arXiv subjects

Hiromasa Nakatsuka

Publications and source records attributed to Hiromasa Nakatsuka.

At least 19 recordsLinked to original sources

arXiv2023

Inflation with two-form field: the production of primordial black holes and gravitational waves

Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space-based laser interferometers.

astro-ph.CO↗

arXiv2022

SU($N$)-natural inflation

We study SU($N$) gauge fields that couple to the inflaton through the Chern-Simons term. We provide a general procedure to construct homogeneous, isotropic, and attractor solutions of the gauge fields during inflation. The gauge fields develop various VEVs corresponding to different spontaneous symmetry breaking patterns of SU($N$) where embedded SU($2$) subgroups are broken with the spatial rotation SO($3$) symmetry. As specific examples, we construct the stable solutions for $N = 3$ and $4$. We also numerically solve the gauge field dynamics and confirm that our analytic solutions are complete and attractor. It is straightforward to apply our procedure to the other simple Lie groups.

hep-ph↗

arXiv2022

Stochastic effects on observation of ultralight bosonic dark matter

Ultralight bosonic particles are fascinating candidates of dark matter (DM). It behaves as classical waves in our Galaxy due to its large number density. There have been various methods proposed to search for the wave-like DM, such as methods utilizing interferometric gravitational-wave detectors. Understanding the characteristics of DM signals is crucial to extract the properties of DM from data. While the DM signal is nearly monochromatic with the angular frequency of its mass, the amplitude and phase are gradually changing due to the velocity dispersion of DMs in our Galaxy halo. The stochastic amplitude and phase should be properly taken into account to accurately constrain the coupling constant of DM from data. Previous works formulated a method to obtain the upper bound on the coupling constant incorporating the stochastic effects. One of these works compared the upper bound with and without the stochastic effect in a measurement time that is much shorter than the variation time scale of the amplitude and phase. In this paper, we extend their formulation to arbitrary measurement time and evaluate the stochastic effects. Moreover, we investigate the velocity-dependent signal for dark photon DM including an uncertainly of the velocity. We demonstrate that our method accurately estimates the upper bound on the coupling constant with numerical simulations. We also estimate the expected upper bound of the coupling constant of axion DM and dark photon DM from future experiments in a semi-analytic way. The stochasticity especially affects constraints on a small mass region. Our formulation offers a generic treatment of the ultralight bosonic DM signal with the stochastic effect.

astro-ph.CO↗

arXiv2022

Is cosmic birefringence due to dark energy or dark matter? A tomographic approach

A pseudoscalar "axionlike" field, $ϕ$, may explain the $3σ$ hint of cosmic birefringence observed in the $EB$ power spectrum of the cosmic microwave background (CMB) polarization data. Is $ϕ$ dark energy or dark matter? A tomographic approach can answer this question. The effective mass of dark energy field responsible for the accelerated expansion of the Universe today must be smaller than $m_ϕ\simeq 10^{-33}$ eV. If $m_ϕ\gtrsim 10^{-32}$ eV, $ϕ$ starts evolving before the epoch of reionization and we should observe different amounts of birefringence from the $EB$ power spectrum at low ($l\lesssim 10$) and high multipoles. Such an observation, which requires a full-sky satellite mission, would rule out $ϕ$ being dark energy. If $m_ϕ\gtrsim 10^{-28}$ eV, $ϕ$ starts oscillating during the epoch of recombination, leaving a distinct signature in the $EB$ power spectrum at high multipoles, which can be measured precisely by ground-based CMB observations. Our tomographic approach relies on the shape of the $EB$ power spectrum and is less sensitive to miscalibration of polarization angles.

astro-ph.CO↗

arXiv2021

Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of Ultra-light Axion-like Particle

Ultra-light axion-like particle (ULAP) with mass $m \sim 10^{-22} ~\mathrm{eV}$ has recently been attracting attention as a possible solution to the small-scale crisis. ULAP forms quasi-stable objects called oscillons/I-balls, which can survive up to a redshift $z \sim 10$ and affect the structure formation on a scale $\sim \mathcal{O}(0.1)~\mathrm{Mpc}$ by amplifying the density fluctuations. We study the effect of oscillons on 21~cm anisotropies caused by neutral hydrogen in minihalos. It is found that this effect can be observed in a wide mass range by future observations such as Square Kilometer Array~(SKA) if the fraction of ULAP to the total dark matter density is $\mathcal{O}(0.01 \text{--} 0.1)$.

