We show that an axionlike field coupled to a new confining gauge group can generate the primordial density perturbation in the post-inflation universe. The axion decay constant and strong coupling scale are uniquely determined by observations of the density perturbation, which further suggest a temporal deconfinement of the gauge group after inflation. The resulting temperature-dependent axion potential, together with its periodic nature, gives rise to the red-tilted density perturbation, with a positive local-type non-Gaussianity of order unity.
We performed the detailed analysis of the primordial black hole (PBH) formation mechanism in an axionlike curvaton model with a coupling to inflaton. The phase direction of the complex scalar works as a curvaton and produces enough PBHs to explain the black hole binaries ($\sim 30 M_{\odot}$) observed in the LIGO-Virgo Collaboration or PBHs as dark matter (DM) ($\sim 10^{-12} M_{\odot}$). We examine whether our model satisfies the current constraints on the PBH mass spectrum, the curvature perturbation and the secondarily produced gravitational waves. We also take into account ambiguity about …
Production of axionlike particles (ALPs) by primordial magnetic fields may have significant impacts on cosmology. We discuss the production of ALPs in the presence of the primordial magnetic fields. We find a region of the ALP mass and photon coupling which realizes the observed properties of the dark matter with appropriate initial conditions for the magnetic fields. This region may be interesting in light of recent indications for the 3.5 keV lines from galaxy clusters. For a small axion mass, a region of previously allowed parameter spaces is excluded by overproduction of ALPs as a hot/warm…
In this paper, we show how the structure of the landscape potential of the primordial Universe may be probed through the properties of the primordial density perturbations responsible for the origin of the cosmic microwave background anisotropies and the large-scale structure of our Universe. Isocurvature fields -fields orthogonal to the inflationary trajectory- may have fluctuated across the barriers separating local minima of the landscape potential during inflation. We analyze how this process could have impacted the evolution of the primordial curvature perturbations. If the typical distan…
It was pointed out recently that in some inflationary models quantum loops containing a scalar of mass $m$ that couples to the inflaton can be the dominant source of primordial non-Gaussianities. We explore this phenomenon in the simplest such model focusing on the behavior of the primordial curvature fluctuations for small $m/H$. Explicit calculations are done for the three and four point curvature fluctuation correlations. Constraints on the parameters of the model from the CMB limits on primordial non-Gaussianity are discussed. The bi-spectrum in the squeezed limit and the tri-spectrum in t…
We estimate the magnitude today of the primordial magnetic field originating at the electroweak phase transition. We find that the field, which at the electroweak phase transition is originally of order $10^{23}-10^{24}$ G correlated over the Hubble scale, today is of order $10^{-14}$ G at a scale of order 2 kpc. This result is consistent with the lower limit on the strength of intergalactic magnetic fields obtained by Neronov and Vovk from observations of TeV blazars. The field is non-helical. We compare our results with the helical case discussed by Field and Carroll.
It has been pointed out that hypermagnetic helicity decay at the electroweak symmetry breaking may have produced the observed baryon asymmetry of the Universe through the chiral anomaly in the standard model of particle physics. Although fully helical magnetic field that can adequately produce the observed baryon asymmetry is not strong enough to explain the origin of the intergalactic magnetic field inferred by the Fermi satellite, the mixture of helical and nonhelical primordial magnetic fields may explain both baryogenesis and the intergalactic magnetic fields simultaneously. We first show …
Since magnetic fields in galaxies, galactic clusters and even void regions are observed, theoretical attempts to explain their origin are strongly motivated. It is interesting to consider that inflation is responsible for the origin of the magnetic fields as well as the density perturbation. However, it is known that inflationary magnetogenesis suffers from several problems. We explore these problems by using a specific model, namely the kinetic coupling model, and show how the model is constrained. Model independent arguments are also discussed.
