arXiv subjects

Ali Aghamohammadi

Publications and source records attributed to Ali Aghamohammadi.

14 recordsLinked to original sources

arXiv2022

Constraints of anisotropy on warm power-law inflation in light of Planck results

In this article, we examine the effects of anisotropy on a model of canonical warm inflation with the power-law potential. The results of this model are compared to Planck satellite observational data. Using a conventional local scalar fi?eld in the Bianchi type I metric, the slow-roll conditions and the suitable regions, where the free parameters of the model show a good agreement with Planck results, are investigated in detail. Following the usual calculations for warm inflationary approaches, the early universe in two different dissipative regimes, namely the weak dissipative and the strong dissipative ones, is investigated. In this regard, the slow-roll parameters and their observational indices in both regimes are obtained and finally, it is shown that this model is in good agreement with observatio

gr-qc↗

arXiv2020

Inflation in String Field Theory

In this paper, we analyze the inflationary cosmology using string field theory. This is done by using the zero level contribution from string field theory, which is a non-local tachyonic action. We will use the non-local Friedmann equations for this model based on string field theory, and calculate the slow-roll parameters for this model. We will then explicitly obtain the scalar and tensorial power spectrum, their related indices, and the tensor-to-scalar ratio for this model. Finally, we use cosmological data from Planck 2013 to 2018 to constrain the free parameters in this model and find that string field theory is compatible with them.

hep-th↗

arXiv2019

Constraints on warm power-law inflation in light of Planck results

The constraints on a general form of the power-law potential and the dissipation coefficient in the framework of warm single field inflation imposed by Planck data will be investigated. {By Considering a quasi-static Universe, besides a slow-roll condition, the suitable regions in which a pair of theoretical free parameters are in good agreement with Planck results will be estimated}. In this method instead of a set of free parameters, we can visualize a region of free parameters that can satisfy the precision limits on theoretical results. On the other side, when we consider the preformed quantity for the amplitude of scalar perturbations, the conflict between obtained results for free parameters in different steps dramatically will be decreased. {As have done in prominent} literature, based on the friction of the environment, we can divide the primordial Universe to the two different epochs namely weak and strong dissipative regimes. For the aforementioned eras, the free parameters of the model will be constrained and the best regions will be obtained. To do so, the main inflationary observables such as tensor-to-scalar ratio, power-spectra of density perturbations and gravitational waves, scalar and tensor spectral indices, running spectral index and the number of e-folds in both weak and strong regimes will be obtained. Ultimately, it can be visualized, this model can make concord between theoretical results and data originated from cosmic microwave background and Planck $2013$, $2015$ and $2018$.

gr-qc↗

arXiv2019

Constraining chameleon field driven warm inflation with Planck 2018 data

We investigate warm inflationary scenario in which the accelerated expansion of the early Universe is driven by chameleon-like scalar fields. Due to the non-minimal coupling between the scalar field and the matter sector, the energy-momentum tensor of each fluid component is not conserved anymore, and the generalized balance equation is obtained. The new source term in the energy equation can be used to model warm inflation. On the other hand, if the coupling function varies slowly, the model reduces to the standard model used for the description of cold inflation. To test the validity of the warm chameleon inflation model, the results for warm inflationary scenarios are compared with the observational Planck2018 Cosmic Microwave Background data. In this regard, the perturbation parameters such as the amplitude of scalar perturbations, the scalar spectral index and the tensor-to-scalar ratio are derived at the horizon crossing in two approximations, corresponding to the weak and strong dissipative regimes. As a general result it turns out that the theoretical predictions of the chameleon warm inflationary scenario are consistent with the Planck 2018 observations.

gr-qc↗

arXiv2019

Non-canonical scalar field in low anisotropy universe with intermediate inflation