astro-ph.CO↗

arXiv2021

Revisiting CMB constraints on dark matter annihilation

The precision measurements of the cosmic microwave background power spectrum put a strong constraint on the dark matter annihilation cross section since the electromagnetic energy injection by the dark matter annihilation affects the ionization history of the universe. In this paper, we update our previous simulation code for calculating the ionization history with the effect of dark matter annihilation by including Helium interactions and improving the precision of calculations. We give an updated constraint on the annihilation cross section and mass of dark matter using the modified RECFAST code with the Planck 2018 datasets.

astro-ph.CO↗

arXiv2021

Ultralight dark matter searches with KAGRA gravitational wave telescope

Among various dark matter candidates, bosonic ultralight fields with masses below 1~eV are well motivated. Recently, a number of novel approaches have been put forward to search for ultralight dark matter candidates using laser interferometers at various scales. Those include our proposals to search for axion-like particles (ALPs) and vector fields with laser interferometric gravitational wave detectors. ALPs can be searched for by measuring the oscillating polarization rotation of laser light. Massive vector fields weakly coupled to the standard model sector can also be searched for by measuring the oscillating forces acting on the suspended mirrors of the interferometers. In this paper, the current status of the activities to search for such ultralight dark matter candidates using a gravitational wave detector in Japan, KAGRA, is reviewed. The analysis of data from KAGRA's observing run in 2020 to search for vector dark matter, and the installation of polarization optics to the arm cavity transmission ports of the interferometer to search for ALPs in future observing runs are underway.

hep-ph↗

arXiv2021

First observation and analysis of DANCE: Dark matter Axion search with riNg Cavity Experiment

Dark matter Axion search with riNg Cavity Experiment (DANCE) was proposed to search for axion dark matter [Phys. Rev. Lett. 121, 161301 (2018)]. We aim to detect the rotation and oscillation of optical linear polarization caused by axion-photon coupling with a bow-tie cavity. DANCE can improve the sensitivity to axion-photon coupling constant $g_{a γ}$ for axion mass $m_a < 10^{-10}~\rm{eV}$ by several orders of magnitude compared to the best upper limits at present. A prototype experiment DANCE Act-1 is ongoing to demonstrate the feasibility of the method and to investigate technical noises. The optics was assembled and the performance of the cavity was evaluated. The first 12-day observation was successfully performed in May 2021. We reached $3 \times 10^{-6}~\rm{rad/\sqrt{Hz}}$ at $10~\rm{Hz}$ in the one-sided amplitude spectral density of the rotation angle of linear polarization.

physics.ins-det↗

arXiv2021

Constraints on small-scale primordial density fluctuation from cosmic microwave background through dark matter annihilation

The cosmic microwave background (CMB) observation by the Planck satellite precisely determines primordial curvature fluctuations on larger scales than $\mathcal O(1)\,\mathrm{Mpc}$, while the small-scale curvature fluctuation is still less constrained. The constraint on small-scale fluctuations is highly improved if we assume the standard thermal relic dark matter scenario. When small-scale fluctuations are large enough, dense regions collapse to form small halos even in a redshift $z\gtrsim10^3$, which is called ultracompact minihalos. These minihalos enhance the annihilation of the dark matter and it is constrained by observations such as extragalactic gamma rays and the CMB. We revisit the effect of minihalos formed by the small-scale density fluctuations and calculate the ionization history modified by the dark matter annihilation. We perform the Markov Chain Monte Carlo method to constrain the size of small-scale curvature fluctuations by the CMB power spectrum. It is found that the constraint from the CMB power spectrum is comparable to that from the extragalactic gamma rays. We confirm that our constraint mainly comes from the energy injection in early time ($z\gtrsim 100$) and hence it is independent of the uncertainty of minihalo properties in the late time.