A population of primordial black holes formed in the early Universe could contribute to at least a fraction of the black-hole merger events detectable by current and future gravitational-wave interferometers. With the ever-increasing number of detections, an important open problem is how to discriminate whether a given event is of primordial or astrophysical origin. We systematically present a comprehensive and interconnected list of discriminators that would allow us to rule out, or potentially claim, the primordial origin of a binary by measuring different parameters, including redshift, mas…
Primordial Black Hole (PBH) is one of the leading non-particle candidates for dark matter (DM). Although several observations severely constrain the amount of PBHs, it is recently pointed out that there is an uncertainty on the microlensing constraints below $\sim 10^{-10} M_\odot$ which was ignored originally but may weaken the constraints significantly. In this paper, facing this uncertainty, we investigate the possibility that PBHs can make up all DM in a broad mass spectrum. Moreover, we propose a concrete inflation model which can simultaneously produce PBHs for all DM in a broad mass spe…
Primordial black holes (PBHs) from the early Universe constitute an attractive dark matter candidate. First detections of black hole-neutron star (BH-NS) candidate gravitational wave events by the LIGO/Virgo collaboration, GW200105 and GW200115, already prompted speculations about non-astrophysical origin. We analyze, for the first time, the total volumetric merger rates of PBH-NS binaries formed via two-body gravitational scattering, finding them to be subdominant to the astrophysical BH-NS rates. In contrast to binary black holes, a significant fraction of which can be of primordial origin, …
We consider the possibility that the majority of dark matter in our Universe consists of black holes of primordial origin. We determine the conditions under which such black holes may have originated from a single-field model of inflation characterized by a quartic polynomial potential. We also explore the effect of higher-dimensional operators. The large power spectrum of curvature perturbations that is needed for a large black hole abundance sources sizable second order tensor perturbations. The resulting stochastic background of primordial gravitational waves could be detected by the future…
If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs) at the centers of high-redshift quasars, then the gas surrounding these black holes may reveal nucleosynthetic clues to their primordial origins. We present predictions of altered primordial abundances around PBHs massive enough to seed SMBHs at z~6-7.5. We find that if PBHs with initial masses of ~10^5 M$_{\odot}$ are responsible for such SMBHs, they may produce primordial Deuterium and Helium fractions enhanced by >~ 10%, and Lithium abundance depleted by >~10%, at distances of up to ~ a comoving kiloparsec away fro…
We study the gravitational effects of a planar domain wall on quantum fluctuations of a massless scalar field during inflation. By obtaining an exact solution of the scalar field equation in de Sitter space, we show that the gravitational effects of the domain wall break the rotational invariance of the primordial power spectrum without affecting the translational invariance. The strength of rotational violation is determined by one dimensionless parameter $β$, which is a function of two physical parameters, the domain wall surface tension $σ$ and cosmological constant $Λ$. In the limit of sma…
We study the possibility of cogenesis of baryon and dark matter (DM) from the out-of-equilibrium CP violating decay of right handed neutrino (RHN) that are dominantly of non-thermal origin. While the RHN and its heavier partners can take part in light neutrino mass generation via Type-I seesaw mechanism, the decay of RHN into dark and visible sectors can create respective asymmetries simultaneously. The non-thermal sources of RHN considered are {\bf (a)} on-shell decay of inflaton, and {\bf (b)} evaporation of ultralight primordial black holes (PBH). After setting up the complete set of Boltzm…
We study the supermassive black holes (SMBHs) observed in the galactic centers. Although the origin of SMBHs has not been well understood yet, previous studies suggest that seed black holes (BHs) with masses $10^{4-5}M_\odot$ exist at a high redshift ($z \sim 10$). We examine whether primordial black holes (PBHs) produced by inhomogeneous baryogenesis can explain those seed black holes. The inhomogeneous baryogenesis is realized in the modified Affleck-Dine mechanism. In this scenario, there is no stringent constraint from CMB $μ$-distortion in contrast to the scenario where Gaussian fluctuati…
In this article we provide a new closed relationship between cosmic abundance of primordial gravitational waves and primordial blackholes originated from initial inflationary perturbations for inflection-point models of inflation where inflation occurs below the Planck scale. The current Planck constraint on tensor-to-scalar ratio, running of the spectral tilt, and from the abundance of dark matter content in the universe, we can deduce a strict bound on the current abundance of primordial blackholes to be within a range, $9.99712\times 10^{-3}<Ω_{PBH}h^{2}<9.99736\times 10^{-3}$.
