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...
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...
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.
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...
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...
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...
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...
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...
We propose a scenario for the cogenesis of baryon asymmetry and dark matter, realizing spontaneous leptogenesisby by Majoron in Type I seesaw model.
This mechanism requires significant kinetic motion, which we demonstrate can naturally arise from conventional misalignment under conditions of symmetry non-restoration
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.
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...
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.
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 $\overline{\rm D}$...
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...
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...
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.
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...
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...
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.
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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.
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.
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,...
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...
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.
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
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...
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...
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...
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...
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.
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.
Scalar field theory on de Sitter space suffers from infrared (IR) divergences, highlighting the necessity of nonperturbative methods for IR resummation.
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...
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.
