Analysis of EDGES data shows an absorption signal of the redshifted 21-cm line of atomic hydrogen at $z\sim 17$ which is stronger than expected from the standard $\Lambda$CDM model at a 3.8$\sigma$ deviation. We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a $U(1)$ gauge symmetry and a Stueckelberg mechanism...
The recent $(g-2)_\mu$ measurement by the E989 experiment at Fermilab has recently confirmed the previous results at the Brookhaven experiment. The current tension between experiment and the Standard Model (SM) predictions stands at $4.2~\sigma$. In light of this tantalizing result, it is tempting to reconsider the few low-energy extensions of the SM that may explain the discrepancy. In...
As primordial black holes (PBHs) are one possible candidate for dark matter (DM), various constraints on PBHs have been placed in wide mass ranges. Especially in the mass range above 10^-1 M_sun, the method using gas accretion on PBH has been taken. Here, we newly consider the gas accretion process in dust tori in active galactic nuclei (AGNs). The dust torus region is typically the central...
Light relics are new degrees of freedom which decoupled from the Standard Model while relativistic. Nearly massless relics will both contribute to the radiation energy budget and, for relics with masses on the eV scale (meV-10 eV), will become non-relativistic before today, behaving as matter instead of radiation. Such relics leave an imprint in the large-scale structure of the universe as...
We derive an equation of state (EOS) for magnetized charge-neutral nuclear matter relevant for a neutron star (NS). The calculations are performed within an effective chiral model based on the generalization of the σ model with nonlinear self-interactions of the σ mesons along with the ρ−σ cross-coupling term. This model is extended by introducing the contributions of a strong magnetic field...
We study possible particle-antiparticle asymmetry in the dark sector in two distinct scenarios. In both the scenarios dark matter (DM) scatterings play defining role in deciding the asymmetry as well as the density. In the first case, we demonstrate a general semi-annihilation of DM particles, leading to maximal asymmetry in DM sector (Ref :JHEP 08 (2020), 149). In the second case, We find an...
The baryon asymmetry of the universe may be explained by rotations of the QCD axion in field space and baryon number violating processes. We consider the minimal extension of the Standard Model by a non-Abelian gauge interaction, $SU(2)_R$, whose sphaleron process violates baryon number. Assuming that axion dark matter is also created from the axion rotation by the kinetic misalignment...
Axion-like particles (ALPs), a class of pseudoscalars common to many extensions of the Standard Model, have the capacity to drain energy from the interiors of stars and consequently can be constrained through their impact on stellar evolution. In this talk I will derive a new constraint on ALPs which couple exclusively to photons, based on their effects on the white dwarf initial-final mass...
Supernova (SN) explosions are the most powerful cosmic factories of all-flavors, MeV-scale, neutrinos. Their detection is of great importance not only for astrophysics, but also to shed light on neutrino properties. Since the first observation of a SN neutrino signal in the 1987, the international network of SN neutrinos observatories has been greatly expanded, in order to detect the next...
In the early universe, primordial black holes (PBHs) can no longer be described by the simple Schwarzschild metric-- we need a metric which is locally surrounded by the cosmological fluid and asymptotically FLRW. It turns out that the phenomenology of PBHs is very sensitive to the choice of such a metric. In particular, the Thakurta metric stands out as perhaps the most justifiable metric for...
A large amount of data from dwarf galaxies to galaxy clusters appears to indicate that dark matter (DM) acts like a collisional fluid at galaxy scales to a collisionless fluid at the scale of galaxy clusters. We will discuss a particle physics model with the standard model extended with a gauged abelian hidden sector to explain this phenomenon. In this model dark matter consists of fermions of...
Dark matter (DM) particles are predicted to decay into Standard Model particles which would produce signals of neutrinos, gamma-rays, and other secondary particles. Neutrinos provide an avenue to probe astrophysical sources of DM particles. We review the decay of dark matter into neutrinos over a range of dark matter masses from MeV/c2 to ZeV/c2. We examine the expected contributions to the...
We present prospects for discovering dark matter scattering in gravitational wave detectors. We study how a potential signal from a dark matter particle compares to typical background noises in gravitational wave detectors. The dark matter signal is modelled as an elastic scattering event with the interferometer components. For the background we focus on suspension thermal noise and quantum...
