5 research outputs found
Decay and Decoupling of heavy Right-handed Majorana Neutrinos in the L-R model
Heavy right-handed neutrinos are of current interest. The interactions and
decay of such neutrinos determine their decoupling epoch during the evolution
of the universe. This in turn affects various observable features like the
energy density, nucleosynthesis, CMBR spectrum, galaxy formation, and
baryogenesis. Here, we consider reduction of right-handed electron-type
Majorana neutrinos, in the left-right symmetric model, by the WR+ - WR- channel
and the channel originating from an anomaly, involving the SU(2)R gauge group,
as well as decay of such neutrinos. We study the reduction of these neutrinos
for different ranges of left-right model parameters, and find that, if the
neutrino mass exceeds the right-handed gauge boson mass, then the neutrinos
never decouple for realistic values of the parameters, but, rather, decay in
equilibrium. Because there is no out-of-equilibrium decay, no mass bounds can
be set for the neutrinos.Comment: Latex, 16 pages, No figures. Some additions in the text and
references. Conclusions unaffected. To appear in Eur. Phys. J.
Decoupling of Massive Right-handed Neutrinos
We investigate the effect of B+L - violating anomalous generation of massive
right-handed neutrinos on their decoupling, when the right-handed neutrino mass
is considerably greater than the right-handed gauge boson masses. Considering
normal annihilation channels, the Lee-Weinberg type of calculation, in this
case, gives an upper bound of about 700 Gev, which casts doubt on the existence
of such a right-handed neutrino mass greater than right-handed gauge boson
masses. We examine the possibility that a consideration of anomalous effects
related to the SU(2)_R gauge group may turn this into a lower bound of the
order of 100 Tev.Comment: 28 Pages, Latex, 2 figure
Late-time Entropy Production from Scalar Decay and Relic Neutrino Temperature
Entropy production from scalar decay in the era of low temperatures after
neutrino decoupling will change the ratio of the relic neutrino temperature to
the CMB temperature, and, hence, the value of N_eff, the effective number of
neutrino species. Such scalar decay is relevant to reheating after thermal
inflation, proposed to dilute massive particles, like the moduli and the
gravitino, featuring in supersymmetric and string theories. The effect of such
entropy production on the relic neutrino temperature ratio is calculated in a
semi-analytic manner, and a recent lower bound on this ratio, obtained from the
WMAP satellite and 2dF galaxy data, is used to set a lower bound of ~ 1.5 x
10^-23 Gev on the scalar decay constant, corresponding to a reheating
temperature of about 3.3 Mev.Comment: 13 pages, to appear in PR