Registration A registration desk will be setup outside the conference venue: LH-5. All participants must sign the registration sheet and collect their Conference IDs. These IDs must be carried at all times.

Welcome Address - Sachindeo Vaidya, CHEP, IISc

Invited Talk - Causal Set Theory and the Closeness of Lorentzian Geometries - Sumati Surya, RRI, Bengaluru In this talk I will introduce the causal set approach to quantum gravity, and the founding idea that causality or order, combined with the local volume element determines  spacetime geometry.  Associated with  every causal spacetime and a discreteness scale,  is a random causal set, or a locally finite partially ordered set, which captures all the relevant spacetime geometry. One can thus reconstruct the spacetime geometry and topology from the causal set, upto this scale.  I will describe recent  work  that uses the underlying random causal sets  to define a closeness function over the space of  Lorentzian geometries, which can in turn be used to determine the approach to the continuum in causal set theory.  Session Chair : Sachindeo Vaidya

Contributed Talk - Normal Modes of the Stretched Horizon - Pradipta Shankar Pathak, CHEP, IISc Black hole horizons carry entropy but without an explicit state-counting interpretation. There has been considerable progress in understanding its microstructure, but all of them are in BPS-protected/near-BPS cases. Even there, we lack a bulk description of typical microstates (set aside AdS/CFT duality). Understanding bulk microstates seems essential for a satisfying resolution of the information paradox. In this talk, I will present a bottom-up construction to model the bulk microstructure of large AdS black holes far from extremality and supersymmetry. The key ingredients we will need are a Stretched Horizon and excitations on top of it. Session Chair : Sachindeo Vaidya

Invited Talk - Covariant entropy bounds in higher derivative theories of gravity - Nilay Kundu, IIT Kanpur In this talk we will try to understand how one can argue a classical Bousso bound for higher derivative corrections to general relativity. We will focus on theories for which the higher derivative terms are considered as small corrections in the Lagrangian to Einstein’s two-derivative theory of general relativity (GR), we prove the classical version of the covariant entropy bound (also known as the Bousso bound) in arbitrary diffeomorphism invariant gravitational theories. Even if the higher derivative corrections are treated perturbatively, we provide instances of specific configurations for which they can potentially violate the Bousso bound. To tackle this obstruction, we propose a modification in the Bousso bound that incorporates the offending contributions from the higher derivative corrections. We argue that the modified Bousso bound that we propose holds to all orders in the higher curvature corrections. Our proposed modifications are equivalent to replacing the Bekenstein-Hawking area term by Wald’s definition for the black hole entropy. Session Chair : Sachindeo Vaidya

Contributed Talk - EFT Corrections to Majumdar-Papapetrou Black Holes - Shuvayu Roy, IIT Gandhinagar Recent studies on extremal black holes within effective field theories (EFT) of gravity have revealed an intriguing phenomenon: tidal forces near the horizon experience significant enhancement due to EFT corrections, potentially leading to a breakdown of the EFT framework. In this talk, we will discuss this effect in a two-black-hole Majumdar-Papapetrou spacetime modified by four-derivative EFT correction terms. While the scaling exponents, which measure the strength of the tidal forces near the horizon, remain unchanged under EFT corrections in $D=4$, they decrease for higher dimensions, enhancing the near-horizon tidal forces. However, even in the presence of EFT corrections, these scaling exponents stay well-behaved, and no such cases arise where the two-derivative contributions vanish and only the higher-derivative terms contribute. We find an expression for the EFT corrections to the scaling exponents till $D \le 10$ and demonstrate that the metric corrections can be structured such that only the near-horizon $AdS_2$ throat undergoes angle-dependent modifications, while the transverse $S^{D-2}$ sector remains unaffected. Session Chair : Kartik Prabhu

Invited talk - Quantum origin of cosmological perturbations? - Krishna Mohan Parattu, IIT Mandi The standard paradigm for the origin of the large scale structure we see in the universe as well as the large scale fluctuations we see, for example, in the cosmic microwave background (CMB) posits that they originated from quantum fluctuations in the quantum field that the drove the epoch of inflationary expansion of the universe. From the 1990s onward, there were efforts to show how the classical structure emerges from the quantum fluctuations. But over the last decade or so, there has been considerable interest in finding some smoking gun signal of the proposed quantum origin. I shall give an overview of these efforts, describe some recent developments and conclude with some comments on open questions. Session Chair : Kartik Prabhu

Invited talk - Beyond Einstein: Search for New Gravitational Physics - Sudipta Sarkar, IIT Gandhinagar Einstein’s General Theory of Relativity (GR) has remained remarkably successful under a century of observational tests. However, various theoretical considerations increasingly indicate that GR may represent a low-energy effective limit of a more fundamental gravitational theory. This seminar will explore gravitational phenomena that extend beyond the Einsteinian framework by examining a range of possible modifications and generalizations of GR. Emphasis will be placed on maintaining theoretical consistency, ensuring unitarity, causality and stability while also addressing potential observational consequences in strong-field regimes, gravitational wave signals, and black hole dynamics. Particular emphasis will be placed on identifying imprints in black hole spacetimes, such as modifications in quasinormal mode spectra and in tidal Love numbers, which could offer critical empirical windows into possible modifications of gravity at a fundamental level. Session Chair : Kartik Prabhu

