arXiv subjects

A. A. Usmani

Publications and source records attributed to A. A. Usmani.

At least 19 recordsLinked to original sources

arXiv2026

On energy-dependent scaling factor for the charge-changing cross sections of light elements

In this study, the scaling factor for $^{28}$\rm Si + $^{12}$\rm C charge-changing cross sections (CCCSs) at 90-1296 MeV/nucleon has been used as a basis to introduce the energy dependence in the scaling factor for the light elements. To test the extracted scaling factor, we predict the charge-changing cross sections for $^{7,9-12,14}$\rm Be, $^{10-15,17}$\rm B, $^{11-19}$\rm C, $^{13-22}$\rm N, $^{15-24}$\rm O, and $^{18-21,23-26}$\rm F isotopes at 200-991 MeV/nucleon in the framework of the Glauber model. The calculations use descriptions of nuclei in terms of the Slater determinant involving harmonic oscillator single-particle wave functions, which reproduce the charge radii obtained earlier [Phys. Rev. C {\bf 110} (2024) 014623; {\bf 111} (2025) 064601]. It is found that the theoretical results provide quite a satisfactory explanation of the experimental data in all the cases, and the extracted scaling factor shows systematic energy dependence for the isotopes of a given element. In conclusion, we expect that the present way of finding the scaling factor could be successfully used in the analysis of CCCSs for the elements Z $\leq$ 9 at any desired energy in the range 90-1296 MeV/nucleon. This result may further add that the present work provides a practical scheme for predicting the charge-changing cross sections (and inferring proton radii) of \rm Be-\rm F isotopes, where measurements are scarce.

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arXiv2025

Theoretical investigation of charge-changing cross section and interaction cross section for Be, B, C, N, O, and F isotopes on $^{12}$C at 200-1050 MeV/nucleon

To establish credibility for the use of the Slater determinant harmonic oscillator (SDHO) density in predicting root-mean-square proton and neutron radii for Be, B, C, N, O, and F isotopes [M. Imran et al., {\color{blue}Phys. Rev. C {\bf 110}, 014623 (2024)}], in this work we propose to study charge-changing and interaction cross sections for the said isotopes on $^{12}$C at a wider range of incident energies (200-1050 MeV/nucleon), involving different density distributions; the calculations also assess the importance of nuclear medium effects. Working within the framework of the Glauber model, we involve two-parameter Fermi (2pF) and three-parameter Fermi (3pF) shapes of density distributions, and use the in-medium as well as free behavior of the nucleon-nucleon (NN) amplitude. The results provide enough basis to support the matter radii of exotic isotopes obtained using SDHO densities.

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arXiv2025

Charge-changing cross section and interaction cross sections for 4$\leq$Z$ \leq$9 isotopes

The root-mean-square proton and neutron radii for $^{7,9-12,14}$\rm Be, $^{10-15,17}$\rm B, $^{12-19}$\rm C, $^{14,15,17-22}$\rm N, $^{16,18-24}$\rm O, and $^{18-21,23-26}$\rm F isotopes are deduced from a systematic analysis of experimental charge-changing and interaction cross sections in the framework of Glauber model. The calculations involve descriptions of nuclei based on Slater determinants using harmonic oscillator single-particle wave functions. The extracted proton and neutron radii have been examined in the light of some important features such as neutron skin thickness/halo-like structure/subshell closure observed in exotic isotopes.

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arXiv2023

Magnetic-Field Induced Deformation in Hybrid Stars

The effects of strong magnetic fields on the deconfinement phase transition expected to take place in the interior of massive neutron stars are studied in detail for the first time. For hadronic matter, the very general density-dependent relativistic mean-field (DD-RMF) model is employed, while the simple, but effective vector-enhanced bag model (vBag) model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwell's equations. We find that for large values of magnetic dipole moment, the maximum mass, canonical mass radius, and dimensionless tidal deformability obtained for stars using spherically symmetric Tolman-Oppenheimer-Volkoff (TOV) equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that, unlike what was assumed previously in the literature, magnetic field thresholds for the approximation of isotropic stars and the acceptable use of TOV equations depend on the matter composition and interactions.

