[show abstract][hide abstract] ABSTRACT: We study the evolution of curvature perturbations and the cosmic microwave background (CMB) power spectrum in the presence of an hypothesized extra anisotropic stress which might arise, for example, from the dark radiation term in brane-world cosmology. We evolve the scalar modes of such perturbations before and after neutrino decoupling and analyze their effects on the CMB spectrum. A novel result of this work is that the cancellation of the neutrino and extra anisotropic stress could lead to a spectrum of residual curvature perturbations which is similar to the observed CMB power spectrum. This implies a possible additional consideration in the determination of cosmological parameters from the CMB analysis. Comment: 13 pages, 2 figures; improved discussion
Journal of Cosmology and Astroparticle Physics 10/2009; · 6.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Possible existence of the primordial magnetic fields has affected the structure formation of the universe. In this paper it is shown that the initial conditions for density perturbations with magnetic fields derived in previous works are inconsistent with Einstein equations. We find that this inconsistency arises due to the unwanted cancellation of contributions from the magnetic fields and primordial radiations. A complete set of equations and consistent initial conditions in the long wavelength limit are given with an explicit derivation in the covariant approach with CDM frame, by newly taking into account a non-relativistic matter contribution in the radiation dominated era. By solving these equations numerically, we derive the angular spectrum of cosmic microwave background anisotropies and the matter power spectrum with magnetic fields. We find that the amplitude of the angular power spectrum of CMB anisotropies can alter at most a order of magnitude at $l \lesssim 4000$ compared with the previous results in the literature.
[show abstract][hide abstract] ABSTRACT: If a primordial magnetic field (PMF) is present during photon decoupling and afterward, a finite neutrino mass can affect all modes of the CMB. In this work, we expand on earlier studies of the scalar mode effects by constructing the vector and tensor mode equations in the presence of massive neutrinos and a PMF. We compute the power spectrum of the various modes in an illustrative example and find that the neutrino mass can significantly affect the vector and tensor modes when a PMF exists, while the effects are negligible for no PMF. The most prominent result of the present analysis is the behavior of the EE component of the tensor mode at low multipoles. For massive neutrinos the EE mode can become comparable to the observed primary anisotropy. Therefore, if and when the EE mode power spectrum is measured at low multipoles the possibility exists to place a strong constraint on the sum of the neutrino masses.
[show abstract][hide abstract] ABSTRACT: Neutrino is a tiny weakly interacting massive particle, but it has strong impacts on various cosmological and astrophysical phenomena. Neutrinos play a critical role in nucleosynthesis of light-to-heavy mass elements in core-collapse supernovae. The light element synthesis is particularly affected by neutrino oscillation (MSW) effect through the nu-process. We propose first that precise determination of sin2 2theta13 and mass hierarchy can be made by a theoretical study of the observed 7Li/11B ratio in stars and presolar grains which are produced from SN ejecta. Theoretical sensitivity in our proposed method is shown to be superior to ongoing long-baseline neutrino experiments for the parameter region 10-4
Modern Physics Letters A 01/2008; 23:2427-2442. · 1.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: Our previous work  showed that if a primordial magnetic field (PMF) was present during photon decoupling and afterward, massive neutrinos affect all modes of the CMB. This is because of the compensation of anisotropic stress between the neutrinos and the PMF. In order to study the observability of this new effect, we need careful analysis of the passive mode  generated by the PMF. Here, we focus on the polarization of the CMB and study the observability of the finite neutrino mass effect.