Conveners
Contributed: Leonid Gurvits - "Multi-messaging prelude: precursors of gravitational wave emitters at the milliarcsecond scale"
- Chair: Hyunbae Park
Contributed: Vicharit Yingcharoenrat - "Large n-point functions in resonant inflation"
- Chair: Yuhang Zhu
Contributed: Bum-Hoon Lee - "Cosmic Gravitational Microwave Backgrounds and the Einstein-dilaton-Gauss-Bonnet Cosmology"
- Chair: Ivan Rybak
Contributed: Daiki Saito, Yi-Zen Chu
- Chair: Yuhang Zhu
Contributed: Swagat Saurav Mishra, Toshiki Takadera
- Chair: Ivan Rybak
Contributed: Perseas Christodoulidis, S Mahesh Chandran
- Chair: Rinku Maji
Contributed: Zahra Davari, Purba Mukherjee
- Chair: Boris Kamenetskaia
Contributed: Ido Ben-Dayan - "Suppressed Intrinsic Curvature Gravity"
- Chair: Georg Trenkler
Contributed: Konstantinos F. Dialektopoulos - "Primordial black holes as cosmic expansion accelerators"
- Chair: Fumio Uchida
Contributed: Pritha Bari, Tomotaka Kuroda
- Chair: Fumio Uchida
Contributed: Pavel Petrov, Eve Dones
- Chair: Georg Trenkler
Contributed: Rinku Maji, Michiru Uwabo-Niibo
- Chair: Hao Jiao
Contributed: Valentina Danieli, Dong Ha Lee
- Chair: Pavel Petrov
Contributed: Jeong-Hyuck Park - "Gravity of String Theory: Next Einstein Equation"
- Chair: Hui-Yu Zhu
Contributed: Javier Moreno, Che-Yu Chen
- Chair: Theodoros Nakas
Contributed: Mang Hei Gordon Lee, Calvin Chen
- Chair: Theodoros Nakas
Contributed: Stephen Angus, Masroor C. Pookkillath
- Chair: Hui-Yu Zhu
Contributed: Jibril Ben Achour - "Jet launching and acceleration of charged particles in the Kerr magnetosphere: An electrogeodesic approach"
- Chair: Eve Dones
Contributed: Minxi He, Joakim Flinckman, Zi-Yu Tang, Yusuke Manita
- Chair: Masroor Pookkillath
Contributed: Hugo Roussille
- Chair: Eve Dones
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27/04/2026, 16:30
Formation of super-massive black hole binaries (SMBHB) is deemed to be inevitable in various cosmological models. Their search poses one of the most challenging problems of modern observational astrophysics. Dissipation of kinetic energy in SMBHB controls the evolution of these objects and leads to coalescing into a single black hole. This process (often called “inspiralling”) is accompanied...
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28/04/2026, 14:00
After the motivation for frameworks beyond Einstein's gravity and the ΛCDM paradigm, we explain the Cosmology of the Einstein-dilaton-Gauss-Bonnet (EdGB) gravity, one of the simplest extensions through the inclusion of higher-curvature terms. Particular attention is given to the emergence of a novel phase within dEGB cosmology at high temperatures, supplementing the established radiation,...
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28/04/2026, 14:00
In this talk, I will first review the derivation of the unitarity bound in a single-field inflationary model with small and rapid oscillatory potential. I will show that this revised unitarity cutoff is somewhat higher than the naïve cutoff, 4 \pi f. Using this new cutoff, in contrast to the standard scenario where most of the observable information is encoded in the power spectrum, in this...
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28/04/2026, 14:40
We extend the gradient-expansion (separate-universe) approach to anisotropic inflationary backgrounds driven by a scalar field coupled to a U(1) gauge field. By choosing an appropriate gauge, we establish a correspondence between linear perturbations and background variations, where the background geometry is given by Bianchi type I spacetimes. We identify a conserved quantity W that...
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28/04/2026, 14:40
Recent high-precision observations from the DESI collaboration, combined with CMB and supernova data, suggest that DE might be dynamical in nature. Remarkably, the data indicate that the DE equation of state (EoS) may have transitioned from a phantom-like regime (w < −1) in the past to a quintessence-like one (w > −1) today, implying a recent crossing of the phantom divide at w = −1. In this...
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28/04/2026, 15:00
The large-scale structure of the Universe is one of the most promising probes of the nature of gravity. In this talk, we focus on halos and voids, and study their evolution and abundance in Horndeski and DHOST theories. Using the Effective Field Theory (EFT) of dark energy framework, we investigate the impact of individual EFT parameters on the formation and abundance of these structures. We...
