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Aroonkumar Beesham

Publications and source records attributed to Aroonkumar Beesham.

34 records · Page 2Linked to original sources
arXiv2020

LRS Bianchi I model with constant expansion rate in $f(R,T)$ gravity

An LRS Bianchi-I space-time model is studied with constant Hubble parameter in $f(R,T)=R+2λT$ gravity. Although a single (primary) matter source is considered, an additional matter appears due to the coupling between matter and $f(R,T)$ gravity. The constraints are obtained for a realistic cosmological scenario, i.e., one obeying the null and weak energy conditions. The solutions are also extended to the case of a scalar field (normal or phantom) model, and it is found that the model is consistent with a phantom scalar field only. The coupled matter also acts as phantom matter. The study shows that if one expects an accelerating universe from an anisotropic model, then the solutions become physically relevant only at late times when the universe enters into an accelerated phase. Placing some observational bounds on the present equation of state of dark energy, $ω_0$, the behavior of $ω(z)$ is depicted, which shows that the phantom field has started dominating very recently, somewhere between $0.2\lesssim z\lesssim0.5$.

gr-qc↗
arXiv2020

Plane symmetric model with constant deceleration parameter

A plane symmetric Bianchi I model is considered with constant deceleration parameter, $q=α-1$, where $α\geq0$. The model with $α=0$ violates the NEC throughout the evolution, and hence provides a physically unrealistic scenario. The model with $α\neq0$ obeys the NEC and WEC at late times, which shows that the models in this case can render a physical realistic cosmological scenario, though for a restricted period of time. It is also shown that the physical and kinematical behaviour of both models remain similar to an LRS Bianchi I model.

gr-qc↗
arXiv2019

LRS Bianchi I model with constant deceleration parameter

An LRS Bianchi I model is considered with constant deceleration parameter, $q=α-1$, where $α\geq0$ is a constant. The physical and kinematical behaviour of the models for $α=0$ and $α\neq0$ is studied in detail. The model with $α=0$ describes late time acceleration, but eternal inflation demands a violation of the NEC and WEC. The acceleration is caused by phantom matter which approaches a cosmological constant at late times. The solutions with a scalar field also show that the model is compatible with a phantom field only. A comparison with the observational outcomes indicates that the universe has entered into the present accelerating phase in recent past somewhere between $0.2\lesssim z\lesssim0.5$. The model obeys the "cosmic no hair conjecture". The models with $0<α<1$ describe late time acceleration driven by quintessence dark energy. A violation of the NEC and WEC is required to accommodate the early inflationary epoch caused by phantom matter. The models with $1<α<3$ describe decelerating phases which are usually occur in the presence of dust or radiation. These models are also found anisotropic at early times and attain isotropy at late times. The model for $α=3$ represents a stiff matter era which also has shear at early stages and becomes shear free at late times, but it evolves with an insignificant ceaseless anisotropy. The models with $α>3$ violate the DEC and the corresponding scalar field models have negative potential which is physically unrealistic.

gr-qc↗
arXiv2019

LRS Bianchi I model with perfect fluid equation of state

The general solution of the field equations in LRS Bianchi-I space-time with perfect fluid equation-of-state (EoS) is presented. The models filled with dust, vacuum energy, Zel'dovich matter and disordered radiation are studied in detail. A unified and systematic treatment of the solutions is presented, and some new solutions are found. The dust, stiff matter and disordered radiation models describe only a decelerated universe, whereas the vacuum energy model exhibits a transition from a decelerated to an accelerated phase.

