String theory, Gravitation, and Cosmology 2026 (SGC 2026)

Jul 6, 2026, 9:00 AM → Jul 10, 2026, 1:40 PM Asia/Seoul

Seoul National University Siheung Campus Hotel & Convention Center

Seung Hun Oh (Tech University of Korea)

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The Strings, Gravitation, and Cosmology (SGC) workshop has a rich history spanning 16 years, renowned for its role in fostering interdisciplinary collaboration and intellectual exchange among researchers in these pivotal fields of theoretical physics.

SGC 2026 aims to continue this by convening a distinguished assembly of leading experts from around the globe. SGC 2026 will cover a wide range of topics, including string theory, quantum gravity, black holes, cosmology, and astrophysics. Renowned experts from around the globe will share their latest research findings and insights. Participants will have ample opportunities to network with colleagues, establish new collaborations, and discuss potential research projects.

SGC 2026 will serve as a dynamic format for participants to delve into the latest advancements, exchange innovative ideas, and explore new research frontiers in string theory, gravitation, and cosmology. As the largest and unique international conference in South Korea focused on gravity and cosmology, SGC 2026 offers an opportunity for domestic researchers to broaden their horizons and gain exposure to diverse research topics that may not be widely covered within the local academic landscape.

By facilitating access to global research trends and fostering a collaborative environment, SGC 2026 aims to elevate the level of the Korean hep-th community significantly. The workshop will provide a stimulating intellectual experience for both established researchers and promising young scientists, fostering the development of new research directions and collaborations.

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Supported by

SGC_2026_Official_Poster.pdf

Monday, July 6

1:30 PM → 2:10 PM Opening remarks: Registration & Opening remarks

2:10 PM → 2:50 PM Euclidean wormholes and applications to physical cosmology

In Euclidean quantum gravity, Euclidean wormholes are allowed, which explains the creation of paired twin universes. Each universe is then in a mixed state, and the mutual entanglement shall leave signatures in the cosmic microwave background (CMB) power spectrum. Invoking the Klebanov-Susskind-Banks wormhole as a toy model for tractability, we show that entanglement selects a novel, unique nonthermal global vacuum for the total inflaton perturbations in both universes. This is equivalent to imposing a simple harmonic oscillator boundary condition on the Euclidean wave function of the total perturbations, and it turns out that the entanglement enhances the CMB power spectrum for long-wavelength modes. Such a birthmark renders our notion refutable.

Speaker: Prof. Dong-han Yeom (Pusan National University)

2:50 PM → 3:30 PM Gravitational-Wave Astrophysics in the Next Decade with Ground-Based Detectors

I will review the highlights and lessons learned from gravitational-wave (GW) observations with the LIGO-Virgo-KAGRA detectors. I will then discuss the opportunities and challenges for GW astrophysics with next generation detectors. This talk will focus on compact binaries consisting of black holes and neutron stars and on observations with ground-based gravitational-wave detectors.

Speaker: Chunglee Kim (Ewha Womans University)

3:30 PM → 4:00 PM Coffee break

4:00 PM → 4:40 PM Quantum suppression of mass inflation in Reissner–Nordström interiors via Wheeler–DeWitt equation

The classical instability of the Reissner-Nordström black hole's inner Cauchy horizon leads to mass inflation. To address this, we construct a canonical quantization of the black hole interior using the Wheeler-DeWitt equation within the Einstein-Maxwell framework. We find that horizon boundary conditions dictate distinct quantum evolution scenarios: monotonic decay, quantum bounce, or "annihilation-to-nothing". Crucially, imposing an "annihilation-to-nothing" condition shifts the Cauchy horizon to the causal past of the quantum bounce, operationally removing its physical structure and suppressing mass inflation. Furthermore, the charge-neutral limit yields a strictly bounded, monotonically decaying state for the Schwarzschild black hole. These findings suggest that such quantum behaviors are generic, offering a robust pathway to resolve inner horizon instabilities.

