arXiv subjects

Masahiro Kawasaki

Publications and source records attributed to Masahiro Kawasaki.

At least 127 records · Page 7Linked to original sources

arXiv2014

Baryogenesis from the Gauge-mediation type Q ball and the New type of Q ball as dark matter

We investigate that the two types of the Q balls explain the baryon asymmetry and the dark matter of the universe in the gauge-mediated supersymmetry breaking. The gauge-mediation type Q balls of one flat direction produce baryon asymmetry, while the new type Q balls of another flat direction become the dark matter. We show that the dark matter new type Q balls are free from the neutron star constraint. n=5 gauge mediation type and n=6 new type Q balls are displayed as an example, where the potential is lifted by the superpotential Phi^n. These dark matter Q balls may be detected by future observations, such as in advanced IceCube-like observations.

hep-ph↗

arXiv2014

Curvaton in large field inflation

We comprehensively explore the quadratic curvaton models in the chaotic inflation. In the light of the BICEP2 result $r \approx 0.2$, all model parameters and relevant observables are computed. It is found the curvaton field value is constrained into a narrow range, $σ_* = \mathcal{O}(10^{-2}$-$10^{-1})$ and the running of the spectral index is $n_s' \gtrsim -10^{-3}$. We show that if the curvaton is added, the models are heavily degenerated on the $n_s$ - $r$ plane. However, introducing a new plane, the degeneracy can be resolved. To distinguish the curvaton models, precise measurements of not only $r$ but also $n_s'$ and the tensor tilt $n_T$ are required.

astro-ph.CO↗

arXiv2014

Relaxing Isocurvature Bounds on String Axion Dark Matter

If inflation scale is high, light scalars acquire large quantum fluctuations during inflation.If sufficiently long-lived, they will give rise to CDM isocurvature perturbations, which are highly constrained by the Planck data. Focusing on string axions as such light scalars, we show that thermal inflation can provide a sufficiently large entropy production to dilute the CDM isocurvature perturbations. Importantly, efficient dilution is possible for the string axions, because effectively no secondary coherent oscillations are induced at the end of thermal inflation, in contrast to the moduli fields. We also study the viability of the axion dark matter with mass of about 7 keV as the origin of the 3.5 keV X-ray line excess, in the presence of large entropy production.

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arXiv2014

A solution to the baryon-DM coincidence problem in the CMSSM with a 126-GeV Higgs boson

We show that the baryon-dark matter coincidence problem is solved in the CMSSM. The baryons and dark matter are generated simultaneously through the late-time decay of non-topological solitons, Q-balls, which are formed after the Affleck-Dine baryogenesis. A certain relation between the universal scalar mass, $m_0$, and the universal gaugino mass, $M_{1/2}$, is required to solve the coincidence problem, marginally depending on the other CMSSM parameters, and the result is consistent with the observation of the 126-GeV Higgs boson.

hep-ph↗

arXiv2014

Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies

Recently, BICEP2 has reported the large tensor-to-scalar ratio $r=0.2^{+0.07}_{-0.05}$ from the observation of the cosmic microwave background (CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode but also the temperature fluctuations on large scales, to realize the consistent temperature fluctuations with the Planck result we should consider suppression of scalar perturbations on corresponding large scales. To realize such a suppression, we consider anti-correlated iso-curvature perturbations which could be realized in the simple curvaton model.

astro-ph.CO↗

arXiv2014

Dark Matter Production in Late Time Reheating

We estimate dark matter density for the Universe with a reheating temperature smaller than the mass of dark matter, assuming dark matter to be a weakly interacting massive particle. During the reheating process, an inflaton decays and releases high-energy particles, which are scattered inelastically by the thermal plasma and emit many particles. Dark matters are produced through these inelastic scattering processes and pair creation processes by high-energy particles. We properly take account of the Landau-Pomeranchuk-Migdal effect on inelastic processes and show that the resultant energy density of dark matter is much larger than that estimated in the literature and can be consistent with that observed when the mass of dark matter is larger than $O(100)$ GeV.

