arXiv subjects

Priyanka Garg

Publications and source records attributed to Priyanka Garg.

11 recordsLinked to original sources

arXiv2025

Anisotropic cosmology using observational datasets: exploring via machine learning approaches

In the current study, we present the observational data constraints on the parameters space for an anisotropic cosmological model of Bianchi I type spacetime in general relativity (GR). For the analysis, we consider observational datasets of Cosmic Chronometers (CC), Baryon Acoustic Oscillation (BAO), and Cosmic Microwave Background Radiation (CMBR) peak parameters. The Markov chain Monte Carlo (MCMC) technique is utilized to constrain the best-fit values of the model parameters. For this purpose, we use the publicly available Python code from CosmoMC and have developed the contour plots with different constraint limits. For the joint dataset of CC, BAO, and CMBR, the parameter's best-fit values for the derived model are estimated as $ H_0 = 69.9\pm 1.4$ km/s/Mpc, $ \Omega_{m0}=0.277^{+0.017}_{-0.015}$, $ \Omega_{\Lambda 0} = 0.722^{+0.015}_{-0.017}$, and $\Omega_{\sigma 0} = 0.0009\pm0.0001$. To estimate $H(z)$, we explore machine learning (ML) techniques like linear regression, Artificial Neural Network (ANN), and polynomial regression and thereafter analyze the results with the theoretically developed $H(z)$ for the proposed model. Among these ML techniques, the polynomial regression exceeds the performance compared to other techniques. Further, we also note that larger dataset provides a better understanding of the cosmological scenario in terms of ML view point.

gr-qc↗

arXiv2023

Quintessence scalar field model in Weyl-type $f(Q,T)$ Gravity with $w_D-w'_D$ analysis

In the present study, we explore the dynamical characteristics of the quintessence cosmological model in Weyl-type $f(Q,T)$ gravity. Here, $T$ represents the trace of the matter energy-momentum tensor, and $Q$ symbolizes the nonmetricity tensor. We propose a solution to the field equation using the specific parametrization in the form$H(z) = H_{0} (1+z)^{1+α+β} e^{\left(\frac{- βz}{1+z}\right)}$, which depicts the necessary transition of cosmos from decelerating era to the current accelerating scenario. The values of model parameters are estimated as $H_0 = 71.17\pm 0.25 $, $α= -0.663\pm0.030$, and $β= 1.488\pm0.087$ using the MCMC analysis and limiting the model with a joint dataset of Pantheon, BAO, and OHD. We discuss the cosmic behavior of many features of the derived model like EoS parameters, energy density, and cosmic pressure. Further, we have also explored the cosmological behavior of the quintessence model in Weyl $f(Q,T)$gravity. We have described the cosmic behavior of the model by $ω_D-ω_D'$ analysis. The diagnosis of the model is also performed using state finders and jerk parameters. In the end, we have discussed the energy conditions for the proposed model. Our analysis shows that the suggested model is well consistent with the recent findings.

gr-qc↗

arXiv2023

Exploring the Cosmological Model in $f(R,T^ϕ)$ Gravity with Observational Constraints

We have investigated an isotropic and homogeneous cosmological model of the universe in $f(R, T^ϕ)$ gravity, where $T^ϕ$ is the trace of the energy-momentum tensor and $R$ is the Ricci scalar. We developed and presented exact solutions of field equations of the proposed model by taking the parametrization $q(z) =α+ \frac{βz}{1+z}$, where $α$ and $β$ are arbitrary constants. The best possible values of the model's free parameters are estimated using the latest observational data sets of OHD, BAO, and Pantheon by applying the MCMC statistical technique. Some kinematic properties like density parameter $ρ_ϕ$, pressure $p_ϕ$, and equation of state parameter $ω_ϕ$ are derived. We have also discussed the behavior of the scalar potential $V(ϕ)$ in the $f(R, T^ϕ)$ gravity theory. The behaviors of scalar fields for quintessence and phantom models are explored. Furthermore, we have discussed the behavior of energy conditions and sound speed in $f(R, T^ϕ)$ cosmology.

gr-qc↗

arXiv2023

Barrow entropic Quintessence and Dilation dark energy Models with Generalized HDE cut-off

In the present work, we have analyzed the behaviors of extension of generalized Barrow holographic dark energy(`BHDE'). A ``generalized BHDE model based on the particle and the future horizon using infrared cut-off" was proposed by Nojiri et al. (2022). In this work, we have reviewed the generalized BHDE extension under the assumption of a generalized HDE cut-off. Using a scale factor of the form $a = k t^m$, the dynamics of the cosmos have been discussed through graphic demonstration. By applying the ``open-source emcee Python package", the values of the free parameters $k$ and $m$ are estimated on 57 OHD points by the Markov Chain Monte Carlo (MCMC) technique. We have examined the behavior of the equation of state (EoS) parameter, $( p_{de})$, and dark energy density $(ρ_{de})$. We have also discussed the equivalence of holographic dark energy (DE) with the Barrow entropic DE and its extension. Also, we have explained quintessence and dilation dark energy models in the context of Barrow entropic DE.

