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Raymond Volkas (U of Melbourne)07/07/2025, 17:00
The standard DFSZ axion model features stable domain walls, so requires a pre-inflationary axion. This means the density of axion dark matter depends on an unknowable initial misalignment angle and thus predictivity is compromised compared to the post-inflationary axion case. I present a systematic classification of flavour-dependent DFSZ Peccei-Quinn symmetry variants that have no domain wall...
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Mohammad Ali Gorji (IBS CTPU-CGA)07/07/2025, 17:30
Spectator fields which provide additional tensor degrees of freedom, on top of the standard metric tensor perturbations, can produce significant amounts of gravitational waves (GWs). Employing the effective field theory approach for spin-2 fields, we find a universal prediction that linear mixing between the metric and extra tensor modes inevitably induces oscillatory features in the GW...
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Kiwoon Choi (IBS CTPU-PTC)08/07/2025, 09:00
I discuss the PQ quality and scale hierarchy of extra dimensional axions in the context of 5-dimensional orbifold field theory on S^1/Z_2.
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Stefano Scopel (Sogang U)08/07/2025, 09:30
The WIMP indirect detection signal is enhanced by the square of the WIMP density, and celestial bodies can catalyze WIMP annihilation by accumulating WIMPs with their gravitational potential. In particular, WIMP annihilation can induce a GeV neutrino signal from the Sun, the increase of the total luminosity of White Dwarfs in nearby Globular Clusters, or a sizeable radio emission from the Dark...
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Bin Wang (SJTU/Yangzhou)08/07/2025, 10:00
The interaction between DM and DE has been proved successful in alleviating the coincidence problem and shown allowed by observations. The BINGO radio telescope is specifically designed to study the properties of DE and its interaction with DM during the late-time cosmic acceleration. We introduce the BINGO-ABDUS project, its current status, future development and its specific aim at providing...
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Seokhoon Yun (IBS CTPU-PTC)08/07/2025, 11:10
During the accretion phase of a core-collapse supernova (SN), dark-photon (DP) cooling can be largest in the gain layer below the stalled shock wave. In this way, it could counteract the usual shock rejuvenation by neutrino energy deposition and thus prevent the explosion. This peculiar energy-loss profile derives from the resonant nature of DP production. The largest cooling and thus...
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Jeonghyeon Song (Konkuk U)08/07/2025, 11:10
We investigate strong first-order electroweak phase transitions in the Type-I two-Higgs-doublet model's inverted Higgs scenario (where the 125 Giga-electron Volt Higgs boson is the heavier CP-even scalar), motivated by its potential for electroweak baryogenesis. A comprehensive parameter scan, incorporating current theoretical and experimental constraints (including flavor, Higgs, and...
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Anthony Villano (U of Colorado, Denver)08/07/2025, 11:30
Many low-mass dark matter experiments focus on highly segmented detectors with low particle detection thresholds. For these situations in particular, the neutron capture process is important to consider for direct low-energy calibrations and a possible background source. I will summarize the effect of this process on dark matter searches, specifically focusing on the SuperCDMS collaboration...
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Abhishek Roy (CQUeST)08/07/2025, 11:30
We present an extension of the SM involving three triplet fermions, one triplet scalar and one singlet fermion, which can explain both neutrino masses and dark matter. One triplet of fermions and the singlet are odd under a symmetry, thus the model features two possible dark matter candidates. The two remaining even triplet fermions can reproduce the neutrino masses and oscillation parameters...
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Siyao Li (IBS CTPU-CGA)08/07/2025, 11:50
Oscillons are long-lived, spherically symmetric solitons that can arise in real scalar field theories with potentials shallower than quadratic. They are considered to form via parametric resonance during the preheating stage after inflation and serve as localized storagies of the inflaton field’s energy. Due to their extended lifetimes, oscillons may play a significant role in the early...
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Vincent Gene Otero (National Taiwan Normal U)08/07/2025, 11:50
We propose a novel mechanism to detect terrestrial cosmic neutrino background’s (CNB) limit of electric charge by employing Mach-Zehnder interferometer with asymmetrical arm placement – one at the Earth’s surface and the other is placed underground. Assuming that relic neutrinos possess a small but nonzero charge, their coherent forward scattering with photons induces measurable phase shift in...
