arXiv subjects

Jitendra Kumar

Publications and source records attributed to Jitendra Kumar.

At least 37 records · Page 2Linked to original sources

arXiv2025

Study on physical properties and characteristics of an anisotropic compact star model using Karmarkar Condition in F(Q) gravity

The main aim of this study is to examine the behaviour of physical parameters of an anisotropic compact star model demonstrating spherical symmetry in F(Q) modified gravity. To evaluate the behaviour and the stability of an anisotropic compact star model, we utilise the measured mass and radius of an anisotropic compact star model. This study obtained an anisotropic compact star model by solving Einstein field equations. The field equations have been simplified by an appropriate selection of the metric elements and the Karmarkar condition. By solving the field equation to develop a differential equation that establishes a relationship between two essential components of spacetime. A physical analysis of this model reveals that the resulting stellar structure for anisotropic matter distribution is a physically plausible representation of a compact star with an energy density of order $10^14 g/cm^3$. Using the Tolman-Oppenheimer-Volkoff equation, causality condition and Harrison-Zeldovich-Novikov Condition, we investigate the hydrostatic equilibrium and stability of the compact star Cen X-3. We further determined the mass-radius relation of this compact star for different values of delta}1.

gr-qc↗

arXiv2025

Experimental limits on quantum decoherence from $B$ meson systems

Neutral $B$-meson systems serve as critical tests of the Standard Model and play a key role in limiting its extensions. While these systems are typically studied under the assumption of perfect quantum coherence, interactions with the environment can lead to decoherence. Such decoherence effects can obscure the measured values of key parameters such as the oscillation frequency $ Δm $ and $CP$-violating parameter $ \sin 2β$. Using the experimental data, we present the first combined analysis of mixing asymmetry and $CP$-asymmetry measurements for $ B_d $-mesons, which indicates that $ λ_d $ is non-zero at approximately $ 6 \,σ$. We also establish the first experimental constraints on the decoherence parameter $ λ_s $ for $ B_s $-mesons, finding it to be non-zero at $ 3 \,σ$.

hep-ph↗

arXiv2024

An Intelligent Quantum Cyber-Security Framework for Healthcare Data Management

Digital healthcare is essential to facilitate consumers to access and disseminate their medical data easily for enhanced medical care services. However, the significant concern with digitalization across healthcare systems necessitates for a prompt, productive, and secure storage facility along with a vigorous communication strategy, to stimulate sensitive digital healthcare data sharing and proactive estimation of malicious entities. In this context, this paper introduces a comprehensive quantum-based framework to overwhelm the potential security and privacy issues for secure healthcare data management. It equips quantum encryption for the secured storage and dispersal of healthcare data over the shared cloud platform by employing quantum encryption. Also, the framework furnishes a quantum feed-forward neural network unit to examine the intention behind the data request before granting access, for proactive estimation of potential data breach. In this way, the proposed framework delivers overall healthcare data management by coupling the advanced and more competent quantum approach with machine learning to safeguard the data storage, access, and prediction of malicious entities in an automated manner. Thus, the proposed IQ-HDM leads to more cooperative and effective healthcare delivery and empowers individuals with adequate custody of their health data. The experimental evaluation and comparison of the proposed IQ-HDM framework with state-of-the-art methods outline a considerable improvement up to 67.6%, in tackling cyber threats related to healthcare data security.

cs.CR↗

arXiv2024

A generalized solution for anisotropic compact star model in F(Q) gravity

In this work, we investigate an anisotropic compact star's physical properties and stability in F(Q) gravity. The study focuses on the significance of F(Q) gravity on the structure and stability of compact star, considering non-perfect fluid. Buchdahl ansatz along with transformation used to solve the Einstein field equations. We investigate the physical parameters of the 4U1820-30 compact star using a static spherical metric in the interior region and a Schwarzschild (anti) de-sitter metric in the exterior region. We investigate the behaviour of energy density(rho), radial pressure(pr), tangential pressure(pt), anisotropy, metric potentials, energy state parameters, and energy requirements in the interior of the proposed stellar object. The equilibrium state of this star is analysed using the Tolman-Oppenheimer-Volkoff(TOV) equation and their stability is determined using the regularity condition, causality condition, the adiabatic index(Gamma) method, and Herrera cracking method.

gr-qc↗

arXiv2024

Genuine lepton-flavor-universality-violating observables in the $τ-μ$ sector of $B \to (K,\,K^*) \ell \ell $ decays

