Influence of Plasma Collective Effects on Cosmological Evolution

It is well-known that the universe was in a plasma state both before decoupling and after reionization. However, the conventional wisdom has been that the plasma effects are largely Debye-shielded and can thus be safely ignored when considering large scale evolutions. Recently we showed that large scale structure formation in the universe may actually be suppressed by the plasma collective effect. Indeed, observational data indicate that the conventional theoretical formula tends to overestimate the matter power spectrum at scales $k>1h{\rm Mpc}^{-1}$. In this paper, we further develop our theory through a more thorough and general derivation of the Maxwell-Einstein-Boltzmann equation. In addition to baryon density perturbation post reionization, we apply this general formulation to investigate the possible plasma effect on CMB anisotropy. As expected, while the plasma effect does render an observable effect to the former, its impact on the latter is totally negligible.Comment: 8 pages, no figur

Plasma Suppression of Large Scale Structure Formation in the Universe

We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce a residual long-range electrostatic potential which, working together with the baryon thermal pressure, would counter the gravitational collapse. As a result the effective Jean's length, $\tilde{\lambda}_J$, is increased by a factor, $\tilde{\lambda}_J/\lambda_J=\sqrt{8/5}$, relative to the conventional one. For scales smaller than the effective Jean's scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect depend on the starting time and the initial temperature of reionization, but roughly lie in the range $0.5 h{\rm Mpc}^{-1}< k$, which corresponds to the region of the Lyman-$\alpha$ forest from the inter-galactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach $1-(\Omega_{dm}/\Omega_m)^2\sim 1-(5/6)^2\sim 30$.Comment: 4 pages and 2 figure

Signatures of the neutrino mass hierarchy in supernova neutrinos

The undetermined neutrino mass hierarchy may leave an observable imprint on the neutrino fluxes from a core-collapse supernova (SN). The interpretation of the observables, however, is subject to the uncertain SN models and the flavor conversion mechanism of neutrinos in a SN. We attempt to propose a qualitative interpretation of the expected neutrino events at terrestrial detectors, focusing on the accretion phase of the neutrino burst. The flavor conversions due to neutrino self-interaction, the MSW effect, and the Earth regeneration effect are incorporated in the calculation. It leads to several distinct scenarios that are identified by the neutrino mass hierarchies and the collective flavor transitions. Consequences resulting from the variation of incident angles and SN models are also discussed.Comment: 15 pages, 9 figure

On Possibility of Determining Neutrino Mass Hierarchy by the Charged-Current and Neutral-Current Events of Supernova Neutrinos in Scintillation Detectors

One of the unresolved mysteries in neutrino physics is the neutrino mass hierarchy. We present a new method to determine neutrino mass hierarchy by comparing the events of inverse beta decays (IBD), $\bar{\nu}_e + p\rightarrow n + e^+$, and neutral current (NC) interactions, $\nu(\overline{\nu}) + p\rightarrow\nu(\overline{\nu}) + p$, of supernova neutrinos from accretion and cooling phases in scintillation detectors. Supernova neutrino flavor conversions depend on the neutrino mass hierarchy. On account of Mikheyev-Smirnov-Wolfenstein effects, the full swap of $\bar{\nu}_e$ flux with the $\bar{\nu}_x$ ($x=\mu,~\tau$) one occurs in the inverted hierarchy, while such a swap does not occur in the normal hierarchy. In consequence, the ratio of high energy IBD events to NC events for the inverted hierarchy is higher than in the normal hierarchy. Since the luminosity of $\bar{\nu}_e$ is larger than that of $\nu_x$ in accretion phase while the luminosity of $\bar{\nu}_e$ becomes smaller than that of $\nu_x$ in cooling phase, we calculate this ratio for both accretion and cooling phases. By analyzing the change of this event ratio from accretion phase to cooling phase, one can determine the neutrino mass hierarchy.Comment: one column, 16 pages, 3 figure

Neutrino Flavor Ratio on Earth and at Astrophysical Sources

We present the reconstruction of neutrino flavor ratios at astrophysical sources. For distinguishing the pion source and the muon-damped source to the 3$\sigma$ level, the neutrino flux ratios, $R\equiv\phi(\nu_\mu)/(\phi(\nu_e)+\phi(\nu_\tau))$ and $S\equiv\phi(\nu_e)/\phi(\nu_\tau)$, need to be measured in accuracies better than 10%.Comment: 3 pages, 8 figures. Talk presented by T.C. Liu in ERICE 2009, Sicily