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Yechan Kim (KAIST)08/07/2025, 12:10
We study a novel leptogenesis scenario with the temperature-dependent mass of heavy Majorana neutrino by the wave dark matter to explain the matter-antimatter asymmetry of the Universe. The leptogenesis happens twice in this scenario: the first leptogenesis occurs above the electroweak scale, while the second leptogenesis occurs below it. The sphaleron process converts the lepton asymmetry to...
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Chian-Shu Chen (Tamkang U)08/07/2025, 12:10
In this talk I will briefly introduce some previous researches I have gone through on the topic of self-interacting dark matter (SIDM). For particle aspect, I will review the inclusion of SIDM, the enhancement of potential DM accumulating in the core of stellar objects and its potential observations. For astrophysical aspect, I will introduce the properties of exotic stellar objects...
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Eung Jin Chun (KIAS)08/07/2025, 14:00
We propose a scenario for the cogenesis of baryon asymmetry and dark matter, realizing spontaneous leptogenesisby by Majoron in Type I seesaw model.
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This mechanism requires significant kinetic motion, which we demonstrate can naturally arise from conventional misalignment under conditions of symmetry non-restoration -
Masahiro Kawasaki (ICRR/U of Tokyo)08/07/2025, 14:30
The recent determination of the primordial abundance of He4 suggests that our universe has a large lepton asymmetry. We consider the Q-ball scenario that produces the large lepton asymmetry without generating a large baryon asymmetry. We also discuss the enhancement of gravitational waves and resonant production of sterile neutrinos in the scenario.
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Ue-Li Pen (Academia Sinica)08/07/2025, 15:00
Using the tanh potential as an example, we present a new class of real time instantons corresponding to general equivalence classes. The Euler-Lagrange equation solutions to saddle points are not unique for complex saddles: any contour in the equivalence classes maps to the same action due to Cauchy’s theorem. This new tool resolves a number of existing puzzles, including curved space particle...
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Yudai Suwa (U of Tokyo)08/07/2025, 15:30
Neutrinos emerge promptly from the cores of collapsing massive stars and are the most direct messengers of the microphysics that drives stellar core collapse. Owing to their small interaction cross-sections, they propagate with negligible attenuation, so their time- and energy-dependent flux records the full evolution from shock formation to the birth of a neutron star, or, if accretion...
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Jianqiao Deng (CUHK)08/07/2025, 16:40
From topological supergravity, we have found that the action for gravitino contains a coupling between the gravitino and a scalar field. By analogy with the Yukawa coupling, we integrate out the gravitino to obtain an effective action for this scalar field, which may furnish a potential microscopic theory for scalar dark matter.
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Adil Jueid (IBS CTPU-PTC)08/07/2025, 16:40
The detection of cosmic antideuterons at kinetic energies below a few GeV/n could provide a smoking gun signature for dark matter (DM). However, the theoretical uncertainties arising from the choice of coalescence models were so far one of the main limiting factors for precise predictions of the $\overline{\rm D}$ flux. In this talk, we present a novel calculation of the $\overline{\rm D}$...
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Hyeonmo Koo (U of Seoul)08/07/2025, 17:00
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 dwarf spheroidal (dSph) galaxy's globular clusters. Using the Gross-Pitaevskii-Poisson equations, we derive the dynamical friction force considering soliton density profiles for both non-interacting and strongly...
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Sarif Khan (CAU)08/07/2025, 17:00
In this work, we have explored the conversion-driven freeze-out scenario, where the next-to-lightest stable particle (NLSP) sets the dark matter (DM) abundance through
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the process ``NLSP SM $\leftrightarrow$ DM SM". Although DM is produced via
freeze-out mechanism, its interaction strength with the visible sector can
range from weak-scale to feeble-scale couplings. This leads to a vast,... -
Cheuk Nam Chu (CUHK)08/07/2025, 17:20
White dwarfs (WDs) are compact remnants of stars, supported by electron degeneracy pressure, and their structures are generally considered to be well understood. However, there are notable discrepancies between the observed mass-radius (MR) relationship of WDs and the predicted values. We explore the possibility that WDs could serve as a portal to dark matter (DM) physics by investigating the...
