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Kazunori Nakayama

Publications and source records attributed to Kazunori Nakayama.

At least 163 records · Page 9Linked to original sources
arXiv2011

Number-Theory Dark Matter

We propose that the stability of dark matter is ensured by a discrete subgroup of the U(1)B-L gauge symmetry, Z_2(B-L). We introduce a set of chiral fermions charged under the U(1)B-L in addition to the right-handed neutrinos, and require the anomaly-cancellation conditions associated with the U(1)B-L gauge symmetry. We find that the possible number of fermions and their charges are tightly constrained, and that non-trivial solutions appear when at least five additional chiral fermions are introduced. The Fermat theorem in the number theory plays an important role in this argument. Focusing on one of the solutions, we show that there is indeed a good candidate for dark matter, whose stability is guaranteed by Z_2(B-L).

hep-ph↗
arXiv2011

Constraint on the gravitino mass in hybrid inflation

We revisit the F-term hybrid inflation model in supergravity. In particular, we point out that a constant term in the superpotential has significant effects on the inflaton dynamics. It is shown that the hybrid inflation model suffers from several potential problems: tuning of the initial condition, gravitino overproduction and formation of cosmic strings, for both minimal and non-minimal Kahler potentials. These problems can only be avoided in gauge-mediated SUSY breaking models where the gravitino is relatively light and the constant term in the superpotential is not important. Implications on the non-thermal leptogenesis scenario are also described.

hep-ph↗
arXiv2011

Cosmological constraints on dark matter models with velocity-dependent annihilation cross section

We derive cosmological constraints on the annihilation cross section of dark matter with velocity-dependent structure, motivated by annihilating dark matter models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models with annihilation cross section increasing with decreasing dark matter velocity, big-bang nucleosynthesis and cosmic microwave background give stringent constraints.

hep-ph↗
arXiv2011

On the waterfall behavior in hybrid inflation

We revisit the hybrid inflation model focusing on the dynamics of the waterfall field in an analytical way. It is shown that inflation may last long enough during the waterfall regime for some parameter regions, confirming the claim of Clesse. In this case the scalar spectral index becomes red, and can fall into the best fit range of the WMAP observation.

astro-ph.CO↗
arXiv2010

Inflation from a Supersymmetric Axion Model

We show that a supersymmetric axion model naturally induces a hybrid inflation with the waterfall field identified as a Peccei-Quinn scalar. The Peccei-Quinn scale is predicted to be around 10^{15}GeV for reproducing the large-scale density perturbation of the Universe. After the built-in late-time entropy-production process, the axion becomes a dark matter candidate. Several cosmological implications are discussed.

hep-ph↗
arXiv2010

A theory of extra radiation in the Universe

Recent cosmological observations, such as the measurement of the primordial 4He abundance, CMB, and large scale structure, give preference to the existence of extra radiation component, Delta N_nu > 0. The extra radiation may be accounted for by particles which were in thermal equilibrium and decoupled before the big bang nucleosynthesis. Broadly speaking, there are two possibilities: 1) there are about 10 particles which have very weak couplings to the standard model particles and decoupled much before the QCD phase transition; 2) there is one or a few light particles with a reasonably strong coupling to the plasma and it decouples after the QCD phase transition. Focusing on the latter case, we find that a light chiral fermion is a suitable candidate, which evades astrophysical constraints. Interestingly, such a scenario may be confirmed at the LHC. As a concrete example, we show that such a light fermion naturally appears in the E_6-inspired GUT.

hep-ph↗
arXiv2010

B-mode polarization induced by gravitational waves from kinks on infinite cosmic strings

We investigate the effect of the stochastic gravitational wave (GW) background produced by kinks on infinite cosmic strings, whose spectrum was derived in our previous work, on the B-mode power spectrum of the cosmic microwave background (CMB) anisotropy. We find that the B-mode polarization due to kinks is comparable to that induced by the motion of the string network and hence the contribution of GWs from kinks is important for estimating the B-mode power spectrum originating from cosmic strings. If the tension of cosmic strings μis large enough i.e., Gμ>~ 10^{-8}, B-mode polarization induced by cosmic strings can be detected by future CMB experiments.

astro-ph.CO↗
arXiv2010

Higgs Chaotic Inflation in Standard Model and NMSSM

We construct a chaotic inflation model in which the Higgs fields play the role of the inflaton in the standard model as well as in the singlet extension of the supersymmetric standard model. The key idea is to allow a non-canonical kinetic term for the Higgs field. The model is a realization of the recently proposed running kinetic inflation, in which the coefficient of the kinetic term grows as the inflaton field. The inflaton potential depends on the structure of the Higgs kinetic term. For instance, the inflaton potential is proportional to phi^2 and phi^{2/3} in the standard model and NMSSM, respectively. It is also possible to have a flatter inflaton potential.

hep-ph↗
arXiv2010

General Analysis of Inflation in the Jordan frame Supergravity

We study various inflation models in the Jordan frame supergravity with a logarithmic Kahler potential. We find that, in a class of inflation models containing an additional singlet in the superpotential, three types of inflation can be realized: the Higgs-type inflation, power-law inflation, and chaotic inflation with/without a running kinetic term. The former two are possible if the holomorphic function dominates over the non-holomorphic one in the frame function, while the chaotic inflation occurs when both are comparable. Interestingly, the fractional-power potential can be realized by the running kinetic term. We also discuss the implication for the Higgs inflation in supergravity.