It was previously shown that unlike the ratios $R_K^{μe} \equiv R_K \equiv Γ(B \to K μ^+ μ^-)/Γ(B \to K e^+ e^-)$ and $R_{K^*}^{μe} \equiv R_{K^*} \equiv Γ(B \to K^* μ^+ μ^-)/Γ(B \to K^* e^+ e^-)$, the ratios $R_K^{τμ}$ and $R_{K^*}^{τμ}$ can deviate from their Standard Model (SM) predictions even with universal new physics couplings. This observation highlights the critical need to identify and establish genuine lepton flavor universality violating (LFUV) observables in the $τ-μ$ sector. This work embarks on establishing genuine LFUV ratio observables in $B \to K \ell \ell$ and $B \to K^* \ell \ell$ decays through comprehensive analysis of their angular distributions. We find that like $R_{K^*}^{τμ}$, the ratios $R_{A_{FB}}^{τμ}$ and $R_{f_L}^{τμ}$ do not qualify as genuine LFUV observables, whereas the ratios of all optimized observables in $B \to K^* \ell \ell$ decays within the $τ-μ$ sector definitively do. In the case of $B \to K \ell \ell$ decays, similar to $R_K^{τμ}$, the ratio $R_{F_H}$ is influenced by mass effects and therefore cannot be considered a genuine LFUV observable in the $τ-μ$ sector. However, the ratio $Γ_τ(1-F_{H}^τ)/Γ_μ(1-F_{H}^μ)$ stands as the sole genuine LFUV observable in $B \to K \ell \ell$ decays. Furthermore, by making use of new physics Lorentz structures which provide a better fit to the current $b \to s \ell \ell$ data as compared to the SM, we demonstrate how the non-genuine LFUV ratios $R_{A_{FB}}^{τμ}$ and $R_{f_L}^{τμ}$ can be employed to distinguish between framework with solely universal lepton couplings and those with both universal and non-universal couplings.

hep-ph↗

arXiv2024

Hidden photoexcitations probed by multi-pulse photoluminescence

Time-resolved photoluminescence is a validated method for tracking the photoexcited carrier dynamics in luminescent materials. This technique probes the photoluminescence decays upon a periodic excitation by short laser pulses. Herein, we demonstrate that this approach cannot directly detect hidden photoexcitations with much slower dynamics than the photoluminescence decay. We demonstrate a new method based on a multi-pulse excitation scheme that enables an unambiguous detection and an easily interpreted tracking of these hidden species. The multi-pulse excitation consists of a single pulse (Read) followed by a burst of many closely separated pulses (Write) and finally another single pulse (Read). To illustrate the efficacy of the Read-Write-Read excitation scheme, we apply it to metal halide perovskites to directly visualize carrier trapping, extract the concentration of trapped charges and determine the rate constant of trap depopulation. The developed approach allows studying performance-limiting processes in energy devices using a versatile, highly applicable all-optical method.

physics.optics↗

arXiv2023

Memlumor: a luminescent memory device for photonic neuromorphic computing

Neuromorphic computing promises to transform the current paradigm of traditional computing towards Non-Von Neumann dynamic energy-efficient problem solving. Thus, dynamic memory devices capable of simultaneously performing nonlinear operations (volatile) similar to neurons and also storing information (non-volatile) alike brain synapses are in the great demand. To satisfy these demands, a neuromorphic platform has to possess intrinsic complexity reflected in the built-in diversity of its physical operation mechanisms. Herein, we propose and demonstrate the novel concept of a memlumor - an all-optical device combining memory and luminophore, and being mathematically a full equivalence of the electrically-driven memristor. By utilizing metal halide perovskites as a memlumor material platform, we demonstrate the synergetic coexistence of both volatile and non-volatile memory effects within a broad timescale from ns to days. We elucidate the origin of such complex response to be related to the phenomena of photodoping and photochemistry activated by a tunable light input and explore several possible realizations of memlumor computing. Leveraging on the existence of a history-dependent photoluminescent quantum yield in various material platforms, the memlumor device concept will trigger multiple new research directions in both material science and optoelectronics. We anticipate that the memlumor, as a new optical dynamic computing element, will add a new dimension to existing optical technologies enabling their transition into application in photonic neuromorphic computing.

physics.optics↗

arXiv2023

Ehrenfest Paradox: A Careful Examination

The Ehrenfest paradox for a rotating ring is examined and a kinematic resolution, within the framework of the special theory of relativity, is presented. Two different ways by which a ring can be brought from rest to rotational motion, whether by keeping the rest lengths of the blocks constituting the ring constant or by keeping their lengths in the inertial frame constant, are explored and their effect on the length of the material ring in the inertial as well as the co-rotating frame is checked. It is found that the ring tears at a point in the former case and remains intact in the latter case, but in neither of the two cases is the motion of the ring Born rigid during the transition from rest to rotational motion.