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28/04/2026, 15:00
Our understanding of gravitational waves produced by isolated astrophysical systems is primarily based on gravitational perturbation theory off a flat spacetime background. This leads to the common identification of gravitational radiation with massless spin-2 waves. In this talk, I will argue that gravitational waves may no longer be solely "spin-2" in character once the background spacetime...
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28/04/2026, 15:50
We construct a gravitational open extension of the effective field theory of inflation in the Schwinger-Keldysh framework. While physical symmetries allow many open operators in the Schwinger-Keldysh action, most of them overconstrain the equations of motion, yielding inconsistent dynamics. We identify the minimal open operators compatible with propagating scalar and tensor modes and build the...
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28/04/2026, 15:50
We present a likelihood-guided framework to interpret tomographic Alcock--Paczy\'{n}ski (AP) measurements in physically motivated quintessence dark-energy models. Rather than constraining scalar-field potentials directly from data, we map external constraints on the Chevallier--Polarski--Linder (CPL) parametrization—derived from tomographic AP measurements, Type~Ia supernovae, and DESI baryon...
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28/04/2026, 16:10
We propose the experimental simulation of cosmological perturbations governed by a Planck-scale induced Lorentz violating dispersion, aimed at distinguishing between early-universe models that generate a scale-invariant power spectrum. Employing a novel variant of the scaling approach for the evolution of a Bose-Einstein condensate with both contact and dipolar interactions, we capture the...
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28/04/2026, 16:10
I will discuss a model-independent reconstruction of the late-time expansion history of the Universe based on characteristic redshifts extracted from low-redshift distance data. Using DESI DR2 BAO and DES supernova observations, we identify seven anchor redshifts that allow a direct determination of H(z) without assuming any specific dark energy parametrization. The reconstruction reveals the...
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29/04/2026, 14:00
We consider various mechanisms of modifying the effect of intrinsic curvature in gravity with respect to general relativity. Two primary approaches are studied. First, by considering a Lagrange multiplier or an auxiliary field. Second, by non-minimal coupling between a scalar field and the intrinsic curvature scalar. We reproduce the basic solutions of FLRW cosmology, black hole solutions,...
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29/04/2026, 14:00
I will present a novel mechanism for cosmic acceleration driven by primordial black holes with effective repulsive behavior. Using a new Swiss Cheese cosmological framework, I will discuss four black hole spacetimes—Hayward, Bardeen, Dymnikova, and de Sitter-Schwarzschild—to show that this acceleration emerges naturally from the geometry itself. The results suggest that ultra-light PBHs could...
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29/04/2026, 14:40
We investigate a range of non-singular cosmological scenarios within the framework of Horndeski gravity. In particular, we construct a bouncing Universe model and propose a minimal setup that realizes a non-pathological Genesis scenario. Both constructions allow for a fully stable transition to the kination epoch, during which General Relativity (GR) is restored. These scenarios successfully...
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29/04/2026, 14:40
Primordial gravitational waves (GWs), beyond their direct detection prospects, can induce second-order scalar perturbations. These tensor-induced scalar modes evolve similarly to standard matter perturbations and leave distinct imprints on the large-scale structure (LSS). In this talk, I will present a detailed study of these effects, including analytical results for the evolution of induced...
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29/04/2026, 15:00
With the advent of third-generation gravitational-wave detectors, it has become crucial to extend analytical frameworks used to model waveforms from compact binary systems to alternative theories of gravity. In this talk, I will present recent results on radiation-reaction effects in a class of scalar–tensor theories. Using the post-Newtonian multipolar post-Minkowskian (PN–MPM) formalism, we...
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29/04/2026, 15:00
The stochastic formalism can be understood as an effective field theory for IR modes, which incorporates quantum corrections from UV modes at the coarse-graining scale. As the name suggests, the dynamics are described by Langevin equations. In general, the system is non-Markovian, meaning it depends on past history by construction in stochastic inflation. In this talk, I will present and...
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29/04/2026, 15:50
Grand unified theory (GUT) provides a rationale for the arbitrariness of the Standard Model (SM) and explains many enigmas of nature at the outset of a single gauge group. The GUTs predict the proton decay and the spontaneous symmetry breaking (SSB) of the higher symmetry group may lead to the formation of topological defects, which are indispensable in the context of cosmological...
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29/04/2026, 15:50
Magnetically levitated superconductors provide a promising platform for detecting ultra-light dark matter through precision force measurements. In this talk, I will discuss our study of spin-2 dark matter—the dark graviton—and its effects on such systems via both matter and electromagnetic couplings. The former induces a tidal, strain-like force similar to a continuous gravitational wave,...
