arXiv subjects

Abolhassan Mohammadi

Publications and source records attributed to Abolhassan Mohammadi.

29 records · Page 2Linked to original sources

arXiv2021

The tripartite quantum-memory-assisted entropic uncertainty relation and upper bound on shareability of quantum discord

Quantum discord and quantum uncertainty are two important features of the quantum world. In this work, the relation between entropic uncertainty relation and the shareability of quantum discord is studied. First, by using tripartite quantum-memory-assisted entropic uncertainty relation, an upper bound for the shareability of quantum discord among different partites of a composite system is obtained. It is also shown that, for a specific class of tripartite states, the obtained relation could be expressed as monogamy of quantum discord. Moreover, it is illustrated that the relation could be generalized and an upper bound for the shareability of quantum discord for multipartite states is derived.

quant-ph↗

arXiv2021

Tsallis holographic dark energy for inflation

The application of holographic principle in very early time is studied. The consideration of the principle in the late-time evolution will be a good motivation to study its role at the time of inflation. Since the length scale is expected to be small during inflation, the resulted energy density form the holographic principle is expected to be large enough to drive inflation. The entropy of the system is the main part of the holographic principle, in which modifying entropy will leads to a modified energy density. Here, instead of the original entropy, we are going to apply a modified entropy, known as Tsallis entropy which includes quantum corrections. The length scale is assumed to be GO length scale. Finding an analytical solution for the model, the slow-roll parameters, scalar spectral index, and tensor-to-scalar ratio are calculated. Comparing the result, with Planck $r-n_s$ diagram, we could find a parametric space for the constants of the model. Then, a correspondence between the holographic dark energy and the scalar field is constructed, and the outcome potentials are investigated.

gr-qc↗

arXiv2021

Brane inflation and Trans-Planckian censorship conjecture

The constraint of trans-Planckian censorship conjecture on brane inflation model is considered. The conjectures put an upper bound on the main parameter including temperature, inflation time, potential, and the tensor-to-scalar ratio parameter $r$. It is determined that the resulting constraint could be more stronger than what we have for the standard inflationary models. The constraint in general depends on the brane tension and it is concluded that the conjecture also confined the value of brane tension in order to have consistency for the model. Confining the brane tension turns into a determining value for the five-dimensional Planck mass.

hep-th↗

arXiv2020

Revisiting Scalar Tensor inflation by swampland criteria and Reheating

The scenario of the slow-roll inflation is studied in the frame of the scalar-tensor theory of gravity where the scalar field has a non-minimal coupling to the geometric part. After deriving the main dynamical and perturbation equations, the model is investigated in detail for different functions of the potential and the coupling function. Considering the consistency of the model with observational model results into specific ranges for the free constants of the model. Then, the obtained ranges are reconsidered to realize whether they satisfy the swampland criteria. It is found that the swampland criteria impose another limitation and reduce the ranges. Using the final outcomes for the free constants of the model, we briefly consider the reheating phase to find out about the number of e-fold for the phase and the reheating temperature.

gr-qc↗

arXiv2020

Brane Constant-roll Inflation

The scenario of constant-roll inflation in the frame of the RSII brane gravity model is considered. Based on the scenario, the smallness of the second slow-roll parameter is released and it is assumed as a constant which could be of the order of unity. Applying the Hamilton-Jacobi formalism, the constancy of the parameter gives a differential equation for the Hubble parameter which leads to an exact solution for the model. Reconsidering the perturbation equations we show there are some modified terms appearing in the amplitude of the scalar perturbations and in turn in the scalar spectral index and tensor-to-scalar ratio. Comparing the theoretical results of the model with observational data, the free parameters of the model are determined. Then, the consistency of the model with the swampland criteria is investigated for the obtained values of the free parameters. As the final step, the attractor behavior of the model is considered.