Both inflationary and ekpyrotic scenarios can account for the origin of the large scale structure of the universe. It is often said that detecting primordial gravitational waves is the key to distinguish both scenarios. We show that this is not true if the gauge kinetic function is present in the ekpyrotic scenario. In fact, primordial gravitational waves sourced by the gauge field can be produced in an ekpyrotic universe. We also study scalar fluctuations sourced by the gauge field and show that it is negligible compared to primordial gravitational waves. This comes from the fact that the fas…
Primordial black holes may owe their origin to the small-scale enhancement of the comoving curvature perturbation generated during inflation. Their mass fraction at formation is markedly sensitive to possible non-Gaussianities in such large, but rare fluctuations. We discuss a path-integral formulation which provides the exact mass fraction of primordial black holes at formation in the presence of non-Gaussianity. Through a couple of classes of models, one based on single-field inflation and the other on spectator fields, we show that restricting to a Gaussian statistics may lead to severe ina…
Building on the insight that primordial black holes can arise from the formation and subsequent gravitational collapse of bound states of stable supermassive elementary particles during the early radiation era, we offer a comprehensive picture describing the evolution and growth of the resulting mini-black holes through both the radiation and matter dominated phases, until the onset of (small scale) inhomogeneities. This is achieved by means of an exact metric solving Einstein's equations throughout both phases. We show that, thanks to a special enhancement effect producing an effective horizo…
In this thesis, we have studied the generation and evolution of the magnetic field in the early Universe. We investigated the generation of magnetic fields in the presence of chiral symmetry and gravitational anomaly. We have used modified kinetic theory by Berry curvature and derived expressions for magnetic and vortical conductivities. We have also shown that there are two length scales: kinetic and viscous, which is one of the important results. In the latter part of the thesis, we have shown the effect of second-order viscous effects on the modes of the magnetic fields.
The LIGO/Virgo Collaboration has recently observed GW190521, the first binary black hole merger with at least the primary component mass in the mass gap predicted by the pair-instability supernova theory. This observation disfavors the standard stellar-origin formation scenario for the heavier black hole, motivating alternative hypotheses. We show that GW190521 cannot be explained within the Primordial Black Hole (PBH) scenario if PBHs do not accrete during their cosmological evolution, since this would require an abundance which is already in tension with current constraints. On the other han…
We present the strongest constraints to date on anisotropies of cosmic microwave background (CMB) polarization rotation derived from 150 GHz data taken by the BICEP2/Keck Array CMB experiments up to and including the 2014 observing season (BK14). The definition of the polarization angle in BK14 maps has gone through self-calibration in which the overall angle is adjusted to minimize the observed TB and EB power spectra. After this procedure, the QU maps lose sensitivity to a uniform polarization rotation but are still sensitive to anisotropies of polarization rotation. This analysis places con…
The origin of life and the origin of the universe are among the most important problems of science and they might be inextricably linked. Hydro-gravitational-dynamics (HGD) cosmology predicts hydrogen-helium gas planets in clumps as the dark matter of galaxies, with millions of planets per star. This unexpected prediction is supported by quasar microlensing of a galaxy and a flood of new data from space telescopes. Supernovae from stellar over-accretion of planets produce the chemicals (C, N, O, P etc.) and abundant liquid water domains required for first life and the means for wide scattering…
The origin of magnetic fields in clusters of galaxies is still an unsolved problem, which is largely due to our poor understanding of initial seed magnetic fields. If the seed magnetic fields have primordial origins, it is likely that large-scale pervasive magnetic fields were present before the formation of the large-scale structure. On the other hand, if they were ejected from astrophysical bodies, they were highly localized in space at the time of injection. In this paper, using turbulence dynamo models for high magnetic Prandtl number fluids, we find constraints on the seed magnetic fields…
The hypermagnetic helicity density at the electroweak phase transition (EWPT) exceeds many orders of magnitude the galactic magnetic helicity density. Together with previous magnetic helicity evolution calculations after the EWPT and hypermagnetic helicity conversion to the magnetic one at the EWPT, the present calculation completes the description of the evolution of this important topological feature of cosmological magnetic fields. It suggests that if the magnetic field seeding the galactic dynamo has a primordial origin, it should be substantially helical. This should be taken into account…
As a candidate bound for the Binary Black Hole (BBH) merger events detected by LIGO/Virgo, Primordial Black Holes (PBHs) provide a useful tool to investigate the primordial curvature perturbations on small scales. Using the GWTC-1 to GWTC-3 catalogs, under the scenario that PBHs originate from large primordial curvature perturbations on small scales during inflationary epoch, we for the first time reconstruct the power spectrum of primordial curvature perturbations on small scales. It is found that the value of the amplitude of the primordial power spectrum is enhanced to $\mathcal{O}(10^{-2})…