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arXiv2022

Theoretical studies on structural properties and decay modes of $^{284-375}$119 isotopes

In this manuscript, we analyze the structural properties of $Z=119$ superheavy nuclei in the mass range of 284 $\le$ A $\le$ 375 within the framework of axially deformed relativistic mean field theory (RMF) and calculate the binding energy, radii, quadrupole deformation parameter, separation energies and density profile. To investigate the phenomenon of shape coexistence the RMF calculations are performed within three possible solutions i.e. prolate, oblate and spherical configurations. To get a better visualization of nucleon and total matter distribution, two-dimensional contour representation of density distribution for $^{291}$119 and $^{303}$119 has been made. Further, a competition between possible decay modes such as $α-$decay, $β-$decay and spontaneous fission (SF) of the isotopic chain of $Z=119$ superheavy nuclei under study is systematically analyzed within self-consistent relativistic mean field model. Our analysis confirmed that $α-$decay is restricted within the mass range 284 $\leq$ A $\leq$ 296 and thus being the dominant decay channel in this mass range. There is no possibility of $β-$decay for the considered isotopic chain. In addition, we forecasted the $α-$decay chain of fission survival nuclides i.e. $^{284-296}$119 and found as one $α$ chain from $^{284}$119 and $^{296}$119, two consistent $α$ chains from $^{285}$119 and $^{295}$119, three consistent $α$ chains from $^{286}$119 and $^{294}$119, four consistent alpha chains from $^{287}$119, six consistent alpha chains from $^{288-293}$119. Thus, such studies can be of great significance to the experimentalists in very near future for synthesizing $Z=119$ superheavy nuclei.

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arXiv2021

Study of nuclear matter properties for Hybrid EoS

We study the nuclear matter properties like symmetry energy, slope parameter, curvature, skewness and incompressibility for Hybrid EoS. The hybrid EoS is constructed using the recently proposed Effective-Field-Theory motivated Relativistic Mean-Field model (E-RMF) for the hadron phase with different parameter sets and MIT Bag model for the quark phase with different Bag constants to construct hybrid EoS. The mixed-phase formed by the hadron-quark phase transition is studied using the Gibbs construction. The nuclear matter properties for hybrid EoS are calculated and their variation with the bag constant is determined.

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arXiv2021

Hadron-Quark phase transition in the context of GW190814

The properties of the neutron stars are calculated for the hadronic matter within the density-dependent relativistic mean-field model (DD-RMF). The phase transition to the quark matter is studied and the hybrid star matter properties are systematically calculated using the Vector-Enhanced Bag model (vBag). The maximum mass of neutron star with DD-LZ1 and DD-RMF parameter sets is found to be around 2.55$M_{\odot}$ for pure hadronic phase and around 2$M_{\odot}$ for hadron-quark mixed phase using both Gibbs and Maxwell construction. The tidal deformability for the hybrid EoS at 1.4$M_{\odot}$, $Λ_{1.4}$, remains unchanged from the pure hadronic EoS with Maxwell construction, but decreases with the increasing neutron star mass for Gibbs construction. While the pure hadron matter EoS satisfies the mass constraint from recently observed GW190814 data, implying a stiff neutron star EoS, the hadron-quark phase transition satisfies the constraints from the recent observations GW170817. Therefore, we cannot exclude the possibility of the secondary object in GW190814 as a neutron star with a phase transition to the quark matter that satisfies the 2$M_{\odot}$ maximum mass limit.