Commonly known as Boltzmann suppression is the key ingredient to create chemical imbalance for thermal dark matter. In a degenerate/quasi degenerate dark sector chemical imbalance can also be generated from a different mechanism which is analogous to the radioactive decay law, known as co-decaying dark matter. In this work, we have studied the dynamics of a multicomponent thermally decoupled...
The 5:1 ratio between the cosmological mass densities of dark matter (DM) and visible matter (VM) hints at a deep connection between the origins of the two sectors. While models connecting the number densities of DM and VM have been well-explored, very little work has focused on relating the mass of DM to the proton mass. This can be achieved if the DM is a confining state of a dark QCD gauge...
In certain extensions of the Standard Model, the interactions between some new scalars and SU(2)_L Higgs doublet(s) can cause the electroweak(EW) symmetry to remain broken at temperatures well above the EW scale. We found that new fermions from renormalizable models can also induce this EW symmetry non-restoration effect, provided that they have the appropriate temperature-dependent masses....
In the scenario in which the axion is born after inflation, the field develops significant inhomogeneity and evolves in a highly nonlinear fashion. Understanding the eventual abundance and distribution of axionic dark matter in this scenario therefore requires dedicated numerical simulations. Here, we go beyond the QCD axion, and perform a suite of simulations for a range of possible...
We investigate the resummation of infrared logarithms in inflationary Universe from holographic perspective. By the renormalization group, we derive gravitational Fokker-Planck and Langevin equations as the effective theory at the Horizon scale. We investigate the time evolution of the de Sitter entropy $S=¥pi/G_N H^2(t)$. $H(t)$ is the time dependent effective Hubble parameter and $G_N$ is...
Simplified models of light new physics provide an important theoretical and experimental benchmark. Models that extend such minimal scenarios by introducing other degrees of freedom are popular and well motivated ways to go beyond the Standard Model (SM). In this talk, I will focus on the light dark Higgs portal that connects the dark sector consisting of, among others, heavy, TeV-scale...
We explore a new kind of NLED field as a source of gravity, which can accelerate the universe during the inflationary era. We propose a new type of NLED lagrangian which is characterized by two parameters: α (dimensionless parameter) and β (dimensionful parameter). We investigate the classical stability and the causality aspects of this model of inflationary expansion by demanding that the...
Next energy frontier accelerators like ILC or CLIC are with immense possibilities to improve our understanding with nature's fundamental building block and to discover new particles e.g. WIMP dark matters along with other physics phenomena. In scenarios where dark matter does not or feebly couple with quarks, we can consider the dominant coupling of dark matter with charged leptons. We...
An abundance of hints from recent neutrino experiments leads to the hypothesis of the existence of light sterile neutrinos; however, there are also many constraints from laboratory experiments experimentally and cosmological observations that constrain its mixing and mass. In light of these observations, we present a new model of light sterile neutrinos that aims to elucidate this confusing...
The standard model(SM) is augmented by a $U(1)_{B-L}$ gauge symmetry. Three right-handed neutrinos(RHN) are added with $B-L$ charge -4,-4 and 5 required for the anomaly cancellation. Two vector-like fermion doublets(N_i), a doublet scalar(\eta), and two singlet scalars(\chi_1,\chi_2) are also added having nontrivial charges under the B-L group except \chi_1 particle. A Z_2 symmetry is also...
Dark matter is one of the cornerstones of the standard cosmological model although we do not know its fundamental nature. Huge effort has been made in order to perform a direct detection of this dark matter component but up to now we have only seen it interacting gravitationally. In this regard the indirect detection is a promising method to search for dark matter, where we try to look at...
We present a simple extension of the Standard Model with three right-handed neutrinos in a SUSY framework, with an additional U(1)_F abelian flavor symmetry with a non standard leptonic charge for lepton doublets and arbitrary right-handed charges. We show how it is possible to provide the correct predictions for the mixing angles of the PMNS matrix and for the r=(∆m_sun)^2/(∆m_atm)^2...
