Neutrino mass from cosmology: Impact of high-accuracy measurement of the Hubble constant (2009)
Sekiguchi, Toyokazu, Ichikawa, Kazuhide, Takahashi, Tomo, Greenhill, Lincoln
Non-zero neutrino mass would affect the evolution of the Universe in observable ways, and a strong constraint on the mass can be achieved using combinations of cosmological data sets. We focus on the...
Density Fluctuations in Thermal Inflation and Non-Gaussianity (2009)
Kawasaki, Masahiro, Takahashi, Tomo, Yokoyama, Shuichiro
We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 $e$-folds after the standard inflation, the time of horizon-exit during inflation...
Effect of Background Evolution on the Curvaton Non-Gaussianity (2009)
Enqvist, Kari, Takahashi, Tomo
We investigate how the background evolution affects the curvature perturbations generated by the curvaton, assuming a curvaton potential that may deviate slightly from the quadratic one, and...
Cosmology with Long-Lived Charged Massive Particles (2009)
Kohri, Kazunori, Takahashi, Tomo
We investigate the evolution of the bound state of negatively charged massive particles (CHAMPs) with light elements and discuss its cosmological consequences and the constraint. By numerically...
Constraining light gravitino mass from cosmic microwave background (2009)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Takahashi, Tomo
We investigate the possibilities of constraining the light gravitino mass m3/2 from future cosmic microwave background (CMB) surveys. A model with light gravitino with the mass m3/2< O (10)eV is of...
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,...
The Subdominant Curvaton (2009)
Enqvist, Kari, Nurmi, Sami, Rigopoulos, Gerasimos, Taanila, Olli, Takahashi, Tomo
We present a systematic study of the amplitude of the primordial perturbation in curvaton models with self-interactions, treating both renormalizable and non-renormalizable interactions. In...
Constraining Light Gravitino Mass from Cosmic Microwave Background (2009)
Ichikawa, Kazuhide, Kawasaki, Masahiro, Nakayama, Kazunori, Sekiguchi, Toyokazu, Takahashi, Tomo
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}
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...
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...
Constraints on Neutrino Masses from Weak Lensing (2008)
Ichiki, Kiyotomo, Takada, Masahiro, Takahashi, Tomo
The weak lensing (WL) distortions of distant galaxy images are sensitive to neutrino masses by probing the suppression effect on clustering strengths of total matter in large-scale structure. We use...
Non-Gaussianity and Baryonic Isocurvature Fluctuations in the Curvaton Scenario (2008)
We discuss non-Gaussianity and baryonic isocurvature fluctuations in the curvaton scenario, assuming that the baryon asymmetry of the universe originates only from the decay products of the inflaton....
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...
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...
Signatures of Non-Gaussianity in the Curvaton Model (2008)
Enqvist, Kari, Takahashi, Tomo
We discuss the signatures of non-Gaussianity in the curvaton model where the potential includes also a non-quadratic term. In such a case the non-linearity parameter f_NL can become very small, and...
Probing the Effective Number of Neutrino Species with Cosmic Microwave Background (2008)
Ichikawa, Kazuhide, Sekiguchi, Toyokazu, Takahashi, Tomo
We discuss how much we can probe the effective number of neutrino species N_nu with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI and BOOMERANG experiments, we obtain a...
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...
Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast (2007)
Ichikawa, Kazuhide, Sekiguchi, Toyokazu, Takahashi, Tomo
We studied a constraint on the primordial helium abundance Y_p from current and future observations of CMB. Using the currently available data from WMAP, ACBAR, CBI and BOOMERANG, we obtained the...
The Hubble constant and dark energy from cosmological distance measures (2007)
Ichikawa, Kazuhide, Takahashi, Tomo
We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and...
Constraints on Generalized Dark Energy from Recent Observations (2007)
Ichiki, Kiyotomo, Takahashi, Tomo
Effects of a generalized dark energy fluid is investigated on cosmic density fluctuations such as cosmic microwave background. As a general dark energy fluid, we take into consideration the...
Dark Energy Parametrizations and the Curvature of the Universe (2006)
Ichikawa, Kazuhide, Takahashi, Tomo
We investigate observational constraints on the curvature of the universe not restricting ourselves to a cosmological constant as dark energy, in particular allowing a dark energy equation of state...
Cosmological Avatars of the Landscape II: CMB and LSS Signatures (2006)
Holman, R., Mersini-Houghton, Laura, Takahashi, Tomo
This is the second paper in the series that confronts predictions of a model of the landscape with cosmological observations. We show here how the modifications of the Friedmann equation due to the...
Cosmological Avatars of the Landscape I: Bracketing the SUSY Breaking Scale (2006)
Holman, R., Mersini-Houghton, L., Takahashi, Tomo
We investigate the effects of quantum entanglement between our horizon patch and others due to the tracing out of long wavelength modes in the wavefunction of the Universe as defined on a particular...
Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing (2006)
Hisano, Junji, Inoue, Kaiki Taro, Takahashi, Tomo
We propose to observe QSO-galaxy strong lens systems to give a new constraint on the damping scale of the initial fluctuations. We find that the future observation of submilliarc scale astrometric...
