Tomo Takahashi

Effects of cosmological moduli fields on cosmic microwave background

Abstract We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field φ once dominates the universe, the CMB we observe today is from the decay of φ and 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.

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 classes 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.

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.

Dark energy evolution and the curvature of the universe from recent observations

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 Supernova Legacy Survey (SNLS), the baryon acoustic oscillation peak detected in the SDSS luminous red galaxy survey and cosmic microwave background. Because of the degeneracy among the parameters which describe the time dependence of the equation of state and the curvature of the universe, the constraints on them can be weakened when we try to constrain them simultaneously, in particular, when we use a single observational data. However, we show that we can obtain relatively severe constraints when we use all data sets from observations above even if we consider the time-varying equation of state and do not assume a flat universe. We also found that the combined data set favors a flat universe even if we consider the time variation of the dark energy equation of state.

Implications of dark energy parametrizations for the determination of the curvature of the universe

We investigate how the nature of dark energy affects the determination of the curvature of the universe, using recent observations. For this purpose, we consider the constraints on the matter and dark energy density using observations of type Ia supernovae, the baryon acoustic oscillation peak and the cosmic microwave background with dark energy equations of state of several types. Although it is usually said that the combination of current observations favours a flat universe, we found that a relatively large parameter space allows the universe to be open for a particular model of dark energy. We also discuss what kind of dark energy model or prior allows a non-flat universe.

Reexamining the constraint on the helium abundance from the CMB

We revisit the constraint on the primordial helium mass fraction

Photoproduction of η-mesons off C and Cu nuclei for photon energies below 1.1 GeV

{Y}_{p}

Making waves on CMB power spectrum and inflaton dynamics

from observations of cosmic microwave background (CMB) alone. By minimizing

Isocurvature fluctuations in tracker quintessence models

{\ensuremath{\chi}}^{2}

Charge asymmetry of hadronic events in e+e− annihilation at √s=57.9 GeV

of recent CMB experiments over 6 other cosmological parameters, we obtained rather weak constraints as