The behaviour of a non-canonical scalar field within an anisotropic Bianchi type I, spatially homogeneous, Universe in the framework of the intermediate inflation will be studied. It will be examined on the condition that both the anisotropy and non-canonical sources come together and is there any improvement in compatibility with the observational data originated from plank $2015$?. Based on this investigation it can be observed that automatically a steep potential which can manage inflation in a better way will be obtained. Additionally, as a common procedure for an inflationary study, we shall try to calculate the related inflationary observables such as the amplitude of the scalar perturbations, scalar and tensor spectral indices, tensor-to-scalar ratio, the running spectral index, and the number of e-folds. As an exciting part of our results, we will find that our model has a good consistency compared to data risen by CMB and different Planck results. To justify our claims, the well known canonical inflationary scenario in an anisotropic Bianchi type I Universe also will be evaluated.

physics.gen-ph↗

arXiv2018

Effects of low anisotropy on interacting holographic and new agegraphic scalar fields models of dark energy

A spatially homogeneous and anisotropic Bianchi type I universe is studied with the interacting holographic and new agegraphic scalar fields models of dark energy. Given, the framework of the anisotropic model, both the dynamics and potential of these scalar field models according to the evolutionary behavior of both dark energy models are reconstructed. We also investigate the cosmological evolution of interacting dark energy models, and compare it with observational data and schematic diagram. In order to do so, we focus on observational determinations of the expansion history $H(z)$. Next, we evaluate effects of anisotropy on various topics, such as evolution of the growth of perturbations in the linear regime, statefinder diagnostic, Sandage-Loeb (SL) test and distance modulus from holographic and new agegraphic dark energy models and compare the results with standard FRW and $Λ$CDM and $w$CDM models. Our numerical result show the effects of the interaction and anisotropy on the evolutionary behavior the new agegraphic scalar field models

gr-qc↗

arXiv2018

Anisotropy effects on Baryogenesis in $f(R)$-Theories of Gravity

We study the $f(R)$ theory of gravity in an anisotropic metric and its effect on the baryon number to entropy ratio. The mechanism of gravitational baryogenesis based on the CPT-violating gravitational interaction between derivative of the Ricci scalar curvature and the baryon-number current is investigated in the context of the $f(R)$ gravity. The gravitational baryogenesis in the Bianchi type I universe is examined. We survey the effect of anisotropy of the universe on the baryon asymmetry from point of view the $f(R)$-theories of gravity and its effect on $n_{b}/s$ for radiation dominant regime.

physics.gen-ph↗

arXiv2018

Noether Symmetry in f(T) Theory at the anisotropic universe

As it is well known, symmetry plays a crucial role in the theoretical physics. On other hand, the Noether symmetry is a useful procedure to select models motivated at a fundamental level, and to discover the exact solution to the given lagrangian. In this work, Noether symmetry in f(T) theory on a spatially homogeneous and anisotropic Bianchi type I universe is considered. We discuss the Lagrangian formalism of f(T) theory in anisotropic universe. The point-like Lagrangian is clearly constructed.The explicit form of f(T) theory and the corresponding exact solution are found by requirement of Noether symmetry and Noether charge. A power-law f(T), the same as the FRW universe, can satisfy the required Noether symmetry in the anisotropic universe with power- law scale factor. It is regarded that positive expansion is satisfied by a constrain between parameters.

physics.gen-ph↗

arXiv2016

Hamilton-Jacobi formalism for inflation with non-minimal derivative coupling

In inflation with nonminimal derivative coupling there is not a conformal transformation to the Einstein frame where calculations are straightforward, and thus in order to extract inflationary observables one needs to perform a detailed and lengthy perturbation investigation. In this work we bypass this problem by performing a Hamilton-Jacobi analysis, namely rewriting the cosmological equations considering the scalar field to be the time variable. We apply the method to two specific models, namely the power-law and the exponential cases, and for each model we calculate various observables such as the tensor-to-scalar ratio, and the spectral index and its running. We compare them with 2013 and 2015 Planck data, and we show that they are in a very good agreement with observations.

gr-qc↗

arXiv2016

The effect of de Sitter like background on increasing the zero point budget of dark energy

