arXiv subjects

Z. Naik

Publications and source records attributed to Z. Naik.

12 recordsLinked to original sources

arXiv2023

Cosmological Model with Cosmic transit behaviour in Brans-Dicke Theory

We have constructed a dark energy cosmological model in the framework of generalized Brans Dicke theory (GBD) with a self-interacting potential. The source of dark energy is considered through a unified dark fluid (UDF) characterized by a linear equation of state (EoS). A time varying deceleration parameter simulating the cosmic transit behaviour has been introduced to get the dynamical behaviour of the model. The $H(z)$ data have been explored to constrain the model parameters and to study the dynamical aspects of the Brans-Dicke parameter and the scalar field.

gr-qc↗

arXiv2023

Evolution of Generalized Brans-Dicke parameter within a Superbounce scenario

We have studied a superbounce scenario in a set up of Brans-Dicke (BD) theory. The BD parameter is considered to be time dependent and is assumed to evolve with the Brans-Dicke scalar field. In the superbounce scenario, the model bounces at an epoch corresponding to a Big Crunch provided the ekpyrotic phase continues until that time. Within the given superbounce scenario, we investigate the evolution of the BD parameter for different equations of state. We chose an axially symmetric metric that has an axial symmetry along the x-axis. The metric is assumed to incorporate an anisotropic expansion effect. The effect of asymmetric expansion and the anisotropic parameter on the evolving and the non-evolving part of the BD parameter is investigated.

gr-qc↗

arXiv2020

Unified Dark Fluid and Cosmic Transit Models in Brans-Dicke Theory

Some dark energy cosmological models are constructed in the framework of a generalised Brans-Dicke theory which contains a self interacting potential and a dynamical coupling parameter. The dark sector of the universe is considered through a unified linear equation of state. The parameters of the unified dark fluid have been constrained from some physical basis. Since the universe is believed to have undergone a transition from an early deceleration to a late time acceleration, the deceleration parameter should have a signature flipping behaviour at the transition redshift. We have used a hybrid scale factor to simulate the dynamical behaviour of the deceleration parameter. Basing upon the observational constraints on the transition redshift, we have constructed four different transitioning dark energy models. The constructed models are confronted with observational data. For all the models, the behaviour of the dynamical scalar field, Brans-Dicke parameter, Self interacting potential are investigated. Also, on the basis of the generalised Brans-Dicke theory, we have estimated the time variation of the Newtonian gravitational constant.

gr-qc↗

arXiv2019

Microscopic study of K-Selection Rule Violation in $^{182}$W K=10$^+$ Isomer Decay

In this paper we study the microscopic mechanism for the retarded decay of K-isomers to lower K bands. We do angular momentum projection from suitable intrinsic states. The retardation arises from poor overlap between the low K and high K bands in the integral over Euler angles. Deformed HF and angular momentum projection calculations are done for the decay of the $K=10^+$ isomer band to the ground band of $^{182}W$. K-mixing is unimportant and the K quantum numbers of the bands are quite good. There is significant difference in the reduced matrix elements of transition operators in our formalism and that in the rotational model. Angular momentum projection gives J-selection rule but there is no K selection rule for reduced matrix elements of electromagnetic multipole operators. Thus, E2 and M1 transitions from the K isomer to the ground band of $^{182}W$ are finite but retarded in angular momentum projection theory, as in experiments. This provides a theoretical basis for the study of K-isomers and their decay modes. Quantitative results are presented. The microscopic model gives J-selection rule and angular momentum conservation for combined matter and radiation systems.

nucl-th↗

arXiv2018

Calculating charged particle observables using modified Wood Saxon model in HIJING for U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV

We have implemented spherical harmonics in default Wood Saxon distribution of the HIJING model and calculated various physical observables such as transverse momentum, charged particle multiplicity, nuclear modification factor and particle ratios for charged particles at top RHIC energy with collisions of Uranium (U) nuclei. Results have been compared with available experimental data. We observe that, a particular type of collision configuration can produce significant magnitude change in observables. We have noticed that the tip-tip configuration shows higher magnitude of particle yield in central collisions, while the body-body configuration shows higher value in the cases of peripheral collisions, with the flip in the trend occurring for the mid-central U+U collisions. We observe that particle ratios are independent of configuration type.

nucl-th↗

arXiv2018

Application of Nilsson model for deformed nucleus in relativistic heavy ion collisions