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Jiheon Lee (KAIST)08/07/2025, 17:20
We investigate dark gauge-mediated supersymmetry breaking with an unbroken U(1) gauge symmetry and a massless dark photon. Messengers charged under both Standard Model and dark gauge groups generate new soft SUSY-breaking terms via gauge kinetic mixing. Large mixing significantly alters superpartner spectra compared to standard GMSB, reduces the μ parameter, and predicts a relatively light...
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Qianhang Ding (IBS CTPU-CGA)08/07/2025, 17:40
In current concordance cosmological model, Lambda-CDM model, we are facing serious cosmic tensions, such as Hubble tension, S_8 tension, dipole tension, etc. These problems challenge the basic assumption of cosmology, cosmological principle. In this talk, I will show how a local structure, a Gpc-scale void, impacts our understanding on Hubble tension, S_8 tension, and dipole tension, and a...
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Geonwoo Kang (SNU)08/07/2025, 17:40
We present a numerical proof of the concept that the void spin distributions can provide a tight constraint on the amplitude of matter density fluctuation on the scaleof 8 h inverse Mpc (σ8) without being severely deteriorated by the degeneracies of σ8 with cold dark matter density parameter multiplied by the dimensionless Hubble parameter square (Ωcdmh^2), total neutrino mass (Mν) and dark...
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08/07/2025, 18:00
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Jing-Cheng Chang (Lanzhou U)08/07/2025, 18:00
In recent years, the holographic duality between $T\bar{T}$-deformed conformal field theory (CFT) and Anti-de Sitter (AdS) spacetime with finite radial cutoff has received significant attention. The study of $T\bar{T}$ deformation within the framework of de Sitter (dS)/CFT duality has also progressed. In this talk, we generalize the replica method in both AdS and dS holography to derive a...
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Misao Sasaki (APCTP/IPMU)09/07/2025, 09:00
Stochastic gravitational wave backgrounds have become a hot topic in cosmology. However, very few studies have been done on gravitational waves on intergalactic scales. I discuss possible sources on these scales which could even be parity violating, and present a method to probe such gravitational waves.
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Rinku Maji (IBS CTPU-CGA)09/07/2025, 09:30
The 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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Jun'ichi Yokoyama (IPMU)09/07/2025, 10:00
The phase transition of a false vacuum due to a first-order phase transition has been studied by analysis using Euclidean time conventionally. Such analysis has also been performed for curved spacetimes, and a certain thermodynamic interpretation has been given to phase transitions in de Sitter spacetimes and spacetimes containing black holes. In this talk, I will distinguish myself from such...
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Yuhang Zhu (IBS CTPU-CGA)09/07/2025, 11:10
Cosmological correlation functions are fundamental observables in early universe cosmology and offer a remarkable window into the fundamental laws that governed the Universe’s earliest moments. In this talk, the speaker will derive a correlator-to-correlator factorisation formula under mild assumptions, establishing a profound relationship between different observables in the context of...
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Kazunori Kohri (NAOJ)09/07/2025, 11:10
I report the latest results of our group for the new mass ranges of primordial black hole to be dark matter if we seriously consider the memory burden effect.
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Perseas Christodoulidis (Ewha Womans U)09/07/2025, 11:30
I will discuss how to construct an open systems EFT for gauge fields and gravity based on recent developments in Schwinger-Keldysh EFTs. I will then apply the EFT to two representative examples: Maxwell theory and inflation.
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Philip Lu (KIAS)09/07/2025, 11:30
Light primordial black holes (PBHs) can be formed in a variety of scenarios from inflationary scenarios to first order phase transitions. Extremely light PBHs with masses M<10^8 g evaporate before the era of BBN, leaving behind little trace of their existence except for gravitational waves. We show that if these PBHs are produced in high enough abundances to initiate an early matter-dominated...
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Michiru Uwabo-Niibo (IBS CTPU-CGA)09/07/2025, 11:50
We formulate the statistics of peaks of non-Gaussian random fields and implement it to study the sphericity of peaks. For non-Gaussianity of the local type, we present a general formalism valid regardless of how large the deviation from Gaussian statistics is. For general types of non-Gaussianity, we provide a framework that applies to any system with a given power spectrum and the...
