Primordial black holes (PBHs) are black holes which are believed to have formed in the very early Universe. Recently an idea that asteroid mass PBHs may be dark matter of the Universe is attracting a lot of attention. Their size is icroscopic; they are of the size of a hydrogen atom or smaller.
In this talk, I first briefly review our knowledge about dark matter and black holes, then...
Gauge symmetry can naturally accommodate dark matter stability or longevity. Hidden sectors (or dark sectors) with dark gauge symmetry would contain multiple particles , and then multi-component dark matter models become generic. , and they are not an ad hocextension of the WIMP paradigm—it is a natural consequence of a rich hidden gauge sector. Future experiments should search for rich dark...
Type-I seesaw models with a spontaneously broken B-L symmetry provide a natural framework for spontaneous leptogenesis driven by a Majoron. The kinetic background of the Majoron acts as a CP-violating source, generating a lepton asymmetry both through the decay of right-handed neutrinos and through equilibration via inverse-decay processes. We construct the Boltzmann equations in a fully...
The DESI collaboration interpret a discrepancy in the LCDM parameter Ωₘ at different effective redshifts as a dynamical dark energy signal. I will identify a number of hurdles that need to be cleared before one can fully buy into the claim.
In this talk, I will discuss an alternative production mechanism for long-lived heavy neutrinos within the framework of neutrinophilic Higgs doublet models, where an additional Higgs doublet couples exclusively to the Standard Model (SM) lepton doublets and right handed neutrinos (RHNs). This structure allows the vacuum expectation value (VEV) of the extra Higgs doublet to be much smaller than...
We explore the phenomenology of the Dark Photon iDM (A'iDM) model, one of the simplest and most direct realisations of the inelastic Dark Matter (iDM) scenario. In this framework, the Standard Model (SM) is extended by a dark sector with an additional U(1)_D gauge symmetry. All SM particles are neutral under this symmetry, which couples to the SM hypercharge gauge boson via a kinetic mixing...
The detection of gamma-ray signals from primordial black holes (PBHs) could provide compelling
evidence for their role as a dark matter candidate, particularly through the observation of their
Hawking radiation. Future gamma-ray observatories, such as e-ASTROGAM, and the next-generation
telescopes, are poised to explore this possibility by measuring both Standard Model (SM) and...
We consider the quadratic effective energy-momentum tensor that plays the role of cosmological back-reaction. We evaluate this from the cosmological perturbations during inflation. We present the recent results in uniform-expansion and uniform-density gauge conditions, and compare with the previous results in other (longitudinal, spatially-flat, comoving) gauge conditions.
We study a string-motivated theoretical prior on the quintessential dark energy model with exponential potential, ( V(φ) = V₀ e^-λ φ ), allowing for non-zero spatial curvature. First, we formulate the corresponding dynamical system and investigate its cosmological evolution numerically, illustrating the phase-space behaviour and the influence of curvature on the background dynamics. In open...
The low-energy limit of string theory contains additional gravitational degrees of freedom, the B-field and dilaton, that are not present in general relativity. Together with the metric, these three fields are naturally embedded in the O(D,D)-symmetric framework of double field theory (DFT). Furthermore, extending the O(D,D) symmetry to additional matter fixes a modified minimal coupling in...
We introduce field theory version of wormhole in disorder theory and consider the analogy of quantum gravity and disorder theory.
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...
Ultralight scalar field dark matter (ULDM) provides a compelling alternative to the standard cold dark matter paradigm, exhibiting wave-like behavior on galactic and cosmological scales. After a brief review of ULDM and self-interacting ULDM (SI-ULDM), we discuss how SI-ULDM can alleviate the Hubble and S₈ tensions. We also briefly explore possible connections between the SI-ULDM framework,...
According to the holographic principle—one of the most influential frameworks in contemporary physics—gravitational physics in a bulk spacetime is dual to the quantum physics of a system defined on its boundary. We employ a deep learning approach to reconstruct the bulk spacetime geometry from boundary quantum data, such as conductivity and entanglement entropy. This method offers novel...
