Large scale evolution of the curvature perturbation in Horava-Lifshitz cosmology (2009)
Kobayashi, Tsutomu, Urakawa, Yuko, Yamaguchi, Masahide
In the non-relativistic theory of gravity recently proposed by Horava, the Hamiltonian constraint is not satisfied locally at each point in space. The absence of the local Hamiltonian constraint...
Primordial Non-Gaussianity in Models with Dark Matter Isocurvature Fluctuations (2009)
Takahashi, Tomo, Yamaguchi, Masahide, Yokoyama, Shuichiro
We investigate primordial non-Gaussianity and dark matter isocurvature fluctuations in the modulated reheating and the curvaton scenarios. In these scenarios, large non-Gaussianity can be generated,...
Gravitino Dark Matter and Non-Gaussianity (2009)
Takahashi, Tomo, Yamaguchi, Masahide, Yokoyama, Jun'ichi, Yokoyama, Shuichiro
We investigate density fluctuations in a scenario with gravitino dark matter in the framework of modulated reheating, which is known to generate large non-Gaussianity. We show that gravitino dark...
Constraints on neutrino masses from WMAP5 and BBN in the lepton asymmetric universe (2009)
Shiraishi, Maresuke, Ichikawa, Kazuhide, Ichiki, Kiyotomo, Sugiyama, Naoshi, Yamaguchi, Masahide
In this paper, we put constraints on neutrino properties such as mass $m_{\nu}$ and degeneracy parameters $\xi_i$ from WMAP5 data and light element abundances by using a Markov chain Monte Carlo...
Limits on Isocurvature Perturbations from Non-Gaussianity in WMAP Temperature Anisotropy (2008)
Hikage, Chiaki, Koyama, Kazuya, Matsubara, Takahiko, Takahashi, Tomo, Yamaguchi, Masahide
We study the effect of primordial isocurvature perturbations on non-Gaussian properties in CMB temperature anisotropies. We consider generic forms of the non-linearity of isocurvature perturbations...
Chiba, Takeshi, Yamaguchi, Masahide
As an extension of our previous study, we derive slow-roll conditions for multiple scalar fields which are non-minimally coupled with gravity and for generalized gravity theories of the form...
Adiabatic fluctuations from cosmic strings in a contracting universe (2008)
Brandenberger, Robert H., Takahashi, Tomo, Yamaguchi, Masahide
We show that adiabatic, super-Hubble, and almost scale invariant density fluctuations are produced by cosmic strings in a contracting universe. An essential point is that isocurvature perturbations...
Extended Slow-Roll Conditions and Rapid-Roll Conditions (2008)
Chiba, Takeshi, Yamaguchi, Masahide
We derive slow-roll conditions for a scalar field which is non-minimally coupled with gravity in a consistent manner and express spectral indices of scalar/tensor perturbations in terms of the...
Primordial Curvature Fluctuation and Its Non-Gaussianity in Models with Modulated Reheating (2008)
Ichikawa, Kazuhide, Suyama, Teruaki, Takahashi, Tomo, Yamaguchi, Masahide
We investigate non-Gaussianity in the modulated reheating scenario where fluctuations of the decay rate of the inflaton generate adiabatic perturbations, paying particular attention to the...
Reheating in Chaotic D-Term Inflation (2008)
Kawano, Teruhiko, Yamaguchi, Masahide
A simple model is discussed to give rise to successful reheating in chaotic D-term inflation with a quadratic inflaton potential, introducing a trilinear coupling in the K\"ahler potential....
Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton Models (2008)
Ichikawa, Kazuhide, Suyama, Teruaki, Takahashi, Tomo, Yamaguchi, Masahide
We study non-Gaussianity, the spectral index of primordial scalar fluctuations and tensor modes in models where fluctuations from the inflaton and the curvaton can both contribute to the present...
New D-term chaotic inflation in supergravity and leptogenesis (2008)
Kadota, Kenji, Kawano, Teruhiko, Yamaguchi, Masahide
We present a new model of D-term dominated chaotic inflation in supergravity. The F-flat direction present in this model is lifted by the dominant D-term, which leads to chaotic inflation and...
Martin, Jerome, Yamaguchi, Masahide
Models where the dark energy is a scalar field with a non-standard Dirac-Born-Infeld (DBI) kinetic term are investigated. Scaling solutions are studied and proven to be attractors. The corresponding...