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Minxi He (IBS CTPU-PTC)09/07/2025, 11:50
The latest observation from ACT on the scalar spectral index $n_s$ on the cosmic microwave background (CMB) favors a larger value than previous results. To account for this, we propose a class of inflation models, dubbed regularized pole inflation, with a regularized second order pole in the kinetic term of the inflaton which can increase $n_s$ and fit the new data. The regularized pole...
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Tomotaka Kuroda (IBS CTPU-CGA)09/07/2025, 12:10
The stochastic formalism is an effective theory of long-wavelength modes that incorporates probabilistic noise from short-wavelength modes as they exit the horizon. This is expected to have non-perturbative properties, particularly useful in the context of primordial black hole (PBH) formation. Indeed, PBHs are formed from large perturbations exceeding a threshold when they re-enter the...
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Chiang-Mei Chen (NCU)09/07/2025, 12:10
We study the spontaneous emission of spin-1/2 fermions in a uniform electric field in the global coordinates of two-dimensional (anti-)de Sitter space. The production of fermion pairs is enhanced in de Sitter (dS) space. However, it is reduced in anti-de Sitter (AdS) in which weak electric fields below the BF bound prohibits pair production. We discover a reciprocal relation between the mean...
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Bum-Hoon Lee09/07/2025, 14:00
Observational data, such as the Hubble constant (H0) and cosmic birefringence, challenge the ΛCDM model. The Hubble tension indicates differing expansion rates between CMB measurements and direct observations of supernovae/Cepheid variables. Cosmic birefringence causes rotation in the CMB polarization plane. We briefly review on the Early Dark Energy Models (EDE) and explain known results that...
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Ryosuke Sato (Osaka U)09/07/2025, 14:30
The annihilation cross section of dark matter has an important role in dark matter phenomenology. If dark matter couples to a light force mediator, the exchange of the mediator non-perturbatively distorts the wave function of the dark matter from the plane wave. This effect significantly modifies the annihilation cross section .This effect is called as the Sommerfeld effect. In this talk, I...
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Yuta Hamada (KEK)09/07/2025, 15:00
On the one hand, it is known that the electroweak symmetry breaking (EWSB) in the Standard Model (SM) is a crossover. On the other hand, in the last decade, the notion of the symmetry has been greatly generalized by recognizing that the symmetry is equivalent to the presence of the topological operators. This enables us to discover new symmetries in the SM. After reviewing how these new...
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Phillip Urquijo (U of Melbourne)09/07/2025, 15:30
SABRE is an international collaboration that will operate similar particle detectors in the Northern (SABRE North) and Southern Hemispheres (SABRE South). This innovative approach aims to distinguish potential dark matter signals from seasonal backgrounds: a pioneering strategy only feasible with a Southern Hemisphere experiment. SABRE South is located at the Stawell Underground Physics...
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Atsuhisa Ota (Chongqing U)09/07/2025, 16:40
We study the analogy between graviton emission and absorption in a thermal radiation environment and the laser mechanism, in which photons of the same momentum and polarization are amplified. Using interaction-picture perturbation theory, we analyze the time evolution of the graviton number operator and its expectation value in a squeezed vacuum state, which characterizes the inflationary...
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Hisaaki Shinkai (Osaka Institute of Technology)09/07/2025, 16:40
Independent component analysis (ICA) is a method to extract a set of time-series data using ``statistical independency" of each component. We applied ICA to extract gravitational wave (GW) signals directly from the detector data. Our idea is to extract a coherent signal that is included in multiple detectors and find it by shifting the data set around its arrival time. In this article, we...
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Chan Park (Henan Academy of Science)09/07/2025, 17:00
Modern gravitational wave (GW) detectors primarily utilize electromagnetic waves (EMWs) in the geometric optics regime. Geometric optics is applicable when the wavelength of the EMWs is much shorter than the characteristic scale of spacetime curvature or variations in the medium. In this work, we explore the potential of using EMWs beyond the geometric optics regime for GW detection. To this...
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Pritha Bari (IBS CTPU-CGA)09/07/2025, 17:00
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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Ho Ching Luk (CUHK)09/07/2025, 17:20
Numerical simulations of strange quark stars (QSs) are challenging due to the strong density discontinuity at the stellar surface. This issue becomes even more problematic in merger scenarios, as any ejected strange matter droplets also exhibit discontinuous density surfaces. In this work, we perform general-relativistic simulations of binary QS merger and observe the formation of spiral arms...