gr-qc↗

arXiv2020

Warm Tachyon Inflation and Swampland Criteria

The scenario of two components warm tachyon inflation is considered where the tachyon field plays the role of inflaton and drives inflation. During inflation, the tachyon scalar field interacts with the other component of the Universe which is considered as photon gas, i.e. radiation. The interacting term contains a dissipation coefficient, and the study is modeled based on two different and familiar choices of the coefficient that have been {studied} in the literature. By applying the latest observational data, the acceptable ranges for the free parameters of the model are obtained. For any choice inside the {estimated} ranges, there is an acceptable concordance between the theoretical predictions and observations. Whereas the model is established based on some assumptions, it is vital to check their validity for the obtained values of the free parameters of the model. It is realized that the model is not self-consistent for all values of the ranges and sometimes the assumptions are violated. Therefore, {to have both self-consistency and agreement with data} the parameters of the model need to be {constrained} again. After that, we are going to consider the recently proposed swampland conjecture, which imposes two conditions on the inflationary models. These criteria could rule out some of the inflationary models, however, warm inflation is known as one of those models that could successfully satisfy the swampland criteria. A precise investigation determines that the proposed warm tachyon inflation could not satisfy the swampland criteria for some cases. In fact, for the first case of the dissipation coefficient, where there is dependency only on the scalar field, the model could agree with observational data ...

gr-qc↗

arXiv2019

Beta-function formalism for k-essence constant-roll inflation

The beta function formalism is being used to study the constant-roll inflation in the k-essence model. Assuming the second slow-roll parameter as a constant leads to a first-order differential equation for $β$-function which is much easier to solve and find a solution than the second (non-linear) order equation that we have in corresponding standard constant-roll inflation. Many cosmological models are known as a subclass of k-essence, so we will try to consider the model as general as possible. It is determined that the second slow-roll parameter should be positive to produce a small value for the first slow-roll parameter. The scenario is considered for three well-known cosmological models, and it is clarified that for the non-canonical and tachyon model, the scalar spectral index never reaches the observational range, however for the DBI model, we could arrive at a result consistent with observational data.

gr-qc↗

arXiv2019

Observational constraints on DBI constant-roll inflation

Using the constant-roll approach, DBI inflationary scenario will be studied and it is sought to compare the result with observational data. By considering the cosmological perturbations of the model, it is realized that some extra terms appear in the amplitude of scalar perturbations which indicate that there shuold be a modified version of the scalar spectral index and tensor-to-scalar ratio. In order to compare the model with observational data, some specific functions of scalar field are assumed for the function $f(ϕ)$ function. For the power-law and exponential functions, a constant slow-roll parameter $ε$ is obtained which produced difficulties for the graceful exit from inflation. Then, a product of linear and exponential function, and also a hyperbolic function of scalar field are selected for $f(ϕ)$ that result in a $ε$ with an end for accelerated expansion phase. Considering the scalar spectral index, the amplitude of scalar perturbations and tensor-to-scalar ratio shows that for some values of the constant $η= β$ there could be a good consistency between the model predictions and observational data. In addition, based on the form of the equation of motion of the scalar field, a new interesting definition for the second slow-roll parameters is presented and the behavior of the perturbations is reconsidered. The results come to good consistency with data. Finally, the attractor behavior of these two cases is investigated and it is determined that this feature could be satisfied.

gr-qc↗

arXiv2019

Constant-roll approach to non-canonical inflation

The scenario of constant-roll inflation is studied where the inflaton is a scalar field with modified kinetic term, known as non-canonical scalar field. This modification leads to some changes in the slow-roll parameters, and also by taking the second slow-roll parameter as a constant, the differential equation for the Hubble parameter is altered as well. Assuming $η=β$ and reconsidering the perturbation equations makes it clear that there should be some modified terms in the scalar spectral index and amplitude of scalar perturbations. After finding the exact solution, the main perturbation parameters are obtained at the horizon crossing time. Then by plotting the $r-n_s$ diagram it is shown that for some specific values of $β$ one could find a good agreement with observational data. In addition, considering the attractor behavior of the model leads to this result that this feature could be appropriately satisfied.

astro-ph.CO↗

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↗

arXiv2011

$γ$ Parameter and Solar System constraint in Chameleon Brans Dick Theory

The post Newtonian parameter is considered in the Chameleon-Brans-Dicke frame. In the first step, the general form of this parameter and also effective gravitational constant is obtained. An arbitrary function for $f(Φ)$, which indicates the coupling between matter and scalar field, is introduced to investigate validity of solar system constraint. It is shown that Chameleon-Brans-Dicke model can satisfy the solar system constraint and gives us an $ω$ parameter of order $10^4$, which is in comparable to the constraint which has been indicated in {\cite{17-a}}.

gr-qc↗