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Bijit Singha

Publications and source records attributed to Bijit Singha.

9 recordsLinked to original sources
arXiv2023

Properties of Infinite Nuclear Medium from QCD Sum Rules and the Neutron Star-Black Hole Mass Gap

A non-perturbative framework is provided to connect QCD with nuclear phenomenology in the intermediate and high density regime. Using QCD Sum Rules, in-medium scalar and vector self-energies of nucleons are calculated as functions of the density of an infinite nuclear medium. The self-energies are used in the relativistic mean field theory lagrangian of a high-density nuclear medium to find the binding energy of in-medium nucleons and the value of light quark condensate, $\langle \bar{q} q \rangle_{\rm{vac}} = -~(0.288 ~\rm{GeV})^3$, in the Borel-improved resummation scheme. The critical mass of an ideal neutron star is obtained by coupling a uniform saturation energy density of cold, dense nuclear matter to Einstein equation in hydrostatic equilibrium. Since it is less likely for a neutron star core to avoid deconfinement and enter the rigid vector repulsion phase where the speed of sound can smoothly approach from conformal to causal limit, a gap should exist in the stellar mass spectrum, $[3.48M_\odot, 5.47M_\odot]$, where it would be rare to find any isolated, cold, non-rotating neutron star or a black hole.

hep-ph↗
arXiv2021

Mass varying neutrinos with different quintessence potentials

The mass-varying neutrino scenario is analyzed for three trial quintessence potentials (Ferreira-Joyce, inverse exponential, and thawing oscillating). The neutrino mass is generated via Yukawa coupling to the scalar field which represents dark energy. The inverse exponential and oscillating potentials are shown to successfully generate the neutrino masses in the range $m \sim 10^{-2}-10^{-3}~$eV and to yield the current dark energy density in the regime of the late-time acceleration of the Universe. Depending on the choice of potentials, the acceleration could occur in two different regimes: (1) the regime of instability, and (2) the stable regime. The first regime of instability is after the Universe underwent a first-order transition and is rolling toward the new stable vacuum. The imaginary sound velocity $c^2_s < 0$ in this regime implies growing fluctuations of the neutrino density (clustering). In the second regime, the Universe smoothly changes its stable states via a continuous transition. Since $c^2_s > 0$, the neutrino density is stable. For all cases the predicted late-time acceleration of the Universe is asymptotically very close to that of the $Λ$CDM model. Further extensions of the theory to modify the neutrino sector of the Standard Model and to incorporate inflation are also discussed. It is also shown that in the stable regimes where the neutrino mass is given by the minimum of the thermodynamic potential, the tree-level dynamics of the scalar field is robust with respect to one-loop bosonic and fermionic corrections to the potential.

hep-ph↗
arXiv2019

Gravitational Radiation From Pulsar Creation

We estimate the gravitational wave amplitude as a function of frequency produced during the creation of pulsars from the gravitational collapse of a massive star. The three main quantities needed are the magnitude of the magnetic field producing pulsar kicks, the temperature which determines the velocity of the pulsar and the duration time for the gravitational radiation.res

astro-ph.HE↗
arXiv2019

Charmed Baryon Decay to a Strange Baryon Plus a Pion Using QCD Sum Rules

This is an extension of the prediction of strange baryon decays to the decays of charmed baryons using QCD Sum Rules. Using QCD Sum Rules we estimate the decay $Λ^+_c (udc) \rightarrow Λ^o_s(uds)+ π^+$. Although some weak decays of the $Λ^+_c$ have been measured, since it is difficult to measure $Λ^+_c \rightarrow Λ^o_s+ π^+$ our estimates should be useful for future experiments

hep-ph↗
arXiv2018

Kinetics of Vesicle Growth

A mechanism is proposed for the growth of vesicles dispersed in a liquid solvent and a size distribution function is obtained for the vesicles, both from the first principles calculations. This distribution function is shown to be positively skewed and evolving in time obeying a Fokker-Planck type equation. The critical size of the spherical vesicles is shown to grow in time with an exponent of 0.25. A constant is suggested that characterizes how easily a vesicle can absorb amphiphiles into its periphery.

physics.bio-ph↗
arXiv2017

B Production In p-p and A-A Collisions

This is an extension of our recent work on $D^+(c\bar{d}),D^o(c\bar{u})$ production from p-p and d-Au collisions to $B^+(b\bar{d}),B^o(b\bar{u})$ production from p-p and A-A collisions. The rapidity cross sections for $B^+(c\bar{d}),B^o(b\bar{u})$ production from both p-p and A-A collisions are estimated. Our present work makes use of previous work on $J/Ψ$, $Ψ'(2S)$, $Υ(nS)$ production in p-p and A-A collisions, with the main new aspect being the fragmentation probability, $D_{b \rightarrow b\bar{q}}$, which turns out to be similar to the fragmentation probability $D_{c \rightarrow c\bar{q}}$ used in our recent work.

hep-ph↗
arXiv2017

Scattering from finite-volume energies including higher partial waves and multiple decay channels

A new implementation of estimating the two-to-two $K$-matrix from finite-volume energies based on the Luescher formalism is described. The method includes higher partial waves and multiple decay channels, and the fitting procedure properly includes all covariances and statistical uncertainties. The method is also simpler than previously used procedures. Formulas and software for handling total spins up to $S=2$ and orbital angular momenta up to $L=6$ are presented.

hep-lat↗
arXiv2017

Estimating the two-particle $K$-matrix for multiple partial waves and decay channels from finite-volume energies

An implementation of estimating the two-to-two $K$-matrix from finite-volume energies based on the Lüscher formalism and involving a Hermitian matrix known as the "box matrix" is described. The method includes higher partial waves and multiple decay channels. Two fitting procedures for estimating the $K$-matrix parameters, which properly incorporate all statistical covariances, are discussed. Formulas and software for handling total spins up to $S=2$ and orbital angular momenta up to $L=6$ are obtained for total momenta in several directions. First tests involving $ρ$-meson decay to two pions include the $L=3$ and $L=5$ partial waves, and the contributions from these higher waves are found to be negligible in the elastic energy range.

hep-lat↗