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Amitayus Banik (CBNU)09/07/2025, 17:20
We study primordial gravitational waves (GWs) generated from first-order phase transitions (PTs) during cosmic reheating. Using a minimal particle physics model, and a general parametrization of the inflaton energy density and the evolution of the Standard Model temperature, we explore the conditions under which PTs occur and determine the corresponding PT parameters (the PT temperature,...
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Pavel Petrov (IBS CTPU-CGA)09/07/2025, 17:40
We present a minimal setup within the framework of Horndeski gravity that can describe a nonpathological Genesis scenario. Our setup allows for a fully stable transition to the kination epoch, during which General Relativity (GR) is restored. This Genesis scenario circumvents the no-go theorem at the cost of encountering the risk of strong coupling in the past. Interestingly, our scenario...
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Yu-Qi Dong (Lanzhou U)09/07/2025, 17:40
In this talk, we present the discovery of two previously unrecognized gravitational wave polarization modes—namely, shear modes. We explore the polarization structure of gravitational waves in torsionless spacetimes with non-metricity, which constitute one of the most widely studied classes of non-Riemannian geometries. Since gravitational wave polarization modes are characterized by the...
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Tomo Takahashi (Saga U)10/07/2025, 09:00
High-energy physics often motivates multi-field inflationary scenarios where stochastic effects play a crucial role. Peculiar to multi-field models, the noise-induced centrifugal force results in a longer duration of inflation depending on the number of fields, even when the stochastic noises themselves are small. We show that, in such small-noise regimes, the number of fields generically...
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Ming-Chung Chu (CUHK)10/07/2025, 09:30
The standard Planck ΛCDM model is well known to encounter several tensions when
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confronted with various cosmological data, including the neutrino mass and the DESI BAO
tensions. The former tension refers to the neutrino mass constraint from CMB fitting being
substantially below the lower bound from neutrino oscillation experiments. In the latter, the
BAO scales measured by DESI disagree... -
Sebastian Bahamonde (IPMU)10/07/2025, 10:00
General Relativity is based on Riemannian geometry, where gravity is solely represented by the metric degrees of freedom. This framework can be generalized by introducing torsion and nonmetricity into the underlying geometry. In this talk, I will describe how to construct such theories and how these geometrical quantities might lead to new effects on astrophysical and cosmological scales. I...
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Sang Pyo Kim (Kunsan Nat'l U)10/07/2025, 11:10
Black holes in the Einstein-Maxwell theory are Reissner-Nordstrom (RN) and Kerr-Newman (KN) black holes. In this talk black holes are studied in the nonlinear electrodynamics (NED) of Plebanski class of the Maxwell scalar and pseudo scalar. These NED black holes exhibit many interesting features and modify the photon propagation.
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Junkai Wang (Tsinghua U)10/07/2025, 11:10
As an implication from Quantum Gravity, the swamplandish Trans‐Planckian Censorship Conjecture (TCC) prohibits eternal cosmological acceleration, a prediction that aligns naturally with the quintom-B behavior from the latest DESI DR2 data. Primarily, we implement TCC bounds within the framework of dynamical dark energy, especially in the w0waCDM parametrization and f(T), f(Q) modified...
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Nils Albin Nilsson (IBS CTPU-CGA)10/07/2025, 11:30
Bumblebee gravity is currently a popular topic, and models are ubiquitus in the literature. In this talk, I will first review the current state of the art; then, I will describe a surprising connection between the bumblebee field and dark energy, as well as results from perturbation theory which rules out a large class of models.
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Junsup Shim (Academia Sinica)10/07/2025, 11:30
Recent 2σ–4σ deviations from the cosmological constant $\Lambda$ suggest that dark energy (DE) may be dynamical, based on baryon acoustic oscillations and full-shape galaxy clustering analyses. This calls for even tighter DE constraints to narrow down its true nature. In this talk, I present how galaxy intrinsic alignments (IA) can enhance the full-shape galaxy clustering–based DE constraints,...