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arXiv2021

Rotating neutron stars with quark cores

The rotating neutron star properties are studied with a phase transition to quark matter. The density-dependent relativistic mean-field model (DD-RMF) is employed to study the hadron matter, while the Vector-Enhanced Bag model (vBag) model is used to study the quark matter. The star matter properties like mass, radius,the moment of inertia, rotational frequency, Kerr parameter, and other important quantities are studied to see the effect on quark matter. The maximum mass of rotating neutron star with DD-LZ1 and DD-MEX parameter sets is found to be around 3$M_{\odot}$ for pure hadronic phase and decreases to a value around 2.6$M_{\odot}$ with phase transition to quark matter, which satisfies the recent GW190814 constraints. For DDV, DDVT, and DDVTD parameter sets, the maximum mass decreases to satisfy the 2$M_{\odot}$. The moment of inertia calculated for various DD-RMF parameter sets decreases with the increasing mass satisfying constraints from various measurements. Other important quantities calculated also vary with the bag constant and hence show that the presence of quarks inside neutron stars can also allow us to constraint these quantities to determine a proper EoS. Also, the theoretical study along with the accurate measurement of uniformly rotating neutron star properties may offer some valuable information concerning the high-density part of the equation of state.

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arXiv2021

Heavy Magnetic Neutron Stars

We systematically study the properties of pure nucleonic and hyperonic magnetic stars using a density-dependent relativistic mean field (DD-RMF) equations of state. We explore several parameter sets and hyperon coupling schemes within the DD-RMF formalism. We focus on sets that are in better agreement with nuclear and other astrophysical data, while generating heavy neutron stars. Magnetic field effects are included in the matter equation of state and in general relativity solutions, which in addition fulfill Maxwell's equations. We find that pure nucleonic matter, even without magnetic field effects, generates neutron stars that satisfy the potential GW190814 mass constraint; however, this is not the case for hyperonic matter, which instead only satisfies the more conservative 2.1 M$_{\odot}$ constraint. In the presence of strong but still somehow realistic internal magnetic fields $\approx10^{17}$ G, the stellar charged particle population re-leptonizes and de-hyperonizes. As a consequence, magnetic fields stiffen hyperonic equations of state and generate more massive neutron stars, which can satisfy the possible GW190814 mass constraint but present a large deformation with respect to spherical symmetry.

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arXiv2020

Constraining Bag constant for Hybrid Neutron stars

We study the star matter properties for Hybrid equation of state (EoS) by varying the bag constant. We use the Effective-Field-Theory motivated Relativistic Mean-Field model (E-RMF) for hadron phase with recently reported FSUGarnet, G3 and IOPB-I parameter sets. The result of NL3 and NL3${ωρ}$ sets are also shown for comparison. The simple MIT Bag model is applied for the quark phase to construct the hybrid EoS. The hybrid neutron star mass and radius are calculated by varying with $B^{1/4}$ to constrain the $B^{1/4}$ values. It is found that $B^{1/4}$=130-160 MeV is suitable for explaining the quark matter in neutron stars.

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arXiv2017

A Study of Multi$Λ$ hypernuclei within Spherical Relativistic Mean-field Approach

This research article is a follow up of earlier work by M. Ikram et al., reported in International Journal of Modern Physics E {\bf{25}}, 1650103 (2016) wherein we searched for $Λ$ magic numbers in experimentally confirmed doubly magic nucleonic cores in light to heavy mass region (ie.$^{16}O - ^{208}Pb$) by injecting $Λ$'s into them. In present manuscript, working within the state-of-art relativistic mean field theory with inclusion of $ΛN$ and $ΛΛ$ interaction in hypernuclei using the predicted doubly magic nucleonic cores ie. $^{292}$120, $^{304}$120, $^{360}$132, $^{370}$132, $^{336}$138, $^{396}$138 of elusive superheavy mass regime. In analogy to well established signatures of magicity in conventional nuclear theory, the prediction of hypernuclear magicity are made on the basis of one-, two-$Λ$ separation energy ($S_Λ, S_{2Λ}$) and two lambda shell gaps ($δ_{2Λ}$) in multi-$Λ$ hypernuclei. The calculations suggest that the $Λ$ numbers 92, 106, 126, 138, 184, 198, 240, and 258 might be the $Λ$ shell closures after introducing the $Λ$'s in elusive superheavy nucleonic cores. Moreover, in support of $Λ$ shell closure the investigation of $Λ$ pairing energy and effective $Λ$ pairing gap has also been made. The appearance of new lambda shell closures other than the nucleonic ones predicted by various relativistic and non-relativistic theoretical investigations can be attributed to the relatively weak strength of spin-orbit coupling in hypernuclei compared to normal nuclei.