astro-ph.CO↗

arXiv2021

Gauge Field Production and Schwinger Reheating in Runaway Axion Inflation

In a class of (pseudoscalar) inflation, inflationary phase is followed by a kination phase, where the Universe is dominated by the kinetic energy of the inflaton that runs away in a vanishing scalar potential. In this class of postinflationary evolution of the Universe, reheating of the Universe cannot be achieved by the inflaton particle decay, which requires its coherent oscillation in a quadratic potential. In this study, we explore the U(1) gauge field production through the Chern-Simons coupling between the pseudoscalar inflaton and the gauge field during the kination era and examine the subsequent pair-particle production induced by the amplified gauge field known as the Schwinger effect, which can lead to reheating of the Universe. We find that with a rough estimate of the Schwinger effect for the Standard Model hyper U(1) gauge field and subsequent thermalization of the pair-produced particles, a successful reheating of the Universe can be achieved by their eventual domination over the kinetic energy of the inflaton, with some reasonable parameter sets. This can be understood as a concrete realization of the "Schwinger reheating". Constraints from the later-time cosmology are also discussed.

hep-ph↗

arXiv2021

Strong clustering of primordial black holes from Affleck-Dine mechanism

Primordial black hole (PBH) is a fascinating candidate for the origin of binary merger events observed by LIGO-Virgo collaboration. The spatial distribution of PBHs at formation is an important feature to estimate the merger rate. We investigate the clustering of PBHs formed by Affleck-Dine (AD) baryogenesis, where dense baryon bubbles collapse to form PBHs. We found that formed PBHs show a strong clustering due to the stochastic dynamics of the AD field. Including the clustering, we evaluate the merger rate and isocurvature perturbations of PBHs, which show significant deviations from those without clustering.

astro-ph.CO↗

arXiv2021

Free Streaming Length of Axion-Like Particle After Oscillon/ I-ball Decays

Axion-like particles (ALPs) are pseudoscalar bosons predicted by string theory. The ALPs have a shallower potential than a quadratic one, which induces the instability and can form the solitonic object called oscillon/I-ball. Although the lifetime of oscillons can be very long for some type of potentials, they finally decay until the present. We perform the numerical lattice simulations to investigate the decay process of oscillons and evaluate the averaged momentum of ALPs emitted from the oscillon decay. It is found that, if oscillons decay in the early universe, the free-streaming length of ALPs becomes too long to explain the small-scale observations of the matter power spectrum. We show that oscillons with long lifetimes can change the density fluctuations on small scales, which leads to stringent constraints on the ALP mass and the oscillon lifetime.

hep-ph↗

arXiv2021

Axion dark matter search using arm cavity transmitted beams of gravitational wave detectors

Axion is a promising candidate for ultralight dark matter which may cause a polarization rotation of laser light. Recently, a new idea of probing the axion dark matter by optical linear cavities used in the arms of gravitational wave detectors has been proposed [Phys. Rev. Lett. 123, 111301 (2019)]. In this article, a realistic scheme of the axion dark matter search with the arm cavity transmission ports is revisited. Since photons detected by the transmission ports travel in the cavity for odd-number of times, the effect of axion dark matter on their phases is not cancelled out and the sensitivity at low-mass range is significantly improved compared to the search using reflection ports. We also take into account the stochastic nature of the axion field and the availability of the two detection ports in the gravitational wave detectors. The sensitivity to the axion-photon coupling, $g_{aγ}$, of the ground-based gravitational wave detector, such as Advanced LIGO, with 1-year observation is estimated to be $g_{aγ} \sim 3\times10^{-12}$ GeV$^{-1}$ below the axion mass of $10^{-15}$ eV, which improves upon the limit achieved by the CERN Axion Solar Telescope.

hep-ph↗

arXiv2021

Gravitational waves from type II axion-like curvaton model and its implication for NANOGrav result

The recent report of NANOGrav is gathering attention since its signal can be explained by the stochastic gravitational waves (GWs) with $Ω_{\rm GW}\sim 10^{-9}$ at $f\sim 10^{-8}$Hz. The PBH formation scenario is one of the candidates for the NANOGrav signal, which can simultaneously explain the observed $30 M_\odot$ black holes in the binary merger events in LIGO-Virgo collaboration. We focus on the type II axion-like curvaton model of the PBH formation. In type II model the complex field whose phase part is the axion rolls down from the origin of the potential. It is found that type II model achieves the broad power spectrum of the density perturbations and can simultaneously explain the LIGO-Virgo events and the NANOGrav signal. We also improve the treatment of the non-Gaussianity of perturbations in our model to accurately estimate the amplitude of the induced GWs.

astro-ph.CO↗

arXiv2021

Detection of isotropic cosmic birefringence and its implications for axion-like particles including dark energy