Particulate dark matter captured by a population of neutron stars distributed around the galactic center while annihilating through long-lived mediators can give rise to an observable neutrino flux. We examine the prospect of an idealized gigaton detector like IceCube/KM3Net in probing such scenarios. Within this framework, we report an improved reach in spin-dependent and spin-independent...
In secluded dark sector scenario, thermal equilibrium between dark and visible sector depends on the strength of portal coupling. To study the non-adiabatic evolution of the dark sector, we have considered a $U(1)_{L_\mu - L_\tau} \otimes U(1)_X$ extension of the standard model (SM). Here in this model the dark sector is charged only under $U(1)_X$ gauge symmetry whereas the SM fields are...
A mechanism for the formation of primordial black holes is proposed. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry. The large amount of energy stored in the colour flux tubes connecting the quark pair leads to black-hole formation. These are much lighter and can be of higher spin than...
We study neutrino oscillations within the framework of extended theories of gravity. Based on the covariant reformulation of Pontecorvo’s formalism, we evaluate the oscillation probability of neutrinos propagating in static spacetimes described by gravitational actions quadratic in the curvature invariants. Calculations are carried out in the two-flavor approximation, for oscillations both in...
Based on the geometry of the codimension-2 surface in general spherically symmetric spacetime, we give a quasi-local definition of a photon sphere as well as a photon surface. This new definition is the generalization of the one provided by Claudel, Virbhadra, and Ellis but without referencing any umbilical hypersurface in the spacetime. The new definition effectively excludes the photon...
The inferred abundance of dark matter in the Universe could be explained with heavy decaying dark matter. According to heavy dark matter models, the decay of dark matter in astronomical objects can produce highly energetic neutrinos detectable at the Earth. The IceCube Neutrino Observatory, located at the geographic South Pole, is to date the world’s largest neutrino telescope. Over the past...
Effective range theory, which was originated in Bethe, was developed to study nucleon scattering. We applied this in the context of self-interacting dark matter (SIDM). We studied what kind of combination of parameters fit to the MCMC simulation of dark matter cross section from dwarf scale to cluster scale. As a result, scattering length is longer than our naive expectation. So we...
Heavy neutral leptons (HNLs) have been proposed to extend the standard model to explain the MiniBooNE anomaly. We demonstrate that, in the minimal scenario, this model is ruled out by a combination of neutrino beam experiments and cosmological constraints. However, HNLs could be portals to a dark sector. An extension of this model that incorporates a dark U(1) gauge theory can avoid the...
A bright and statistically significant flux of GeV-scale gamma rays has been detected from the region surrounding the Galactic Center. While the spectrum, angular distribution, and intensity of this signal is consistent with the predictions of annihilating dark matter matter particles, it has also been suggested that these gamma rays could potentially be produced by a large population of...
I will discuss gaps in our coverage of the gravitational spectrum and possible new methods for filling them. Atom interferometry shows promise for detecting gravitational waves in the frequency range around a Hz, the “mid-band” between LIGO and LISA. Intermediate-scale atomic detectors are currently under construction. These would demonstrate the technology, paving the way for full-scale...
I will describe a new measurement of the small-scale matter power spectrum using UV luminosity-functions (UVLFs) from the Hubble Space Telescope. These data trace the abundance of the first galaxies forming during the epoch of reionization. Since the first galaxies were much less massive than their counterparts today, they provide us with a handle on the clustering of dark matter at smaller...
Neutrino decay modifies neutrino propagation in a unique way; not only is there flavor changing as there is in neutrino oscillations, there is also energy transport from initial to final neutrinos. The most sensitive direct probe of neutrino decay is currently IceCube which can measure the energy and flavor of neutrinos traveling over extragalactic distances. For the first time we calculate...
Superradiant instabilities may create clouds of ultralight bosons around black holes, forming so-called “gravitational atoms.” It was recently shown that the presence of a binary companion can induce resonant transitions between a cloud's bound states. When these transitions backreact on the binary's orbit, they lead to qualitatively distinct signatures in the gravitational waveform that can...