Contributed Talk - Violation of Bell inequality from squeezed coherent state of Inflationary perturbations. - Aurindam Mondal, Indian Statistical Institute, Kolkata In this project, we investigate the quantum nature of primordial perturbations by studying the violation of Bell inequality when the initial state is taken to be a coherent state rather than the usual Bunch-Davies vacuum. As inflation progresses, the coherent state evolves into a squeezed coherent state, and we derive an analytical expression for the expectation value of the Bell operator constructed from pseudo-spin operators. Our analysis shows that although the expectation value of the Bell operator initially deviates from the vacuum case, it asymptotically saturates to the same value. Notably, this saturation occurs more rapidly for non-zero coherent state parameters, indicating that a larger one-point correlation function accelerates the approach to maximal Bell inequality violation. Session Chair : Kartik Prabhu

Invited Talk - Thermodynamics of black holes: corrections to the first law and the Hawking spectrum  - Ayan Chatterjee, Central University of Himachal Pradesh, Dadroli The thermodynamic properties of black holes are known to receive corrections due to higher curvature corrections to the action. In particular, the first and the second laws of black hole mechanics are modified due to such terms. In the context of Isolated horizons, the equilibrium version of the first law of black hole mechanics for Lovelock gravity had remained unexplored. We derive the corrections to the zeroth and the first law of black hole mechanics for black holes in these theories. Furthermore, we shall show that if black holes are placed in a thermal bath, even the Hawking spectrum gets corrected. The exact expressions for thermal corrections to the Schwarzschild and the Kerr black holes shall be obtained.  Session Chair : Sanved Kolekar

Contributed Talk - Complex Metrics and Degeneracies in Quantum Cosmology - Manishankar Ailiga, CHEP, IISc Picard–Lefschetz theory has been a powerful tool for identifying the relevant saddle points of the Lorentzian gravitational path integral. However, this method becomes ill-defined when degeneracies arise in the system, and such issues must first be resolved. Once addressed, the relevant saddle points can be determined unambiguously. In general, these saddle points are complex, and it has been shown that they can correspond to both physical and unphysical scenarios.  This naturally arises the question of whether there exists any systematic way to classifying the complex metrics. Recently, Witten has addressed this question, providing a bound the helps in the distinction.  In my talk, within the minisuperspace approximation, I will discussing about a natural cure offered by the system in resolving degeneracy problem, followed by the compatibility of relevant saddle points with the Witten criterion. Session Chair : Sanved Kolekar

Invited Talk - Super-translation Transitions of Black Hole Horizons - Avirup Ghosh, Kulti College, West Bengal The memory effect and its relation to supertranslations at asymptotic Null infinity has been studied extensively. In this talk we try to decipher whether such a notion can be defined on a black hole horizon as well. A condition will be defined such that it can be said that a supertranslation has been induced, in the course of a general evolution, from one stationary horizon phase to another. The primary aim here, will be to check the viability of this condition, by considering different fluxes, that lead to an evolution of a stationary horizon. Finally, we will try to understand whether any observable signatures, at asymptotic infinity, can be extracted from this. Session Chair : Sanved Kolekar

Invited Talk - On Parametric Renormalization of the S-matrix - Alok Laddha, CMI, CHennai Session Chair : Gaurav Narain

Invited Talk - A connection between the missing mass and the cosmological constant from galactic rotation curves - Sandipan Sengupta, IIT Kharagpur We discuss an analogue of the Schwarzschild-(anti) de Sitter class of metrics for the outer region of spiral galaxies. These are shown to emerge as solutions to Einstein equations are associated with a constant Ricci scalar in four dimensions, being supported by anisotropic pressure and positive definite ‘mass’. The flatness of rotation curves at large radii emerges as a dynamical consequence. This is shown to imply that the (bare) cosmological constant must be related to the energy momentum tensor of the missing mass, being exactly zero if the latter is traceless. We also elucidate some specific observational implications of these galactic spacetime solutions. Session Chair : Gaurav Narain

Contributed Talk - (dS) Hartle-Hawking wave function from Lorentzian path integral - Shubhashish Mallik, CHEP, IISc The (H-H) no boundary proposal is a very natural and mathematically elegant proposal for computing the wavefunction of the universe. Although this proposal has existed since 1990, it is not clear how to get it as a saddle geometry of the quantum gravity path integral. In the first part of the talk, I will briefly describe how to get that following the recent work and our work as well. I will use the Picard-Lefschetz method and the Lorentzian contour prescription. I will also emphasise the importance of the initial boundary choices which leads to no boundary. In the second part of my talk, I will focus on the small fluctuation around the no-boundary universe (going beyond minisuperspace). While it is well known that such fluctuations are Gaussian and hence akin to the BD-vacuum, the one-loop properties are not so well known. I will describe, following our work, the one-loop computation around such geometry. It turns out that one-loop effects (virtual graviton contribution) grow as the universe expands, overpowering the leading order. We see it as a signature of IR-divergence, characteristics in de-Sitter space. Session Chair : Gaurav Narain