Electron scattering methods, involving nucleus which have little or no intrinsic deformation suggest nucleon distribution to be of Fermi type. This distribution is further parameterised as Wood Saxon (WS) distribution, where an uniform charge density with smoothed-out surface have been implemented. Incorporating shape modification in WS, earlier attempts were made to explain observables in deformed nuclear collisions, such as charged particle multiplicity. In this work, we use an alternate approach known as Nilsson model or Modified Harmonic Oscillator (MHO), to explain charged particle multiplicity in U+U collisions at top RHIC energy. We have implemented the formalism in HIJING model and we found that the model describes the experimental data to an extent.

nucl-th↗

arXiv2017

Azimuthal correlations of D-mesons in $p$+$p$ and $p$+Pb collisions at LHC energies

We study the correlations of D mesons produced in $p$+$p$ and $p$+Pb collisions. These are found to be sensitive to the effects of the cold nuclear medium and the transverse momentum ($p_T$) regions we are looking into. In order to put this on a quantitative footing, as a first step we analyse the azimuthal correlations of D meson-charged hadron(Dh), and then predict the same for D meson -anti D meson ($D\overline{D}$) pairs in $p$+$p$ and $p$+Pb collisions with strong coupling at leading order $\cal{O}$($α_{s}^{2}$) and next to leading order $\cal{O}$($α_{s}^{3}$) which includes space-time evolution (in both systems), as well cold nuclear matter effects (in $p$+Pb). This also sets the stage and baseline for the identification and study of medium modification of azimuthal correlations in relativistic collision of heavy nuclei at the Large Hadron Collider.

hep-ph↗

arXiv2016

Production of D-mesons in $p$+$p$ and $p$+Pb collisions at LHC energies

We present theoretical model comparison with published ALICE results for D-mesons (D$^0$, D$^+$ and D$^{*+}$) in $p$+$p$ collisions at $\sqrt{s}$ = 7 TeV and $p$+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. Event generator HIJING, transport calculation of AMPT and calculations from NLO(MNR) and FONLL have been used for this study. We found that HIJING and AMPT model predictions are matching with published D-meson cross-sections in $p$+$p$ collisions, while both under-predict the same in $p$+Pb collisions. Attempts were made to explain the $R_{pPb}$ data using NLO-pQCD(MNR), FONLL and other above mentioned models.

hep-ph↗

arXiv2012

Small Quadrupole Deformation for the Dipole Bands in 112In

High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\sim$ 20$\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.

nucl-ex↗

arXiv2011

Rotational Bands and Electromagnetic Transitions of some even-even Neodymium Nuclei in J-Projected Hartree-Fock Model

Rotational structures of even-even $^{148-160}$Nd nuclei are studied with the self-consistent deformed Hartree-Fock (HF) and angular momentum (J) projection model. Spectra of ground band, recently observed $K=4^{-}$, $K=5^{-}$ and a few more excited, positive and negative parity bands have been studied upto high spin values. Apart from these detailed electromagnetic properties (like E2, M1 matrix elements) of all the bands have been obtained. There is substantial agreement between our model calculations and available experimental data. Predictions are made about the band structures and electromagnetic properties of these nuclei. Some 4-qasiparticle K-isomeric bands and their electromagnetic properties are predicted.

nucl-th↗

arXiv2009

Study of nuclei in the vicinity of the "Island of Inversion" through fusion-evaporation reaction

We report the first observation of high-spin states in nuclei in the vicinity of the "island of inversion", populated via the 18O+18O fusion reaction at an incident beam energy of 34 MeV. The fusion reaction mechanism circumvents the limitations of non-equilibrated reactions used to populate these nuclei. Detailed spin-parity measurements in these difficult to populate nuclei have been possible from the observed coincidence anisotropy and the linear polarization measurements. The spectroscopy of 33,34P and 33S is presented in detail along with the results of calculations within the shell model framework.

nucl-ex↗

arXiv2009

Multi-quasiparticle gamma-band structure in neutron-deficient Ce and Nd isotopes

The newly developed multi-quasiparticle triaxial projected shell-model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce- and Nd-isotopes. It is observed that gamma-bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K-states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface gamma-oscillation in deformed nuclei based on the ground-state to gamma-bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in 134Ce and both exhibiting a neutron character.

nucl-th↗