During this work, using subtraction renormalization mechanism, zero point quantum fluctuations for bosonic scalar fields in a de-Sitter like background are investigated. By virtue of the observed value for spectral index, $n_s(k)$, for massive scalar field the best value for the first slow roll parameter, $ε$, is achieved. In addition the energy density of vacuum quantum fluctuations for massless scalar field is obtained. The effects of these fluctuations on other components of the Universe are studied. By solving the conservation equation, for some different examples, the energy density for different components of the Universe are obtained. In the case which, all components of the Universe are in an interaction, the different dissipation functions, $\tilde{Q}_{i}$, are considered. The time evolution of ${ρ_{DE}(z)}/{ρ_{cri}(z)}$ shows that $\tilde{Q}=3 γH(t) ρ_{m}$ has best agreement in comparison to observational data including CMB, BAO and SNeIa data set.

gr-qc↗

arXiv2016

Interacting scalar tensor cosmology in light of SNeIa, CMB, BAO and OHD observational data sets

During this work, an interacting chameleon like scalar field scenario, by considering SNeIa, CMB, BAO and OHD data sets is investigated. In fact, the investigation is realized by introducing an ansatz for the effective dark energy equation of state, which mimics the behaviour of chameleon like models. Based on this assumption, some cosmological parameters including Hubble, deceleration and coincidence parameters in such mechanism are analysed. It is realized that, to estimate the free parameters of a theoretical model, by regarding the systematic errors it better the whole of the above observational data sets to be considered. In fact, if one considers SNeIa, CMB and BAO but disregards OHD it maybe leads to different results. Also to get a better overlap between the counters with the constraint $χ_{\rm{m}}^2\leq 1$, the $χ_{\rm{T}}^2$ function could be re-weighted. The relative probability functions are plotted for marginalized likelihood $\mathcal{L} (Ω_{\rm{m0}} ,ω_1, β)$ according to two dimensional confidence levels $68.3\%$, $90\%$ and $95.4\%$. Meanwhile, the value of free parameters which maximize the marginalized likelihoods using above confidence levels are obtained. In addition, based on these calculations the minimum value of $χ^2$ based on free parameters of an ansatz for the effective dark energy equation of state are achieved.

astro-ph.CO↗

arXiv2015

Non-commutative and commutative vacua effects in a scalar torsion scenario

In this work, the effects of non-commutative and commutative vacua on the phase space generated by a scalar field in a scalar torsion scenario are investigated. For both classical and quantum regimes, the commutative and non-commutative cases are compared. To take account the effects of non-commutativity, two well known non-commutative parameters, $θ$ and $β,$ are introduced. It should be emphasized, the effects of $β$ which is related to momentum sector has more key role in comparison to $θ$ which is related to space sector. Also the different boundary conditions and mathematical interpretations of non-commutativity are explored.

gr-qc↗

arXiv2008

Connection between matrix-product states and superposition of Bernoulli shock measures

We consider a generalized coagulation-decoagulation system on a one-dimensional discrete lattice with reflecting boundaries. It is known that a Bernoulli shock measure with two shock fronts might have a simple random-walk dynamics, provided that some constraints on the microscopic reaction rates of this system are fulfilled. Under these constraints the steady-state of the system can be written as a linear superposition of such shock measures. We show that the coefficients of this expansion can be calculated using the finite-dimensional representation of the quadratic algebra of the system obtained from a matrix-product approach.

cond-mat.stat-mech↗

arXiv2008

Finite-dimensional representation of the quadratic algebra of a generalized coagulation-decoagulation model

The steady-state of a generalized coagulation-decoagulation model on a one-dimensional lattice with reflecting boundaries is studied using a matrix-product approach. It is shown that the quadratic algebra of the model has a four-dimensional representation provided that some constraints on the microscopic reaction rates are fulfilled. The dynamics of a product shock measure with two shock fronts, generated by the Hamiltonian of this model, is also studied. It turns out that the shock fronts move on the lattice as two simple random walkers which repel each other provided that the same constraints on the microscopic reaction rates are satisfied.

cond-mat.stat-mech↗