Speaker: Dr WOO SUNG SONG (Pusan National University)

4:40 PM → 5:20 PM Conformal Mapping Method for Black-Hole Horizon Multipoles Beyond Axisymmetry

Building on the conformal construction proposed by Ashtekar et al., we implement a conformal-mapping method (CMM) to compute geometrically defined black-hole horizon multipoles without assuming axisymmetry. Unlike approximate-symmetry-based methods, which can suffer from abrupt frame changes when the preferred axis becomes unstable, the CMM provides smooth multipole evolution in a fixed reference frame. Validated against analytic Kerr results and applied to an equal-mass, non-spinning binary merger, the method captures quadrupole growth during inspiral and ringdown-like decay after merger.

Speaker: Young-Hwan Hyun (Chung-Ang University)

5:20 PM → 7:20 PM Welcome Dinner

Tuesday, July 7

10:00 AM → 10:40 AM Displacement memory effect and Carroll symmetry

In this talk I will discuss the displacement memory effect of gravitational wave firstly. Then the local Carroll symmetry of gravitational waves formulated in Baldwin-Jeffery-Rosen coordinates is extended to a globally well-defined symmetry via a coordinate transformation to Brinkmann coordinates. Two independent global solutions to the Sturm-Liouville equation are derived to characterize the corresponding symmetries—including translations and Carroll boosts—and geodesic motions of the system. Specifically, one solution satisfies specialized initial conditions with zero initial momentum, whereas the other solution possesses nonvanishing initial momentum. Pure displacement occurs when the nonvanishing momentum solution is suppressed and the wave parameters adopt specific values corresponding to integer half-wave numbers. At last, the general theoretical conclusions are verified and demonstrated using the Pöschl-Teller profile as a typical example.

Speaker: Prof. Pengming Zhang (Sun Yat-sen University)

10:40 AM → 11:20 AM Scalar-induced tensor perturbations

A tensor-type cosmological perturbation, defined as a transverse and traceless spatial metric fluctuation, is interpreted as gravitational waves. It decouples from scalar perturbations at linear order but is sourced by them at second order. These induced tensor modes are widely studied, yet all previous work adopts the zero-shear gauge without justification. We show that the induced tensor perturbation is generically gauge dependent: the gravitational wave power spectrum depends on the hypersurface condition chosen for the linear scalar perturbation. During matter domination the induced modes dominate over the linearly evolved primordial amplitude for k ≳ 10⁻² h/Mpc, even in the gauge that minimizes them and for r = 0.1. They therefore must be modeled correctly for each observational strategy targeting primordial gravitational waves from large-scale structure, such as the parity-odd mode of weak lensing or clustering fossils. Taking the CMB B-mode polarization from the relative velocity as an example, we show how a gauge-invariant observable is constructed. Finally, we show that the gauge ambiguity disappears once the induced tensor modes are expressed through the local tidal field.

Speaker: Prof. Donghui Jeong (Penn State University)

11:20 AM → 12:00 PM Revisiting the instanton universe for successful inflation

We revisit instanton-induced compactification in eight-dimensional Einstein–Yang–Mills theory, where a self-dual SU(2) instanton on the internal $S^4$ triggers four-dimensional expansion — extending arXiv:1810.12291 (Kim et al) (2018). We show that the minimal model fails to support successful inflation- it has neither a stabilized vacuum nor a slow-roll plateau. Introducing an eight-dimensional cosmological constant $\Lambda_8$ together with the one-loop Casimir energy of the internal space cures both defects, yielding a five-term Einstein-frame radion potential with a flat hilltop and a Minkowski minimum.

