arXiv subjects

Srubabati Goswami

Publications and source records attributed to Srubabati Goswami.

136 records · Page 8Linked to original sources

arXiv2001

MSW mediated neutrino decay and the solar neutrino problem

We investigate the solar neutrino problem assuming simultaneous presence of MSW transitions in the sun and neutrino decay on the way from sun to earth. We do a global $χ^2$-analysis of the data on total rates in Cl, Ga and Superkamiokande (SK) experiments and the SK day-night spectrum data and determine the changes in the allowed region in the $\dm - \tan^2θ$ plane in presence of decay. We also discuss the implications for unstable neutrinos in the SNO experiment.

hep-ph↗

arXiv2000

Status of the neutrino decay solution to the solar neutrino problem

We re-examine the neutrino decay solution to the solar neutrino problem in the light of the SuperKamiokande (SK) data. For the decay solution the SK spectrum data by its own can provide a fit comparable to the fit obtained from the MSW solution. However when one combines the results from the total rates of the $^{37}{Cl}$ and $^{71}{Ga}$ experiments the fit becomes much poorer.

hep-ph↗

arXiv2000

Is neutrino decay really ruled out as a solution to the atmospheric neutrino problem from Super-Kamiokande data?

In this paper we do a detailed $χ^2$-analysis of the 848 days of Super-Kamiokande(SK) atmospheric neutrino data under the assumptions of $ν_μ- ν_τ$ oscillation and neutrino decay. For the latter we take the most general case of neutrinos with non-zero mixing and consider the possibilities of the unstable component in $ν_μ$ decaying to a state with which it mixes (scenario (a)) and to a sterile state with which it does not mix (scenario (b)). In the first case $Δm^2$ (mass squared difference between the two mass states which mix) has to be $>$ 0.1 $eV^2$ from constraints on $K$ decays while for the second case $Δm^2$ can be unconstrained. For case (a) $Δm^2$ does not enter the $χ^2$-analysis while in case (b) it enters the $χ^2$-analysis as an independent parameter. In scenario (a) there is \dm averaged oscillation in addition to decay and this gets ruled out at 100.0% C.L. by the latest SK data. Scenario (b) on the other hand gives a reasonably good fit to the data for \dm $\sim 0.001 ~eV^2$.

hep-ph↗

arXiv1999

Vacuum Oscillation solutions of the Solar Neutrino Problem : A status Report

We re-examine vacuum oscillation solutions of the solar neutrino problem taking (a) the results on total rates, electron energy spectrum, and the seasonal variations from the 708 day SuperKamiokande data and (b) those on total rates from the Chlorine and Gallium experiments. Best fit values for the mixing angle and mass splitting are found for oscillations to sequential and sterile neutrinos and the 90% C.L. allowed regions are determined.

hep-ph↗

arXiv1998

Constraints on Neutrino Mixing from r-process Nucleosynthesis in Supernovae

In this paper we note that for neutrino mass squared differences in the range $10^{-4} - 10^{-1} eV^2$, vacuum neutrino oscillations can take place between the neutrino-sphere and the weak freeze-out radius in a type II supernova. Requiring that such oscillations are consistent with the r-process nucleosynthesis from supernovae one can constrain the mixing of $ν_e$ with $ν_μ$ (or $ν_τ$) down to $10^{-4} eV^2$. We first do a two-flavor study and find that the neutron rich condition $Y_e < 0.5$ is satisfied for all values of mixing angles. However if we take the criterion $Y_e < 0.45$ for a successful r-process and assume $ν_μ- ν_e$ oscillations to be operative then this mode as a possible solution to the atmospheric neutrino anomaly is ruled out in accordance with the recent CHOOZ result. Furthermore since we can probe mass ranges lower than CHOOZ the narrow range that was allowed by the CHOOZ data at 99% C.L. is also ruled out. Next we do a three-generation analysis keeping $Δm_{12}^2 \sim 10^{-5} eV^2$ or $10^{-11} eV^2$ (solar neutrino range) and $Δm_{13}^2 \approx Δm_{23}^2 \sim 10^{-4} - 10^{-1} eV^2$ (atmospheric neutrino range) and use the condition $Y_e < 0.45$ to give bounds on the mixing parameters and compare our results with the CHOOZ bound. We also calculate the increase in the shock-reheating obtained by such oscillations.

hep-ph↗

arXiv1997

Emission of electron density waves by neutrinos in a dense medium

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.

hep-ph↗

arXiv1997

Excited States of 71Ge above the Neutron Emission Threshold and Solar Neutrino Capture rates for Ga Detectors

In Gallium detectors for solar neutrinos, the capture rate due to Gamow-Teller transitions to excited states of 71Ge beyond the neutron emission threshold is usually neglected. We make a model calculation to estimate its effect and find that this yields an additional contribution which may be as much as 0.4 SNU, even larger than that from the Isobaric Analog State in 71Ge reached by Fermi transitions, which is normally included in the standard predictions.

astro-ph↗

arXiv1995

Accelerator, reactor, solar and atmospheric neutrino oscillation: beyond three generations

We perform a phenomenological analysis of neutrino oscillation in a four generation framework introducing an additional sterile neutrino. In such a scenario, more than one pattern is possible that can accommodate three hieararchically different mass squared differences as required by the present experiments. We considered two different spectrums. Choosing the ${Δ{m}}^2$s in the ranges suitable for the LSND, atmospheric and solar neutrino oscillation, limits on the mixing angles are derived, consistent with the most restrictive accelerator and reactor data as well as the atmospheric and solar neutrino results. The allowed mixing angles are found to be constrained very severely in both cases. For one mass pattern in the combined allowed zone the atmospheric anomaly can be explained by $ν_e - ν_μ$ oscillation whereas for the other the $ν_μ - ν_τ$ channel is preferred. The accelerator experiments CHORUS and NOMAD have different sensitivities in these regions and they can distinguish between the two choices.

hep-ph↗

arXiv1995

Accelerator, reactor and atmospheric neutrino data: a three flavour oscillation analysis

We perform a three flavour analysis of the atmospheric, accelerator and reactor neutrino data from the Kamiokande, LSND and Bugey experiments respectively. Choosing the values of ${Δ{m}}^2$ obtained from two flavour fits of the first two experiments, the allowed ranges of the three generation mixing angles are determined. The accelerator experiments CHORUS and NOMAD are found to be most sensitive to regions of the allowed parameter space which correspond to genuine three generation solutions for the atmospheric neutrino anomaly.

hep-ph↗

arXiv1995

Resonant neutrino oscillations and shock revival in type-II supernovae

The role of matter enhanced resonant neutrino oscillations in reviving a stalled shock in a type-II supernova through delayed neutrino heating is investigated. The extent of neutrino heating is estimated for the allowed possibility of complete flavour conversion self-consistently with the changes in nuclear equilibrium. The average internal energy per nucleon is substantially increased indicating the possiblty of a robust explosion.

hep-ph↗