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Jianhao Wu (CUHK)10/07/2025, 11:50
Recent observations from the James Webb Space Telescope revealed a surprisingly large number of galaxies at high redshift, challenging the standard Lambda Cold Dark Matter cosmology with a power-law primordial power spectrum. Previous studies alleviated this tension with a blue tilted primordial power spectrum ($P(k)\propto k^{m_s}$ with $m_s>1$ at small scales $>1~{\rm Mpc}^{-1}$). In this...
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Stephen Angus (Sogang U)10/07/2025, 11:50
The low-energy limit of string theory contains additional gravitational degrees of freedom that are not present in general relativity. Together with the metric, these fields are naturally embedded in the O(D,D)-symmetric framework of double field theory (DFT). First I will explain how the O(D,D) symmetry uniquely prescribes the interactions between the extended gravitational sector and other...
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Theodoros Nakas (IBS CTPU-CGA)10/07/2025, 12:10
We consider higher-order derivative gauge-field corrections that arise in the fundamental context of dimensional reduction of string theory and Lovelock-inspired gravities and obtain an exact and asymptotically flat black-hole solution, in the presence of nontrivial dilaton configurations. Specifically, by considering the gravitational theory of Euler-Heisenberg nonlinear electrodynamics...
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Song He (Ningbo U)10/07/2025, 12:10
This work explores holographic correlators within the frameworks of two-dimensional Boundary Conformal Field Theory (BCFT) and Crosscap Conformal Field Theory (XCFT). Utilizing the AdS/CFT correspondence, we compute stress tensor correlators in BCFT, considering both tensionless and tensionful end-of-the-world (EOW) brane scenarios. We derive recurrence relations for two-point and three-point...
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Rong-Gen Cai (ITP/Ningbo)10/07/2025, 14:00
Recently, a 3∼4σ preference for dynamical dark energy has been reported by the Dark Energy Spectroscopic Instrument (DESI) collaboration, which has inspired hot debates on new physics or systematics. In this letter, we reveal that this preference is significantly biased by an external low-redshift supernova (low-z SN) sample, which was combined with the Dark Energy Survey SN program (DES-SN)...
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Tuan Quoc Do (Phenikaa U)10/07/2025, 14:30
Recently, the cosmological principle, an underlying assumption of modern cosmology, has been questioned extensively due to the emergence of observational anomalies associated with not only an early phase but also a late-time phase of our observable universe. Consequently, a stable anisotropic inflation seems to be a reasonable mechanism for connecting an early anisotropic inflationary phase to...
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Arman Shafieloo (KASI)10/07/2025, 15:00
Reconstructing the expansion history of the universe and the properties of dark energy have been among the main goals of physical cosmology. I will discuss reconstructing dark energy in light of the most recent cosmological observations, including DESI-2025 BAO observations, various supernova compilations, and Planck CMB data. I will also discuss some theoretical implications of the parametric...
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Jounghun Lee (SNU)10/07/2025, 15:30
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Sunghoon Jung (SNU)10/07/2025, 16:40
De sitter space may have its version of information problem. This may manifest as non-trivial behavior of correlation functions with spatial separation. We study one of wormhole contributions to the two-point function in the 2-dimensional JT gravity. We speculate on the nature of problem and resolution via wormholes.
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Jaeok Yi (KAIST)10/07/2025, 16:40
Theoretical understanding of deep learning remains elusive despite its empirical success. In this study, we propose a novel “synaptic field theory” that describes the training dynamics of synaptic weights and biases in the continuum limit. Unlike previous approaches, our framework treats synaptic weights and biases as fields and interprets their indices as spatial coordinates, with the...
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Kin Ho Luo (CUHK)10/07/2025, 17:00
Dark sector interactions can be explored via the so-called Type 3 model where dark matter and dark energy exchange momentum, so as to minimize deviations from the ΛCDM background expansion history, which agrees well with various observations. Using N-body simulations, we analyze the imprint of Type 3 model parameters, the momentum exchange coupling constant β and the slope of scalar field...
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Kaloian Lozanov (APCTP)10/07/2025, 17:00
I am going to talk about a scalar field theory with a Minkowski false vacuum and an unbounded (or very deep) true vacuum. We will see compelling evidence that an AdS bubble of vanishing total energy, embedded in asymptotically flat spacetime, generically undergoes a spherical collapse which leads to a space-like curvature singularity after the formation of trapped surfaces and apparent...
