arXiv subjects

Takeo Moroi

Publications and source records attributed to Takeo Moroi.

At least 145 records · Page 8Linked to original sources

arXiv2005

Implications of the Curvaton on Inflationary Cosmology

We study implications of the curvaton, a late-decaying light scalar field, on inflationary cosmology, paying particular attentions to modifications of observable quantities such as the scalar spectral index of the primordial power spectrum and the tensor-to-scalar ratio. We consider this issue from a general viewpoint and discuss how the observable quantities are affected by the existence of the curvaton. It is shown that the modification owing to the curvaton depends on class of inflation models. We also study the effects of the curvaton on inflation models generated by the inflationary flow equation.

astro-ph↗

arXiv2005

Big-Bang Nucleosynthesis and Hadronic Decay of Long-Lived Massive Particles

We study the big-bang nucleosynthesis (BBN) with the long-lived exotic particle, called X. If the lifetime of X is longer than \sim 0.1 sec, its decay may cause non-thermal nuclear reactions during or after the BBN, altering the predictions of the standard BBN scenario. We pay particular attention to its hadronic decay modes and calculate the primordial abundances of the light elements. Using the result, we derive constraints on the primordial abundance of X. Compared to the previous studies, we have improved the following points in our analysis: The JETSET 7.4 Monte Carlo event generator is used to calculate the spectrum of hadrons produced by the decay of X; The evolution of the hadronic shower is studied taking account of the details of the energy-loss processes of the nuclei in the thermal bath; We have used the most recent observational constraints on the primordial abundances of the light elements; In order to estimate the uncertainties, we have performed the Monte Carlo simulation which includes the experimental errors of the cross sections and transfered energies. We will see that the non-thermal productions of D, He3, He4 and Li6 provide stringent upper bounds on the primordial abundance of late-decaying particle, in particular when the hadronic branching ratio of X is sizable. We apply our results to the gravitino problem, and obtain upper bound on the reheating temperature after inflation.

astro-ph↗

arXiv2005

Dark Matter and Baryon Asymmetry of the Universe in Large-Cutoff Supergravity

We propose a consistent scenario of the evolution of the universe based on the large cutoff supergravity (LCSUGRA) hypothesis of supersymmetry breaking, where the gravitino and sfermion become as heavy a $\sim O(1-10 {\rm TeV})$. With such a heavy gravitino, baryon asymmetry of the universe can be generated by the non-thermal leptogenesis via an inflaton decay without conflicting the serious gravitino problem. We also see that, in the LCSUGRA scenario, relic density of the lightest superparticle becomes consistent with the WMAP value of the dark matter density in the parameter region required for the successful non-thermal leptogenesis.

hep-ph↗

arXiv2005

Relaxing Constraints on Inflation Models with Curvaton

We consider the effects of the curvaton, late-decaying scalar condensation, to observational constraints on inflation models. From current observations of cosmic density fluctuations, severe constraints on some class of inflation models are obtained, in particular, on the chaotic inflation with higher-power monomials, the natural inflation, and the new inflation. We study how the curvaton scenario changes (and relaxes) the constraints on these models.

hep-ph↗

arXiv2004

Hadronic decay of the gravitino in the early universe and its implications to inflation

We discuss the effects of the gravitino on the big-bang nucleosynthesis (BBN), paying particular attention to the hadronic decay mode of the gravitino. We will see that the hadronic decay of the gravitino significantly affect the BBN and, for the case where the hadronic branching ratio is sizable, very stringent upper bound on the reheating temperature after inflation is obtained.

hep-ph↗

arXiv2004

Correlated Isocurvature Fluctuation of Quintessence and Curvaton Scenario

We consider cosmic microwave background (CMB) anisotropy in models with quintessence taking into account of isocurvature fluctuation in the quintessence. It is shown that, if the primordial fluctuation of the quintessence has a correlation with the adiabatic density fluctuations, CMB angular power spectrum $C_l$ at low multipoles can be suppressed. Possible scenario of generating correlated mixture of the quintessence and adiabatic fluctuations is also discussed.