We show that inflationary magnetogenesis can occur without modifying the microscopic Maxwell action. The observable photon sector inside a de Sitter causal patch is treated as a reduced subsystem that relaxes at a finite rate toward a horizon-selected quasi-static branch. Because the physical photon frequency continuously redshifts during inflation, this reduced dynamics cannot track the...
We construct black hole solutions in four-dimensional Einstein-Yang-Mills theory with U(2) gauge group. We take a near-extremal limit of the black hole solutions coupled with Yang-Mills instantons which reduces to Witten's multi-instanton solutions described by the Liouville theory in two-dimensional Abelian Higgs model.
We consider a semi-classical quantization of the near-extremal black...
We study particular gravity duals to the inhomogeneously mass-deformed ABJM (ImABJM) theory. The final goal of this paper is to obtain the ABJM theory deformed by a delta function-type mass. The resultant theory can be interpreted as the ABJM theory with defects. The mass operators of the mass-deformed ABJM (mABJM) theory are identified with these defect operators. Corresponding gravity duals...
One-loop partition functions encode the leading-order quantum corrections to the gravitational path integral and can be constructed from quasinormal modes. We investigate how exact computations of these quantities can be extended beyond highly symmetric backgrounds. Trace formulas provide a powerful framework connecting spectral data of differential operators to geometric data of the...
Primordial black holes (PBHs) provide a unique window into the physics of the early Universe and offer an important avenue for probing gravity beyond General Relativity. In this talk, I will discuss the formation and properties of primordial black holes in the framework of Einstein–Dilaton–Gauss–Bonnet (EdGB) gravity, where a scalar dilaton field is non-minimally coupled to the Gauss–Bonnet...
We revisit the dynamics of black holes using the canonical approach to quantum gravity. By introducing time slices that cover both the inside and the outside of the horizon, we obtain the Wheeler-DeWitt equation. It is not possible to solve it directly, but it is possible to see potential dynamics and boundary conditions. From this, we can conclude that we cannot provide a coherent state that...
We explore O(2N) scalar theory with fractional Laplacian, √(-∇²) in d-dimension and its Hamiltonain dynamics which is described by a Schrodinger type equation. 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 investigate D-instanton effects on the holographic Weyl semimetal in a top-down approach. From the free energy of the D7 brane embedding solutions, we get a phase diagram in terms of the electron mass, instanton number, and temperature in the unit of the weyl parameter. We calculate non-linear conductivities from the regularity condition of the probe D7 brane and investigate anomalous Hall...
We study scalarized extremal black holes in the Einstein-Maxwell-scalar theory with two different scalar couplings to two U(1) fields. This theory is inspired by the bosonic sector of N=4 supergravity. Two scalarzied extremal black holes are found with constant secondary scalar hair. We confirm that these are exactly obtained from the standard scalarization and entropy function...
I discuss the recent progress on the microstates of the supersymmetric AdS black holes under the AdS/CFT framework. In detail, I will discuss the possible black hole microstates in AdS5 from its dual four dimensional maximal Super-Yang-Mills theory.
In this talk we discuss various aspects of the effective dynamics of Maxwell-Einstein scalar theories in the background of static, spherically symmetric and extremal black hole solution in (1+3) dimensions. We show that the effective one dimensional action (governed by the Attractor mechanism) from which the effective black hole potential (introduced by Ferrara-Gibbons-Kallosh) is usually...
In this talk, I will discuss on-shell actions for type IIB supergravity and 11D M-Theory based on my recent papers (JHEP 06 (2026) 271 and 260X.XXXXX). In these works, we have consistently incorporated suitable topological terms that can be evaluated for a
large number of backgrounds. We also show that the on-shell actions for the original 10D and 11D supergravities obtained in our papers...
We present a perturbative construction of the Nicolai map for four-dimensional N = 1 pure supergravity around flat Minkowski space, as an alternative to the coupling-flow-operator approach. Using the second-order formalism and the background-field expansion of the vielbein in the gravitational coupling κ, we derive the on-shell BRST structure and formulate the defining conditions for a Nicolai...
