119080917
Large lepton asymmetry from Q -balls
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 produced lepton numbers are absorbed into Q-balls (L-balls). If the lifetime of the L-balls is longer than the onset of electroweak phase transition but shorter than the epoch of big bang nucleosynthesis (BBN), the large lepton asymmetry in the L-balls is protected from sphaleron effects. On the other hand, small (negative) lepton numbers are evaporated from the L-balls due to thermal effects, which are converted into the observed small baryon asymmetry by virtue of sphaleron effects. Large and positive lepton asymmetry of electron type is often requested from BBN. In our scenario, choosing an appropriate flat direction in the minimal supersymmetric standard model (MSSM), we can produce positive lepton asymmetry of electron type but totally negative lepton asymmetry.
121017824
Hybrid Inflation and Axionic Isocurvature Fluctuations in Supergravity
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.
16749378
MeV-scale reheating temperature and thermalization of the neutrino background
The late-time entropy production by the massive particle decay induces the various cosmological effects in the early epoch and modify the standard scenario. We investigate the thermalization process of the neutrinos after the entropy production by solving the Boltzmann equations numerically. We find that if the large entropy are produced at t $\sim$ 1 sec, the neutrinos are not thermalized very well and do not have the perfect Fermi-Dirac distribution. Then the freeze-out value of the neutron to proton ratio is altered considerably and the produced light elements, especially He4, are drastically changed. Comparing with the observational light element abundances, we find that $T_R$ 2.5 MeV - 4 MeV, for the hadronic branching ratio $B_h = 10^{-2} - 1$. Possible influence of late-time entropy production on the large scale structure formation and temperature anisotropies of cosmic microwave background is studied. It is expected that the future satellite experiments (MAP and PLANCK) to measure anisotropies of cosmic microwave background radiation temperature can detect the vestige of the late-time entropy production as a modification of the effective number of the neutrino species $N_{\nu}^{\rm eff}$.
119397472
Evolution of Axionic Strings and Spectrum of Axions Radiated from Them
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 solution with a significantly smaller number density than the case of local strings. The power spectrum of axions radiated from them is calculated from the simulation data, which is found to be highly peaked around the Hubble scale, and a more accurate constraint on the Peccei-Quinn breaking scale is obtained.
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.
14714748
Study of the Long-Term Stability of Two Anomalous X-Ray Pulsars, 4U 0142+61 and 1E 1048.1?5937, with ASCA
We present new observations of two anomalous X-ray pulsars (AXPs), 4U 0142+61 and 1E 1048.1-5937, made in 1998 with ASCA. The energy spectrum of each of these two AXPs is found to consist of two components, a power-law and a blackbody emission from the neutron star surface. These observations, when compared with earlier ASCA observations in 1994, show remarkable stability in the intensities, spectral shapes, and pulse profiles. However, we find that the spin-down rate in 1E 1048.1-5937 is not constant. In this source, we have clearly identified three epochs with spin-down rates different from each other and from the average value. This has very strong implications for the magnetar hypothesis for AXPs. We also note that the spin-down rate and its variations in 1E 1048.1-5937 are much larger than can normally be produced by an accretion disk with a very low mass accretion rate corresponding to its low X-ray luminosity.
119940843
Performance of the X-ray CCDs aboard the ASCA satellite after 5-year operation in space
Abstract The performance of the charge coupled devices on-board the ASCA satellite has been traced for five years after the launch. We found the gradual increase of the dark current and the decrease of the charge transfer efficiency. These changes may be explained by charge traps due to the radiation damage. The nature of the radiation damage is investigated in detail using various methods.
14658153
ASCA Observations of the Supernova Remnant IC 443: Thermal Structure and Detection of Overionized Plasma
We present the results of X-ray spatial and spectral studies of the "mixed-morphology" supernova remnant IC 443 using ASCA. IC 443 has a center-filled image in the X-ray band, contrasting with the shell-like appearance in radio and optical bands. The overall X-ray emission is thermal, not from a synchrotron nebula. We observed IC 443 three times with ASCA, covering the whole remnant. From the image analysis, we find that the softness-ratio map reveals a shell-like structure. At the same time, its spectra require two (1.0 and 0.2 keV) plasma components; the emission of the 0.2 keV plasma is stronger in the region near the shell than in the center. These results can be explained by a simple model that IC 443 has a hot (1.0 keV) interior surrounded by a cool (0.2 keV) outer shell. From the emission measures, we infer that the 0.2 keV plasma is denser than the 1.0 keV plasma, suggesting pressure equilibrium between the two. In addition, we find that the ionization temperature of sulfur, obtained from the H-like to He-like Kα intensity ratio, is 1.5 keV, significantly higher than the gas temperature of 1.0 keV suggested from the continuum spectrum. The same can be concluded for silicon. Neither an additional, hotter plasma component nor a multitemperature plasma successfully account for this ratio, and we conclude that the 1.0 keV plasma is overionized. This is the first time that overionized gas has been detected in a supernova remnant (SNR). For the gas to become overionized in the absence of a photoionizing flux, it must cool faster than the ions recombine. Thermal conduction from the 1.0 keV plasma to the 0.2 keV plasma could cause the 1.0 keV plasma to become overionized, which is plausible within an old (3 × 104 yr) SNR.