gr-qc↗

arXiv2023

Strong Gravitational Lensing by Loop Quantum Gravity Motivated Rotating Black Holes and EHT Observations

We investigate gravitational lensing in the strong deflection regime by loop quantum gravity (LQG)-motivated rotating black hole (LMRBH) metrics with an additional parameter $l$ besides mass $M$ and rotation $a$. The LMRBH spacetimes are regular everywhere, asymptotically encompassing the Kerr black hole as a particular case and, depending on the parameters, describe black holes with one horizon only (BH-I), black holes with an event horizon and a Cauchy horizon (BH-II), black holes with three horizons (BH-III), or black holes with no horizons (NH) spacetime. It turns out that as the LQG parameter $l$ increases, the unstable photon orbit radius $x_{ps}$, the critical impact parameter $u_{ps}$, the deflection angle $α_D(θ)$ and angular position $θ_{\infty}$ also increases. Meanwhile, the angular separation $s$ decreases, and relative magnitude $r_{mag}$ increases with increasing $l$ for prograde motion but they show opposite behaviour for the retrograde motion. For Sgr A*, the angular position $θ_{\infty}$ is $\in$ (16.4, 39.8) $μ$as, while for M87* $\in$ (12.33, 29.9) $μ$as. The angular separation $s$, for SMBHs Sgr A* and M87*, differs significantly, with values ranging $\in$ (0.008-0.376) $μ$as for Sgr A* and $\in$ (0.006-0.282) $μ$as for M87*. We estimate the time delay between the first and second relativistic images using twenty supermassive galactic centre black holes as lenses. Our analysis concludes that, within the $1 σ$ region, a significant portion of the BH-I and BH-II and for a small portion of BH-III parameter space agrees with the EHT results of M87* and Sgr A* whereas NH is completely ruled out. We discover that the EHT results of Sgr A* place more stringent limits on the parameter space of LMRBH black holes than those established by the EHT results of M87*.

gr-qc↗

arXiv2023

Performance Analysis of Machine Learning Centered Workload Prediction Models for Cloud

The precise estimation of resource usage is a complex and challenging issue due to the high variability and dimensionality of heterogeneous service types and dynamic workloads. Over the last few years, the prediction of resource usage and traffic has received ample attention from the research community. Many machine learning-based workload forecasting models have been developed by exploiting their computational power and learning capabilities. This paper presents the first systematic survey cum performance analysis-based comparative study of diversified machine learning-driven cloud workload prediction models. The discussion initiates with the significance of predictive resource management followed by a schematic description, operational design, motivation, and challenges concerning these workload prediction models. Classification and taxonomy of different prediction approaches into five distinct categories are presented focusing on the theoretical concepts and mathematical functioning of the existing state-of-the-art workload prediction methods. The most prominent prediction approaches belonging to a distinct class of machine learning models are thoroughly surveyed and compared. All five classified machine learning-based workload prediction models are implemented on a common platform for systematic investigation and comparison using three distinct benchmark cloud workload traces via experimental analysis. The essential key performance indicators of state-of-the-art approaches are evaluated for comparison and the paper is concluded by discussing the trade-offs and notable remarks.

cs.DC↗

arXiv2023

Investigating Loop Quantum Gravity with EHT Observational Effects of Rotating Black holes

A mathematically consistent rotating black hole model in loop quantum gravity (LQG) is yet lacking. The scarcity of rotating black hole solutions in LQG substantially hampers the development of testing LQG from observations, e.g., from the Event Horizon Telescope (EHT) observations. The EHT observation revealed event horizon-scale images of the supermassive black holes Sgr A* and M87*. The EHT results are consistent with the shadow of a Kerr black hole of general relativity. We present LQG-motivated rotating black hole (LMRBH) spacetimes, which are regular everywhere and asymptotically encompass the Kerr black hole as a particular case. The LMRBH metric describes a multi-horizon black hole in the sense that it can admit up to three horizons, such that an extremal LMRBH, unlike the Kerr black hole, refers to a black hole with angular momentum $a>M$. The metric, depending on the parameters, describes (1) black holes with only one horizon (BH-I), (2) black holes with an event horizon and a Cauchy horizons (BH-II), (3) black holes with three horizons (BH-III) or (4) no-horizon (NH) spacetime, which, we show, is almost ruled out by the EHT observations. We constrain the LQG parameter with the aid of the EHT shadow observational results of M87* and Sgr A*,respectively, for an inclination angle of $17^0$ and $50^0$. In particular, the VLTI bound for the Sgr A*, $δ\in (-0.17,0.01)$, constrains the parameters ($a,l$) such that for $0< l\leq 0.347851M\; (l\leq 2\times 10^6$ km), the allowed range of $a$ is $(0,1.0307M)$. Together with the EHT bounds of Sgr A$^*$ and M87$^*$ observables, our analysis concludes that a substantial part of BH-I and BH-II parameter space agrees with the EHT results of M87* and Sgr A*. While the EHT M87* results totally rule out the BH-III, but not that by Sgr A*.