Speaker: Prof. Seoktae Koh (Jeju National University)

12:00 PM → 1:30 PM Lunch

1:30 PM → 2:10 PM Grav Wave with High freq-Higher Curvatue Effect--one of future directions

Among the various sources, the hot plasma in the early universe is quite interesting since it produces the Cosmic Gravitational Cosmic Microwave (CGMB) signal. Lambda CDM gives quite small value to be detected from the present technology based detectors. We show that the higher curvature term can enhance the signal. To be specific, the Einstein-dilaton-Gauss-Bonnet (EdGB) Gravity, one of the simplest extensions of Einstein's gravity with the higher curvature term, will be considered. We briefly mention, Unlike Einstein's gravity, there exists a minimum mass below which the black hole cannot be formed. EdGB cosmology will be shown to have the new phases at high temperature. Among many phenomena applicable we show the enhance the Cosmic Gravitational Cosmic Microwave (CGMB) signal, which can be used to constrain the theory.

Speaker: Prof. Bum-Hoon Lee (Sogang University)

2:10 PM → 2:50 PM Gravitational radiation from the particle around the wormhole and ringdown of the wormhole.

In this talk, we consider the Ellis-Bronnikov wormhole to see the gravitational waves generation due to the particle motion around the wormhole. The orbiting-around and the falling-into cases are also discussed. The ringdown phase of the wormhole is also studied from the perturbation equation driven by the particle motion.

Speaker: Sung-Won Kim (Ewha Woman's University)

2:50 PM → 3:30 PM Scalarized EEH black holes

We investigate scalarized Einstein-Euler-Heisenberg (EEH) black holes
in the EEH-scalar theory. Firstly, we carry out negative potential-induced scalarization by considering the minimally scalar coupling. Spontaneous scalarization of EEH black hole is also performed by introducing an exponential scalar coupling to Maxwell term and nonlinear electrodynamics (NED) term.

Speaker: yun soo MYUNG (CQUeST, Sogang University)

3:30 PM → 4:00 PM Coffee break

4:00 PM → 4:40 PM Inflationary Magnetogenesis from Non-Adiabatic Photon Squeezing

We propose an inflationary mechanism for primordial magnetic-field generation based on the reduced open-system dynamics of photon modes in de~Sitter space. The observable photon sector inside a causal patch is treated as a Gaussian subsystem, while the de~Sitter horizon acts as an effective environment at the Gibbons--Hawking temperature. Since the reduced state relaxes only with a finite rate toward a horizon-selected quasi-static branch, the redshift of the physical photon frequency drives imperfect tracking. This tracking failure appears as squeezing of the reduced Gaussian state and generates a super-horizon electromagnetic relic.

We solve the reduced Gaussian evolution in exact exponential inflation and derive the super-horizon relic spectrum. For the infrared-turnover branch (\alpha_0>4), the magnetic component yields a broad, non-helical primordial seed spectrum on astrophysically relevant scales for suitable reheating temperature and turnover position. After reheating, the electric component is screened by the radiation plasma, whereas the magnetic component remains frozen on cosmological scales.

The non-adiabatic electromagnetic energy density is parametrically small, (\rho_{\rm EM}^{\rm nad}\sim H^4), so it does not backreact for (H\ll M_{\rm Pl}). The mechanism requires no explicit non-minimal coupling in the Maxwell action; conformal tracking is instead effectively broken by finite-rate reduced open-system dynamics.

Speaker: Hyeong-Chan Kim (Korea National University of Transportation)

4:40 PM → 5:20 PM Reassessing Dynamical Dark Energy Hints: Structural Limitations of Distance Probes and the Robustness of $\Lambda$CDM

Recent baryon acoustic oscillation and supernova data have stimulated renewed interest in possible departures from the cosmological constant, often interpreted within (w)CDM or (w_0w_a)CDM parametrizations. In particular, redshift-dependent trends in the dark-energy equation of state have been discussed as potential evidence for dynamical dark energy. In this talk, I argue that such an interpretation should be treated with caution.

