arXiv subjects

Kenji Kadota

Publications and source records attributed to Kenji Kadota.

At least 55 records · Page 3Linked to original sources

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

Axion inflation with cross-correlated axion isocurvature perturbations

We study the inflation scenarios, in the framework of superstring theory, where the inflaton is an axion producing the adiabatic curvature perturbations while there exists another light axion producing the isocurvature perturbations. We discuss how the non-trivial couplings among string axions can generically arise, and calculate the consequent cross-correlations between the adiabatic and isocurvature modes through concrete examples. Based on the Planck analysis on the generally correlated isocurvature perturbations, we show that there is a preference for the existence of the correlated isocurvature modes for the axion monodromy inflation while the natural inflation disfavors such isocurvature modes.

hep-ph↗

arXiv2014

Cosmologically probing ultra-light particle dark matter using 21 cm signals

There can arise ubiquitous ultra-light scalar fields in the Universe, such as the pseudo-Goldstone bosons from the spontaneous breaking of an approximate symmetry, which can make a partial contribution to the dark matter and affect the large scale structure of the Universe. While the properties of those ultra-light dark matter are heavily model dependent and can vary in a wide range, we develop a model-independent analysis to forecast the constraints on their mass and abundance using futuristic but realistic 21 cm observables as well as CMB fluctuations, including CMB lensing measurements. Avoiding the highly nonlinear regime, the 21 cm emission line spectra are most sensitive to the ultra-light dark matter with mass m ~10^{-26} eV for which the precision attainable on mass and abundance bounds can be of order of a few percent.

hep-ph↗

arXiv2014

The Effects of Dark Matter-Baryon Scattering on Redshifted 21 cm Signals

We demonstrate that elastic scattering between dark matter (DM) and baryons can affect the thermal evolution of the intergalactic medium at early epochs and discuss the observational consequences. We show that, due to the interaction between DM and baryons, the baryon temperature is cooled after decoupling from the CMB temperature. We illustrate our findings by calculating the 21 cm power spectrum in coexistence with a velocity-dependent DM elastic scattering cross section. For instance, for a DM mass of 10 GeV, the 21 cm brightness temperature angular power spectrum can be suppressed by a factor 2 within the currently allowed DM-baryon cross section bounded by the CMB and large-scale structure data. This scale-independent suppression of the angular power spectrum can be even larger for a smaller DM mass with a common cross section (for instance, as large as a factor 10 for $m_d\sim 1$ GeV), and such an effect would be of great interest for probing the nature of DM in view of forthcoming cosmological surveys.

astro-ph.CO↗

arXiv2014

Constraints on Light Magnetic Dipole Dark Matter from the ILC and SN 1987A

To illustrate the complementarity of the linear collider and astrophysics bounds on the light (MeV-scale mass) dark matter (DM), we study the constraints on the magnetic dipole DM from the DM-electron interactions at the proposed International Linear Collider (ILC) and in supernova (SN) 1987A. We in particular focus on the $e^+ e^-$ annihilation which is the common process for producing DM pairs both at the ILC and in the SN. We estimate the bounds on the DM magnetic dipole moment from the mono-photon signals at the ILC and also from the energy loss rate due to the freely streaming DM produced in the SN. The SN bounds can be more stringent than those from the ILC by as much as a factor ${\cal O}(10^5)$ for a DM mass below $10^2$ MeV. For larger DM masses, on the other hand, SN rapidly loses its sensitivity and the collider constraints can complement the SN constraints.

hep-ph↗

arXiv2014

The influence of primordial magnetic fields on the spherical collapse model in cosmology

Despite the ever growing observational evidence for the existence of the large scale magnetic fields, their origin and the evolution are not fully understood. If the magnetic fields are of primordial origin, they result in the generation of the secondary matter density perturbations and the previous studies show that such density perturbations enhance the number of dark matter halos. We extend the conventional spherical collapse model by including the Lorentz force which has not been implemented in the previous analysis to study the evolution of density perturbations produced by primordial magnetic fields. The critical over-density $δ_{\rm c}$ characterizing the halo mass function turns out to be a bigger value, $δ_{\rm c}\simeq 1.78$, than the conventional one $δ_{\rm c}\simeq 1.69$ for the perturbations evolved only by the gravitational force. The difference in $δ_{\rm c}$ between our model and the fully matter dominated cosmological model is small at a low redshift and, hence, only the high mass tail of the mass function is affected by the magnetic fields. At a high redshift, on the other hand, the difference in $δ_{\rm c}$ becomes large enough to suppress the halo abundance over a wide range of mass scales. The halo abundance is reduced for instance by as large a factor as $\sim10^5$ at $z=9$.