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Hocheol Lee (Dongguk U)10/07/2025, 17:20
We investigate the bound on chaos for a charged probe particle in charged, rotating, AdS black hole backgrounds, particularly in the Kerr–Newman–AdS and Kerr–Sen–AdS spacetimes. By analyzing the particle’s radial dynamics near the local extremum of the effective potential, we compute the Lyapunov exponent and examine potential violations of the bound on chaos proposed by Maldacena, Shenker,...
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Boris Hoi-Lun Ng (CUHK)10/07/2025, 17:20
Recent cosmological measurements suggest the possibility of an anisotropic universe. As a result, the Bianchi Type I model, being the simplest anisotropic extension to the standard Friedmann-Lemaître-Robertson-Walker metric has been extensively studied. In this work, we show how the recombination history should be modified in an anisotropic universe and derive observables by considering the...
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De-Chang Dai (Nat'l Dong Hwa U, Taiwan)10/07/2025, 17:40
If two particles collide in the vicinity of a black hole horizon, their center of mass energy is practically unlimited, so another black hole with a large mass and thus entropy can be created. The resulting black hole
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can then merge with the original one. If the black hole is created very close to the horizon, its energy will be highly redshifted for ansymptotic observer. However, its... -
Mauricio Valencia-Villegas (Lomonosov Moscow State U)10/07/2025, 17:40
The near luminality and non-decay of Gravitational Waves (GWs) has ruled out all quartic and quintic Beyond Horndeski theories with a minimally coupled photon. In this talk, I show that --- with specific couplings between the scalar and the photon --- one can ensure luminal GWs and their suppressed decay in at least one viable Beyond Horndeski theory. I also discuss extensions of these...
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Kota Numajiri (YITP, Kyoto U)10/07/2025, 18:00
When quantum fields live in curved spacetime, their behavior is highly sensitive to the choice of vacuum, which reflects the global structure of the background spacetime. Furthermore, their renormalized stress-energy tensor (RSET) requires the introduction of a local higher-order curvature effect, which induces the trace anomaly. These facts highlight that both the global and local properties...
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Cheung Siu Hei (CUHK)10/07/2025, 18:00
Magnetars, which are neutron stars with a surface magnetic field strength of order 10^14 G, are the most magnetic objects in the universe. However, their formation channels are not yet fully understood. We present the first two-dimensional axisymmetric MHD simulations of accretion-induced collapse (AIC) of rotating white dwarfs (WDs). Unlike previous studies of AIC that imposed an ad hoc...
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Xiao-Gang He (TDLI)11/07/2025, 09:00
We explore the potential presence of new physics in the recent NA62 observation of the kaon decay K+ → π++E̸ with missing energy E̸ in the context of a dark-matter (DM) scenario that can explain the Belle II finding of enhanced rate of the b-meson decay B+ → K++E̸ compared to the standard-model expectation, assuming that a light real scalar boson φ plays the role of DM. The DM particle is...
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David McKeen (TRIUMF)11/07/2025, 09:30
Dark sectors which may contain the dark matter required by observation have become increasingly well studied in recent years. One of the virtues of dark matter in a dark sector is the simplicity of such models, allowing for very general results. I’ll discuss recent work on simple dark sectors that naturally give rise to slightly more complicated phenomenology, focusing on models of dark matter...
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Haipeng An (Tsinghua U)11/07/2025, 10:00
The large excursion of the inflaton field can significantly alter the properties of coupled spectator fields during inflation. This dynamic may trigger phase transitions in the spectator sector, leading to rich phenomenological implications. In this talk, I will discuss the observable signatures of such phase transitions, including gravitational waves, topological defects, and primordial...
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Han Gil Choi (IBS CTPU-CGA)11/07/2025, 11:10
Gravitational waves emitted from binary black hole mergers exhibit highly distinctive characteristics. When these waves undergo gravitational lensing, the resulting distortions in amplitude and phase can be identified. This phenomenon can thus be leveraged to probe small-scale dark matter structures that may have originated in the early universe. In this talk, I will discuss recent advances in...
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Sam Wong (CUHK)11/07/2025, 11:10
In this talk, I will discuss recent progress in understanding non-linear tidal responses and gravitational-wave tails in black hole perturbation theory. In the first part, I will present new findings demonstrating that GR black holes possess an infinite number of vanishing non-linear tidal Love numbers. These results are derived systematically using a worldline effective field theory...