hep-ph↗

arXiv2004

Hadronic Decay of Late-Decaying Particles and Big-Bang Nucleosynthesis

We study the big-bang nucleosynthesis (BBN) scenario with late-decaying exotic particles with lifetime longer than $\sim 1$ sec. With a late-decaying particle in the early universe, predictions of the standard BBN scenario can be significantly altered. Therefore, we derive constraints on its primordial abundance. We pay particular attention to hadronic decay modes of such particles. We see that the non-thermal production process of D, ${\rm ^{3}He}$ and ${\rm ^6Li}$ provides a stringent upper bound on the primordial abundance oflate-decaying particles with hadronic branching ratio.

astro-ph↗

arXiv2004

Curvaton mechanism and its implications to sneutrino cosmology

I describe basic features of the curvaton scenario where the primordial fluctuation of a late-decaying scalar field, called ``curvaton,'' becomes the dominant source of the cosmic density fluctuations. I also discuss its implications to sneutrino cosmology.

hep-ph↗

arXiv2004

The masses of weakly-coupled scalar fields in the early Universe

We consider the effective mass-squared in the early Universe, of a scalar field which has only Planck-suppressed couplings with light fields and whose true mass is less than the Hubble parameter $H$. A detailed investigation shows that the effective mass-squared generically is of order $\pm H^2$ during inflation and matter-domination, but much smaller during radiation domination. We consider the special circumstances under which the mass-squared may be much bigger or much smaller than the generic value.

hep-ph↗

arXiv2004

Curvaton Scenario with Affleck-Dine Baryogenesis

We discuss the curvaton scenario with the Affleck-Dine baryogenesis. In this scenario, non-vanishing baryonic entropy fluctuation may be generated even without primordial fluctuation of the Affleck-Dine field. Too large entropy fluctuation is inconsistent with the observations and hence constraints on the curvaton scenario with the Affleck-Dine baryogenesis are obtained. We calculate the baryonic entropy fluctuation (as well as other cosmological density fluctuations) in this case and derive constraints. Implications to some of the models of the curvaton are also discussed.

hep-ph↗

arXiv2004

Can MSSM Particle be the Inflaton?

We consider the possibility of using one of the $D$-flat directions in the minimal supersymmetric standard model (MSSM) as the inflaton. We show that the flat direction consisting of (first generation) left- and right-handed up-squarks as well as the up-type Higgs boson may play the role of the inflaton if dominant part of the up-quark mass is radiatively generated from supersymmetric loop diagrams. We also point out that, if the R-parity violating Yukawa coupling is of $O(10^{-7})$, $R$-odd $D$-flat directions may be another possible candidate of the inflaton. Such inflation models using $D$-flat directions in the MSSM are not only testable with collider experiments but also advantageous to resolve the problem how the inflaton reheats the universe.

hep-ph↗

arXiv2004

Correlated Isocurvature Fluctuation in Quintessence and Suppressed CMB Anisotropies at Low Multipoles

We consider cosmic microwave background (CMB) anisotropy in models with quintessence taking into account of isocurvature fluctuation in the quintessence. It is shown that, if the primordial fluctuation of the quintessence has a correlation with the adiabatic density fluctuations, CMB angular power spectrum $C_l$ at low multipoles can be suppressed without affecting $C_l$ at high multipoles. Possible scenario of generating correlated mixture of the quintessence and adiabatic fluctuations is also discussed.

astro-ph↗

arXiv2003

Curvatons in Supersymmetric Models

We study the curvaton scenario in supersymmetric framework paying particular attention to the fact that scalar fields are inevitably complex in supersymmetric theories. If there are more than one scalar fields associated with the curvaton mechanism, isocurvature (entropy) fluctuations between those fields in general arise, which may significantly affect the properties of the cosmic density fluctuations. We examine several candidates for the curvaton in the supersymmetric framework, such as moduli fields, Affleck-Dine field, $F$- and $D$-flat directions, and right-handed sneutrino. We estimate how the isocurvature fluctuations generated in each case affect the cosmic microwave background angular power spectrum. With the use of the recent observational result of the WMAP, stringent constraints on the models are derived and, in particular, it is seen that large fraction of the parameter space is excluded if the Affleck-Dine field plays the role of the curvaton field. Natural and well-motivated candidates of the curvaton are also listed.