gr-qc↗
arXiv2019

Emergence of warm inflation in curved space-time between accelerating branes

It appears that having our own brane to somehow interact with other branes could give rise to quite an interesting system and that that interaction could lead to some observable effects. We consider the question of whether or not these signatures of interaction between the branes can be observed. To answer this question, we investigate the effect induced by the inflaton in the WMAP7 data using the warm inflationary model. In this model, slow-roll and perturbation parameters are given in terms of the inflaton thermal distribution. We show that this distribution depends on the orbital radius of the brane motion under the interaction potential of other branes in extra dimensions. Thus, an enhancement in the brane inflation can be a signature of an orbital motion in extra dimensions and consequently, some signals of other branes can be detected by observational data. According to experimental data, the N = 50 case leads to ns = 0:96, where N and ns are the number of e-folds and the spectral index, respectively. This standard case may be found in the range 0:01 < R(Tensor-scalar) < 0:22, where R(Tensor-scalar) is the tensor-scalar ratio. We find that at this point, the radial distance between our brane and another brane is R = 1/(1:5GeV ) in intermediate, and R = 1/(0:02225GeV ) in logamediate inflation.

hep-th↗
arXiv2019

A Dark Energy Quintessence Model of the Universe

In this paper, we have presented a model of the FLRW universe filled with matter and dark energy fluids, by assuming an ansatz that deceleration parameter is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating-accelerating transition phase of the universe. This is a quintessence model $ω_{(de)}\geq -1$. The quintessence phase remains for the period $(0 \leq z \leq 0.5806)$. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated.

gr-qc↗
arXiv2019

Tachyonic $δ$-Tsallis entropy of a thermal tachyonic BIon

When a brane and an anti-brane come close to each other, the tachyonic potential between them increases and a tachyon wormhole is formed. This configuration, which consists of two branes and a tachyonic wormhole, is called a thermal tachyonic BIon. By considering the thermodynamic behaviour of this system, one finds that its entropy has the same form as that of the Tsallis one. By decreasing the separation between the branes, the tachyonic potential increases, and the entropy grows.

hep-ph↗
arXiv2019

Expansion and contraction of accretion disks of a rotating thermal BIon in a Rindler space-time

In this paper, we consider the evolution of accretion disks of a rotating BIon in a Rindler space-time. This space-time emerges because of the acceleration of the disks in a BIon. A BIon is constructed from a pair of accretion disks that are connected by a wormhole. We will show that in a rotating BIon, by increasing the rotation velocity, the area of one accretion disk grows, while the area of the other shrinks. Also, we consider four types of accreion disks which are produced in a Rindler space-time.

gr-qc↗
arXiv2019

Emergence and expansion of cosmic space in an accelerating BIon

We generalize the Padmanabhan [arXiv:hep-th/1206.4916] mechanism to an accelerating BIon and show that the difference between the number of degrees of freedom on the boundary surface and the number of degrees of freedom in a bulk region causes the accelerated expansion of a BIon. We also consider the evolution of a universe which emerges on this BIon, and obtain its Hubble parameter and energy density.

gr-qc↗
arXiv2019

A look into the cosmological consequences of a dark energy model with higher derivatives of $H$ in the framework of Chameleon Brans-Dicke Cosmology

In this paper, we study some relevant cosmological features of a Dark Energy (DE) model with Granda-Oliveiros cut-off, which is just a specific case of Nojiri-Odintsov holographic DE unifying phantom inflation with late-time acceleration, in the framework of Chameleon Brans-Dicke (BD) Cosmology. Choosing a particular ansatz for some of the quantities involved, we derive the expressions of some important cosmological quantities, like the Equation of State (EoS) parameter of DE $w_D$, the effective EoS parameter $w_{eff}$, the pressure of DE $p_D$ and the deceleration parameter $q$. Moreover, we study the behavior of statefinder parameters $r$ and $s$, of the cosmographic parameters $j$, $s_{cosmo}$, $l$ and $m$ and of the squared speed of the sound $v_s^2$ for both case corresponding to non interacting and interacting Dark Sectors. We also plot the quantities we have derived and we calculate their values for $t\rightarrow 0$ (i.e. for the beginning of the Universe history), for $t\rightarrow \infty$ (i.e. for far future) and for the present time, indicated with $t_0$. The EoS parameters have been tested against various observational values available in the literature.

