arXiv subjects

Parviz Goodarzi

Publications and source records attributed to Parviz Goodarzi.

11 recordsLinked to original sources

arXiv2025

Gravitational baryogenesis in $F(R)$ gravity's rainbow

We investigate the gravitational baryogenesis scenario within the context of $F(R)$ gravity's rainbow which incorporates both modified gravity and energy-dependent spacetime. This study explores a mechanism for generating baryon asymmetry based on the interaction between the derivative of the Ricci scalar $R$ and the baryon current within the framework of $F(R)$ gravity's rainbow. The rainbow functions, arising from quantum gravity effects, modify the gravitational interaction and the Friedmann equations, leading to a distinct evolution of the baryon asymmetry compared to standard $F(R)$ gravity. We analyze the conditions under which a viable baryon asymmetry can be produced, taking into account the constraints from cosmological observations and the specific form of the $F(R)$ function. By examining the cosmological equations in the context of $F(R)$ gravity's rainbow, we obtain power-law solutions for these equations. We also identify the decoupling temperature and the ratio of baryonic number to entropy density in this model, depending on the model's parameters. First, we discuss the acceptable intervals of the model's parameters which are defined by constraints on the background quantity. We note that the decoupling temperature and the ratio of baryon-to-entropy in these models depend on the value of the rainbow function. We compare the predictions of this model with the existing observational data. Our results suggest that $F(R)$ gravity's rainbow provides a novel mechanism for gravitational baryogenesis, potentially explaining the observed baryon asymmetry in the universe while incorporating quantum gravity corrections.

gr-qc↗

arXiv2024

Inflation and primordial fluctuations in $f(Q,T)$ gravity

We investigate slow roll inflation and the creation of primordial density fluctuations in the framework of $f(Q,T)$ gravity. Our focus is on constraining the evolution of both the background and perturbations in this theory, specifically using the form $f(Q,T) = \alpha Q + g(T)$, where $g(T)$ is an arbitrary function of the trace of the stress-energy tensor $T$. We derive the Mukhanov-Sasaki equations for scalar and tensor perturbations, and by solving these equations in the slow-roll regime, we compute the power spectra and spectral index for both modes within the general functional framework of $g(T)$. In particular, we examine power law functional forms of $g(T)$ to establish the observational constraints associated with quadratic potential. By imposing constraints on the model's parameters, we obtain results that align closely with the Planck 2018 data and BAO data for the tensor-to-scalar ratio. Notably, a model that includes $g(T) = \beta T^2$ and a quadratic potential yields the best-fit values consistent with the spectral index and tensor-to-scalar ratio suggested by the Planck and BICEP2 results.

gr-qc↗

arXiv2024

Perturbation Spectra of Warm Inflation in $f(Q, T)$ Gravity

We investigate the warm inflationary scenario within the context of the linear version of f (Q, T ) gravity, coupled with both the inflaton scalar field and the radiation field, under the conditions of the strong dissipation regime. First, we calculate the modified Friedmann equations and the modified slow-roll parameters. Subsequently, we apply the slow-roll approximations to derive the scalar power spectrum and the tensor power spectrum. Also, we develop formulations of the scalar and tensor perturbations for the f (Q, T ) gravity with the warm inflation scenario. Furthermore, we scrutinize two different forms of the dissipation coefficient, a constant and a function of the inflaton field, to determine the scalar spectral index, the tensor-to-scalar ratio and the temperature for the power-law potential case. By imposing some constraints on the free parameters of the model, we attain results in good agreement with both the Planck 2018 data and the joint Planck, BK15 and BAO data for the tensor-to-scalar ratio, and consistent results aligned with the Planck 2018 data for the scalar spectral index. In addition, the obtained results are within the range of observational data for the amplitude of the scalar power spectrum. Consequently, we are able to revive the power-law potential that was previously ruled out by observational data. Moreover, for both dissipation coefficients, the model leads to a scalar spectral index with the blue and red tilts in agreement with the WMAP three years data.

gr-qc↗

arXiv2024

Intermediate inflation in generalized non-minimal derivative coupling model

In this work, we consider intermediate inflation in context of the Generalized Non-Minimal Derivative Coupling (GNMDC) model. In this model, inflation is driven by a canonical scalar field that is coupled not only to gravity but also to the derivative of the scalar field. The GNMDC model introduces new dynamics and features during the inflationary epoch. We find inflationary solutions with a power law scalar field for the power law coupling function. Additionally, we determine the inflaton potential that generates intermediate expansion of the scale factor. We also discuss the background equations in the high friction limit and derive constraints on the parameters of our model. Furthermore, we investigate the cosmological perturbations in the slow roll approximation within the GNMDC model, We calculate the scalar and tensor spectral index and the tensor-to-scalar ratio during the intermediate inflation. We compare the results of this model with the observational data that can be used to test the model using the cosmic microwave background radiation data. Overall, we establish conditions for the inflaton potential that ensure the continuation of accelerated expansion during the slow roll inflation. We numerically analyze the power spectrum and spectral index for scalar and tensor modes in intermediate inflation in the high friction limit. Moreover, we use the Planck 2018 data, to obtain constraints on the parameters of the model. We demonstrate that intermediate inflation in the GNMDC model is successful in evaluation and explanation of the background and perturbational quantities using observational data.

