arXiv subjects
Publications and source records attributed to Sarira Sahu.
We study the production of electron density waves by neutrinos propagating through a plasma. We treat this process in field theoretically as a Cerenkov emission of phonons (quanta of electron density waves) by neutrinos. We compute the energy transfered to the plasma by the neutrinos and apply it to the shock wave revival problem of supernovae.
We have calculated the dispersion relation for the high energy cosmic rays (protons, electrons and neutrinos) propagating in the Bose gas as well as Bose condensate medium of the pseudo-scalar particles. For cosmic rays propagating in the Bose gas, the mass of the particle will decrease and this is proportional to the boson density in the medium. If the propagating fermion is massless then it will develop an imaginary mass and thus will be absorbed in the medium. But if the condition $m^2/m_ϕp_0\simeq 1$ is satisfied, then the cosmic rays will propagate freely without loosing energy in the Bose condensate medium.
We show that in a supernova core the longitudinal photon (plasmon) has a space-like dispersion and Cerenkov absorption and emission of such photons is kinematically allowed. If the neutrino has a non-zero magnetic moment, then helicity flipping Cerenkov absorption of a plasmon $ν_L+γ\toν_R$ is the most efficient cooling mechanism of the supernova core, and this allows us to put a restrictive bound on the neutrino magnetic moment $μ_ν~<~0.7\times 10^{-13}μ_B$.
The helicity changing Cerenkov radiation in a supernova core was used earlier to put a restrictive bound on the neutrino magnetic moment. Subsequently it was pointed out, that this result was based on a numerical error in the calculationn of the refractive index of the SN core and using the correct numbers it was shown that the photons in a SN core do not have a space-like dispersion relation, so the Cerenkov process would not occur. Here we show that the earlier estimate of refractive index was based on the thermodynamic formula for susceptibility which is inapplicable for real photons or plasmons. However in an ultrarelativistic plasma the plasmon has a space-like branch in the dispersion relation hence the Cerenkov radiation of a plasmon is kinematically allowed. We show that the observations of neutrino flux from SN1987A put a constraint on the neutrino magnetic moment $μ_ν < 0.6\times 10^{-11}μ_B$.
The active-sterile neutrino conversion probability is calculated for neutrino propagating in a medium in the presence of random magnetic field fluctuations. Necessary condition for the probability to be positive definite is obtained. Using this necessary condition we put constraint on the neutrino magnetic moment from active-sterile electron neutrino conversion in the early universe hot plasma and in supernova.
In a relativistic plasma neutrino can emit plasmons by the Cerenkov process which is kinematically allowed for a range of frequencies for which refractive index is greater than one. We have calculated the rate of energy emission by this process. We compute the energy deposited in a stalled supernova shock wave by the Cerenkov process and find that it is much smaller than the Bethe-Wilson mechanism.
The momentum projected SU(3) Chiral Color Dielectric Model (CCDM) is employed to calculate the charge root mean square radii and charge distributions of hyperons. We compare our result with Skyrme, MIT bag and Cloudy Bag model results. The charge distribution of $Λ$ in CCDM is similar to that of Skyrme Model prediction.
We study the low energy effective field theory of fermions with electric and magnetic dipole moments at finite temperature. We find that at one loop there is an interaction term of the Chern-Simon form ${\cal L_I}=m_μ\>A_ν{\tilde F}^{μν}$. The four vector $m_μ\simeq d_i μ_i m_i^2 ~{\partial_μ}\>(ln T)$ is interpreted as a Chern- Simon type mass of photons, which is determined by the electric (magnetic) dipole moments $d_i$ ($μ_i$) of the fermions in the vacuum polarisation loop diagram. The physical consequence of such a photon mass is that, photons of opposite circular polarisations, propagating through a hot medium, have different group velocities. We estimate that the time lag between the arrival times of the left and right circularly polarised light signals from pulsars. If the light propagates through a hot plasma (where the temperature in some regions is $T \sim 100 MeV$) then the time lag between the two circularly polarised signals of frequency $ω$ will be $Δt(ω) \simeq 10^{-6} /ω$. It may be possible to observe this effect in pulsar signals which propagate through nebula at high temperatures.