We study for the first time the possibility of probing long-range fifth forces utilizing asteroid astrometric data, via the fifth force-induced orbital precession. We examine nine Near-Earth Object (NEO) asteroids whose orbital trajectories are accurately determined via optical and radar astrometry. Focusing on a Yukawa-type potential mediated by a new gauge field (dark photon) or a...
A precise characterization of the astrophysical neutrino flux is feasible as neutrino telescopes collect data. IceCube has already measured the spectral shape and flavor composition of this flux. Several projected experiments will be able to further constrain the nature of cosmic neutrinos. Most of these experiments look for neutrinos that cross the Earth, so it is fundamental to understand...
Measurements of the cosmic microwave background, the Lyman-Alpha forest and future 21-cm results can set significant constraints on dark matter annihilation or decay. To obtain such limits, a good understanding of how dark matter energy injection affects the ionization and thermal history of the universe is crucial. In this talk, I will present an open-source code package called DarkHistory,...
We investigate Hawking evaporation of a population of primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN) as a mechanism to achieve asymmetric reheating of two sectors coupled solely by gravity. While the visible sector is reheated by the inflaton or a modulus, the dark sector is reheated by PBHs. Compared to inflationary or modular reheating of both sectors, there are two...
We establish a paradigm where the (QCD) axion’s novel cosmological evolution, a rotation in the field space, gives rise to dark matter and the baryon asymmetry. The axion rotations also provide a natural origin for a kination era, where the total energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. We investigate the effects of this...
Neutrinos passing through the Earth can scatter off nuclei and produce heavy neutral leptons (HNLs). For HNL decay lengths on the order of, or shorter than, the radius of the Earth these HNLs can be efficiently detected by searching for their decay products in large volume detectors. I will discuss prospects for discovery of HNLs produced from solar and atmospheric neutrinos in large volume detectors.
The pp-chain of nuclear reactions is the primary route for energy production in the Sun. The first step in that reaction sequence converts two protons to a deuterium nucleus with the emission of a positron and electron neutrino. This reaction is extremely slow because it is a weak interaction, and significantly, it involves quantum tunneling through the Coulomb barrier. Though the reaction...
Primordial Black Holes (PBH) in the intermediate mass range can be seeds for supermassive black holes and recent LIGO detections of black hole mergers in the mass gap suggest PBH progenitors. I present a novel constraint on the PBH mass fraction spanning PBH masses of ~10-10^6 solar masses from thermal equilibrium considerations. A population of PBH in the central region of the dwarf galaxy...
A generic low-energy prediction of string theory is the existence of a large collection of axions, commonly known as a string axiverse. In a realistic axiverse, string axions can be distributed densely over many orders of magnitude in mass, and are expected to interact with one another through their joint potential. In this talk, I will show how non-linearities in this potential can lead to a...
Cosmology plays a central role in understanding the nature of dark matter (DM), with the power to test models which are hard to access by other means. The ultra-light axion is a compelling particle candidate that is motivated, e.g., by the string theory "axiverse" and as a possible solution to the so-called "small-scale crisis" of the cold dark matter model, if its mass is ~ 10^-22 eV. I will...
Gravitational waves provide a unique method of testing theories with extended gauge symmetries. In particular, spontaneous symmetry breaking can lead to a detectable stochastic gravitational wave background generated by cosmic strings and first order phase transitions in the early universe. I will discuss the unique gravitational wave signature of a dark matter model with gauged baryon and...
The dark photon is a massive hypothetical particle that interacts with the Standard Model by kinetically mixing with the visible photon. Due to the similarity with the electromagnetic signals generated by axions, many putative bounds on dark photon signals are simply reinterpretations of historical bounds set by axion haloscopes. However, the dark photon has a property that the axion does not:...
Heavy stars can explode at their ends. This phenomenon is called supernova. Supernovae are very complicated systems so we need high cost computation to understand them. Supernovae release a lot of neutrinos at their explosion. If a supernova happens in our galaxy, a few thousands events could be detected with neutrino detectors in the world for about more than 10 seconds. We need long time...
Unusual masses of black holes being discovered by gravitational wave experiments pose fundamental questions about their origin. More interestingly, black holes with masses smaller than the Chandrasekhar limit (∼ 1.4 solar mass) are essentially impossible to produce through any standard stellar evolution. Primordial black holes, with fine-tuned parameters, and with no compelling formation...
