arXiv subjects

A Saha

Publications and source records attributed to A Saha.

4 recordsLinked to original sources

arXiv2024

QCD coupling constant ($\alpha_c$) and nonzero value of strange quark mass ($m_s\neq 0$) dependent stable stellar structure admitting observational results

This work discuses the effect of the QCD coupling constant ($\alpha_c$) on various physical properties of compact stars in the framework of the Tolman IV potential admitting the equation of state of MIT bag model with nonzero value of mass of strange quark mass ($m_s$). The internal matter, consisting of the deconfined phase of the $3$-flavour quark, is overall charge neutral due to the presence of electrons and is assumed to be strongly interacting. Interestingly, it is noted that the coupling constant $\alpha_c$ has an upper limit due to thermodynamic consistency and affects the stability of the stellar structure in terms of energy per baryon ($E_B$). Present model is suitable to study the properties of stars with mass of approximately $\leq 2.00~M_{\odot}$. The predicted radii of a few known stars from our model are in good agreement with the estimated values of radius obtained from the observations. Necessary energy conditions are obeyed inside the stellar configuration. Various stability conditions are carried out and it is found that within the range of parameter space used here the model is stable.

gr-qc↗

arXiv2021

Precise Beam Energy Determination for Hall A after the CEBAF 12 GeV Upgrade

Precise and accurate measurements of the beam energy delivered to the experimental halls at the Thomas Jefferson Accelerator Facility (Jefferson Lab) is required by many experiments for proper data analysis and physics event reconstruction. During the 6 GeV era of Jefferson Lab, the energy delivered to experimental Hall A was determined to 2E-4 dE/E with multiple measurements; but after the machine was upgraded to 12 GeV, the accelerator's beam energy calculations needed to be re-calibrated. In order to link the 6 GeV era calibrations to the 12 GeV era, the Hall A ARC energy measurement system was left unmodified. After the upgrade, this system was used to determine the absolute beam energy being delivered into Hall A and find the new calibrations for the main machine. To ensure the validity of these results, they have been cross checked using elastic scattering data as well as spin precession data.

physics.acc-ph↗

arXiv2021

Orbital Magnetism of Active Viscoelastic Suspension

We consider a dilute suspension of active (self-propelling) particles in a visco-elastic fluid. Particles are charged and constrained to move in a two dimensional harmonic trap. Their dynamics is coupled to a constant magnetic field applied perpendicular to their motion via Lorentz force. Due to the finite activity, the generalised fluctuation-dissipation relation (GFDR) breaks down, driving the system away from equilibrium. While breaking GFDR, we have shown that the system can have finite classical orbital magnetism only when the dynamics of the system contains finite inertia. The orbital magnetic moment has been calculated exactly. Remarkably, we find that when the elastic dissipation time scale of the medium is larger (smaller) than the persistence time scale of the self-propelling particles, the system is diamagnetic (paramagnetic). Therefore, for a given strength of the magnetic field, the system undergoes a novel transition from diamagnetic to paramagnetic state (and vice-versa) simply by tuning the time scales of underlying physical processes, such as, active fluctuations and visco-elastic dissipation. Interestingly, we also find that the magnetic moment, which vanishes at equilibrium, behaves non-monotonically with respect to increasing persistence of self-propulsion, that drives the system out of equilibrium

cond-mat.stat-mech↗

arXiv2008

Probability for Primordial Black Holes in Multidimensional Universe with Nonlinear Scalar Curvature Terms

We investigate multi-dimensional universe with nonlinear scalar curvature terms to evaluate the probability of creation of primordial black holes. For this we obtain Euclidean instanton solution in two different topologies: (a) $S^{D-1}$ - topology which does not accommodate primordial black holes and (b) $S^1\times S^{D-2}$-topology which accommodates a pair of black holes. The probability for quantum creation of an inflationary universe with a pair of black holes has been evaluated assuming a gravitational action which is described by a polynomial function of scalar curvature with or without a cosmological constant ($Λ$) using the framework of semiclassical approximation of Hartle-Hawking boundary conditions. We discuss here a class of new gravitational instantons solution in the $R^4$-theory which are relevant for cosmological model building.

astro-ph↗