Shanghai-APCTP-Sogang-GIST workshop on Gravity, Astroparticle, and Cosmology (SASGAC 2025)

Session

Morning I

Dec 27, 2025, 9:30 AM

Sogang University

Conveners

Morning I: Dec. 27 (Sat)

• Xian-Hui Ge ()

Morning I: Dec. 27 (Sat)

• Wonwoo Lee ()

Morning I: Dec. 27 (Sat)

• Wonwoo Lee (CQUeST, Sogang University)

Morning I: Gravity

• Yu-Qi Lei ()

Morning I

• There are no conveners in this block

Morning I

• Kilar Zhang ()

Morning I

• Hyun-Sik Jeong ()

Description

A session about AsstroParticle Physics

Contribution list Timetable

3. Black Holes as Laboratories for Dark Matter

Dr Qianhang Ding (Institute for Basic Science)

12/27/25, 9:30 AM

The dark matter surrounding black hole would form dense dark environment, studying the imprint of dark matter on the observational signals from black hole via accretions and dynamical friction could be a dark matter probe. In this talk I am going to talk about how to study the nature of dark matter from radio and gravitational wave channels. With these studies, black hole would be a promising...

4. Exploring the complementarity of WIMP direct detection and capture in celestial bodies using WimPyDD and WimPyC

Dr Sunghyun Kang (CQUeST)

12/27/25, 10:00 AM

I introduce WimPyDD and WimPyC which are object-oriented and customizable Python codes that calculate accurate predictions for the expected rates in WIMP direct detection experiments and WIMP capture rate in celestial bodies within the framework of Galilean invariant non-relativistic effective theory. Due to the experimental threshold direct detection can not explore signals at low WIMP...

5. Thermodynamic phase structures and Quasi-normal mode of Nonlinear charged black hole (5)

Dr Yu-Qi Lei

12/27/25, 11:00 AM

We investigate the connection between thermodynamic phase transitions and quasi-normal modes (QNMs) in charged black holes with a positive curvature constant, within the framework of F (R)-Euler-Heisenberg gravity. Nonlinear electromagnetic fields lead to rich thermodynamic phase struc-tures and significantly a!ect the QNMs of massless scalar fields. By analyzing the QNMs spectrum, we find that...

6. New thermodynamic phases and probes in Lyapunov exponents of EEH-AdS black holes

Mr ZiYu Hou

12/27/25, 11:30 AM

We illustrate the thermodynamics of the non-linear charged AdS black hole within the framework of Einstein-Euler-Heisenberg (EEH) gravity. During different thermodynamic ensembles, specifically the canonical thermodynamic ensemble with fixed charge and the grand canonical thermodynamic ensemble with fixed potential, new phases emerge. We draw the phase diagrams and probe the new phases by...

7. Gravitational Wave signals of FOPT in SO(10)

Mr Injun Jeong

12/27/25, 11:50 AM

"We investigate gravitational wave signals in a non-supersymmetric grand unified model where the group SO(10) is broken in two steps to the Standard Model gauge group. We calculate the analytical form of the one-loop effective potential responsible for the first step of symmetry breaking and show that it can lead to a first-order phase transition with gravitational wave production. The present...

29. Effective field theory of coupled dark energy and dark matter

Masroor Pookkillath (Center for Quantum Spacetime, Sogang University)

12/27/25, 12:20 PM

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...

8. The Routhian way of Attractor mechanism

Dr Sourav Roychowdhury

12/28/25, 9:30 AM

In this talk we consider static, extremal and spherically symmetric black hole solution of general Maxwell-Einstein-scalar (1+3)d theory with no scalar potential. We show that the effective one dimensional action, from which the effective black hole potential is usually computed, is the one dimensional effective Routhian of the original (1+3)d action. We further discuss this Routhian framework...

9. Improved PST Action for IIB Supergravity & Holography Beyond the AdS5xS5 Solutions

Dr Soumya Adhikari

12/28/25, 10:00 AM

In ten-dimensional type IIB supergravity, the action evaluated on the AdS5 \times S5 background vanishes, whereas the five-dimensional effective action obtained via dimensional reduction on S5 yields a non-zero result consistent with the AdS/CF T correspondence. This apparent discrepancy is resolved by incorporating an appropriate boundary term into the Pasti–Sorokin–Tonin (PST) action, which...

10. Gravitational charges and radiation in asymptotically locally de Sitter spacetimes

Dr Aaron Poole

12/28/25, 11:00 AM

This talk is motivated by the broad aim of a developing a fully nonlinear understanding of the nature of gravitational waves in asymptotically locally de Sitter (dS) spacetimes. I will begin with a review of the asymptotics of dS spacetimes, before showing (via the covariant phase space formalism) that spacetimes admitting suitable symmetries have spatially invariant charges. Relaxing the...

11. Equivalence of Stability Criteria for Neutron-Dark Matter Mixed Stars

Prof. Kilar Zhang

12/28/25, 11:30 AM

We present a rigorous proof establishing the mathematical equivalence between two independent criteria for the marginal stability of multi-fluid relativistic stars: the dynamical criterion based on the vanishing of the fundamental radial pulsation mode's eigenfrequency, and the static criterion derived from the geometric alignment of mass and particle number gradients in the parameter space....

12. Cosmological Potential of Gravitational Wave Memory with Future Detectors

Dr Susmita Jana

12/28/25, 1:30 PM

While the ΛCDM model successfully explains the late-time accelerated expansion of the universe, accumulating observational evidence suggests significant deviations from this standard cosmological framework. Determining the correct cosmological model and its parameters remains a crucial open problem in gravity and cosmology. Leveraging the enhanced sensitivity of next-generation gravitational...

17. Unbounded Radius of Innermost Stable Circular Orbit in Higher-Dimensional Black Holes

Dr Hocheol Lee (Dongguk University)

12/28/25, 2:00 PM

In this talk, I will introduce the innermost stable circular orbit (ISCO) in higher-dimensional, static, spherically symmetric, asymptotically flat black holes with anisotropic energy-momentum tensors. Assuming the weak energy condition, a non-positive trace, and constrained radial and tangential pressures, we analyze timelike geodesics via the effective potential. We show that, unlike in four...

14. Prospects of heavy dark Z_D at multi-TeV muon colliders

Dr Prasenjit Sanyal

12/28/25, 3:00 PM

In most Dark Matter (DM) models, the DM particles interact with each other through an unknown force carrier, the dark Z_D boson, which is associated with a broken hidden U(1)_D gauge symmetry. The DM particles can communicate to the visible sector only when Z_D develops a tiny coupling to the electromagnetic current due to a small kinetic mixing between the SM hypercharge and Z_D field...

15. Illuminating Scalar Dark Matter Co-Scattering in EFT with Monophoton Signatures

Dr Abhishek Roy

12/28/25, 3:30 PM

We investigate the co-scattering mechanism for dark matter production in an EFT framework which contains new $Z_2$-odd singlets, namely two fermions $N_{1,2}$ and a real scalar $\chi$. The singlet scalar $\chi$ is the dark matter candidate. The dimension-5 operators play a vital role to set the observed DM relic density. We focus on a nearly degenerate mass spectrum for the $Z_2$ odd...