Kawaguchi, Toshihiro, Kawasaki, Masahiro, Takayama, Tsutomu, Yamaguchi, Masahide, Yokoyama, Jun'ichi
Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology if the primordial perturbation spectrum has a large and negative running of...
Non-Gaussianity in the modulated reheating scenario (2007)
Suyama, Teruaki, Yamaguchi, Masahide
We investigate the non-Gaussianity of primordial curvature perturbation in the modulated reheating scenario where the primordial perturbation is generated due to the spacial fluctuation of the...
D-term chaotic inflation in supergravity (2007)
Kadota, Kenji, Yamaguchi, Masahide
Even though the chaotic inflation is one of the most popular inflation models for its simple dynamics and compelling resolutions to the initial condition problems, its realization in supergravity has...
Effective Search Templates for a Primordial Stochastic Gravitational Wave Background (2007)
Chiba, Takeshi, Himemoto, Yoshiaki, Yamaguchi, Masahide, Yokoyama, Jun'ichi
We calculate the signal-to-noise ratio (SNR) of the stochastic gravitational-wave background in an extreme case that its spectrum has a sharp falloff with its amplitude close to the detection...
Warped Leptogenesis with Dirac Neutrino Masses (2007)
Gherghetta, Tony, Kadota, Kenji, Yamaguchi, Masahide
We show how leptogenesis can occur at the TeV scale with neutrinos that possess almost purely Dirac masses and negligible Majorana mass contributions as a consequence of the small wavefunction...
Axino warm dark matter and $\Omega_b - \Omega_{DM}$ coincidence (2007)
Seto, Osamu, Yamaguchi, Masahide
We show that axinos, which are dominantly generated by the decay of the next-to-lightest supersymmetric particles produced from the leptonic $Q$-ball ($L$-ball), become warm dark matter suitable for...
Lepton asymmetry in the primordial gravitational wave spectrum (2006)
Ichiki, Kiyotomo, Yamaguchi, Masahide, Yokoyama, Jun'Ichi
Effects of neutrino free streaming is evaluated on the primordial spectrum of gravitational radiation taking both neutrino chemical potential and masses into account. The former or the lepton...
Time variation of proton-electron mass ratio and fine structure constant with runaway dilaton (2006)
Chiba, Takeshi, Kobayashi, Tatsuo, Yamaguchi, Masahide, Yokoyama, Jun'ichi
Recent astrophysical observations indicate that the proton-electron mass ratio and the fine structure constant have gone through nontrivial time evolution. We discuss their time variation in the...
Effects of Cosmic Strings on Free Streaming (2006)
Takahashi, Tomo, Yamaguchi, Masahide
We study the effect of free streaming in a universe with cosmic strings with time-varying tension as well as with constant tension. Although current cosmological observations suggest that fluctuation...
Implications of cosmic strings with time-varying tension on CMB and large scale structure (2006)
Ichikawa, Kazuhide, Takahashi, Tomo, Yamaguchi, Masahide
We investigate cosmological evolution and implications of cosmic strings with time-dependent tension. We derive basic equations of time development of the correlation length and the velocity of such...
Power Spectrum of the Density Perturbations From Smooth Hybrid New Inflation Model (2006)
Kawasaki, Masahiro, Takayama, Tsutomu, Yamaguchi, Masahide, Yokoyama, Jun'ichi
We numerically investigate density perturbations generated in the smooth hybrid new inflation model, a kind of double inflation model that is designed to reproduce the running spectral index...
Density fluctuations in one-field inflation (2005)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
Any one-field inflation is actually realized in a multifield configuration because the inflaton must have couplings with other fields to reheat the universe and is coupled to all other fields at...
Cosmological evolution of cosmic strings with time-dependent tension (2005)
We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling...
Electroweak Baryogenesis with Embedded Domain Walls (2005)
Brandenberger, Robert H., Kelly, Wessyl, Yamaguchi, Masahide
We consider electroweak baryogenesis mediated by embedded domain walls. Embedded domain walls originating from a symmetry breaking phase transition are stabilized by thermal plasma effects, so that...
Black Strings in Our World (2005)
Nakano, Hiroyuki, Nakao, Ken-ichi, Yamaguchi, Masahide
The brane world scenario is a new approach to resolve the problem on how to compactify the higher dimensional spacetime to our 4-dimensional world. One of the remarkable features of this scenario is...
