arXiv subjects

Z. Sakhi

Publications and source records attributed to Z. Sakhi.

14 recordsLinked to original sources

arXiv2025

Benchmarking VQE Configurations: Architectures, Initializations, and Optimizers for Silicon Ground State Energy

Quantum computing presents a promising path toward precise quantum chemical simulations, particularly for systems that challenge classical methods. This work investigates the performance of the Variational Quantum Eigensolver (VQE) in estimating the ground-state energy of the silicon atom, a relatively heavy element that poses significant computational complexity. Within a hybrid quantum-classical optimization framework, we implement VQE using a range of ansatz, including Double Excitation Gates, ParticleConservingU2, UCCSD, and k-UpCCGSD, combined with various optimizers such as gradient descent, SPSA, and ADAM. The main contribution of this work lies in a systematic methodological exploration of how these configuration choices interact to influence VQE performance, establishing a structured benchmark for selecting optimal settings in quantum chemical simulations. Key findings show that parameter initialization plays a decisive role in the algorithm's stability, and that the combination of a chemically inspired ansatz with adaptive optimization yields superior convergence and precision compared to conventional approaches.

quant-ph↗

arXiv2024

Signatures of the Early Universe: Uncovering Cosmological Footprints

The post-inflationary epochs are critical for comprehending the early evolution of our Universe. This article delves into the cosmological signatures that shed light on these early epochs, particularly focusing on the generation of various phenomena such as matter production via inflaton oscillation and parametric resonance, primordial black holes, and gravitational waves. We review the theoretical frameworks that could produce these signatures and discuss the current observational constraints along with prospects for future detection. Furthermore, we explore the implications of such observations for our understanding of the physics of the early Universe.

gr-qc↗

arXiv2023

Dark matter via Baryogenesis: Affleck-Dine Mechanism in the Minimal Supersymmetric Standard Model

We conducted an investigation into Affleck-Dine baryogenesis within the context of D-term inflation, specifically focusing on its relationship with a recent reheating formalism. It was found that by considering a specific reheating temperature, the observed baryon asymmetry can be accounted through Affleck-Dine baryogenesis. Additionally, the majority of gravitinos are inferred to be generated from the decay of the next-to-lightest supersymmetric particle, with Q-balls potentially serving as a source of gravitinos via NSP decay. The temperature at which decay occurs depends on the charge of the Q-balls, which is determined by the fragmentation of the Affleck-Dine condensate. Remarkably, the gravitino mass required for dark matter aligns naturally with the theoretical gravitino mass.

hep-ph↗

arXiv2023

Quintessence like behavior of symmetric teleparallel dark energy: Linear and nonlinear model

In Einstein's General Relativity (GR), the gravitational interactions are described by the spacetime curvature. Recently, other alternative geometric formulations and representations of GR have emerged in which the gravitational interactions are described by the so-called torsion or non-metricity. Here, we consider the recently proposed modified symmetric teleparallel theory of gravity or $f\left( Q\right) $ gravity, where $Q$ represents the non-metricity scalar. In this paper, motivated by several papers in the literature, we assume the power-law form of the function $% f\left( Q\right) $ as $f\left( Q\right) =αQ^{n+1}+β$ (where $% α$, $β$, and $n$ are free model parameters) that contains two models: Linear ($n=0$) and nonlinear ($n\neq 0$). Further, to add constraints to the field equations we assume the deceleration parameter form as a divergence-free parametrization. Then, we discuss the behavior of various cosmographic and cosmological parameters such as the jerk, snap, lerk, $Om$ diagnostic, cosmic energy density, isotropic pressure, and equation of state (EoS) parameter with a check of the violation of the strong energy condition (SEC) to obtain the acceleration phase of the Universe. Hence, we conclude that our cosmological $f(Q)$ models behave like quintessence dark energy (DE).