I will summarize a series of analyses showing that distance-based observables possess intrinsic structural limitations in constraining the time evolution of dark energy. An exact linear-response and Fisher-eigenmode analysis reveals that most of the information carried by distance data is compressed into a small number of geometric modes, while the remaining directions in the dark-energy function space are weakly constrained. As a result, apparent preferences for time-varying dark energy can be sensitive to parametrization choices, matter-density priors, sound-horizon assumptions, and redshift-resolved projection effects.

Using DESI DR2 BAO data, I compare (\Lambda)CDM, (w)CDM, and (w_0w_a)CDM fits, with particular attention to the role of (r_d), the matter-density prior (\Omega_{m0}), and the robustness of the CPL parametrization under basis and prior variations. These studies indicate that the apparent dynamical-dark-energy signal is not yet a model-independent detection of evolving dark energy. Rather, it can arise from the interplay between geometric degeneracies and the limited effective dimensionality of distance probes.

I will also discuss the complementary role of growth observables. While distance probes constrain the integrated expansion history, growth measurements access different physical directions and are therefore essential for testing whether the observed trends correspond to genuine dynamics or to projection artifacts. Taken together, the current evidence remains consistent with (\Lambda)CDM once structural limitations, prior dependence, and cross-probe consistency are properly accounted for.

Speaker: Seokcheon Lee (Sungkyunkwan University)

5:20 PM → 6:00 PM Probing primordial black holes by scalar-induced gravitational waves

I will briefly review the recent progress in the primordial black hole (PBH) and the scalar-induced gravitational wave (IGW). I will introduce how to construct a gauge-independent observable at second order, which removes the gauge ambiguity in such waves. I will briefly discuss the non-Gaussianity generated on superhorizon scales, which affect the crosscheck of PBH abundance and IGW amplitude. As an example, a population of planet-mass PBHs can interpret the microlensing events reported by Subaru-HSC and AMPM, which is also consistent with the nanohertz stochastic GW background found by PTAs.

Speaker: Prof. Pi Shi (ITP-CAS)

Wednesday, July 8

10:00 AM → 10:40 AM Strong gravitational lensing effects around black holes with quantum hair

According to the classical no-hair theorem, stationary black holes are uniquely characterized by their mass, charge, and angular momentum. In this talk, we derive the quantum-corrected black hole metric within the Barvinsky-Vilkovisky formalism and explore the effect of quantum hair in the metric, which is defined by the number of massless quantum fields. The quantum-corrected metric is obtained perturbatively around flat spacetime without assuming either the commutativity between the nonlocal operator and covariant derivatives or the nonlocal Gauss-Bonnet theorem, both of which are adopted in previous studies. Using this metric, we evaluate the deflection angle in the strong-field limit and compute the associated strong gravitational lensing observables, such as the angular separation and the relative magnification. We find that as the quantum hair increases, the photon sphere radius, the strong deflection angle, and the relative magnification all increase, whereas the angular separation decreases. As a result, we show that the quantum hair affects not only the black hole geometry but also its strong gravitational lensing effects.

Speaker: Sojeong Cheong (CQUeST)

10:40 AM → 11:20 AM Dynamical friction for circular orbits in self-interacting ultralight dark matter and Fornax globular clusters

We investigate the impact of repulsive self-interaction in ultralight dark matter (ULDM)on dynamical friction in circular orbits in ULDM halos and its implications for the Fornax dwarfspheroidal (dSph) galaxy's globular clusters. Using the Gross-Pitaevskii-Poisson equations, wederive the dynamical friction force considering soliton density profiles for both non-interactingand strongly self-interacting ULDM. Our results show that self-interactions reduce the dynamicalfriction effect further than both the non-interacting ULDM and standard cold dark matter models.Furthermore, we derive the low Mach number approximation to simplify the analysis in the subsonicmotion, where the tangential component of dynamical friction dominates. Applying these findingsto the Fornax dSph, we calculate the infall timescales of globular clusters, demonstrating thatstrong self-interaction can address the timing problem more effectively. We constrain theparameter space for ULDM particle mass and self-coupling constant, which are consistent with otherconstraints from astronomical and cosmological observations. This talk is based on my recent paper (arXiv:2504.19219) published in JCAP.

