arXiv subjects

Masahiro Kawasaki

Publications and source records attributed to Masahiro Kawasaki.

At least 91 records · Page 5Linked to original sources

arXiv2017

New-Type Charged Q-ball Dark Matter in Gauge Mediated SUSY Breaking Models

We examined the viability of new-type charged Q-ball dark matter scenario. We considered the case where the relics can be treated as ordinary ions, to which we applied the observational constraint from MICA experiment, where no trail of heavy ion-like object is observed in $10^9$ years old ancient muscovite mica. We have found that the allowed parameter region exists but is smaller than the neutral Q-ball dark matter case. We have also discussed whether our scenario is actually consistent with Affleck-Dine mechanism.

hep-ph↗

arXiv2017

Relaxation leptogenesis, isocurvature perturbations, and the cosmic infrared background

Observations of cosmic infrared background (CIB) radiation exhibit significant fluctuations on small angular scales. A number of explanations have been put forth, but there is currently no consensus on the origin of these large fluctuations. We consider the possibility that small-scale fluctuations in matter-antimatter asymmetry could lead to variations in star formation rates which are responsible for the CIB fluctuations. We show that the recently proposed Higgs relaxation leptogenesis mechanism can produce such small-scale baryonic isocurvature perturbations which can explain the observed excess in the CIB fluctuations.

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arXiv2016

Simple Cosmological Solution to the Higgs Instability Problem in the Chaotic Inflation and Formation of Primordial Black Holes

We revisit the compatibility between the chaotic inflation, which provides a natural solution to the initial condition problem, and the metastable electroweak vacuum, which is suggested by the results of LHC and the current mass measurements of top quark and Higgs boson. It is known that the chaotic inflation poses a threat to the stability of the electroweak vacuum because it easily generates large Higgs fluctuations during inflation or preheating and triggers the catastrophic vacuum decay. In this paper, we propose a simple cosmological solution in which the vacuum is stabilized during chaotic inflation, preheating and after that. This simple solution naturally predicts the formation of primordial black holes. We find interesting parameter regions where the present dark matter density is provided by them. Also, the thermal leptogenesis can be accommodated in our scenario.

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arXiv2016

PBH Dark Matter in Supergravity Inflation Models

We propose a novel scenario to produce abundant primordial black holes (PBHs) in new inflation which is a second phase of a double inflation in the supergravity frame work. In our model, some preinflation phase before the new inflation is assumed and it would be responsible for the primordial curvature perturbations on the cosmic microwave background scale, while the new inflation produces only the small scale perturbations. Our new inflation model has linear, quadratic, and cubic terms in its potential and PBH production corresponds with its flat inflection point. The linear term can be interpreted to come from a supersymmetry-breaking sector, and with this assumption, the vanishing cosmological constant condition after inflation and the flatness condition for the inflection point can be consistently satisfied.

astro-ph.CO↗

arXiv2016

Revisiting constraints on small scale perturbations from big-bang nucleosynthesis

We revisit the constraints on the small scale density perturbations ($10^4\,\mathrm{Mpc}^{-1}\lesssim k \lesssim10^5\,\mathrm{Mpc}^{-1}$) from the modification of the freeze-out value of the neutron-proton ratio at big-bang nucleosynthesis era. Around the freeze-out temperature $T\sim 0.5\,\mathrm{MeV}$, the universe can be divided into several local patches which have different temperatures since any perturbation which enters the horizon after the neutrino decoupling has not diffused yet. Taking account of this situation, we calculate the freeze-out value in detail. We find that the small scale perturbations decrease the n-p ratio in contrast to previous works. With use of the latest observed $^4$He abundance, we obtain the constraint on the power spectrum of the curvature perturbations as $Δ^2_\mathcal{R}\lesssim 0.018$ on $10^4\,\mathrm{Mpc}^{-1}\lesssim k \lesssim 10^5\,\mathrm{Mpc}^{-1}$.

astro-ph.CO↗

arXiv2016

Can massive primordial black holes be produced in mild waterfall hybrid inflation?