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29/04/2026, 16:10
The nature of dark energy has been a growing point of debate in recent years, particularly after the DESI measurements of the Baryon Acoustic Oscillations. While frequentist metrics appear to indicate a growing preference for a dynamical dark energy, some bayesian approaches indicate otherwise. Beyond this, there also lies the question of whether there exists a physical motivation behind any...
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29/04/2026, 16:10
The Cosmic Neutrino Background (CNB) is a robust thermal relic of the Big Bang and a potential probe of neutrino mass properties and of the Universe at O(1) second. A leading direct-detection strategy is neutrino capture on tritium, where observing a distinct capture peak requires excellent effective energy resolution. In practice, binding and solid-state effects can broaden the endpoint...
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30/04/2026, 14:00
It has been recently established in Phys. Lett. B861 (2025) 139260 that asymptotically flat black holes exist in pure gravity theories in dimension greater than four. We extend this result to asymptotically five dimensional Anti-de Sitter spacetimes and perform bottom-up holographic explorations: Hawking-Page phase transitions, quasinormal modes of black holes providing decay times of...
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30/04/2026, 14:00
I will introduce Double Field Theory as the gravitational framework of string theory, describing the massless sector of closed strings. It is built on a novel differential geometry that goes beyond conventional Riemannian geometry and provides a testable, robust alternative to General Relativity. I will then discuss its relevance to late-time cosmological observations, with particular emphasis...
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30/04/2026, 14:20
Understanding the possible observational features of black holes in quantum theory is a promising avenue to bridge the theoretical formulation of quantum gravity and astrophysical observations. In this talk, I will consider models of compact objects in the presence of horizon-scale quantum modifications, in which the objects have no horizon in the usual sense. Focusing on the shadow images of...
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30/04/2026, 14:40
I will discuss how to construct positivity bounds for cosmological correlators
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30/04/2026, 14:40
The low-energy limit of string theory contains additional gravitational degrees of freedom, which together with the metric are naturally embedded in the O(D,D)-symmetric framework of double field theory (DFT). Extending this O(D,D) symmetry to additional matter fixes a modified minimal coupling in string frame, while the resulting DFT energy-momentum tensor is enhanced to include dilaton...
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30/04/2026, 15:00
It is well-known that conformal transformations and closely related to holomorphicity in two dimensions. In particular, holomorphic operators such as the stress tensor in a conformal field theory can be used to show holomorphic splitting of the classical phase space of solutions. In this talk, I will argue this is also a feature of certain massive scalar fields in (A)dS_2 with integer scaling...
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30/04/2026, 15:00
We formulate an effective field theory (EFT) of coupled dark energy (DE) and dark matter (DM) interacting through energy and momentum transfers. In the DE sector, we exploit the EFT of vector-tensor theories with the presence of a preferred time direction on the cosmological background. This prescription allows one to accommodate shift-symmetric and non-shift-symmetric scalar-tensor theories...
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30/04/2026, 15:50
The launch of relativistic jets of plasma on astrophysical to cosmological scales is observed in a variety of astrophysical sources. While these jets can be reproduced by general relativistic magneto-hydrodynamics (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited....
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30/04/2026, 15:50
A non-minimally coupled scalar field with quartic self-coupling is widely studied in the literature but the estimation of the unitarity violation scale has not been consistently discussed, especially in the Jordan frame. In this talk, I will show how to consistently calculate the cutoff scale in both the Jordan frame and the Einstein frame, emphasizing the importance of potential of the scalar...
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30/04/2026, 16:10
The fundamental interactions of nature are formulated in terms of fields classified by mass and spin. Two of the most successful theories, General Relativity (GR) and the Standard Model (SM), can be derived from fields of fixed mass and spin by imposing theoretical consistency conditions. The SM contains well-understood interactions for fields with spin s<2, whereas local interacting theories...
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30/04/2026, 16:30
It is known that the axion-photon coupling can lead to quantum stimulated emission of photons and classic exponential amplification of electromagnetic (EM) fields at half the axion mass frequency, when the axion density or the coupling constant is sufficiently large. In this work, we studied the EM photon cloud induced from an axion cloud around a Kerr black hole in the first order of the...
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30/04/2026, 16:50
Quasi-normal modes (QNMs) govern the ringdown of perturbed black holes and encode key information about the remnant's mass, spin, and strong-field geometry. However, their non-orthogonality makes unambiguous mode decomposition a persistent challenge. In the first part of this talk, I present two agnostic, data-driven methods — the Matrix Pencil Method (MPM) and AAA rational approximation —...
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Warm inflation (WI) provides an alternative to the standard cold inflation paradigm, in which a subdominant radiation bath coexists with the inflaton field and continuously extracts energy through dissipative interactions. This framework allows for a smooth transition to a radiation-dominated universe and can accommodate steeper inflationary potentials due to the presence of additional...
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