Speaker: Hyeonmo Koo (IBS CTPU-PTC)

11:20 AM → 12:00 PM Phase Transitions with Lyapunov Exponents under Einstein and String Frames in Dilatonic Reissner-Nordstrom-AdS Black Holes

We investigate Lyapunov exponents as dynamical probes of black hole phase transitions in dilatonic Reissner-Nordstrom-AdS black holes within Einstein-Maxwell-dilaton theory. Thermodynamic quantities and the Lyapunov exponent of charged probe particles are analyzed in both the Einstein and string frames, providing a direct comparison between the thermodynamic phase structure of the black hole and that captured by the Lyapunov exponent. Thermodynamic quantities, including the Hawking temperature and Wald entropy, are invariant under conformal frame transformations, yielding identical phase structures in the two frames. By contrast, the Lyapunov exponent exhibits a nontrivial frame dependence for massive probe particles due to the dilaton coupling, while the frame dependence disappears in the massless limit. Numerical analysis shows that the phase structure captured by the Lyapunov exponent, including characteristic cusp behavior and transition points, is independent of the choice of frame, despite the frame-dependent value of the Lyapunov exponent itself. Therefore, the Lyapunov exponent exhibits frame-dependent values, whereas the critical structure it captures is preserved across conformal frames.

Speaker: Dr Hocheol Lee

12:00 PM → 1:30 PM Lunch

1:30 PM → 2:10 PM History of SGC

Speaker: Prof. Jungjai Lee

2:10 PM → 2:50 PM quantum liquid and spacetime

I review my personal contribution to the dark matter as the Bose liquid and the holographic mean field theory of non-fermi liquid.
Finally I will describe how disorders can introduce the non-locality out of local quantum field theory, which is essential for the recent development of
the strange metal.

Speaker: Sang-Jin Sin (Hanyang University)

2:50 PM → 3:30 PM BPS structure of nonrelativistic Abelian Higgs model

We show BPS structure of nonrelativistic Abelian Higgs model. Since complex scalar field is nonrelativistic but Abelian gauge field is relativistic, it is believed that no BPS structure has been expected for long time due to mismatch of propagating speeds. In the framework of SUSY theory,this BPS structure is also strange since the obtained nonrelativistic Abelian Higgs model in BPS limit must be identified as a bosonic part of SUSY theory. Application to condensed matter system including superconductivity and extension to the BPS theory with inhomogeneity are also discussed.

Speaker: Yoonbai Kim

3:30 PM → 4:10 PM Gravitational Wave Science

Gravitational wave science has emerged as one of the most transformative fields in modern physics, offering an entirely new way to observe and understand the universe. Predicted by Albert Einstein’s general theory of relativity in 1916, gravitational waves are ripples in spacetime produced by the acceleration of massive objects. Their first direct detection in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO), originating from a binary black hole merger, marked the beginning of gravitational wave astronomy.

This presentation provides a comprehensive overview of the development, current status, and future prospects of gravitational wave science. We begin with the theoretical foundations, outlining the key principles of general relativity that predict gravitational radiation and its properties. We then describe the major detection methods, focusing on ground-based interferometers such as LIGO, Virgo, and KAGRA, as well as planned space-based observatories like LISA. The discussion highlights instrumental techniques, sensitivity challenges, and data analysis methods required to extract signals from noise.

Subsequently, we review major observational milestones, including binary black hole mergers, neutron star collisions, and their role in advancing astrophysics, cosmology, and fundamental physics. These discoveries have enabled precise tests of general relativity in the strong-field regime, insights into stellar evolution, and independent measurements of cosmological parameters.

Finally, we explore emerging directions in the field, including multi-messenger astronomy, next-generation detectors, and unresolved questions such as the nature of dark matter and the stochastic gravitational wave background. By integrating theoretical, experimental, and observational perspectives, this presentation aims to highlight how gravitational wave science is reshaping our understanding of the universe and opening new frontiers in physics.