Invited Talk - Black holes, higher curvature gravity and von Neumann algebras - Suneeta Vardarajan, IISER Pune In recent years, the application of von Neumann algebras to black hole physics has yielded new insights. In the first half of the talk, we discuss the generalized second law (GSL) of black holes in semiclassical gravity. Using von Neumann algebras, in particular, the crossed product, various divergent quantities like the entanglement entropy can be rendered finite. We show how to prove the GSL in crossed product constructions for asymptotically AdS and asymptotically flat black holes including Kerr. In the second half of the talk, we discuss the question of what is the geometry that a string sees. Are horizons a well-defined notion? Recent work in AdS/CFT that answers this question using von Neumann algebras points to the possibility of different fields seeing different horizons. We discuss the connection of these ideas to our recent characteristic surface analysis of higher curvature gravity theories. Session Chair : Nirmalya Kajuri

Contributed Talk - Information Scrambling with Higher–Form Fields - Abhishek Chowdhury, IIT Bhubaneswar The late time behaviour of OTOCs involving generic non–conserved local operators shows exponential decay in chaotic many-body systems. However, it has been recently observed that the OTOC involving the U (1) conserved current for a gauge field varies diffusively at late times for specific holographic theories. The present work generalises this observation to conserved currents corresponding to higher–form symmetries belonging to a broader class of generalised symmetries, generalised by computing the late-time behaviour of OTOCs involving U (1) current operators in five-dimensional AdS-Schwarzschild black hole geometry for the 2–form antisymmetric B-fields. The bulk solution for the B-field exhibits logarithmic divergences near the asymptotic AdS boundary, which can be regularised by introducing a regularised double trace deformation in the boundary CFT. Finally, we consider the more general case with antisymmetric p–form fields in arbitrary dimensions. In the scattering approach, the boundary OTOC can be written as an inner product between asymptotic ‘in’ and ‘out’ states, equivalent to computing the inner product between two bulk fields with and without a shockwave background. We observe that the late-time OTOCs have power-law tails, which seems to be a universal feature of the higher–form fields with U (1) charge conservation. Session Chair : Nirmalya Kajuri

Invited Talk - Quantum phase transitions in matrix model of two-color  QCD - Nirmalendu Acharya, IIT Bhubaneswar $SU(2)$ gauge theory coupled to fundamental or adjoint quarks (two-color QCD) has been the subject of considerable interest and investigation. It has several novel and intriguing features which are worth studying in their own right. Here, we consider the matrix model of two-color QCD: a quantum mechanical model on $S^3 \times \mathbb{R}$ coupled to $N_f$ fermions (which transform in fundamental or adjoint representation of the gauge group). In this model, we use the variational methods to construct the energy eigenstates with $N_f=1$ and $N_f=2$ (in both the weak and the strong coupling regimes). We study the properties of the ground state in the chiral limit and in the heavy fermion limit. Further, we explore situations with large baryon number and isospin chemical potentials. We find that there exists a rich quantum phase transition (QPT) structure in these models and different phases are characterized by different ground states. In the extreme strong coupling regime, we find that the dominant glue contribution to the ground state comes from reducible connections. On the other hand, when the chemical potentials are present, the ground state can have non-zero spin. In such a scenario, the ground state breaks the rotational invariance and this is a reminiscence of the LOFF phases observed in two-color QCD. We estimate the division of the total spin of the ground state between the glue and the quark: the glue contribution is significant, particularly in the strong coupling regime and chiral limit. Session Chair : Nirmalya Kajuri

Invited Talk - Kartik Prabhu, RRI, Bengaluru Session Chair : Nirmalya Kajuri

Contributed Talk - Holographic Entanglement Entropy at Spatial Infinity in Flat Space - Abir Ghosh, IISc In AdS/CFT, entanglement entropy for boundary subregions is computed via Ryu-Takayanagi (RT) surfaces anchored to the conformal boundary. Extending this framework to asymptotically flat spacetimes presents conceptual challenges due to the lack of a causal boundary structure. In this talk, I introduce the notion of a "spi-subregion"—a bi-partitioning of spatial infinity (spi)—and demonstrate how it provides a natural holographic data set for defining entanglement entropy in flat space. I show that the RT surfaces associated with symmetric spi-subregions correspond to the waists of Asymptotic Causal Diamonds, reducing to Rindler horizons in empty flat space and exhibiting phase transitions in the presence of black holes. These transitions mirror those found in AdS black holes, suggesting a deep structural parallel. A key insight is that the radial cut-off in flat space acts as an IR regulator, and the resulting entanglement entropy is UV-finite, consistent with the long string paradigm. This work highlights the viability of holographic entanglement entropy in flat space and its implications for non-local dual descriptions. Session Chair : Nirmalya Kajuri

Vote of Thanks and Closing Remarks