Yamaguchi, Masahide, Yokoyama, Jun'ichi
It is shown that in a smooth hybrid inflation model in supergravity adiabatic fluctuations with a running spectral index with $\ns >1$ on a large scale and $\ns
Note on the Robustness of the Neutrino Mass Bounds from Cosmology (2004)
Brandenberger, Robert H., Mazumdar, Anupam, Yamaguchi, Masahide
The recent high precision maps of cosmic microwave anisotropies combined with measurements of the galaxy power spectrum from new large-scale redshift surveys have allowed stringent bounds on the sum...
Spontaneous baryogenesis in flat directions (2003)
Takahashi, Fuminobu, Yamaguchi, Masahide
We discuss a spontaneous baryogenesis mechanism in flat directions. After identifying the Nambu-Goldstone mode which derivatively couples to the associated $U$(1) current and rotates due to the...
Chaotic hybrid new inflation in supergravity with a running spectral index (2003)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We propose an inflation model in supergravity, in which chaotic and hybrid inflation occurs successively, followed by new inflation. During hybrid inflation, adiabatic fluctuations with a running...
Inflation with a running spectral index in supergravity (2003)
Kawasaki, M., Yamaguchi, Masahide, Yokoyama, Jun'ichi
The first year Wilkinson Microwave Anisotropy Probe data favors primordial adiabatic fluctuation with a running spectral index with $\ns >1$ on a large scale and $\ns 1$ (hybrid inflation) or $\ns
Baryogenesis in a flat direction with neither baryon nor lepton charge (2003)
Chiba, Takeshi, Takahashi, Fuminobu, Yamaguchi, Masahide
We present a new mechanism of spontaneous baryogenesis. Usually such mechanisms require a derivative coupling between a scalar field and baryon current. In our model, the scalar field instead...
Spontaneous baryogenesis in warm inflation (2003)
Brandenberger, Robert H., Yamaguchi, Masahide
We discuss spontaneous baryogenesis in the warm inflation scenario. In contrast with standard inflation models, radiation always exists in the warm inflation scenario, and the inflaton must be...
Generation of cosmological large lepton asymmetry from a rolling scalar field (2002)
We propose a new scenario to simultaneously explain a large lepton asymmetry and a small baryon asymmetry. We consider a rolling scalar field and its derivative coupling to the lepton number current....
Quantitative evolution of global strings from the Lagrangian viewpoint (2002)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We clarify the quantitative nature of the cosmological evolution of a global string network, that is, the energy density, peculiar velocity, velocity squared, Lorentz factor, formation rate of loops,...
Lagrangian evolution of global strings (2002)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We establish a method to trace the Lagrangian evolution of extended objects consisting of a multicomponent scalar field in terms of a numerical calculation of field equations in three dimensional...
Large lepton asymmetry from Q-balls (2002)
Kawasaki, M., Takahashi, Fuminobu, Yamaguchi, Masahide
We propose a scenario which can explain large lepton asymmetry and small baryon asymmetry simultaneously. Large lepton asymmetry is generated through Affleck-Dine (AD) mechanism and almost all the...
Double Inflation in Supergravity and Primordial Black Holes Formation (2002)
In this talk we propose a natural double inflation model in supergravity. Chaotic inflation first takes place by virtue of the Nambu-Goldstone-like shift symmetry. During chaotic inflation, an...
Supersymmetric topological inflation model (2001)
Kawasaki, M., Yamaguchi, Masahide
We propose a topological inflation model in supergravity. In this model, the vacuum expectation value (VEV) of a scalar field takes a value much larger than the gravitational scale $M_{G} \simeq 2.4...
Scaling property and peculiar velocity of global monopoles (2001)
We investigate the scaling property of global monopoles in the expanding universe. By directly solving the equations of motion for scalar fields, we follow the time development of the number density...
We investigate the recently proposed natural double inflation model in supergravity. Chaotic inflation first takes place by virtue of the Nambu-Goldstone-like shift symmetry. During chaotic...
Cosmological Evolution of Global Monopoles (2001)
We investigate the cosmological evolution of global monopoles in the radiation dominated (RD) and matter dominated (MD) universes by numerically solving field equations of scalar fields. It is shown...