gr-qc↗

arXiv2022

Corrected holographic dark energy with power-law entropy and Hubble Horizon cut-off in FRW Universe

In the present work, we investigate the power-law entropy corrected holographic dark energy (PLECHDE) model with Hubble horizon cutoff. We use 46 observational Hubble data points in the redshift range $0 \leq z \leq 2.36$ to determine the present Hubble constant $H_0$ and the model parameter $n$. It represents a phase transition of the universe from deceleration to acceleration and has the transition point at $z_t = 0.71165$. We investigate the observational constraints on the model and calculate some relevant cosmological parameters. We examine the model's validity by drawing state-finder parameters that yield the result compatible with the modern observational data. The model's physical and geometrical characteristics are also explored, and they are shown to match well with current observations of observational Hubble data (OHD) and the latest joint light curves(JLA) datasets.

gr-qc↗

arXiv2022

Highly tunable spin Hall magnetoresistance in room-temperature magnetoelectric multiferroic, $\text{Sr}_{3}\text{Co}_{2}\text{Fe}_{24}\text{O}_{41}|$Pt hybrids

We present spin transport studies on a low-field, room-temperature magnetoelectric multiferroic polycrystalline $\text{Sr}_{3}\text{Co}_{2}\text{Fe}_{24}\text{O}_{41}$ (SCFO)|Pt heterostructure wherein a highly tunable transverse conical magnetic phase is responsible for static and dynamic magnetoelectric coupling. We measured angular dependence of spin Hall magnetoresistance (SMR) at constant magnetic fields ($H$) in the range of 50 to 100 kOe. Application of field below the critical value (2.5 kOe), yielded negative SMR and the $H$-evolution of normalized SMR exhibited a negative gradient. Further, an increase in the $H$ resulted in the positive slope of normalized SMR Vs. $H$ and later at higher $H$ around 14 kOe, a crossover from negative to positive SMR was observed. We employed a simple model for estimating the equilibrium magnetic configuration and computed the SMR modulation at various values of $H$. We argue that the tilting of the cone is dominant and in turn responsible for the observed nature of SMR below 2.5 kOe while, the closing of the cone-angle is pronounced at higher fields causing a reversal in sign of the SMR from negative to positive. Importantly, SMR experiments revealed that a change in the helicity with a reversal of the magnetic field has no influence on the observed SMR. Longitudinal spin Seebeck effect (LSSE) signal was measured to be 500 nV at 280 K, under application of thermal gradient, $ΔT = 23$ K and field, 60 kOe. The observed LSSE signal, originating from pure magnon spin current, showed a similar $H$-dependent behavior as that of the magnetization of SCFO. Our detailed spin transport studies on polycrystalline SCFO|Pt heterostructure demonstrate high tunability of the amplitude and the sign of the SMR, highlighting its potential for novel spintronic devices such as SMR-based spin valves and voltage-controlled spin transport devices.

cond-mat.mtrl-sci↗

arXiv2022

Probing magnetic anisotropy and spin-reorientation transition in 3D antiferromagnet, Ho$_{0.5}$Dy$_{0.5}$FeO$_{3}\vert$Pt using spin Hall magnetoresistance

Orthoferrites ($RE$FeO$_{3}$) containing rare-earth ($RE$) elements are 3D antiferromagnets (AFM) that exhibit characteristic weak ferromagnetism originating due to slight canting of the spin moments and display a rich variety of spin reorientation transitions in the magnetic field ($H$)-temperature ($T$) parameter space. We present spin Hall magnetoresistance (SMR) studies on a $b$-plate ($ac$-plane) of crystalline Ho$_{0.5}$Dy$_{0.5}$FeO$_{3}|$Pt (HDFO$|$Pt) hybrid at various $T$ in the range, 11 to 300 K. In the room temperature $Γ_4(G_x, A_y, F_z)$ phase, the switching between two degenerate domains, $Γ_4(+G_x, +F_z)$ and $Γ_4(-G_x, -F_z)$ occurs at fields above a critical value, $H_{\text{c}} \approx 713$ Oe. Under $H > H_{\text{c}}$, the angular dependence of SMR ($α$-scan) in the $Γ_4(G_x, A_y, F_z)$ phase yielded a highly skewed curve with a sharp change (sign-reversal) along with a rotational hysteresis around $a$-axis. This hysteresis decreases with an increase in $H$. Notably, at $H < H_{\text{c}} $, the $α$-scan measurements on the single domain, $Γ_4(\pm G_x, \pm F_z)$ exhibited an anomalous sinusoidal signal of periodicity 360 deg. Low-$T$ SMR curves ($H$ = 2.4 kOe), showed a systematic narrowing of the hysteresis (down to 150 K) and a gradual reduction in the skewness (150 to 52 K), suggesting weakening of the anisotropy possibly due to the $T$-evolution of Fe-$RE$ exchange coupling. Below 25 K, the SMR modulation showed an abrupt change around the $c$-axis, marking the presence of $Γ_2(F_x,C_y,G_z)$ phase. We have employed a simple Hamiltonian and computed SMR to examine the observed skewed SMR modulation. In summary, SMR is found to be an effective tool to probe magnetic anisotropy as well as a spin reorientation in HDFO. Our spin-transport study highlights the potential of HDFO for future AFM spintronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Role of a periodic varying deceleration parameter in Particle creation with higher dimensional FLRW Universe