gr-qc↗

arXiv2023

Observational constraints on Tachyon inflation and reheating in f(Q) gravity

In this work we study one of the most appealing string theory-motivated models, we present a tachyonic inflationary model in the recently proposed symmetric teleparallel framework, and examine constraints on tachyon inflation with the exponential potential along with the reheating for a chosen $f(Q)$ gravity model. Considering a reheating phase parametrized by a number of e-folds $N_{re},$ a temperature $T_{re}$, and an equation of state $ω_{re}$, we relate the reheating parameters as functions of the exponential tachyon potential, $f(Q)$ model, and\ the spectral index $n_{s}$ parameters. We argue that our model predicts inflationary e-folds bounded as $50\leq N\leq 64$. While for the reheating phase, wide ranges of reheating e-folds numbers and temperatures can be obtained as we increase $ω_{re} $ towards the value $1/4$ according to recent Planck Data.

gr-qc↗

arXiv2022

Primordial black holes and gravitational waves in teleparallel Gravity

In this paper, we consider the possible effect of the teleparallel gravity on the production of the primordial black holes (PBH) and on the gravitational waves (GWs). We investigate the relationship between the slow roll, the e-folds number and the teleparallel parameters. We show that in the case of the teleparallel parameter $δ=3$, the e-folds number reaches the values $50$ and $60$ in consistency with the contour plot of the $(r,n_{s})$ plane obtained by Planck data at $1σ$ and $2σ$ C.L.. Furthermore, we use the fraction of the energy density and the variance of the density perturbations approach to study the abundance of the production PBH. We find that the PBH overproduction can be satisfied for specific values of parameters of the non-adiabatic curvature power spectrum at some narrow parametric resonance. Moreover, to explain the GWs expected by observations, the duration of preheating should be bounded by values less or equal to $2$. This bound is in agreement with values of the tensor-to-scalar ratio and the spectral index constrained by Planck data.

gr-qc↗

arXiv2022

Gravitational Waves from Preheating in Gauss-Bonnet Inflation

We study gravitational wave production in an expanding Universe during the first stages following inflation, and investigate the consequences of the Gauss-Bonnet term on the inflationary parameters for a power-law inflation model with a GB coupling term. Moreover, we perform the analyses on the preheating parameters involving the number of e-folds $N_{pre}$, and the temperature of thermalization $T_{th},$ and show that it's sensitive to the parameters $n$, and $γ$, the parameter $γ$ is proposed to connect the density energy at the end of inflation to the preheating energy density. We set a correlation of gravitational wave energy density spectrum with the spectral index $n_{s}$ detected by the cosmic microwave background experiments$.$ The density spectrum $Ω_{gw}$ shows good consistency with observation for $γ= 10^{3}$ and $10^{6}$. Our findings suggest that the generation of gravitational waves (GWs) during preheating can satisfy the constraints from Planck's data.

gr-qc↗

arXiv2022

Preheating constraints in $α$-attractor inflation and Gravitational Waves production

We propose a scenario where preheating occurs for a specific duration that is parametrized by an e-folds number $N_{pre}$, our results suggest a direct correlation between the preheating duration and the density of gravitational waves (GWs) produced during this phase. Moreover, we investigate the consequences of the inflationary parameters on the $α$-attractor E model in the small $α$ limits. In this framework, we perform investigations on the preheating parameters involving the number of e-folds $N_{pre}$, and the temperature of reheating $T_{re}$, then we show that the parameter $n$ associated with the E model of $α$-attractor inflation has a negligible effect on the preheating duration, and we demonstrate that gravitational wave generation during preheating satisfies the restrictions from Planck's recent data.

gr-qc↗

arXiv2022

Flat FLRW Universe in logarithmic symmetric teleparallel gravity with observational constraints

In this paper, we investigate the homogeneous and isotropic flat FLRW Universe in the logarithmic form of $f\left( Q\right) $ gravity, where $% Q $ is the non-metricity scalar, specifically, $f\left( Q\right) =α+β\log \left( Q\right) $, where $α$ and $β$ are free model parameters. In this study, we consider a parametrization of the Hubble parameter as $H\left( z\right) =η\left[ (z+1)^{-γ}+1\right] $, where $γ$ and $η$ are model/free parameters which are constrained by an $R^{2}$-test from 57 points of the Hubble datasets in the redshift range $0.07<z<2.36$. Further, we investigate the physical properties of the model. We analyze the energy conditions to check the compatibility of the model. We found the SEC is violated for the logarithmic form of $f\left( Q\right) $ gravity due to the reality that the Universe in an accelerating phase. Finally, we discuss some important cosmological parameters in this context to compare our model with dark energy models such as jerk parameter and statefinder parameters.