Speaker: Prof. Hyung Won Lee

4:10 PM → 7:20 PM Excursion & Banquet

Thursday, July 9

10:00 AM → 10:40 AM Three-dimensional Gravity and Thurston Geometries

We review the Chern-Simons gauge theory formulation of three-dimensional gravity. Thurston’s conjecture proved by Perelman states that three-manifolds with a given topology have a canonical decomposition into eight manifolds with high symmetry—the so-called Thurston geometries. We address how to formulate the Thurston geometries in terms of the Chern-Simons gauge theory and discuss their boundary conformal field theories.

Speaker: Prof. Hyun Seok Yang

10:40 AM → 11:20 AM Gravity of String Theory: Next Einstein Equation

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 on its prediction of dynamical dark energy.

Speaker: Jeong-Hyuck Park (Sogang University)

11:20 AM → 12:00 PM Exact Four-Parameter Rotating NS--NS Vacuum in Double Field Theory

We present an exact four-parameter rotating vacuum solution of the pure NS--NS sector, or equivalently of Double Field Theory. The solution is generated by applying a compact (\mathrm{SO}(2)) (S)-duality transformation to a rotating Einstein--scalar seed and is specified by ({m,j,q,\zeta}). It gives analytic expressions for the metric, Kalb--Ramond field, and dilaton, with independent dilaton and (H)-flux charges and without introducing a Maxwell sector. In the non-rotating limit (j\to 0), the geometry does not reduce to the spherical Burgess--Myers--Quevedo branch, but instead to an axial Zipoy--Voorhees branch carrying (H)-flux. Thus an oblate deformation survives after rotation is removed. Although the two static branches agree in their monopole PPN data, their degeneracy is lifted at quadrupole order. The Kerr-shell locus is generically curvature singular, while above a charge threshold polar geodesics are repelled and the rotation axis develops a localized degeneracy suggestive of a non-Riemannian Double Field Theory description.

Speaker: Hun Jang (Sogang University)

12:00 PM → 1:30 PM Lunch

1:30 PM → 2:10 PM Dual gravities from entanglement entropy

Applying a rule-based holographic method, we investigate the reconstruction of dual gravity theories from the quantum field theory (QFT) data, specifically, entanglement entropy. We first derive a three-dimensional black hole geometry from the entanglement entropy of a two-dimensional thermal system. Using the reconstructed solution, we extract various thermodynamic quantities with small numerical errors. Moreover, we explore how to reconstruct the dual gravity theory beyond the geometry itself. For an undeformed conformal field theory (CFT), we show that the dual gravity theory can be constructed analytically from the analytic form of the entanglement entropy. In particular, we demonstrate how to reconstruct the analytic dual geometry by applying the Abel transformation. Finally, we investigate the numerical reconstruction of the dual gravity theory from numerical entanglement entropy data for a relevantly deformed CFT. After reconstructing the dual gravity, we show that additional information about the renormalization group (RG) flow, for instance, the β-function and the c-function can be extracted for the considered relevantly deformed CFT.

Speaker: Prof. Chanyong Park (Gwangju Institute of Science and Technology)

2:10 PM → 2:50 PM Horava Stars Revisited: Old and New Results

I will revisit Horava stars that have been first studied in 2010 since there has been some important progress recently.

Speaker: Mu-In Park

2:50 PM → 3:30 PM Modular L^p Interpolation and Geometric Translation in Black-Hole Information Recovery

We formulate a continuous operator-algebraic recovery path for black-hole information based on modular (L^p)-interpolation. The starting point is the canonical shift of algebraic teleportation, which relocates hidden information from one relative commutant to another. In local quantum field theory, this finite-step picture cannot be implemented through ordinary tensor-factor decompositions because the relevant local algebras are Type III. We therefore pass to the crossed-product envelope and identify the recovery parameter with the noncommutative (L^p)-scale.