The present search focus on the mechanism of gravitationally influenced particle creation (PC) in higher dimensional Friedmann-Lemaitre-Robertson-Walker(FLRW) cosmological models with a cosmological constant (CC). The solution of the corresponding field equations is obtained by assuming a periodically varying deceleration parameter (PVDP) i.e. $q= m \cos kt - 1$ [Shen and Zhao, Chin. Phys. Lett., 31 (2014) 010401] which gives a scale factor $a(t) = a_0 \left[\tan \left(\frac{kt}{2}\right)\right]^\frac{1}{m}$, where $a_0$ is the scale factor at the current epoch. Here $k$ displays the PVDP periodicity and can be regarded as a parameter of cosmic frequency, $m$ is an enhancement element that increases the PVDP peak. Here, we investigated the periodic variation behavior of few quantities such as the deceleration parameter $q$, the energy density $ρ$, PC rate $ψ$, the entropy $S$, the CC $Λ$, Newton's gravitational constant $G$ and discuss their physical significance. We have also explored the density parameter, proper distance, angular distance, luminosity distance, apparent magnitude, age of the universe, and the look-back time with redshift $z$ and have observed the role of particle formation in-universe evolution in early and late times. The periodic nature of various physical parameters is also discussed which are supporting the recent observations.

physics.gen-ph↗

arXiv2020

Cosmological models of generalized ghost pilgrim dark energy (GGPDE) in the gravitation theory of Saez-Ballester

We are studying the mechanism of the cosmic model in the presence of GGPDE and matter in LRS Bianchi type-I space-time by the utilization of new holographic DE in Saez-Ballester theory. Here we discuss all the data for three scenarios, first is supernovae type Ia union data, second is SN Ia data in combination with BAO and CMB observations and third is combination with OHD and JLA observations. From this, we get a model of our universe, where its transit state from deceleration to acceleration phase. Here we have observed that the results yielded by cosmological parameters like $ρ$ (energy density), EoS (equation of state), squared speed of sound $(v_s^2)$, $(ω_D-ω_D^{'})$ and $(r-s)$ plane is compatible with the recent observational data. The $(ω_D-ω_D^{'})$ trajectories in both thawing and freezing regions and the correspondence of the quintessence field with GGPD dark energy are discussed. Some physical aspects of the GGPDE models are also highlighted.

physics.gen-ph↗

arXiv2020

Electronic Transport through DNA Nucleotides in a BC$_3$ Nanogap for Rapid DNA Sequencing

Recently solid state nanopores nanogaps have generated a lot of interest in ultrafast DNA sequencing. However, there are challenges to slow down the DNA translocation process to achieve a single nucleobase resolution. A series of computational tools have been used in an attempt to study the DNA translocations in several model systems. The prospect of finding an efficient nanoelectrode for such human genome sequencing might offer an entirely innovative way of preventive health care. Here, we have studied the performance of a boron carbide BC$_3$ based nanogap setup for DNA sequencing using the density functional theory and non equilibrium Greens function-based methods. The electric current variations under different applied bias voltages are found to be significant due to changes in the nucleotides orientation and lateral position and can even outperform graphene. Computed relatively lower interaction energy for BC$_3$ electrodes compared to graphene electrodes indicates that BC$_3$ is a better nanoelectrode for DNA sequencing. From our results, we have found that the unique identification of all four nucleotides possible in the 0.3 to 0.4 V bias region. Furthermore, each of the four nucleotides exhibits around one order of current difference, which makes it possible to identify all four nucleotides uniquely. Thus, we believe that BC$_3$ based nanoelectrodes may be utilized toward the development of a practical nanodevice for DNA sequencing.

physics.app-ph↗

arXiv2016

Band Gap Opening in Stanene Induced by Patterned B-N doping

Stanene is a quantum spin hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening in stanene by elemental mono- (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties in stanene. A patterned B-N co-doping opens the band gap in stanene and the semiconducting nature persists with strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such doped system. The stress-strain study indicates that such doped system is as stable as pure stanene. Our work function calculations show that stanene and doped stanene has lower work function than graphene and thus promising material for photocatalysis and electronic devices.

cond-mat.mtrl-sci↗