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arXiv2016

Structural and decay properties of $Z=132,138$ superheavy nuclei

In this paper, we analyze the structural properties of $Z=132$ and $Z=138$ superheavy nuclei within the ambit of axially deformed relativistic mean-field framework with NL$3^{*}$ parametrization and calculate the total binding energies, radii, quadrupole deformation parameter, separation energies, density distributions. We also investigate the phenomenon of shape coexistence by performing the calculations for prolate, oblate and spherical configurations. For clear presentation of nucleon distributions, the two-dimensional contour representation of individual nucleon density and total matter density has been made. Further, a competition between possible decay modes such as $α$-decay, $β$-decay and spontaneous fission of the isotopic chain of superheavy nuclei with $Z=132$ within the range 312 $\le$ A $\le$ 392 and 318 $\le$ A $\le$ 398 for $Z=138$ is systematically analyzed within self-consistent relativistic mean field model. From our analysis, we inferred that the $α$-decay and spontaneous fission are the principal modes of decay in majority of the isotopes of superheavy nuclei under investigation apart from $β$ decay as dominant mode of decay in $^{318-322}138$ isotopes.

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arXiv2016

The Finslerian wormhole models

We present models of wormhole under the Finslerian structure of spacetime. This is a sequel of our previous work (Eur Phys J 75:564, 2015) where we constructed a toy model for compact stars based on the Finslerian spacetime geometry. In the present investigation, a wide variety of solutions are obtained that explore wormhole geometry by considering different choices for the form function and energy density. The solutions, like the previous work, are revealed to be physically interesting and viable models for the explanation of wormholes as far as the background theory and literature are concerned.

gr-qc↗

arXiv2015

A Dark Energy Model in Kaluza-Klein Cosmology

We study a dynamic $Λ$ model with varying gravitational constant $G$ under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage $Λ$.

physics.gen-ph↗

arXiv2014

A relativistic mean field study of multi-strange system

We study the binding energies, radii, single-particle energies, spin-orbit potential and density profile for multi-strange hypernuclei in the range of light mass to superheavy region within the relativistic mean field (RMF) theory. The stability of multi-strange hypernuclei as a function of introduced hyperons ($Λ$ and $Σ$) is investigated. The neutron, lambda and sigma mean potentials are presented for light to superheavy hypernuclei. The inclusion of hyperons affects the nucleon, lambda and sigma spin-orbit potentials significantly. The bubble structure of nuclei and corresponding hypernuclei is studied. The nucleon and lambda halo structure are also investigated. A large class of bound multi-strange systems formed from the combination of nucleons and hyperons (n, p, $Λ$, $Σ^+$ and n, p, $Λ$, $Σ^-$) is suggested in the region of superheavy hypernuclei which might be stable against the strong decay. These multi-strange systems might be produced in heavy-ion reactions.

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arXiv2014

The higher dimensional gravastars

A new model of gravastar is obtained in $D$-dimensional Einstein gravity. This class of solutions includes the gravastar as an alternative to D-dimensional versions of the Schwarzschild-Tangherlini black hole. The configuration of this new gravastar consists of three different regions with different equations of state: [I] Interior: 0 \leq r < r_1, ρ= -p; [II] Shell: r_1 \leq r < r_2, ρ= p; [III] Exterior: r_2 < r, ρ= p =0. The outer region of this gravastar corresponds to a higher dimensional Schwarzschild-Tangherlini black hole.

physics.gen-ph↗

arXiv2014

Exact interior solutions in (2 + 1) dimensional spacetime

We provide a new class of exact solutions for the interior in (2 + 1) dimensional spacetime. The solutions obtained for the perfect fluid model both with and without cosmological constant ($Λ$) are found to be regular and singularity free. It assume very simple analytical forms that help us to study the various physical properties of the configuration. Solutions without $Λ$ are found to be physically acceptable.

gr-qc↗

arXiv2013

Oscillatory Universe, dark energy and general relativity

The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the frame work of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The `classical' general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy.

physics.gen-ph↗