hep-ph↗

arXiv2003

Cosmic String from D-term Inflation and Curvaton

We study effects of the cosmic string in the D-term inflation model on the cosmic microwave background (CMB) anisotropy. In the D-term inflation model, gauged cosmic string is usually formed, which may significantly affect the CMB anisotropy. We see that its study imposes important constraint. In order to realize the minimal model of D-term inflation, we see that the coupling constant λin the superpotential generating the inflaton potential should be significantly small, λ\lesssim O(10^{-4}-10^{-5}). We also discuss that a consistent scenario of the D-term inflation with λ\sim 1 can be constructed by adopting the curvaton mechanism where the cosmic density fluctuations are generated by a primordial fluctuation of a late-decaying scalar field other than the inflaton.

hep-ph↗

arXiv2002

Top-Squark Study at a Future e^+e^- Linear Collider

We discuss a potential of studying the production and the decay of the lightest top squark (t-tilde_1) in the framework of the supersymmetric standard model at a future e^+e^- collider. In particular, we consider the process t-tilde_1 -> t chi^0_1 (with chi^0_1 being the lightest neutralino) followed by t -> bW. It is shown that, by the study of the angular distribution of the bottom quark (as well as the production cross section of the top squark), properties of chi_1^0 can be extracted. We also discuss that, if chi^0_1 is gaugino-like, the neutralino mixing parameters (i.e., the so-called mu-parameter and tan beta) may be constrained.

hep-ph↗

arXiv2002

CMB Anisotropy from Baryogenesis by a Scalar Field

We study the cosmic microwave background (CMB) anisotropy in the scenario where the baryon asymmetry of the universe is generated from a condensation of a scalar field. In such a scenario, the scalar condensation may acquire fluctuation during the inflation which becomes a new source of the cosmic density perturbations. In particular, the primordial fluctuation of the scalar condensation may induce correlated mixture of the adiabatic and isocurvature fluctuations. If the scalar condensation decays before it completely dominates the universe, the CMB angular power spectrum may significantly deviate from the conventional adiabatic result. Such a deviation may be observed in the on-going MAP experiment.

hep-ph↗

arXiv2002

Cosmic Microwave Background from Late-Decaying Scalar Condensations

We study the cosmic microwave background (CMB) anisotropy in the scenario with late-decaying scalar condensations which arise in many class of cosmological scenarios based on supersymmetric models. With such a scalar condensation ϕ, the CMB radiation we observe today originates to ϕand hence the CMB anisotropy is affected if ϕhas a primordial fluctuation. In particular, if all the components in the universe (i.e., radiation, baryon, cold dark matter, and so on) are generated from the decay product of ϕ, the dominant source of the cosmic density perturbations can be the primordial fluctuation of ϕ, not the fluctuation of the inflaton field. In this case, the constraints on the inflation models can be drastically relaxed. In other case, the baryon or the CDM may not be from the decay product of ϕand correlated mixture of the adiabatic and isocurvature fluctuations can be generated. If so, the CMB angular power spectrum may not be the same as the adiabatic result and the on-going MAP experiment may observe a deviation from the prediction of the standard inflationary scenario.

hep-ph↗

arXiv2002

Effects of Cosmological Moduli Fields on Cosmic Microwave Background

We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field ϕonce dominates the universe, the CMB we observe today is from the decay of ϕand its anisotropy is affected by the primordial fluctuation in the amplitude of the modulus field. Consequently, constraints on the inflaton potential from the CMB anisotropy can be relaxed. In particular, the scale of the inflation may be significantly lowered. In addition, with the cosmological moduli fields, correlated mixture of adiabatic and isocurvature fluctuations may be generated, which results in enhanced CMB angular power spectrum at higher multipoles relative to that of lower ones. Such an enhancement can be an evidence of the cosmological moduli fields, and may be observed in future satellite experiments.

hep-ph↗