Natural Double Inflation in Supergravity (2001)
We propose a natural double inflation model in supergravity. In this model, chaotic inflation first takes place by virtue of the Nambu-Goldstone-like shift symmetry, which guarantees the absence of...
Natural Chaotic Inflation in Supergravity and Leptogenesis (2000)
Kawasaki, M., Yamaguchi, Masahide, Yanagida, T.
We comprehensively investigate a chaotic inflation model proposed recently in the framework of supergravity. In this model, the form of K\"ahler potential is determined by a symmetry, that is, the...
New inflation in supergravity with a chaotic initial condition (2000)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We propose a self-consistent scenario of new inflation in supergravity. Chaotic inflation first takes place around the Planck scale, which solves the longevity problem, namely, why the universe can...
Topological Inflation in Supergravity (2000)
Kawasaki, M., Sakai, Nobuyuki, Yamaguchi, Masahide, Yanagida, T.
We investigate a topological inflation model in supergravity. By means of numerical simulations, it is confirmed that topological inflation can take place in supergravity. We also show that the...
Natural Chaotic Inflation in Supergravity (2000)
Kawasaki, M., Yamaguchi, Masahide, Yanagida, T.
We propose a chaotic inflation model in supergravity. In the model the K\"ahler potential has a Nambu-Goldstone-like shift symmetry of the inflaton chiral multiplet which ensures the flatness of the...
Kinetically Driven Quintessence (1999)
Chiba, Takeshi, Okabe, Takahiro, Yamaguchi, Masahide
Recently, a novel class of models for inflation has been found in which the inflationary dynamics is driven solely by (non-canonical) kinetic terms rather than by potential terms. As an obvious...
Evolution of a global string network in a matter dominated universe (1999)
Yamaguchi, Masahide, Yokoyama, Jun'ichi, Kawasaki, M.
We evolve the network of global strings in the matter-dominated universe by means of numerical simulations. The existence of the scaling solution is confirmed as in the radiation-dominated universe...
Scaling Property of the global string in the radiation dominated universe (1999)
We investigate the evolution of the global string network in the radiation dominated universe by use of numerical simulations in 3+1 dimensions. We find that the global string network settles down to...
Extended Open Inflation (1999)
Chiba, Takeshi, Yamaguchi, Masahide
We present a new type of one-field models for open inflation utilizing a nonminimally coupled scalar field with polynomial potentials in which the Coleman-de Luccia instanton does exist and slow-roll...
Initial condition for new inflation in supergravity (1999)
Asaka, T., Kawasaki, M., Yamaguchi, Masahide
We study the initial value problem of new inflation models in the scheme of supergravity. We find that an inflaton generally acquires a mass of the order of the Hubble parameter via gravitationally...
Evolution of Axionic Strings and Spectrum of Axions Radiated from Them (1998)
Yamaguchi, Masahide, Kawasaki, M., Yokoyama, Jun'ichi
Cosmological evolution of axionic strings is investigated by numerically solving field equations of a complex scalar field in 3+1 dimensions. It is shown that the global strings relax to the scaling...
Asaka, T., Kawasaki, M., Yamaguchi, Masahide
We investigate cosmological moduli problem in the gauge-mediated supersymmetry breaking (GMSB). A mini-inflation (oscillating inflation) takes place when a scalar field corresponding to the flat...
Numerical analysis of formation and evolution of global strings in 2+1 dimensions (1998)
Yamaguchi, Masahide, Yokoyama, Jun'ichi, Kawasaki, M.
We simulate the formation and the evolution of global strings taking into account the expansion of the universe and the concomitant change of the effective potential, that is, the change from the...
Probability Distribution Function of the Coarse-grained Scalar Field at Finite Temperature (1998)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We present a formalism to calculate the probability distribution function of a scalar field coarse-grained over some spatial scales with a Gaussian filter at finite temperature. As an application, we...
Numerical approach to the onset of the electroweak phase transition (1997)
Yamaguchi, Masahide, Yokoyama, Jun'ichi
We investigate whether the universe was homogeneously in the false vacuum state at the critical temperature of a weakly first-order phase transition such as the electroweak phase transition in terms...
Shibata, Fumiaki, Morikawa, Masahiro, Shiromizu, Tetsuya, Yamaguchi, Masahide
Back reaction of the particle creation on the quantum tunneling process is analyzed in real time formalism. We use quantum potential method in which whole quantum dynamics is exactly projected to a...