gr-qc↗

arXiv2021

Preheating and Reheating Constraints in Supersymmetric Braneworld Inflation

We study the evolution of the Universe at early stages, we discuss also preheating in the framework of hybrid braneworld inflation by setting conditions on the coupling constants $λ$ and $g$\ for effective production of $χ$-particles. Considering the phase between the time observable CMB scales crossed the horizon and the present time, we write reheating and preheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in terms of the scalar spectral index $n_{s}$, and prove that, unlike the reheating case, the preheating duration does not depend on the values of the equation of state $ω^{\ast }$. We apply the slow-roll approximation in the high energy limit to constrain the parameters of D-term hybrid potential. We show also that some inflationary parameters, in particular, the spectral index $n_{s}$ demand that the potential parameter $α$ is bounded as $α\geq 1$ to be consistent with $Planck$'s data, while the ratio $r$ is in agreement with observation for $ α\leq 1 $ considering high inflationary e-folds. We also propose an investigation of the brane tension effect on the reheating temperature. Comparing our results to recent CMB measurements, we study preheating and reheating parameters $N_{re}$, $T_{re}$ and $N_{pre}$ in the Hybrid D-term inflation model in the range $0.8\leq α\leq 1.1$\, and conclude that $T_{re}$ and $N_{re}$ require $α\leq 1$, while for $N_{pre}$ the condition $α\leq 0.9$ must be satisfied, to be compatible with $Planck$'s results.

astro-ph.CO↗

arXiv2020

A new unified model of dark matter and dark energy in 5-dimensional $f(R,ϕ)$ gravity

We propose a new unified model that describes~dark energy and dark matter in the context of $f(R,ϕ)$ gravity using a massive scalar field in five dimensions. The scalar field is considered in the bulk that surrounds the 3-brane in branworld model. We show that for a specific choice of the $% f(R,ϕ)$ function, we can describe the Einstein gravitation in 4-dimensional space-time. We obtain a relationship between the speed of the universe's expansion and the speed of the bulk's expansion. We also propose that the dark matter is represented by the scalar field mass and that the dark energy is a kinetic energy of this field. Finally, we show that, according to conditions, one can obtain the percentages of density\ of dark matter and the density of ordinary matter.

gr-qc↗

arXiv2011

On Braneworld Inflation Models in Light of WMAP7 data

We are interested on studing various inflationary spectrum perturbation parameters in the context of the Randall-Sandrum type 2 Braneworld model. We consider in particular three types of potentials. We apply the slow-roll approximation in the high energy limit to constraint the parameter potentials by confronting our results to recent WMAP7 observations. We show that, for some values of the e-folding number N; the monomial potential provides the best fit results to observations data.

hep-th↗

arXiv2009

WMAP5 Observationnal Constraints on Braneworld New Inflation Model

We study a new inflation potential in the framework of the Randall-Sundrum type 2 Braneworld model. Using the technic developped in(Phys. Rev. D75, 123504 (2007).1), we consider both an monomial and a new inflation potentials and apply the Slow-Roll approximation in high energy limit, to derive analytical expression of relevant perturabtion spectrum. We show that for some values of the parameter n of the potential, we obtain an perturbation spectrum wich present a good agreement with recent WMAP5 observations.

hep-th↗

arXiv2008

On Inflation Potentials in Randall-Sundrum Braneworld Model

We study the inflationary dynamics of the universe in the Randall-Sandrum typeII Braneworld model. We consider both an inverse-power law and exponential potentials and apply the Slow-Roll approximation in high energy limit to derive analytical expression of relevant inflationary quantities. An upper bound for the coupling constant was also obtained and a numerical value of perturbation spectrum is calculated in good agreement with observation.

gr-qc↗