• V K Gupta

Articles written in Pramana – Journal of Physics

• Neutral current effects in the parity violating nuclear force

The measurements of the ΔI = 1 part of the parity violating nuclear force when combined with information on neutral current couplings from neutrino scattering and pion production experiments allow an estimate of the isoscalar admixture in the neutral current if it has a vector axial-vector structure has been shown.

• Coulomb energy of3He and charge-symmetry breaking in nuclear forces

We report a calculation of Coulomb energy of3He with two-term separable potentials of a form proposed recently, and a perturbative calculation of the charge-symmetry-breaking potential, again in a two-term separable form. By using potential sets adjusted to various values of proton-neutron effective range difference, some limit is sought to be placed on this quantity, about which nothing is known experimentally.

• Inelastic interactions of 9.38 GeV/c deuteron in emulsion

Characteristics of the inelastic interactions of 9.38 GeV/c deuterons with nuclear emulsion nuclei have been studied. These have been compared with nucleon-nucleus interactions at a corresponding momentum. The probability of nucleon stripping in deuteron-nucleus interactions has been observed to be 0.5. The charged particle multiplicity in deuteron-nucleus interactions exhibitA-dependence of the typeAα with α=0.08. The experimental data disagree with KNO scaling.

• Electromagnetic form factors of3He and3H

The electric and magnetic form factors of3He and3H are calculated with 3-nucleon wave functions obtained from the solution of Schrödinger equation with separable potentials of two different shapes which have already been employed in the coulomb energy calculation. The effect of important meson exchange corrections is evaluated and their dependence on the wave function studied. The form factors can depend rather sensitively on the nucleon form factors as well, and this dependence is studied by using two different parametrisations for the latter.

• Variation of average charged particle multiplicity inp-nucleus interactions with energy and the two component description of particle production at high energies

Experimental data on average shower particle multiplicity (〈Ns〉) accumulated onp-nucleus interactions in the wide momentum region of 7.1–8000 GeV/c is investigated. It is observed that 〈Ns〉 is represented exceedingly well as a function of (vvS). There are two physical processes which represent the experimental data reasonably well in the two momentum regionsviz 7.1–67.9 GeV/c and 67.9–8000 GeV/c. 〈Ns〉=a(vS)/a+b fits the data in the low momentum region, whereas 〈Ns〉=a +b ln (vvS) fits the experimental data in the high momentum region. The two physical processes are unified and represented by a single equation which is shown to be the consequence of two component theory and collective models.

• Coherent pion-photoproduction by deuterons at intermediate energies

Non-relativistically exact single scattering calculations for coherent pion photoproduction by deuterons at intermediate photon energies (200 MeV to 500 MeV) are presented. For the two-bodyγNπN process we use the well-known dispersion theoretic model by Chewet al and for the deuteron wave-functions we employ the Yamaguchi and the two term Gaussian wave-function. We find that while both the wavefunctions reproduce the deuteron e.m. form factor reasonably well, the results for the pion photoproduction cross-section show, however, a sensitive dependence on their detailed forms. The angular distributions at various energies are found to have considerable variations from the usual impulse approximation calculations but tend to improve the agreement with the data in a large kinematical region.

• Deuteron form factors and the tensor force

Results of a non-relativistic calculation of deuteron form factors are presented for separable potentials with and without tensor force. The tensor term in triplet state is added in such a way as to keep the values of deuteron binding energy,at andr0t unaltered, so that the difference in the form factors can be regarded as the effect of tensor force only. The calculation has been performed for two different shapes of separable potentials and for three differentD-state probabilities to study their comparative effect.

• Nucleon-nucleon interaction with tensor forces in the quark compound bag model

A model forN-N interaction proposed earlier by two of us (VSB and VKG), has been extended to incorporate the tensor component of the nuclear force. Based on the quark compound bag model (QCB), the nucleon-nucleon potential has a short range repulsive core which is non-local and has a characteristic energy dependence and is expressed in terms of the parameters relating to the six-quark compound bag. To account for the low energy properties, this repulsive core interaction is supplemented by a phenomenological non-local potential containing both central (S-wave) and tensor components and operates only outside the QCB. Using this model, we analyse and compare the results with the experimental data for the electromagnetic form factors of the deuteron, theD-state observables, such as the quadrupole moment, theD-state probability, and theD/S ratio along with then-p scattering phase shifts up to about 400 MeV.

• Neutrino emissivity of quark matter at finite temperatures

We evaluate the emissivity rates for d-decay and s-decay by exactly solving the angular integrals involved and without assuming the degeneracy of electrons. We have also studied the effects of QCD coupling constant as well as the s-quark mass on the emissivity rates. We find that these parameters are important in determining the threshold and extinction densities for d- and s-decays.

• Bulk viscosity of neutron stars

Viscosity of neutron stars has been a continuing area of research for many years now. Recently interest in this field has revived because of the possibility of URCA processes in neutron stars. In this paper we report calculation of the bulk viscosity of neutron stars from these processes. For this purpose we have used theβ-decay rates which were calculated without making the usual approximations of neglecting the neutrino momentum and using the nuclear mean field theory for the description of interacting nuclear matter. Also we have not restricted our calculation to the linear regime which corresponds to the assumption that fluctuations in the chemical potential away fromβ-equilibrium remain small: Δμ/kT ≪ 1. We find that for large amplitude fluctuations, where the linear approximation is not valid, bulk viscosity increases by many orders of magnitude. Also, as against strange matter stars, where the viscosity first increases with increasing temperature and then starts decreasing beyond 0.1 MeV, we find that the viscosity increases uniformly with temperature at least up to 2MeV. We discuss the implications of these results for the stability of neutron stars.

• Bulk viscosity of strange quark matter in density dependent quark mass model

We have studied the bulk viscosity of strange quark matter in the density dependent quark mass model (DDQM) and compared results with calculations done earlier in the MIT bag model where u, d masses were neglected and first order interactions were taken into account. We find that at low temperatures and high relative perturbations, the bulk viscosity is higher by 2 to 3 orders of magnitude while at low perturbations the enhancement is by 1–2 order of magnitude as compared to earlier results. Also the damping time is 2–3 orders of magnitude lower implying that the star reaches stability much earlier than in MIT bag model calculations.

• # Pramana – Journal of Physics

Volume 96, 2022
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019