astro-ph.CO↗

arXiv2014

Constraint on Light Dipole Dark Matter from Helioseismology

We investigate the effects of a magnetic dipole moment of asymmetric dark matter (DM) in the evolution of the Sun. The dipole interaction can lead to a sizable DM scattering cross section even for light DM, and the asymmetric dark matter can lead to a large DM number density in the Sun. We find that solar model precision tests, using as diagnostic the sound speed profile obtained from helioseismology data, exclude dipolar dark matter particles with a mass larger than 4.3 GeV and magnetic dipole moment larger than 1.6 $\times \;10^{-17}$ e cm.

astro-ph.SR↗

arXiv2013

Probing Neutrinos from Planck and Forthcoming Galaxy Redshift Surveys

We investigate how much the constraints on the neutrino properties can be improved by combining the CMB, the photometric and spectroscopic galaxy redshift surveys which include the CMB lensing, galaxy lensing tomography, galaxy clustering and redshift space distortion observables. We pay a particular attention to the constraint on the neutrino mass in view of the forthcoming redshift surveys such as the Euclid satellite and the LSST survey along with the Planck CMB lensing measurements. Combining the transverse mode information from the angular power spectrum and the longitudinal mode information from the spectroscopic survey with the redshift space distortion measurements can determine the total neutrino mass with the projected error of O(0.02)eV. Our analysis fixes the mass splittings among the neutrino species to be consistent with the neutrino oscillation data, and we accordingly study the sensitivity of our parameter estimations on the minimal neutrino mass. The cosmological measurement of the total neutrino mass can distinguish between the normal and inverted mass hierarchy scenarios if the minimal neutrino mass < 0.005 eV with the predicted 1-σ uncertainties taken into account.

astro-ph.CO↗

arXiv2012

The effect of quark interactions on dark matter kinetic decoupling and the mass of the smallest dark halos

The kinetic decoupling of dark matter (DM) from the primordial plasma sets the size of the first and smallest dark matter halos. Studies of the DM kinetic decoupling have hitherto mostly neglected interactions between the DM and the quarks in the plasma. Here we illustrate their importance using two frameworks: a version of the Minimal Supersymmetric Standard Model (MSSM) and an effective field theory with effective DM-quark interaction operators. We connect particle physics and astrophysics obtaining bounds on the smallest dark matter halo size from collider data and from direct dark matter search experiments. In the MSSM framework, adding DM-quark interactions to DM-lepton interactions more than doubles the smallest dark matter halo mass in a wide range of the supersymmetric parameter space.

hep-ph↗

arXiv2012

Constraining Scale-Dependent Non-Gaussianity with Future Large-Scale Structure and the CMB

We forecast combined future constraints from the cosmic microwave background and large-scale structure on the models of primordial non-Gaussianity. We study the generalized local model of non-Gaussianity, where the parameter f_NL is promoted to a function of scale, and present the principal component analysis applicable to an arbitrary form of f_NL(k). We emphasize the complementarity between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples, forecast constraints on the power-law f_NL(k) model, and introduce the figure of merit for measurements of scale-dependent non-Gaussianity.

astro-ph.CO↗

arXiv2012

Flavour issues for string-motivated heavy scalar spectra with a low gluino mass: the G2-MSSM case

In recent years it has been learned that scalar superpartner masses and trilinear couplings should both generically be larger than about 20 TeV at the short distance string scale if our world is described by a compactified string or M-theory with supersymmetry breaking and stabilized moduli. Here we study implications of this, somewhat generally and also in detail for a particular realization (compactification of M-theory on a G_2 manifold) where there is significant knowledge of the superpotential and gauge kinetic function, and a light gluino. In a certain sense this yields an ultraviolet completion of minimal flavour violation. Flavour violation stems from off-diagonal and non-universal diagonal elements of scalar mass matrices and trilinear couplings, and from renormalization group running. We also examine stability bounds on the scalar potential. While heavy scalars alone do not guarantee the absence of flavour problems, our studies show that models with heavy scalars and light gluinos can be free from such problems.

hep-ph↗

arXiv2012

Proceedings of the first workshop on Flavor Symmetries and consequences in Accelerators and Cosmology (FLASY2011)

The main goals of the first "Workshop on FLAvor SYmmetries and consequences in accelerators and cosmology" (FLASY) was to summarize the theoretical status of flavor symmetries, bringing together young researchers in the field to stimulate discussions and new collaborations, with the aim of investigating possible new physics scenarios to be tested at the LHC, as well as in future neutrino, cosmology experiments and dark matter searches.