I will review the current status of the search for the QCD axion.
I will review the current status of theoretical work on the QCD axion.
Axion-like fields appear in many string theory constructions. I will discuss a proposed explanation for why they are so ubiquitous: they play a crucial role in eliminating would-be global symmetries from the theory. This also gives a new perspective on axion interactions with magnetic monopoles. I will explain how magnetic monopole loops give rise to an axion potential.
The abundance of dark matter is a key piece of information that informs any fundamental theory aiming to describe its properties. However, mapping this measurement onto the parameters of the underlying theory relies on the cosmology at early times, which is itself not well-anchored by observation. I will describe a few ways in which the properties of the Universe at early times could deviate...
If even a relatively small number of primordial black holes (PBH) were created in the early universe, they will constitute an increasingly large fraction of the total energy density as space expands. It is thus well-motivated to consider scenarios in which the early universe was dominated by short lived PBH (M < 10^9 grams, t < 1 sec) whose Hawking radiation produces both the Standard Model...
Neutrinos are fascinating elementary particles heralding the dawn of the multi-messenger astronomy era. Neutrinos affect the stellar dynamics, drive the formation of new elements, and carry signatures of the yet mysterious physics ruling cosmic accelerators. Recent developments on neutrinos from cosmic sources will be reviewed together with detection prospects.
The discovery of high-energy cosmic neutrinos opened a new window of astroparticle physics. Their origin is a new mystery in the field, which is tightly connected to the long-standing puzzle about the origin of cosmic rays. I will discuss theoretical implications of the latest results on high-energy neutrino and cosmic-ray observations, and demonstrate the power of multi-messenger approaches....
The formation of ultra rare supermassive black holes (SMBHs), with masses of $\ord{10^9 M_{odot}}$, in the first billion years of the Universe remains an open question in astrophysics. At the same time, ultralight dark matter (DM) with mass in the vicinity of $\ord{10^{-20}~\text{eV}}$ has been motivated by small scale DM distributions. Though this type of DM is constrained by various...
Observations show that supermassive black holes (SMBHs) with a mass of one billion solar mass exist when the universe is just 6% of its current age. We propose a scenario where a self-interacting dark matter halo experiences gravothermal instability and its central region collapses into a seed black hole. The presence of baryons in protogalaxies could significantly accelerate the gravothermal...
Black holes are never isolated in realistic astrophysical environments; instead, they are often perturbed by complicated external tidal fields. How does a black hole respond to these tidal perturbations? In this talk, I will discuss both the conservative and dissipative responses of the Kerr black hole to a weak and adiabatic gravitational field. The former describes how the black hole would...
Observations of high-energy astrophysical neutrinos in IceCube have opened the door to multi-messenger astronomy, by way of which questions in particle physics could be explored through a combination of IceCube data and optical experiments such as Fermi-LAT. However, the origin of these astrophysical neutrinos is still largely unknown. Among the tensions that still need to be addressed, for...
Millicharge particles with charge just evading accelerator bounds, possess charge large enough to accumulate on earth and cause gigantic build-up over the age of the earth. I introduce a new idea that sets exquisite bounds on millicharge particle dark matter and promises to reach interesting parameter space in the near future. The new detection concept involves the remarkable sensitivity of...
Black hole superradiance is a powerful probe of light, weakly-coupled hidden sector particles. Particles with a Compton wavelength comparable to the black hole’s radius lead to an instability, extracting mass and angular momentum from the black hole. Many ultralight candidates, such as axions, generically have self-interactions that can influence the evolution of the superradiant instability....
An intriguing possibility for the particle makeup of the dark sector is that a small fraction of the observed abundance is made up of light, feebly-interacting particle species. Neutrinos, with their yet-unresolved masses, are a concrete example in this category, but more exotic candidates readily arise from new physics scenarios. Due to their weakness of interaction but comparatively large...
The discovery of a non-zero mass for neutrinos invites to consider whether they are Dirac or Majorana particles. But those are not the only two possibilities, there is a third one, in which neutrinos are Majorana, but they behave as if they were Dirac particles, that is called pseudo-Dirac particles. The scenario predicts an oscillation between active and sterile neutrinos, with an oscillation...