gr-qc↗

arXiv2022

A Quantum Approach Towards the Adaptive Prediction of Cloud Workloads

This work presents a novel Evolutionary Quantum Neural Network (EQNN) based workload prediction model for Cloud datacenter. It exploits the computational efficiency of quantum computing by encoding workload information into qubits and propagating this information through the network to estimate the workload or resource demands with enhanced accuracy proactively. The rotation and reverse rotation effects of the Controlled-NOT (C-NOT) gate serve activation function at the hidden and output layers to adjust the qubit weights. In addition, a Self Balanced Adaptive Differential Evolution (SB-ADE) algorithm is developed to optimize qubit network weights. The accuracy of the EQNN prediction model is extensively evaluated and compared with seven state-of-the-art methods using eight real world benchmark datasets of three different categories. Experimental results reveal that the use of the quantum approach to evolutionary neural network substantially improves the prediction accuracy up to 91.6% over the existing approaches.

cs.DC↗

arXiv2022

Loop Quantum Gravity motivated multihorizon rotating black holes

With a semiclassical polymerization in the loop quantum gravity (LQG), the interior of Schwarzschild black holes provides a captivating single-horizon regular black hole spacetime. The shortage of rotating black hole models in loop quantum gravity (LQG) substantially restrains the progress of testing LQG from observations. Motivated by this, starting with a spherical LQG black hole as a seed metric, we construct a rotating spacetime using the revised Newman-Janis algorithm, namely, the LQG-motivated rotating black holes (LMRBH), which encompasses Kerr ($l=0$) black holes as an exceptional case. We discover that for any random $l>0$, unlike Kerr black hole, an extremal LMRBH refers to a black hole with angular momentum $a>M$. The rotating metric, in parameter space, describes (1) black holes with an event and Cauchy horizons, (2) black holes with three horizons, (3) black holes with only one horizon or (4) no horizon spacetime. We also discuss the horizon and global structure of the LMRBH spacetimes and its dependence on $l/M$ that exhibits rich spacetime structures in the ($M,\;a,\;l$) parameter space.

gr-qc↗

arXiv2022

Testing strong gravitational lensing effects by supermassive compact objects with regular spacetimes

We compare and contrast gravitational lensing, in the strong-field limit, by photon sphere in spherically symmetric regular electrically charged (REC) black holes ($0 b_E$). Here, $b$ is additional parameter due to charge and the value $b=b_E \approx 0.226$ corresponds to an extremal black hole with degenerate horizons. Interestingly, the spacetime admits photon sphere for $0<b\leq b_P \approx 0.247$ and an anti-photon sphere only for $b_E < b \leq b_P$. With no-horizon spacetime, images by lensing from the inside of the photon sphere ($u<u_{ps}$) can also appear. Interestingly, for the case $u<u_{ps}$ the deflection angle $α_D$ increases with $u$. We analyse the lensing observables by modelling compact objects Sgr A*, M87*, NGC4649, and NGC1332 as black holes and no-horizon spacetimes. The angular position $θ_{\infty}$ and photon sphere radius $x_{ps}$ decrease with increasing parameter $b$. Our findings suggest that the angular separations ($s$) and magnification ($r$) of relativistic images inside the photon sphere may be higher than those outside. Moreover, the time delay for Sgr A* and M87* can reach $\sim$ 8.8809 min and $\sim$ 12701.8 min, respectively, at $b = 0.2$, deviating from Schwarzschild black holes by $\sim$ 2.615 min and $\sim$ 4677 min. These deviations are insignificant for Sgr A* because it is too small, but they are sufficient for astronomical observation of M87* and some other black holes. With EHT bounds on $θ_{sh}$ of Sgr A* and M 87*, within $1 σ$ region, placing bounds on the parameter $b$, our analysis concludes that the REC black holes agree with the EHT results in finite space, whereas the corresponding REC no-horizon spacetimes are completely ruled out.