hep-ph↗

arXiv2012

Cross-correlating the Thermal Sunyaev-Zel'dovich Effect and the Distribution of Galaxy Clusters

We present the analytical formulas, derived based on the halo model, to compute the cross-correlation between the thermal Sunyaev-Zel'dovich (SZ) effect and the distribution of galaxy clusters. By binning the clusters according to their redshifts and masses, this cross-correlation, the so-called stacked SZ signal, reveals the average SZ profile around the clusters. The stacked SZ signal is obtainable from a joint analysis of an arcminute-resolution cosmic microwave background (CMB) experiment and an overlapping optical survey, which allows for detection of the SZ signals for clusters whose masses are below the individual cluster detection threshold. We derive the error covariance matrix for measuring the stacked SZ signal, and then forecast for its detection from ongoing and forthcoming combined CMB-optical surveys. We find that, over a wide range of mass and redshift, the stacked SZ signal can be detected with a significant signal to noise ratio (total S/N \gsim 10), whose value peaks for the clusters with intermediate masses and redshifts. Our calculation also shows that the stacking method allows for probing the clusters' SZ profiles over a wide range of scales, even out to projected radii as large as the virial radius, thereby providing a promising way to study gas physics at the outskirts of galaxy clusters.

astro-ph.CO↗

arXiv2011

Scale-Dependent Non-Gaussianity as a Generalization of the Local Model

We generalize the local model of primordial non-Gaussianity by promoting the parameter fNL to a general scale-dependent function fNL(k). We calculate the resulting bispectrum and the effect on the bias of dark matter halos, and thus the extent to which fNL(k) can be measured from the large-scale structure observations. By calculating the principal components of fNL(k), we identify scales where this form of non-Gaussianity is best constrained and estimate the overlap with previously studied local and equilateral non-Gaussian models.

astro-ph.CO↗

arXiv2010

Supersymmetric Musings on the Predictivity of Family Symmetries

We discuss the predictivity of family symmetries for the soft supersymmetry breaking parameters in the framework of supergravity. We show that unknown details of the messenger sector and the supersymmetry breaking hidden sector enter into the soft parameters, making it difficult to obtain robust predictions. We find that there are specific choices of messenger fields which can improve the predictivity for the soft parameters.

hep-ph↗

arXiv2010

Positrons in Cosmic Rays from Dark Matter Annihilations for Uplifted Higgs Regions in MSSM

We point out that there are regions in the MSSM parameter space which successfully provide a dark matter (DM) annihilation explanation for observed positron excess (e.g. PAMELA), while still remaining in agreement with all other data sets. Such regions (e.g. the uplifted Higgs region) can realize an enhanced neutralino DM annihilation dominantly into leptons via a Breit-Wigner resonance through the CP-odd Higgs channel. Such regions can give the proper thermal relic DM abundance, and the DM annihilation products are compatible with current antiproton and gamma ray observations. This scenario can succeed without introducing any additional degrees of freedom beyond those already in the MSSM.

hep-ph↗

arXiv2009

Enhanced Tau Lepton Signatures at LHC in Constrained Supersymmetric Seesaw

We discuss the possible enhancement of the tau lepton events at LHC when the left-handed stau doublet becomes light (which can be even lighter than the right-handed stau). This is illustrated in the constrained supersymmetric seesaw model where the slepton doublet mass is suppressed by the effects of a large neutrino Yukawa coupling. We study a few representative parameter sets in the sneutrino coannihilation regions where the tau sneutrino is NLSP and the stau coannihilation regions where the stau is NLSP both of which yield the thermal neutralino LSP abundance determined by WMAP.

hep-ph↗

arXiv2009

Heavy Right-Handed Neutrinos and Dark Matter in the $ν$CMSSM

We perform a systematic study of the effects of the type-I seesaw mechanism on the dark matter abundance in the constrained supersymmetric standard model (CMSSM) which includes three right-handed neutrinos (the $ν$CMSSM). For large values of $m_0,m_{1/2}$, we exploit the effects of large neutrino Yukawa couplings on the renormalization group (RG) evolution of the up-type Higgs. In particular, we show that the focus point scale can greatly exceed the electroweak scale resulting in the absence of a focus point region for which the relic density of neutralinos is within the range determined by WMAP. We also discuss the effects of the right-handed neutrinos on the so-called funnel region, where the relic density is controlled by s-channel annihilations through a heavy Higgs. For small values of $m_0,m_{1/2}$, we discuss the possibility of sneutrino coannihilation regions with an emphasis on the suppression of the left-handed slepton doublet masses due to the neutrino Yukawa coupling. We consider two types of toy models consistent with either the normal or inverted hierarchy of neutrino masses.

hep-ph↗