gr-qc↗
arXiv2018

Dynamical analysis of a first order theory of bulk viscosity

We perform a global analysis of curved Friedmann-Robertson-Walker cosmologies in the presence of a viscous fluid. The fluid's bulk viscosity is governed by a first order theory recently proposed in [M. M. Disconzi, T. W. Kephart, and R. J. Scherrer, Phys. Rev. D 91, 043532 (2015)], and the analysis is carried out in a compactified parameter space with dimensionless coordinates. We provide stability properties, cosmological interpretation and thermodynamic features of the critical points.

gr-qc↗
arXiv2018

The method of generating functions in exact scalar field cosmology

Exact solutions construction in scalar fields cosmology is of growing interest. In this work we review the results which obtained with the help of one of the most effective method. Namely, the method of generating functions for exact solutions construction in the scalar field cosmology. We also included into debate the superpotential method which may be considered as the bridge to slow roll approximation equations. Basing on the review, we suggested classification for the generating functions and found connection for all of them with the superpotential.

gr-qc↗
arXiv2017

New Exact Solutions for a Chiral Cosmological Model in 5D EGB Gravity

We consider a chiral cosmological model in the framework of Einstein-Gauss-Bonnet cosmology. Using a decomposition of the latter equations in such a way that the first chiral field is responsible for the Einstein part of the model, while the second field together with the kinetic interaction is connected with the Gauss--Bonnet part of the theory, we find new exact solutions for the 2-component chiral cosmological model with and without the kinetic interaction between fields.

gr-qc↗
arXiv2015

A phase space analysis for nonlinear bulk viscous cosmology

We consider a Friedmann-Robertson-Walker spacetime filled with both viscous radiation and nonviscous dust. The former has a bulk viscosity which is proportional to an arbitrary power of the energy density, i.e. $ζ\propto ρ_v^ν$, and viscous pressure satisfying a nonlinear evolution equation. The analysis is carried out in the context of dynamical systems and the properties of solutions corresponding to the fixed points are discussed. For some ranges of the relevant parameter $ν$ we find that the trajectories in the phase space evolve from a FRW singularity towards an asymptotic de Sitter attractor, confirming and extending previous analysis in the literature. For other values of the parameter, instead, the behaviour differs from previous works.

gr-qc↗
arXiv2015

Observational constraints on Modified Chaplygin Gas from Large Scale Structure

We study cosmological models with modified Chaplygin gas (in short, MCG) to determine observational constraints on its EoS parameters. The observational data of the background and the growth tests are employed. The background test data namely, H(z)-z data, CMB shift parameter, Baryonic acoustic oscillations (BAO) peak parameter, SN Ia data are considered to study the dynamical aspects of the universe. The growth test data we employ here consists of the linear growth function for the large scale structures of the universe, models are explored assuming MCG as a candidate for dark energy. Considering the observational growth data for a given range of redshift from the Wiggle-Z measurements and rms mass fluctuations from Ly-$α$ measurements, cosmological models are analyzed numerically to determine constraints on the MCG parameters. In this case, the Wang-Steinhardt ansatz for the growth index $γ$ and growth function $f$ (defined as $f=Ω_{m}^γ (a)$) are also taken into account for the numerical analysis. The best-fit values of the equation of state parameters obtained here are used to study the variation of the growth function ($f$), growth index ($γ$), equation of state parameter ($ω$), squared sound speed $c^2_{s}$ and deceleration parameter with redshift. The observational constraints on the MCG parameters obtained here are then compared with those of the GCG model for viable cosmology. It is noted that MCG models satisfactorily accommodate an accelerating phase followed by a matter dominated phase of the universe. The permitted range of values of the EoS parameters and the associated parameters ($f$, $γ$, $ω$, $Ω$, $c^2_{s}$, $q$) are compared with those obtained earlier using other observations.

astro-ph.CO↗