We studied the possibility whether the massive primordial black holes (PBHs) surviving today can be produced in hybrid inflation. Though it is of great interest since such PBHs can be the candidate for dark matter or seeds of the supermassive black holes in galaxies, there have not been quantitatively complete works yet because of the non-perturbative behavior around the critical point of hybrid inflation. Therefore, combining the stochastic and $δN$ formalism, we numerically calculated the curvature perturbations in a non-perturbative way and found, without any specific assumption of the types of hybrid inflation, PBHs are rather overproduced when the waterfall phase of hybrid inflation continues so long that the PBH scale is well enlarged and the corresponding PBH mass becomes sizable enough.

astro-ph.CO↗

arXiv2016

Constraining light gravitino mass with 21 cm line observation

We investigate how well we can constrain the mass of light gravitino m_3/2 by using future observations of 21 cm line fluctuations such as Square Kilometre Array (SKA) and Omniscope. Models with light gravitino with the mass m_3/2 < O(10) eV are quite interesting because they are free from the cosmological gravitino problem and consistent with many baryogenesis/leptogenesis scenarios. We evaluate expected constraints on the mass of light gravitino from the observations of 21 cm line, and show that the observations are quite useful to prove the mass. If the gravitino mass is m_3/2 = 1 eV, we found expected 1 sigma errors on m_3/2 are sigma(m_3/2) = 0.25 eV (SKA phase 1), 0.16 eV (SKA phase 2) and 0.067 eV (Omniscope) in combination with Planck + Simons Array + DESI (BAO) + H_0. Additionally, we also discuss detectability of the effective number of neutrino species by varying the effective number of neutrino species for light gravitino N_3/2 and constraints on the mass of light gravitino in the presence of massive neutrinos. We show that 21 cm line observations can detect the nonzero value of N_3/2, and allow us to distinguish the effects of the light gravitino from those of massive neutrino.

astro-ph.CO↗

arXiv2016

Charged Q-ball Dark Matter from $B$ and $L$ direction

We consider nearly equal number of gauge mediation type charged (anti-) Q-balls with charge of $α^{-1}\simeq137$ well before the BBN epoch and discussed how they evolve in time. We found that ion-like objects with electric charges of $+O(1)$ are likely to become relics in the present universe, which we expect to be the dark matter. These are constrained by MICA experiment, where the trail of heavy atom-like or ion-like object in $10^9$ years old ancient mica crystals is not observed. We found that the allowed region for gauge mediation model parameter and reheating temperature have to be smaller than the case of the neutral Q-ball dark matter.

hep-ph↗

arXiv2016

CMB Constraint on Dark Matter Annihilation after Planck 2015

We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

astro-ph.CO↗

arXiv2016

Cosmology with a Heavy Polonyi Field

We consider a cosmologically consistent scenario with a heavy Polonyi field. The Polonyi field with a mass of ${\cal O}(100){\rm\,TeV}$ decays before the Big-Bang Nucleosynthesis (BBN) and avoids the severe constraint from the BBN. However, the abundance of the Lightest Supersymmetric Particle (LSP) produced from the decay often exceeds the observed dark matter density. In our scenario, the dark matter density is obtained by the LSP abundance with an aid of entropy production, and baryon asymmetry is generated by the Affleck-Dine mechanism. We show that the observed baryon-to-dark matter ratio of ${\cal O}(0.1\mathchar`-1)$ is naturally explained in sequestering models with a QCD axion.

hep-ph↗

arXiv2015

Cosmological Problems of the String Axion Alleviated by High Scale SUSY of $m_{3/2}$ $\simeq$ 10-100 TeV

The string axion may provide the most attractive solution to the strong CP problem in QCD. However, the axion energy density easily exceeds the dark matter density in the present universe due to a large decay constant around $10^{16}$ GeV, unless the initial value of the axion field is fine-tuned. We show that this problem is alleviated if and only if the SUSY particle mass scale is 10-100 TeV, since the decay of the saxion can produce a large enough amount of entropy after the QCD phase transition, not disturbing the BBN prediction. The saxion decay also produces a large number of the lightest SUSY particles (LSPs). As a consequence, R-parity needs to be violated to avoid the overproduction of the LSPs. The saxion field can be stabilized with relatively simple Kahler potentials, not inducing a too large axion dark radiation. Despite the large entropy production, the observed baryon number is explained by the Affleck-Dine mechanism. Furthermore, the constraint from isocurvature perturbations is relaxed, and the Hubble constant during inflation can be as large as several $\times$ $10^{10}$ GeV.