hep-ph↗
arXiv2010

Running Kinetic Inflation

We study a recently proposed running kinetic inflation model in which the inflaton potential becomes flat due to rapid growth of the kinetic term at large inflaton field values. As concrete examples, we build a variety of chaotic inflation models in supergravity with e.g. quadratic, linear, and fractional-power potentials. The power of the potential generically increases after inflation, and the inflaton is often massless at the potential minimum in the supersymmetric limit, which leads to many interesting phenomena. First, the light inflaton mass greatly relaxes severe thermal and non-thermal gravitino problems. Secondly, the kination epoch is naturally present after inflation, which may enhance the gravity waves. Thirdly, since the inflaton is light, it is likely coupled to the Higgs sector for successful reheating. The inflaton and its superpartner, inflatino, may be produced at the LHC. Interestingly, the inflatino can be dark matter, if it is the lightest supersymmetric particle.

hep-ph↗
arXiv2010

WIMP dark matter in gauge-mediated SUSY breaking models and its phenomenology

We propose an extended version of the gauge-mediated SUSY breaking models where extra $SU(2)_L$ doublets and singlet field are introduced. These fields are assumed to be parity-odd under an additional matter parity. In this model, the lightest parity-odd particle among them would be dark matter in the Universe. In this paper, we discuss direct detection of the dark matter and the collider signatures of the model

hep-ph↗
arXiv2010

Gravitational waves from kinks on infinite cosmic strings

Gravitational waves emitted by kinks on infinite strings are investigated using detailed estimations of the kink distribution on infinite strings. We find that gravitational waves from kinks can be detected by future pulsar timing experiments such as SKA for an appropriate value of the the string tension, if the typical size of string loops is much smaller than the horizon at their formation. Moreover, the gravitational wave spectrum depends on the thermal history of the Universe and hence it can be used as a probe into the early evolution of the Universe.

astro-ph.CO↗
arXiv2010

Implications of CDMS II result on Higgs sector in the MSSM

We study implications of two dark matter candidate events at CDMS-II on the neutralino dark matter scenario in the supersymmetric standard model, in light of the recent lattice simulation on the strange quark content of a nucleon. The scattering rate of neutralino-nucleon is dominated by Higgs exchange processes and the mass of heavy Higgs boson is predicted for the neutralino of Bino-Higgsino mixing state. In the case of Wino-Higgsino mixing, the Higgs sector may not be constrained.

hep-ph↗
arXiv2009

Gravitational Wave Background and Non-Gaussianity as a Probe of the Curvaton Scenario

We study observational implications of the stochastic gravitational wave background and a non-Gaussian feature of scalar perturbations on the curvaton mechanism of the generation of density/curvature fluctuations, and show that they can determine the properties of the curvaton in a complementary manner to each other. Therefore even if Planck could not detect any non-Gaussianity, future space-based laser interferometers such as DECIGO or BBO could practically exhaust its parameter space.

astro-ph.CO↗
arXiv2009

Non-Gaussianity from Isocurvature Perturbations : Analysis of Trispectrum

Non-Gaussianity may exist in the CDM isocurvature perturbation. We provide general expressions for the bispectrum and trispectrum of both adiabatic and isocurvature pertubations. We apply our result to the QCD axion case, and found a consistency relation between the coefficients of the bispectrum and trispectrum : tau_{NL}^(iso)~10^3 [f_{NL}^(iso)]^{4/3}, if the axion is dominantly produced by quantum fluctuation. Thus future observations of the trispectrum, as well as the bispectrum, will be important for understanding the origin of the CDM and baryon asymmetry.

astro-ph.CO↗
arXiv2009

Constraining Light Gravitino Mass from Cosmic Microwave Background

We investigate the possibilities of constraining the light gravitino mass m_{3/2} from future cosmic microwave background (CMB) surveys. A model with light gravitino with the mass m_{3/2}<O(10) eV is of great interest since it is free from the cosmological gravitino problem and, in addition, can be compatible with many baryogenesis/leptogenesis scenarios such as the thermal leptogenesis. We show that the lensing of CMB anisotropies can be a good probe for m_{3/2} and obtain an expected constraint on m_{3/2} from precise measurements of lensing potential in the future CMB surveys, such as the PolarBeaR and CMBpol experiments. If the gravitino mass is m_{3/2}=1 eV, we will obtain the constraint for the gravitino mass as m_{3/2} < 3.2 eV (95% C.L.) for the case with Planck+PolarBeaR combined and m_{3/2}=1.04^{+0.22}_{-0.26} eV (68% C.L.) for CMBpol. The issue of Bayesian model selection is also discussed.

astro-ph.CO↗
arXiv2009

Effects of Dark Matter Annihilation on the Cosmic Microwave Background

We study the effects of dark matter annihilation during and after the cosmic recombination epoch on the cosmic microwave background anisotropy, taking into account the detailed energy deposition of the annihilation products. It is found that a fairly stringent constraint on the annihilation cross section is imposed for TeV scale dark matter masses from WMAP observations.

astro-ph.CO↗