119545397
Comments on the evolution of strongly degenerate neutrinos in the early universe
We reconsider the evolution of strongly degenerate neutrinos in the early universe. Our chief concern is the validity of the entropy conservation after the neutrino annihilation process has frozen out (so that the establishment of chemical equilibrium is not trivial). We argue that the entropy indeed conserves because elastic scattering keeps the neutrino and antineutrino distribution functions in the equilibrium form and the sum of their chemical potential keeps zero even after the neutrino annihilation freeze-out. We also simulate the evolution of the degenerate neutrino spectrum to support the argument. We conclude that the change in the neutrino degeneracy parameter when the relativistic degrees of freedom in the universe decreases is calculated using the entropy conservation and the lepton number conservation without worrying about at what temperature the neutrino annihilation process freezes out.
118567145
Constraining the time variation of the coupling constants from cosmic microwave background: effect of ΛQCD
We investigate constraints on the time variation of the fine structure constant between the recombination epoch and the present epoch, Δα/α≡(αrec−αnow)/αnow, from cosmic microwave background (CMB) taking into account simultaneous variation of other physical constants, namely the electron mass me and the proton mass mp. In other words, we consider the variation of Yukawa coupling and the QCD scale ΛQCD in addition to the electromagnetic coupling. We clarify which parameters can be determined from CMB temperature anisotropy in terms of singular value decomposition. Assuming a relation among variations of coupling constants governed by a single scalar field (the dilaton), the 95 % confidence level (C.L.) constraint on Δα/α is found to be −8.28 × 10−3 < Δα/α < 1.81 × 10−3, which is tighter than the one obtained by considering only the change of α and me. We also obtain the constraint on the time variation of the proton-to-electron mass ratio μ≡mp/me to be −0.52 < Δμ/μ < 0.17 (95 % C.L.) under the same assumption. Finally, we also implement a forecast for constraints from the PLANCK survey.
19758444
Oscillation effects on thermalization of the neutrinos in the universe with low reheating temperature
We study how the oscillations of the neutrinos affect their thermalization process during the reheating period with temperature O(1) MeV in the early universe. We follow the evolution of the neutrino density matrices and investigate how the predictions of big bang nucleosynthesis vary with the reheating temperature. For the reheating temperature of several MeV, we find that including the oscillations makes different predictions, especially for {sup 4}He abundance. Also, the effects on the lower bound of the reheating temperature from cosmological observations are discussed.
40824918
Constraining the variation of the coupling constants with big bang nucleosynthesis
We consider the possibility of the coupling constants of the $SU(3)\times SU(2)\times U(1)$ gauge interactions at the time of big bang nucleosynthesis having taken different values from what we measure at present, and investigate the allowed difference requiring the shift in the coupling constants not violate the successful calculation of the primordial abundances of the light elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a model in which their relative variations are governed by a single scalar field, dilaton, as found in string theory. The results include a limit on the fine structure constant $-6.0\times10^{-4}<\Delta\alpha_{EM}/\alpha_{EM}<1.5\times10^{-4}$, which is two orders stricter than the limit obtained by considering the variation of $\alpha_{EM}$ alone.
11252959
Big bang nucleosynthesis with a varying fine structure constant and nonstandard expansion rate
We calculate the primordial abundances of light elements produced during big bang nucleosynthesis when the fine structure constant and/or the cosmic expansion rate take nonstandard values. We compare them with the recent values of observed D, ${}^{4}\mathrm{He},$ and ${}^{7}\mathrm{Li}$ abundances, which show a slight inconsistency among themselves in the standard big bang nucleosynthesis scenario. This inconsistency is not solved by considering either a varying fine structure constant or a nonstandard expansion rate separately but solutions are found by their simultaneous existence.
119036206
Constraint on the effective number of neutrino species from the WMAP and SDSS LRG power spectra
We derive a constraint on the effective number of neutrino species Nν from the cosmic microwave background power spectrum of the WMAP and galaxy clustering power spectrum of the SDSS luminous red galaxies (LRGs). Using these two latest data sets of CMB and galaxy clustering alone, we obtain the limit 0.9   2 MeV.
14624888
Solution Generating Technique for Noncommutative Orbifolds
We propose the relationships between the noncommutative solitons and the (fractional) D-branes on the C 2 /Z N orbifold and extend the solution generating technique for the orbifold. As applications, we determine how tachyon condensations occur in various D-D systems on the orbifolds. The calculations give results consistent with BSFT. The extended solution generating technique enables us to calculate more general decay modes of D-D systems.