The resulting path describes a continuous information-resolution process between the full algebraic description and a coarse-grained endpoint. Its boundary direction is generated by the modular momentum associated with the interpolation. We show that the lifted canonical shift has a well-defined boundary generator and that this generator equals twice the modular momentum on the common analytic core. This is a boundary tangent statement, while the interior of the path is controlled by the analyticity of the (L^p)-interpolation.

In geometrically covariant cases, such as half-sided modular inclusions, the modular momentum is realized as a generator of null translations. The continuum limit of the canonical shift then acquires the infinitesimal form of a spacetime translation. In this precise sense, the construction gives an operator-algebraic realization of the principle “teleportation = translation” for Type III black-hole algebras.

Speaker: Dr Jeongwon Ho (Sungkyunkwan University Institute of Basic Science)

3:30 PM → 4:00 PM Coffee break

4:00 PM → 4:40 PM Supermassive black holes and ultralight dark matter

We discuss the role of ultralight dark matter (ULDM) in the formation and merger of supermassive black holes. ULDM can trigger direct-collapse SMBH seeds in the early Universe, potentially explaining the recently observed Little Red Dots, and resolve the final parsec problem through wave dynamical friction, leading to efficient SMBH mergers and potentially observable gravitational-wave signals.

Speaker: Jae-Weon Lee (Jungwon univ.)

4:40 PM → 5:20 PM Scalar theory in different manifolds and their correspndence

We explore O(2N) scalar theory with fractional Laplacian in d-dimension, √–∇² and its Hamiltonian dynamics which is described by a Schrödinger type equation. In classical limit, this reduces to Hamilton-Jacobi equation, which is widely used to describe holographic renormalization group of multi-trace deformation in dual field theory. This equation is a kind of current conservation equation, where one can define a current j(φ) of a probability P(φ), where φ is the scalar field. Naturally, Gibbs entropy S = –∫ [Dφ] P(φ) log P(φ) can be considered to explore the system. We realize that this Gibbs entropy of the O(2N) scalar theory with fractional Laplacian is matched with free energy of O(N) vector model in finite temperature with chemical potential in d-dimension. The precise map between the stochastic fictitious time t and the inverse temperature β is β = 2t. Therefore, the temperature dependence of the thermal O(N) vector model can be realized as a dynamics of time dependent solution satisfying Schrödinger type equation. This free energy is obtained by putting O(N) vector model in S¹ × R_d, where S¹ is thermal circle with its periodicity β. To get d-dimensional theory, we sum up all possible frequencies on the circle (so called Matsubara frequency summation) which gives d-dimensional thermal partition function. We note that the nontrivial t-dependence appears beyond classical limit.
To take into account quantum effects, we solve the Hamiltonian dynamics by keeping ħ corrections. The chemical potential is mediated by a parameter l and so we call this l-deformation. This is related to the boundary condition of the Schrödinger equation. We also note that the two theories are not equivalent to each other and we see their correspondence in the level of one-loop determinant, i.e. zero point function.

Speaker: Prof. Jaehyuk Oh (Hanyang University)

5:20 PM → 6:00 PM Design of an Aperture Torsion Balance for a Part-Per-Million Measurement of the Gravitational Constant

The precise determination of the Newtonian gravitational constant, G, remains one of the most challenging problems in experimental physics, with existing measurements showing significant discrepancies despite continual improvements in accuracy. This work aims to develop a high-precision torsion balance apparatus designed to measure G with a target relative uncertainty of approximately 2 ppm. The experiment design should consist of two independent measurement techniques within the same system—angular acceleration feedback and time-of-swing analysis—allowing systematic effects associated with each method to be investigated and compared directly. The apparatus consists of a rotating outer turntable, attractor masses, and a torsion pendulum, with comprehensive modeling performed to predict the expected gravitational signal and optimize measurement sensitivity. Preliminary studies using a prototype pendulum demonstrate the presence of thermal drift effects, indicating that heat treatment of the suspension fiber can significantly improve signal stability. Several design features have been implemented to minimize uncertainty, including monolithic silicon test masses, increased apparatus dimensions to reduce geometric errors, interferometric position sensing for real-time mass tracking, and the use of a common apparatus for both measurement techniques. By combining multiple methodologies within a single experimental framework, this study aims to provide an improved and internally consistent determination of the gravitational constant and contribute to resolving the long-standing discrepancies among existing measurements of G.
Preliminary measurements using a prototype torsion pendulum revealed significant angular drift. Initial studies indicate that heat treatment of the suspension fiber can improve signal stability and help mitigate drift-related systematic effects.