We investigate the possibility that axion-like particles (ALPs) with various potentials account for the isotropic birefringence recently reported by analyzing the Planck 2018 polarization data. For the quadratic and cosine potentials, we obtain lower bounds on the mass, coupling constant to photon $g$, abundance and equation of state of the ALP to produce the observed birefringence. Especially when the ALP is responsible for dark energy, it is possible to probe the tiny deviation of dark energy equation of state from $-1$ through the cosmic birefringence. We also explore ALPs working as early dark energy (EDE), which alleviates the Hubble tension problem. Since the other parameters are limited by the EDE requirements, we narrow down the ALP-photon coupling to $10^{-19}\, {\rm GeV}^{-1}\lesssim g\lesssim 10^{-16}\, {\rm GeV}^{-1}$ for the decay constant $f=M_\mathrm{pl}$. Therefore, the Hubble tension and the isotropic birefringence imply that $g$ is typically the order of $f^{-1}$, which is a non-trivial coincidence.

astro-ph.CO↗

arXiv2021

Improved sensitivity of interferometric gravitational wave detectors to ultralight vector dark matter from the finite light-traveling time

Recently several studies have pointed out that gravitational-wave detectors are sensitive to ultralight vector dark matter and can improve the current best constraints given by the Equivalence Principle tests. While a gravitational-wave detector is a highly precise measuring tool of the length difference of its arms, its sensitivity is limited because the displacements of its test mass mirrors caused by vector dark matter are almost common. In this Letter we point out that the sensitivity is significantly improved if the effect of finite light-traveling time in the detector's arms is taken into account. This effect enables advanced LIGO to improve the constraints on the $U(1)_{B-L}$ gauge coupling by an order of magnitude compared with the current best constraints. It also makes the sensitivities of the future gravitational-wave detectors overwhelmingly better than the current ones. The factor by which the constraints are improved due to the new effect depends on the mass of the vector dark matter, and the maximum improvement factors are $470$, $880$, $1600$, $180$ and $1400$ for advanced LIGO, Einstein Telescope, Cosmic Explorer, DECIGO and LISA respectively. Including the new effect, we update the constraints given by the first observing run of advanced LIGO and improve the constraints on the $U(1)_B$ gauge coupling by an order of magnitude compared with the current best constraints.

hep-ph↗

arXiv2021

Probing Axion-like Particles via CMB Polarization

Axion-like particles (ALPs) rotate the linear polarization of photons through the ALP-photon coupling and convert the cosmic microwave background (CMB) $E$-mode to the $B$-mode. We derive the relation between the ALP dynamics and the rotation angle by assuming that the ALP $ϕ$ has a quadratic potential, $V=m^2ϕ^2/2$. We compute the current and future sensitivities of CMB observations to the ALP-photon coupling $g$, which can reach $g=4\times 10^{-21}\,\mathrm{GeV}^{-1}$ for $10^{-32}\,\mathrm{eV}\lesssim m\lesssim 10^{-28}\,\mathrm{eV}$ and extensively exceed the other searches for any mass $m\lesssim 10^{-25}\,\mathrm{eV}$. We find that the fluctuation of the ALP field at the observer, which has been neglected in previous studies, can induce significant isotropic rotation of the CMB polarization. The measurements of isotropic and anisotropic rotation allow us to put bounds on relevant quantities such as the ALP mass $m$ and the ALP density parameter $Ω_ϕ$. In particular, if LiteBIRD detects anisotropic rotation, we obtain the lower bound on the tensor-to-scalar ratio as $r > 5 \times 10^{-9}$.

astro-ph.CO↗

arXiv2021

Oscillons of Axion-Like Particle: Mass distribution and power spectrum

In string theory, the simultaneous existence of many Axion-Like Particles (ALPs) are suggested over a vast mass range, and a variety of potentials have been developed in the context of inflation. In such potentials shallower than quadratic, the prominent instability can produce localized dense objects, oscillons. Because of the approximate conservation of their adiabatic invariant, oscillons generally survive quite long, maybe up to the current age of the universe in the case of ultra-light ALPs with $m \sim 10^{-22}\ {\rm eV}$. Such oscillons can have significant effects on the evolution of the recent universe. In this paper, we investigate the oscillons of the pure-natural type potential by classical lattice simulation to explore the key quantities necessary for phenomenological application: the number density of oscillons, the oscillon mass distribution, the energy ratio of oscillons to the ALP field, and the power spectrum. Then, we evolve these values in consideration of the analytic decay rate.

astro-ph.CO↗