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...
Ichikawa, Kazuhide, Kawasaki, Masahiro, Sekiguchi, Toyokazu, Takahashi, Tomo
We investigate how the nature of dark energy affects the determination of the curvature of the universe from recent observations. For this purpose, we consider the constraints on the matter and dark...
Revisiting the Constraint on the Helium Abundance from CMB (2006)
Ichikawa, Kazuhide, Takahashi, Tomo
We revisit the constraint on the primordial helium mass fraction Yp from observations of cosmic microwave background (CMB) alone. By minimizing chi square of recent CMB experiments over 6 other...
Dark Energy Evolution and the Curvature of the Universe from Recent Observations (2005)
Ichikawa, Kazuhide, Takahashi, Tomo
We discuss the constraints on the time-varying equation of state for dark energy and the curvature of the universe using observations of type Ia supernovae from Riess et al. and the most recent...
Ichikawa, Kazuhide, Takahashi, Tomo
We discuss the possibilities of the simultaneous determination of the neutrino masses and the evolution of dark energy from future cosmological observations such as cosmic microwave background (CMB),...
Implications of the Curvaton on Inflationary Cosmology (2005)
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...
Relaxing Constraints on Inflation Models with Curvaton (2005)
Moroi, Takeo, Takahashi, Tomo, Toyoda, Yoshikazu
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...
Correlated Isocurvature Fluctuation of Quintessence and Curvaton Scenario (2004)
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...
Making waves on CMB power spectrum and inflaton dynamics (2004)
Kawasaki, Masahiro, Takahashi, Fuminobu, Takahashi, Tomo
We discuss cosmic microwave background anisotropies in models with an unconventional primordial power spectrum. In particular, we consider an initial power spectrum with some ``spiky'' corrections....
Bigger Rip with No Dark Energy (2004)
Frampton, Paul H., Takahashi, Tomo
By studying a modified Friedmann equation which arises in an extension of general relativity which accommodates a time-dependent fundamental length $L(t)$, we consider cosmological models where the...
Candidates for Inflaton in Quiver Gauge Theory (2004)
Frampton, Paul H., Takahashi, Tomo
The inflaton necessary to implement the mechanism of inflationary cosmology has natural candidates in quiver gauge theory. We discuss the dimensionless coefficients of quartic couplings and enumerate...
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...
Cosmic Degeneracy with Dark Energy Equation of State (2003)
Crooks, James L., Dunn, James O., Frampton, Paul H., Norton, Heather R., Takahashi, Tomo
We discuss a degeneracy between the geometry of the universe and the dark energy equation of state $w_{\rm X}$ which exists in the power spectrum of the cosmic microwave background. In particular,...
Robustness and Predictivity of 4 TeV Unification (2003)
Frampton, Paul H., Rohm, Ryan M., Takahashi, Tomo
The stability of the predictions of two of the standard model parameters, $\alpha_3(M_Z)$ and $\sin^2 \theta(M_Z)$, in a $M_U \sim 4$ TeV unification model is examined. It is concluded that varying...
The Fate of Dark Energy (2002)
Frampton, Paul H., Takahashi, Tomo
By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary...
Cosmic Microwave Background from Late-Decaying Scalar Condensations (2002)
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....
Cosmic Density Perturbations from Late-Decaying Scalar Condensations (2002)
We study the cosmic density perturbations induced from fluctuation of the amplitude of late-decaying scalar condensations (called \phi) in the scenario where the scalar field \phi once dominates the...
Cosmic Microwave Background Anisotropy with Late Time Entropy Production (2001)
We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field \phi once dominates the universe, the CMB we observe today is from the decay of \phi and...
Cosmic Microwave Background Anisotropy in models with Quintessence (2001)
We study the Cosmic Microwave Background (CMB) anisotropies produced by cosine-type quintessence models. In our analysis, effects of the adiabatic and isocurvature fluctuations are both taken into...
Effects of Cosmological Moduli Fields on Cosmic Microwave Background (2001)
We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field \phi once dominates the universe, the CMB we observe today is from the decay of \phi and...
Isocurvature Fluctuations in Tracker Quintessence Models (2001)
Kawasaki, Masahiro, Moroi, Takeo, Takahashi, Tomo
We consider effects of the isocurvature perturbation in the framework of the tracker-type quintessence models. During the inflation, fluctuations in the amplitude of the quintessence field are...
Cosmic Microwave Background Anisotropy with Cosine-Type Quintessence (2001)
Kawasaki, Masahiro, Moroi, Takeo, Takahashi, Tomo
We study the Cosmic Microwave Background (CMB) anisotropies produced by cosine-type quintessence models. In our analysis, effects of the adiabatic and isocurvature fluctuations are both taken into...
Constraints on Natural Inflation from Cosmic Microwave Background (2000)
We study constraints on the natural inflation model from the cosmic microwave background radiation (CMBR). Inflaton \phi for the natural inflation has a potential of the form...