hep-ph↗

arXiv2014

On the estimation of gravitational wave spectrum from cosmic domain walls

We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of field theoretic lattice simulations with grid size $1024^3$, which is larger than the previous study. We have recognized that there exists an error in the code used in the previous study, and the correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its amplitude is consistent with the naive estimation based on the quadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at the present time are estimated. It is shown that for some choices of parameters the signal of gravitational waves is strong enough to be probed in the future gravitational wave experiments.

astro-ph.CO↗

arXiv2014

Decay rates of Gaussian-type I-balls and Bose-enhancement effects in 3+1 dimensions

I-balls/oscillons are long-lived spatially localized lumps of a scalar field which may be formed after inflation. In the scalar field theory with monomial potential nearly and shallower than quadratic, which is motivated by chaotic inflationary models and supersymmetric theories, the scalar field configuration of I-balls is approximately Gaussian. If the I-ball interacts with another scalar field, the I-ball eventually decays into radiation. Recently, it was pointed out that the decay rate of I-balls increases exponentially by the effects of Bose enhancement under some conditions and a non-perturbative method to compute the exponential growth rate has been derived. In this paper, we apply the method to the Gaussian-type I-ball in 3+1 dimensions assuming spherical symmetry, and calculate the partial decay rates into partial waves, labelled by the angular momentum of daughter particles. We reveal the conditions that the I-ball decays exponentially, which are found to depend on the mass and angular momentum of daughter particles and also be affected by the quantum uncertainty in the momentum of daughter particles.

hep-ph↗

arXiv2014

Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH

We investigate the consistency of a scenario in which the baryon asymmetry, dark matters, as well as the cosmic density perturbation are generated simultaneously through the evaporation of primordial black holes (PBHs). This scenario can explain the coincidence of the dark matter and the baryon density of the universe, and is free from the isocurvature perturbation problem. We show that this scenario predicts the masses of PBHs, right-handed neutrinos and dark matters, the Hubble scale during inflation, the non-gaussianity and the running of the spectral index. We also discuss the testability of the scenario by detecting high frequency gravitational waves from PBHs.

astro-ph.CO↗

arXiv2013

Large Scale Cosmic Perturbation from Evaporation of Primordial Black Holes

We present a novel mechanism to generate the cosmic perturbation from evaporation of primordial black holes. A mass of a field is fluctuated if it is given by a vacuum expectation value of a light scalar field because of the quantum fluctuation during inflation. The fluctuated mass causes variations of the evaporation time of the primordial black holes. Therefore provided the primordial black holes dominate the universe when they evaporate, primordial cosmic perturbations are generated. We find that the amplitude of the large scale curvature perturbation generated in this scenario can be consistent with the observed value. Interestingly, our mechanism works even if all fields which are responsible for inflation and the generation of the cosmic perturbation are decoupled from the visible sector except for the gravitational interaction. An implication to the running spectral index is also discussed.

astro-ph.CO↗

arXiv2013

Domain wall and isocurvature perturbation problems in axion models

Axion models have two serious cosmological problems, domain wall and isocurvature perturbation problems. In order to solve these problems we investigate the Linde's model in which the field value of the Peccei-Quinn (PQ) scalar is large during inflation. In this model the fluctuations of the PQ field grow after inflation through the parametric resonance and stable axionic strings may be produced, which results in the domain wall problem. We study formation of axionic strings using lattice simulations. It is found that in chaotic inflation the axion model is free from both the domain wall and the isocurvature perturbation problems if the initial misalignment angle θ_a is smaller than O(10^{-2}). Furthermore, axions can also account for the dark matter for the breaking scale v \simeq 10^{12-16} GeV and the Hubble parameter during inflation H_{inf} \lesssim 10^{11-12} GeV in general inflation models.

hep-ph↗

arXiv2013

Axions as Hot and Cold Dark Matter

The presence of a hot dark matter component has been hinted at 3 sigma by a combination of the results from different cosmological observations. We examine a possibility that pseudo Nambu-Goldstone bosons account for both hot and cold dark matter components. We show that the QCD axions can do the job for the axion decay constant f_a < O(10^10) GeV, if they are produced by the saxion decay and the domain wall annihilation. We also investigate the cases of thermal QCD axions, pseudo Nambu-Goldstone bosons coupled to the standard model sector through the Higgs portal, and axions produced by modulus decay.