Speaker: Sandeep Kumar (Sant Baba Bhag Singh University, Punjab 144030)

Friday, July 10

10:00 AM → 10:40 AM Green’s function construction for late time tails via Pseudo-spectral method

To improve the analytical description of the gravitational-wave ringdown phase, this work investigates black hole spectroscopy via the pseudo-spectral method, which solves eigenvalue problems to compute the full frequency spectrum of black holes. Although highly promising, the complete spectrum remains elusive; while quasinormal modes (QNMs) are well understood, the physical nature of the remaining frequency components is yet to be identified. This work addresses a specific part of the frequency domain: the purely imaginary eigenvalues in the very low-frequency regime. We analyze the perturbed Klein-Gordon equation using Green's function methods, focusing on the branch cut solutions that dominate late-time tails. Unlike traditional approaches utilizing the Wronskian, we adopt a Sturm-Liouville-like formulation to construct the Green’s function from the pseudo-spectral eigenvalues and eigenvectors. Through a comparative analysis of these two Green's functions, we aim to definitively map the low-frequency, purely imaginary eigenvalues to the late-time tail solutions.

Speaker: Dr Miok Park (IBS-CTPU-PTC)

10:40 AM → 11:20 AM Is the observable Universe consistent with the cosmological principle?

In arXiv:2207.05765 we collated an emerging science case challenging the second most fundamental cosmological assumption that there is a global Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime describing the Universe. FLRW is not a fundamental symmetry of Nature, but rather a working approximation for a physical system, so nothing prevents it from breaking down at any given precision. I will argue that this breakdown may be happening today.

Speaker: Prof. Eoin Ó Colgáin

11:20 AM → 12:00 PM Generation of gravitating solutions with Baryonic charge from Einstein–scalar–Maxwell seeds

We establish, for the first time, an exact correspondence between Einstein–scalar–Maxwell theory and gauged Skyrme–Maxwell–Einstein models in (3+1) dimensions. By constructing the simplest consistent ansatz within the gauged Skyrme–Maxwell framework, we reveal a remarkable equivalence in a sector that admits nonvanishing, highly magnetized baryonic charge. This correspondence has a particularly appealing consequence: it transfers the full power of solution-generating techniques developed for electrovacuum systems – many of which naturally accommodate scalar fields – to the considerably more intricate setting of gauged Skyrme–Maxwell theory minimally coupled to General Relativity. As a result, it opens the door to a systematic and much broader exploration of exact solutions in Skyrme—Maxwell–Einstein theory and of their potential applications in cosmology and astrophysics. Notably, the resulting configurations carry nonzero baryonic charge whenever the derivative of the hadronic profile along the magnetic field lines does not vanish. As an illustrative example, we apply this new dictionary to a rotating Kerr–Newman–like spacetime dressed with a scalar field. In the corresponding Skyrme–Maxwell–Einstein solution, the quantization of the baryonic charge enforces a quantization of theKerr rotation parameter. We derive an upper bound on the baryonic charge in terms of the integration constants of the solution and show that, in the regime of small baryonic charge, the rotation parameter depends linearly on the baryonic charge.

Speaker: Prof. Seung Hun Oh (Tech University of Korea)

12:00 PM → 12:30 PM Closing remarks