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arXiv2015

High-scale SUSY from an R-invariant New Inflation in the Landscape

We provide an anthropic reason that the supersymmetry breaking scale is much higher than the electroweak scale as indicated by the null result of collider experiments and observed 125 GeV Higgs boson. We focus on a new inflation model as a typical low-scale inflation model that may be expected in the string landscape. In this model, the R-symmetry is broken at the minimum of the inflaton potential and its breaking scale is related to the reheating temperature. Once we admit that the anthropic principle requires thermal leptogenesis, we obtain a lower bound on gravitino mass, which is related to R-symmetry breaking scale. This scenario and resulting gravitino mass predict the consistent amplitude of density perturbations. We also find that string axions and saxions are consistently implemented in this scenario.

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arXiv2015

Axino dark matter and baryon number asymmetry production by the Q-ball decay in gauge mediation

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arXiv2015

Axino dark matter and baryon number asymmetry from Q-ball decay in gauge mediation

We investigate the Q-ball decay into the axino dark matter in the gauge-mediated supersymmetry breaking. In our scenario, the Q ball decays mainly into nucleons and partially into axinos to account for the baryon asymmetry and the dark matter of the universe simultaneously. The Q ball decays well before the big bang nucleosynthesis so that it is not affected by the decay. The decay into the supersymmetric particles of the minimal supersymmetric standard model is kinematically prohibited until the very end of the decay, and we could safely make their abundances small enough for the successful big bang nucleosynthesis. We show the regions of axino model parameters and the Q-ball parameters which realize this scenario.

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arXiv2015

Suppressing the QCD Axion Abundance by Hidden Monopoles

We study the Witten effect of hidden monopoles on the QCD axion dynamics, and show that its abundance as well as isocurvature perturbations can be significantly suppressed if there is a sufficient amount of hidden monopoles. When the hidden monopoles make up a significant fraction of dark matter, the Witten effect suppresses the abundance of axion with the decay constant smaller than $10^{12}$ GeV. The cosmological domain wall problem of the QCD axion can also be avoided, relaxing the upper bound on the decay constant when the Peccei-Quinn symmetry is spontaneously broken after inflation.

hep-ph↗

arXiv2015

The two-field regime of natural inflation

The simplest two-field completion of natural inflation has a regime in which both fields are active and in which its predictions are within the Planck 1-$σ$ confidence contour. We show this for the original model of natural inflation, in which inflation is achieved through the explicit breaking of a U(1) symmetry. We consider the case in which the mass coming from explicit breaking of this symmetry is comparable to that from spontaneous breaking, which we show is consistent with a hierarchy between the corresponding energy scales. While both masses are comparable when the observable modes left the horizon, the mass hierarchy is restored in the last e-foldings of inflation, rendering the predictions consistent with the isocurvature bounds. For completeness, we also study the predictions for the case in which there is a large hierarchy of masses and an initial period of inflation driven by the (heavy) radial field.

astro-ph.CO↗

arXiv2015

Gravitational waves from domain walls in the next-to-minimal supersymmetric standard model

The next-to-minimal supersymmetric standard model predicts the formation of domain walls due to the spontaneous breaking of the discrete $Z_3$-symmetry at the electroweak phase transition, and they collapse before the epoch of big bang nucleosynthesis if there exists a small bias term in the potential which explicitly breaks the discrete symmetry. Signatures of gravitational waves produced from these unstable domain walls are estimated and their parameter dependence is investigated. It is shown that the amplitude of gravitational waves becomes generically large in the decoupling limit, and that their frequency is low enough to be probed in future pulsar timing observations.

hep-ph↗

arXiv2015

Revisiting Big-Bang Nucleosynthesis Constraints on Dark-Matter Annihilation

We study the effects of dark-matter annihilation during the epoch of big-bang nucleosynthesis on the primordial abundances of light elements. We improve the calculation of the light-element abundances by taking into account the effects of anti-nucleons emitted by the annihilation of dark matter and the interconversion reactions of neutron and proton at inelastic scatterings of energetic nucleons. Comparing the theoretical prediction of the primordial light-element abundances with the latest observational constraints, we derive upper bounds on the dark-matter pair-annihilation cross section. Implication to some of particle-physics models are also discussed.

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