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Register a new userCosmic Neutrinos from Unstable Relic Particles
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We derive constraints on the relic abundance of a generic particle of mass $sim~1-10^{14}$ TeV which decays into neutrinos at cosmological epochs, using data from the Frejus and IMB nucleon decay detectors and the Flys Eye air shower array. The lifetime of such unstable particles which may constitute the dark matter today is bounded to be greater than $sim~10^{14}-10^{18}$ yr, depending on the mass. For lifetimes shorter than the age of the universe, neutrino energy losses due to scattering and the expansion redshift become important and set limits to the ability of neutrino observatories to probe the early universe.
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We investigate the so-called superWIMP scenario with gravitino as the lightest supersymmetric particle (LSP) in the context of non-standard cosmology, in particular, brane world cosmology. As a candidate of the next-to-LSP (NLSP), we examine slepton and sneutrino. Brane world cosmological effects dramatically enhance the relic density of the slepton or sneutrino NLSP, so that the NLSP with mass of order 100 GeV can provide the correct abundance of gravitino dark matter through its decay. We find that with an appropriate five dimensional Planck mass, this scenario can be realized consistently with the constraints from Big Bang Nucleosynthesis (BBN) for both NLSP candidates of slepton and sneutrino. The BBN constraints for slepton NLSP are more stringent than that for sneutrino, as the result, the gravitino must be rather warm in the slepton NLSP case. The energy density of gravitino produced by thermal scattering is highly suppressed and negligible due to the brane world cosmological effects.
We propose a new mechanism producing a non-vanishing lepton number asymmetry, based on decays of heavy Majorana neutrinos. If they are produced out of equilibrium, as occurs in preheating scenario, and are superpositions of mass eigenstates rapidly decaying, their decay rates contains interference terms provided the mass differences $Delta m$ are small compared to widths $Gamma$. The resulting lepton asymmetry, which is the analogue of the time-integrated CP asymmetry in $B^0-bar{B}^0$ system, is found to be proportional to $Delta m/Gamma$.
We forecast constraints on neutrino decay via capture of the Cosmic Neutrino Background on tritium, with emphasis on the PTOLEMY-type experiment. In particular, in the case of invisible neutrino decay into lighter neutrinos in the Standard Model and invisible particles, we can constrain not only the neutrino lifetime but also the masses of the invisible particles. For this purpose, we also formulate the energy spectra of the lighter neutrinos produced by 2-body and 3-body decays, and those of the electrons emitted in the process of the detection of the lighter neutrinos.
A new equation of state is proposed in order to describe the thermal behavior of relic neutrinos. It is based on extensions of the MIT bag model to deal with the gravitational interaction and takes in account the fermionic character of neutrinos. The results for the temperature and entropy of relic neutrinos are compared with those of the cosmic background radiation, treated as a gas of photons at the temperature of 2.726 K. In particular, it is found that the temperature of the relic neutrinos is 3/4 of that of the photon gas. The ratio between the two entropies is also estimate.
In this paper, we calculate the relic abundance of the dark matter particles when they can annihilate into sterile neutrinos with the mass $lesssim 100 text{ GeV}$ in a simple model. Unlike the usual standard calculations, the sterile neutrino may fall out of the thermal equilibrium with the thermal bath before the dark matter freezes out. In such a case, if the Yukawa coupling $y_N$ between the Higgs and the sterile neutrino is small, this process gives rise to a larger $Omega_{text{DM}} h^2$ so we need a larger coupling between the dark matter and the sterile neutrino for a correct relic abundance.
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