hep-th↗

arXiv2023

Gravitational baryogenesis in non-minimal kinetic coupling model

In this work, we consider the gravitational baryogenesis in the framework of non-minimal derivative coupling model. A mechanism to generate the baryon asymmetry based on the coupling between the derivative of the Ricci scalar curvature and the baryon current in context of non-minimal derivative coupling model is investigated. We show that, in this model, the temperature increases during the reheating periods to the end of reheating period or beginning of radiation dominated era. Therefore the reheating temperature is larger then decoupling temperature. It can be demonstrated that, the evaluation of baryon asymmetry is not depends on coupling constant. In this model we can generate baryon asymmetry at low and high reheating temperature, by considering the high friction constraint.

hep-th↗

arXiv2022

Anisotropic inflation in non-minimal kinetic coupling model

We study anisotropic inflation in non-minimal derivative coupling model where the scalar field non-minimally coupled to the $U(1)$ gauge fields and derivative of the scalar field non-minimally coupled to the Einstein tensor. Within the framework we find power-law anisotropic solutions in this model when both the inflaton potential and the gauge kinetic function are power-law type in the high friction regime. We show the ratio of anisotropy to the expansion rate is nearly constant, small and proportional to the slow-roll parameters of the theory. As a demonstration, we consider numerically calculation of the model to show that the behavior of anisotropy by changing the parameters of the model for quadratic inflationary potential. There is anisotropic attractor solution for a wide range of values of the model parameters. We show both numerically and analytically that there are two phases of inflation, similar to those an anisotropic inflation in minimal coupling model, isotropic and anisotropic phase. We can change the number of e-folds corresponding to each phase of slow roll inflation by changing the gauge coupling constant or non-minimal derivative coupling constant. There are the best agreement with the numerically solutions and analytically solutions in this investigation.

hep-th↗

arXiv2017

Warm inflation with an oscillatory inflaton in the non-minimal kinetic coupling model

In the cold inflation scenario, the slow roll inflation and reheating via coherent rapid oscillation, are usually considered as two distinct eras. When the slow roll ends, a rapid oscillation phase begins and the inflaton decays to relativistic particles reheating the Universe. In another model dubbed warm inflation, the rapid oscillation phase is suppressed, and we are left with only a slow roll period during which the reheating occurs. Instead, in this paper, we propose a new picture for inflation in which the slow roll era is suppressed and only the rapid oscillation phase exists. Radiation generation during this era is taken into account, so we have warm inflation with an oscillatory inflaton. To provide enough e-folds, we employ the non-minimal derivative coupling model. We study the cosmological perturbations and compute the temperature at the end of warm oscillatory inflation.

gr-qc↗

arXiv2015

Temperature in warm inflation in non minimal kinetic coupling model

Warm inflation in the non minimal derivative coupling model with a general dissipation coefficient is considered. We investigate conditions for the existence of the slow roll approximation and study cosmological perturbations. The spectral index, and the power spectrum are calculated and the temperature of the universe at the end of the slow roll warm inflation is obtained.

gr-qc↗

arXiv2014

Oscillatory inflation in non-minimal derivative coupling model

Inflation during rapid oscillation of a scalar field in non-minimal derivative coupling model is discussed. Cosmological perturbations originated in this stage are studied and consistency of the results with observational constraints coming from Planck 2013 data are investigated.

astro-ph.CO↗

arXiv2013

Reheating temperature in non-minimal derivative coupling model

We consider the inflaton as a scalar field described by a non-minimal derivative coupling model with a power law potential. We study the slow roll inflation, the rapid oscillation phase, the radiation dominated and the recombination eras respectively, and estimate e-folds numbers during these epochs. Using these results and recent astrophysical data we determine the reheating temperature in terms of the spectral index and the amplitude of the power spectrum of scalar perturbations.

gr-qc↗

arXiv2013

Reheating in nonminimal derivative coupling model

We consider a model with nonminimal derivative coupling of inflaton to gravity. The reheating process during rapid oscillation of the inflaton is studied and the reheating temperature is obtained. Behaviors of the inflaton and produced radiation in this era are discussed.

gr-qc↗