arXiv subjects

S. Chakravarti

Publications and source records attributed to S. Chakravarti.

4 recordsLinked to original sources

arXiv1999

Electron Capture Rates of Mid-fp Shell Nuclei for Supernova and Stellar Evolution

A detailed model is constructed for the calculation of electron capture rates of some fp-shell nuclei for situations prevailing in pre-supernova and collapse phases of the evolution of the core of massive stars leading to supernova explosion. The model uses explicitly the Gamow-Teller strength function obtained through (n,p) reaction studies wherever available. The rates include contribution from the excited states of the mother as well as from the resonant states in equilibrium with the back reaction i.e. the beta decay of the daughter nucleus. Comparisons are made with the shell model results and the earlier calculations by Aufderheide et al. and Fuller, Fowler and Newman. For the nuclei $^{56}$Fe, $^{55}$Mn and $^{60}$Ni with negative Q-values one observes large contribution from the excited states.

astro-ph↗

arXiv1998

Half-lives and pre-supernova weak interaction rates for nuclei away from the stability line

A detailed model for the calculation of beta decay rates of the $fp$ shell nuclei for situations prevailing in pre-supernova and collapse phases of evolution of the core of massive stars leading to supernova explosion has been extended for electron-capture rates. It can also be used to determine the half-lives of neutron-rich nuclei in the $fp/fpg$ shell. The model uses an averaged Gamow-Teller (GT) strength function. But it can also use the experimental log ft values and GT strength function from $(n,p)$ reaction studies wherever available. The calculated rate includes contributions from each of the low-lying excited states of the mother including some specific resonant states ("back resonance") having large GT matrix elements.

nucl-th↗

arXiv1994

Signatures of Virtual LSPs at the Tevatron

Relatively light sneutrinos which are experimentally allowed and are not theoretically disfavoured may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP) ) - the virtual LSPs (VLSPs). The lighter charginos which would be produced in pairs with reasonably large cross-sections at TEVATRON energies, decay dominantly into the hadronically quiet lepton + sneutrino ($\not{E_T}$ ) modes with large branching ratios leading to interesting unlike sign dilepton events which are not swamped by the standard model background. The kinematical cuts required to eliminate the backgrounds from WW, Drell-Yan and $τ$ pair production are discussed in detail. With 100 $pb^{-1}$ luminosity 10 - 35 background free events can be found in a large region of the SUSY parameter space.

hep-ph↗

arXiv1993

S-wave $π$-Nucleus Repulsion and Dirac Phenomenology

A relativistic $π$-nucleon potential is extended to $m^* \neq m$ to investigate the possibility of generating s-wave $π$-nucleus repulsion. We find that relativity does indeed generate significant repulsion, the exact amount depending on the details of the calculation. In contradistinction the $tρ$ approximation gives very little repulsion.

nucl-th↗