We describe a new production mechanism of particle dark matter, which hinges on momentum filtering during a first-order cosmological phase transition. We then show that this mechanism can be modified to provide a new production mechanism of primordial black holes, which have not yet been observed but could solve a number of problems in cosmology.
The IceCube neutrino observatory is the to-date largest neutrino telescope installed in the Antarctic ice. It consists of 5,160 photomultiplier-tubes spread among 86 vertical strings making a total detector volume of more than a cubic kilometer. It detects neutrinos via Cherenkov light of charged relativistic particles from neutrino interactions with the detector volume. IceCube is, due to its...
Colored gravitational instantons, known as Eguchi-Hanson instantons, mediate vacuum-vacuum transitions in an analogous way to the well-known BPST instantons. As a result, a new source of CP-violation is present in gauge theories, described by an additional 'quantum gravity' vacuum angle. This second angle spoils the usual axion as a solution to the strong CP problem. The simplest solution to...
Gravitational microlensing constrains the abundance of massive compact objects in the Galactic halo. Historical studies (MACHO, EROS, OGLE, MOA) have excluded objects lighter than 10 solar masses as a major component of Galactic dark matter. The detection of coalescences of heavier black holes by LIGO/Virgo has rekindled interest in dark matter as compact objects. The effectiveness of previous...
We probe the cosmological consequences of a recently proposed class of solutions to the cosmological constant problem. In these models, the universe undergoes a long period of inflation followed by a contraction and a bounce that sets the stage for the hot big bang era. A requirement of any successful early universe model is that it must reproduce the observed scale-invariant density...
A sizeable fraction of axion dark matter may be today in galactic halos in the form of Bose-Einstein condensate structures, which are known in the literature as “axion stars” or “axion clumps”. In this talk, I will address main astrophysical features associated with such gravitational bound objects and constraints over their abundance via gravitational microlensing, including finite lens and...
To date, the only direct evidence of gravitational waves (GWs) comes from the detection of merging black holes and neutron stars by the LIGO and Virgo detectors. Observations of these mergers have provided a wealth of astrophysical information as well as constraining theories of modified gravity. However, no convincing signs of new physics have yet been found in GW data. In this talk I will...
The latest results from a search for the Diffuse Supernova Neutrino Background (DSNB) at Super-Kamiokande (SK) is presented, incorporating 22.5×2970 kton.days of data from its fourth data-taking phase, covering an overall antineutrino energy range of 9.3−81.3 MeV, and combining results with previous SK data-taking periods, for a combined analysis of nearly 20 years of data. The analysis...
Primordial black holes hypothetically generated in the first instants of life of the Universe are potential dark matter (DM) candidates. Focusing on Primordial black holes masses in the range [5×10^{14}-5×10^{15}]g, we point out that the neutrinos emitted by PBHs evaporation can interact through the coherent elastic neutrino nucleus scattering producing an observable signal in multi-ton Dark...
Many scenarios of physics beyond the Standard Model predict new particles with masses well below the electroweak scale. Low-energy, high luminosity colliders such as BABAR are ideally suited to discover these particles. We present several recent searches for low-mass dark sector particles at BABAR, including leptophilic scalars, new gauge bosons coupling only to the second and third generation...
In this talk I present the recent constraints on primordial black holes (PBHs) with microlensing methods, based on the Subaru Hyper Suprime-Cam (HSC) and the Optical Gravitational Lensing Experiment (OGLE) data. With Subaru HSC data, we obtained the tightest bound on the abundance of PBHs in the mass range of masses from asteroid to moon masses, but found a possible one candidate. We also...
Line intensity mapping (LIM) is a rapidly developing new technique to study astrophysics and cosmology. With LIM, the luminosity density of a given atomic/molecular emission line is mapped in a three-dimensional volume. I will discuss how this technique can be used to determine the distribution of dark matter and to also probe specific dark-matter candidates. I will also describe how the...
I will review some recently proposed scenarios for PBH formation, as well as astrophysical consequences of dark matter in the form of primordial black holes.
