBVP) remains much less understood. To establish a well-posed IBVP, one needs to impose appropriate boundary conditions on the time-like boundary. However, due to the complexity of energy estimate and gauge issue, so far there has not been a canonical choice of boundary conditions. In this talk, I will discuss the local-in-time well-posedness of various choices of geometric boundary conditions for the IBVP based on a series of works joint with Michael Anderson
Workshop: Pau Figueras
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: TBA
Speaker: Pau Figueras
Abstract: TBA
Title: TBA
Speaker: Pau Figueras
Abstract: TBA
Workshop: Students presentations
Time: 1:00 PM - 2:00 PM
Location: SCGP 102
Title: Student presentations
Speaker: Samanta Saha (Case Western U.), Antonia Seifert (Perimeter Institute),Xinkang Wang (Chicago U.), Themistoklis Zikopoulos (Perimeter Institute)
Abstract: See Webpage under Student Presentations for titles and abstracts
Title: Student presentations
Speaker: Samanta Saha (Case Western U.), Antonia Seifert (Perimeter Institute),Xinkang Wang (Chicago U.), Themistoklis Zikopoulos (Perimeter Institute)
Abstract: See Webpage under Student Presentations for titles and abstracts
Workshop: Simone Speziale
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: TBA
Speaker: Simone Speziale
Abstract: TBA
Title: TBA
Speaker: Simone Speziale
Abstract: TBA
Thursday, December 11th, 2025
Workshop: Amr Ahmadain
Time: 9:30 AM - 10:30 AM
Location: SCGP 102
Title: TBA
Speaker: Amr Ahmadain
Abstract: TBA
Title: TBA
Speaker: Amr Ahmadain
Abstract: TBA
Workshop: Silvia Georgescu
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: TBA
Speaker: Silvia Georgescu
Abstract: TBA
Title: TBA
Speaker: Silvia Georgescu
Abstract: TBA
Workshop: Tom Hartman
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: Gravity on a finite region with fixed-area boundary conditions
Speaker: Tom Hartman
Abstract: Gravity can be formulated on a finite region of Euclidean spacetime, with boundary conditions that fix the areas or bending angles at extremal surfaces on the boundary. The path integral with these boundary conditions computes the statistics of black hole operators. I will discuss this approach in general dimensions, and then focus on the semiclassical geometries in 3D gravity with negative cosmological constant, which are built from generalized hyperbolic tetrahedra. These are the geometries underlying recent topological calculations in Virasoro TQFT and Conformal Turaev-Viro theory.
Title: Gravity on a finite region with fixed-area boundary conditions
Speaker: Tom Hartman
Abstract: Gravity can be formulated on a finite region of Euclidean spacetime, with boundary conditions that fix the areas or bending angles at extremal surfaces on the boundary. The path integral with these boundary conditions computes the statistics of black hole operators. I will discuss this approach in general dimensions, and then focus on the semiclassical geometries in 3D gravity with negative cosmological constant, which are built from generalized hyperbolic tetrahedra. These are the geometries underlying recent topological calculations in Virasoro TQFT and Conformal Turaev-Viro theory.
Workshop: Aron Wall
Time: 4:00 PM - 5:00 PM
Location: SCGP 102
Title: Towards Hamiltonian String Field Theory, and Dirichlet Walls
Speaker: Aron Wall
Abstract: I will present preliminary work towards formulating string field theory in a Hamiltonian (equal time slice) formalism. This problem is closely related (via a Wick rotation) to the problem of finding consistent End-Of-The-World boundary conditions for string scattering, in which the metric satisfies Dirichlet boundary conditions (rather than Neumann). In defining the transition amplitudes, two fundamental problems arise: (i) string worldsheets have tadpoles which transgress across the boundary infinitely often, and (ii) when a string does cross the boundary, it can cross multiple times. However, I believe that both of these problems can be overcome (at least at tree level) by clever resummation tricks.
Title: Towards Hamiltonian String Field Theory, and Dirichlet Walls
Speaker: Aron Wall
Abstract: I will present preliminary work towards formulating string field theory in a Hamiltonian (equal time slice) formalism. This problem is closely related (via a Wick rotation) to the problem of finding consistent End-Of-The-World boundary conditions for string scattering, in which the metric satisfies Dirichlet boundary conditions (rather than Neumann). In defining the transition amplitudes, two fundamental problems arise: (i) string worldsheets have tadpoles which transgress across the boundary infinitely often, and (ii) when a string does cross the boundary, it can cross multiple times. However, I believe that both of these problems can be overcome (at least at tree level) by clever resummation tricks.
Friday, December 12th, 2025
Workshop: Vahid Taghiloo (Zoom)
Time: 9:30 AM - 10:30 AM
Location: SCGP 102/ZOOM
Title: Gravity Is Induced By Renormalization Group Flow
Speaker: Vahid Taghiloo
Abstract: In this talk, we study the renormalization group (RG) flow of a holographic CFT in the AdS5/CFT4 framework. Moving from the UV toward the IR along the RG trajectory of the boundary theory, we find that gravitational couplings are gradually generated, giving rise to a dynamical boundary gravity. This surprising result suggests that gravity can emerge dynamically in the infrared rather than being a fundamental interaction.
Title: Gravity Is Induced By Renormalization Group Flow
Speaker: Vahid Taghiloo
Abstract: In this talk, we study the renormalization group (RG) flow of a holographic CFT in the AdS5/CFT4 framework. Moving from the UV toward the IR along the RG trajectory of the boundary theory, we find that gravitational couplings are gradually generated, giving rise to a dynamical boundary gravity. This surprising result suggests that gravity can emerge dynamically in the infrared rather than being a fundamental interaction.
Workshop: Albert Law
Time: 11:00 AM - 12:00 PM
Location: SCGP 102
Title: Horizon Edge Modes in Λ > 0 Quantum Gravity
Speaker: Albert Law
Abstract: We derive the explicit form of the induced boundary gravitational action in the IR regime. The resulting effective theory includes Einstein gravity with a cosmological constant, supplemented by a single higher-derivative correction in the form of a Weyl-squared term. This provides a concrete realization of gravity emerging from holographic renormalization group flow.
Title: Horizon Edge Modes in Λ > 0 Quantum Gravity
Speaker: Albert Law
Abstract: We derive the explicit form of the induced boundary gravitational action in the IR regime. The resulting effective theory includes Einstein gravity with a cosmological constant, supplemented by a single higher-derivative correction in the form of a Weyl-squared term. This provides a concrete realization of gravity emerging from holographic renormalization group flow.
Workshop: Celine Zwikel
Time: 2:30 PM - 3:30 PM
Location: SCGP 102
Title: TBA
Speaker: Celine Zwikel
Abstract: TBA
Title: TBA
Speaker: Celine Zwikel
Abstract: TBA