hep-ph↗

arXiv2013

Revisiting the gravitino dark matter and baryon asymmetry from Q-ball decay in gauge mediation

We reinvestigate the scenario that the amount of the baryons and the gravitino dark matter is naturally explained by the decay of the Q balls in the gauge-mediated SUSY breaking. Equipped by the more correct decay rates into gravitinos and baryons recently derived, we find that the scenario with the direct production of the gravitino dark matter from the Q-ball decay works naturally.

hep-ph↗

arXiv2013

Gravitational waves from smooth hybrid new infation

We calculate the production of the gravitational waves from a double inflation model with lattice simulations. Between the two inflationary stages, gravitational waves with a characteristic frequency are produced by fluctuations of the scalar fields enhanced through parametric resonance. The wavelength of the produced gravitational waves gets extra redshift during the second inflationary stage and it can be in the observable range for the direct gravitational wave detectors. It is found that there is a possibility for the produced gravitational waves to be detected in the planned experiments.

astro-ph.CO↗

arXiv2013

A new algorithm for calculating the curvature perturbations in stochastic inflation

We propose a new approach for calculating the curvature perturbations produced during inflation in the stochastic formalism. In our formalism, the fluctuations of the e-foldings are directly calculated without perturbatively expanding the inflaton field and they are connected to the curvature perturbations by the $δN$ formalism. The result automatically includes the contributions of the higher order perturbations because we solve the equation of motion non-perturbatively. In this paper, we analytically prove that our result (the power spectrum and the nonlinearity parameter) is consistent with the standard result in single field slow-roll inflation. We also describe the algorithm for numerical calculations of the curvature perturbations in more general inflation models.

astro-ph.CO↗

arXiv2013

Gravitational waves from a curvaton model with blue spectrum

We investigate the gravitational wave background induced by the first order scalar perturbations in the curvaton models. We consider the quadratic and axion-like curvaton potential which can generate the blue-tilted power spectrum of curvature perturbations on small scales and derive the maximal amount of gravitational wave background today. We find the power spectrum of the induced gravitational wave background has a characteristic peak at the frequency corresponding to the scale reentering the horizon at the curvaton decay, in the case where the curvaton does not dominate the energy density of the Universe. We also find the enhancement of the amount of the gravitational waves in the case where the curvaton dominates the energy density of the Universe. Such induced gravitational waves would be detectable by the future space-based gravitational wave detectors or pulsar timing observations.

astro-ph.CO↗

arXiv2013

Opening the window to the cogenesis with Affleck-Dine mechanism in gravity mediation

The observed baryon and dark matter densities are equal up to a factor of 5. This observation indicates that the baryon asymmetry and dark matter have the same origin. The Affleck-Dine baryogenesis is one of the most promising mechanisms in this context. Q balls, which are often formed in the early Universe associated with the Affleck-Dine baryogenesis, decay both into supersymmetric particles and into quarks. Recently, it was pointed out that annihilation of squarks into quarks gives a dominant contribution to the Q-ball decay rate and the branching ratio of Q-ball decay into supersymmetric particles changes from the previous estimate. In this paper, the scenario of baryon and dark matter cogenesis from Q ball in gravity mediation is revisited in respect of the improved Q-ball decay rates. It is found that the successful cogenesis takes place when a wino with mass 0.3-1 TeV is dark matter.

hep-ph↗

arXiv2013

Heavy gravitino in hybrid inflation

It is known that supersymmetric hybrid inflation model may require severe tunings on the initial condition for large gravitino mass of order 100 - 1000 TeV due to the constant term in the superpotential. We propose a modified hybrid inflation model, where the constant term is suppressed during inflation and generated after inflation by replacing a constant term with dynamical field. In this modified model, successful inflation consistent with large gravitino mass takes place without severe tunings on the initial condition. Constraint from cosmic strings is also relaxed.

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