The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak $\sim 10^{-16}$ Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatur…
We consider the process of primordial black hole (PBH) formation originated from primordial curvature perturbations produced during waterfall transition (with tachyonic instability), at the end of hybrid inflation. It is known that in such inflation models, rather large values of curvature perturbation amplitudes can be reached, which can potentially cause a significant PBH production in the early Universe. The probability distributions of density perturbation amplitudes in this case can be strongly non-Gaussian, which requires a special treatment. We calculated PBH abundances and PBH mass spe…
We explore the possibility of detecting the first galaxies with the next generation Origins Space Telescope (OST) by applying an analytical model of primordial dust emission. By analysing source densities as a function of redshift (z), and considering deep-field exposures with the Origins Survey Spectrometer, we estimate that the redshift horizon for detecting one individual source would be above z~7 for systems with dust-to-metal ratios higher than those expected for typical primeval galaxies. On the other hand, if confusion limits could be overcome, the Far-infrared Imager and Polarimeter wo…
The black holes detected by current and future interferometers can have diverse origins. Their expected mass and spin distributions depend on the specifics of the formation mechanisms. When a physically motivated prior distribution is used in a Bayesian inference, the parameters estimated from the gravitational-wave data can change significantly, potentially affecting the physical interpretation of certain gravitational-wave events and their implications on theoretical models. As a case study we analyze primordial black holes, which might be formed in the early universe and could comprise at l…
NANOGrav 15-year gravitational-wave signals from binary supermassive black-holes seeded by primordial black holes, and implications for the origins of Little Red Dots
Graduate University for Advanced Studies (SOKENDAI)（高等研究院）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；National Astronomical Observatory of Japan（日本国立天文台）；University of Tokyo（东京大学）；The University of Tokyo（东京大学）
The {\em Planck} DR3 measurements of the temperature and polarization anisotropies power spectra of the cosmic microwave background (CMB) show an excess of smoothing of the acoustic peaks with respect to $Λ$CDM, often quantified by a phenomenological parameter $A_{\rm L}$. A specific feature superimposed to the primordial power spectrum has been suggested as a physical solution for this smoothing excess. Here, we investigate the impact of this specific localized oscillation with a frequency linear in the wavenumber, designed to mimic the smoothing of CMB temperature spectrum corresponding to $…
If the B-mode signal in the CMB polarization seen by the BICEP2 experiment is confirmed, it has dramatic implications for models of inflation. The result is also in tension with Planck limits on standard inflationary models. It is therefore important to investigate whether this signal can arise from alternative sources. If so, this could lessen the pressure on inflationary models and the tension with Planck data. We investigate whether vector and tensor modes from primordial magnetic fields can explain the signal. We find that in principle, magnetic fields generated during inflation can indeed…
The usual account for the origin of cosmic structure during inflation is not fully satisfactory, as it lacks a physical mechanism capable of generating the inhomogeneity and anisotropy of our Universe, from an exactly homogeneous and isotropic initial state associated with the early inflationary regime. The proposal in [A. Perez, H. Sahlmann, and D. Sudarsky, Classical Quantum Gravity, 23, 2317, (2006)] considers the spontaneous dynamical collapse of the wave function, as a possible answer to that problem. In this work, we review briefly the difficulties facing the standard approach, as well a…
Despite their ubiquity, there are many open questions regarding galactic and cosmic magnetic fields. Specifically, current observational constraints cannot rule out if magnetic fields observed in galaxies were generated in the Early Universe or are of astrophysical nature. Motivated by this we use our magnetic tracers algorithm to investigate whether the signatures of primordial magnetic fields persist in galaxies throughout cosmic time. We simulate a Milky Way-like galaxy in four scenarios: magnetised solely by primordial magnetic fields, magnetised exclusively by SN-injected magnetic fields,…
Dynamo action is shown to be induced from homogeneous non-minimal photon-torsion axial coupling in the quantum electrodynamics (QED) framework in Riemann flat spacetime contortion decays. The geometrical optics in Riemann-Cartan spacetime is considering and a plane wave expansion of the electromagnetic vector potential is considered leading to a set of the equations for the ray congruence. Since we are interested mainly on the torsion effects in this first report we just consider the Riemann-flat case composed of the Minkowskian spacetime with torsion. It is also shown that in torsionic de Sit…
The primordial bispectrum has been considered in the past decade as a powerful probe of the physical processes taking place in the early Universe. Within the inflationary paradigm, the properties of the bispectrum are one of the keys that serves to discriminate among competing scenarios concerning the details of the origin of cosmological perturbations. However, all of the scenarios, based on the conventional approach to the so-called "quantum-to-classical transition" during inflation, lack the ability to point out the precise physical mechanism responsible for generating the inhomogeneity and…