gr-qc↗

arXiv2022

Mass conserving global solutions for the nonlinear collision-induced fragmentation model with a singular kernel

This article is devoted to the study of existence of a mass conserving global solution for the collision-induced nonlinear fragmentation model which arises in particulate processes, with the singular type of collision kernel. The above mentioned form includes many practical oriented kernels of both singular and non-singular types. The singularity of the unbounded collision kernel at coordinate axes extends the previous existence result and also exhibits at most quadratic growth at infinity. Finally, uniqueness of solution is also investigated.

math.AP↗

arXiv2022

The classification of interior solutions of anisotropic fluid configurations

The Einstein-Maxwell (or Einstein) system of field equations plays a substantial role in the modeling of compact stars. Although due to its non-linearity getting an exact solution for the system of field equations is a difficult task, the solutions of field equations have a long and rich history. It took a year for Karl Schwarzschild to obtain the first exact solution of Einstein's field equations since general theory of relativity was published. The number of viable solutions has been growing since then. Many authors have adopted several methods to obtain the solution. Different models have been constructed for a variety of applications. To produce feasible models of compact stars, a considerable amount of effort has been applied in gaining an understanding of the properties of anisotropic matter. Theoretical study indicates that pressure within compact stars with extreme internal density and strong gravity is mostly anisotropic. Anisotropy was found sufficient for the study of compact stars with the dense nuclear matter. It is claimed that it is important to consider the pressure experienced to be anisotropic whenever relativistic fluids are involved. In this review article, we have discussed different ways of generating a static spherically symmetric anisotropic fluid model. The purpose of the article is to present a simple classification scheme for static and spherically symmetric anisotropic fluid solutions. The known solutions are reviewed and compartmentalized as per the proposed scheme so that we can illustrate general ideas about these solutions without being exhaustive.

gr-qc↗

arXiv2021

An isotropic compact stellar model in curvature coordinate system consistent with observational data

This paper investigates a spherically symmetric compact relativistic body with isotropic pressure profiles within the framework of general relativity. In order to solve the Einstein's field equations, we have considered the Vaidya-Tikekar type metric potential, which depends upon parameter K. We have presented a perfect fluid model, considering K<0 or K>1, which represent compact stars like SMC X-1, Her X-1, 4U 1538-52, SAX J1808.4-3658, LMC X-4, EXO 1785-248 and 4U1820-30, to an excellent degree of accuracy. We have investigated the physical features such as the energy conditions, velocity of sound, surface redshift, adiabatic index of the model in detail and shown that our model obeys all the physical requirements for a realistic stellar model. Using the Tolman-Oppenheimer-Volkoff equations, we have explored the hydrostatic equilibrium and the stability of the compact objects. This model also fulfils the Harrison-Zeldovich-Novikov stability criterion. The results obtained in this paper can be used in analyzing other isotropic compact objects.

astro-ph.GA↗

arXiv2021

Investigating strong gravitational lensing effects by suppermassive black holes with Horndeski gravity

We study gravitational lensing in strong-field limit by a static spherically symmetric black hole in quartic scalar field Horndeski gravity having additional hair parameter $q$, evading the no-hair theorem. We find an increase in the deflection angle $α_D$, photon sphere radius $x_{ps}$, and angular position $θ_{\infty}$ that increases more quickly while angular separation $s$ more slowly, but the ratio of the flux of the first image to all other images $r_{mag}$ decreases rapidly with increasing magnitude of the hair $q$. We also discuss the astrophysical consequences in the supermassive black holes at the centre of several galaxies and note that the black holes in Horndeski gravity can be quantitatively distinguished from the Schwarzschild black hole. Notably, we find that the deviation $Δθ_{\infty}$ of black holes in Horndeski gravity from their general relativity (GR) counterpart, for supermassive black holes Sgr A* and M87, for $q=-1$ respectively, can reach as much as $25.192~μ$as and $18.92~μ$as while $Δs$ is about $1.121~μ$as for Sgr A* and $0.8424~μ$as for M87*. The ratio of the flux of the first image to all other images suggest that the Schwarzschild images are brighter than those of the black holes in Horndeski gravity, wherein the deviation $|Δr_{mag}|$ is as much as 3.082. The results suggest that observational tests of hairy black holes in Horndeski gravity are indeed feasible.

gr-qc↗