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Luca Baiotti (U of Osaka)11/07/2025, 11:30
I will present our results on how to possibly discriminate equations of state with a quark-hadron crossover with respect to equations of state with purely hadronic matter or with a first-order quark-hadron transition through gravitational waves emitted in binary neutron star mergers.
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Hyewon Han (Dongguk U)11/07/2025, 11:30
We investigated the quasinormal modes of massless scalar perturbation on a near-extreme accelerating black hole. The accelerating black hole spacetime is described by the Plebański-Demiański metric, which can be characterized by seven physical parameters. We showed that the conformally invariant Klein-Gordon equation can be separated through transformations that remove the conformal factor in...
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Sen Yang (Lanzhou U)11/07/2025, 11:50
In this work, we focus on periodic orbits of a small celestial object around a supermassive quantum-corrected black hole in loop quantum gravity and compute the corresponding gravitational waveforms. We view the small celestial object as a massive test particle and obtain its four-velocity and effective potential. We explore the effects of quantum corrections on marginally bound orbits,...
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Xiao-Mei Kuang (Yangzhou U)11/07/2025, 11:50
The black hole image consists of the black hole shadow, photon ring and accretion construction, whose shape and size reflect the strong field properties of the central black hole. In this talk, I will present the images of both spherically and axially symmetric Horndiski black holes, which exhibit novel features, differentiating those of the Schwarzschild black hole in general relativity.
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Zi-Yu Tang (IBS CTPU-CGA)11/07/2025, 12:10
It is known that the coupling between axions and photons can lead to a superradiant growth and cause electromagnetic (EM) bursts when the coupling constant multiplied with the amplitude of the axion clould is larger than a critical value. In the first-order of the coupling constant, we studied how the existence of an axion cloud influences the distribution of EMs around a Kerr black hole, and...
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Huiyu Zhu (IBS CTPU-CGA)11/07/2025, 12:10
Ultralight bosons (ULBs) can form macroscopic superradiant clouds around spinning black holes. We show that for scalar ULB masses $\mu \sim 10^{-22}-10^{-21}$ eV boson cloud dynamical friction drives supermassive black hole (SMBH) final-parsec evolution in $\lesssim 1$~Gyr and suppresses the nanohertz gravitational wave background with turnover. Considering century-monitored OJ287 system, we...
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Spyros Sypsas (Centro de Ciencias Exactas, UBB)11/07/2025, 14:00
Scalar field theory on de Sitter space suffers from infrared (IR) divergences, highlighting the necessity of nonperturbative methods for IR resummation.
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A well-known triad of statements encapsulates the IR issue:
(1) the massless Bunch–Davies vacuum breaks de Sitter invariance;
(2) the coincident limit of the two-point correlator exhibits secular growth; and
(3) stochastic inflation... -
Shi Pi (ITP)11/07/2025, 14:30
In single-field inflation, an ultra-slow-roll stage is needed to enhance the curvature perturbation ζ to generate primordial black holes (PBHs) on small scales, which is usually accompanied by large local non-Gaussianity. I will introduce the recent progress on the non-Gaussian curvature perturbation of a logarithmic form. It can naturally give rise to an exponential-tail or a double...
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Ying-li Zhang (Tongji U)11/07/2025, 15:00
Primordial black holes (PBHs) are a kind of black holes which may form during the early stage of the universe. In this talk, I will discuss a class of inflationary models which seed the formation of PBHs.
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Pavel Petrov (IBS CTPU-CGA)
We present a minimal setup within the framework of Horndeski gravity that can describe a nonpathological Genesis scenario. Our setup allows for a fully stable transition to the kination epoch, during which General Relativity (GR) is restored. This Genesis scenario circumvents the no-go theorem at the cost of encountering the risk of strong coupling in the past. Interestingly, our scenario...
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Rui Hu (CUHK)
Sterile neutrinos with masses on the eV scale are promising candidates to account for the origin of neutrino mass and the reactor neutrino anomalies. The mixing between sterile and active neutrinos in the early universe could result in a large abundance of relic sterile neutrinos, which depends on not only their physical mass $m_{\mathrm{phy}}$ but also their degree of thermalization,...
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