arXiv subjects

Goutam Manna

Publications and source records attributed to Goutam Manna.

32 records · Page 2Linked to original sources

arXiv2023

Evaporation of dynamical horizon with the Hawking temparature in the {\bf K-}essence emergent Vaidya spacetime

In the {\bf K-}essence Vaidya Schwarzschild spacetime, we apply the dynamical horizon equation to measure the mass-loss due to Hawking radiation and the tunneling formalism (Hamilton-Jacobi method) to calculate the hawking temperature. Assuming the Dirac-Born-Infeld kind of non-standard action for the {\bf K-}essence here, the background physical spacetime is a static spherically symmetric black hole, and we constrain the {\bf K-}essence scalar field to be a function only of either forward or backward time. The {\bf K-}essence emergent gravity and the generalizations of Vaidya spacetime have been linked by Manna et al. In this paper, we use Sawayama's modified description of the dynamical horizon to show that the obtained findings deviate from the standard Vaidya spacetime geometry.

gr-qc↗

arXiv2023

Raychaudhuri equation in $k$-essence geometry: conditional singular and non-singular cosmological models

We investigate how the Raychaudhuri equation behaves in the $k$-essence geometry. As far as we are concerned, both the early and current epochs of the universe are relevant to the $k$-essence theory. Here, we have studied the $k$-essence geometry using the Dirac-Born-Infeld (DBI) variety of non-standard action. The corresponding $k$-essence emergent spacetime is not conformally equivalent to the usual gravitational metric. We assume that the background gravitational metric is of the Friedmann-Lemaitre-Robertson-Walker (FLRW) type in this case. We have found that both the conditional singular and non-singular cosmological models of the universe through the modified Raychaudhuri equation are possible where we have used the spacetime as the flat $k$-essence emergent FLRW-type. We have also addressed to the Focusing theorem and conditional caustic universe construction. These conditional effects are caused by the additional interactions that arise as a result of the coupling that exists between the gravity and the $k$-essence scalar field.

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arXiv2022

$f(\bar{R}, L(X))$-gravity in the context of dark energy with power law expansion and energy conditions

The motto of this work is to generate a general formalism of $f(\bar{R}, L(X))-$gravity in the context of dark energy under the framework of the {\bf K-}essence emergent geometry with the Dirac-Born-Infeld (DBI) variety of action, where $\bar{R}$ is the familiar Ricci scalar, $L(X)$ is the DBI type non-canonical Lagrangian with $X={1\over 2}g^{μν}\nabla_μϕ\nabla_νϕ$ and $ϕ$ is the {\bf K-}essence scalar field. The emergent gravity metric $\bar{G}_{μν}$ and the well known gravitational metric $g_{μν}$ are not conformally equivalent. We have constructed a modified field equation using the metric formalism in $f(\bar{R}, L(X))$-gravity incorporating the corresponding Friedmann equations in the framework of the background gravitational metric which is of Friedmann-Lema{î}tre-Robertson-Walker (FLRW) type. The solution of modified Friedmann equations have been deduced for the specific choice of $f(\bar{R}, L(X))$, which is of Starobinsky-type, using power law expansion method. The consistency of the model with the accelerating phase of the Universe has been shown, when we restrict ourselves to consider the value of the dark energy density, as $\dotϕ^{2}=\frac{8}{9}=0.888 <1$, which indicates that the present Universe is dark energy dominated. Graphical plots for the energy density ($ρ$), pressure ($p$) and equation of state parameter ($ω$) w.r.t. time ($t$) based on parametric values are interestingly consistent with the dark energy domination and hence accelerating features. We also put some light on the corresponding energy conditions and constraints of the $f(\bar{R}, L(X))$ theory with one basic example.

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arXiv2022

Collapsing scenario for the k-essence emergent generalised Vaidya spacetime in the context of massive gravity's rainbow

In this paper, we study the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow. For this study, we consider that the background metric is Vaidya spacetime in massive gravity's rainbow. We show that the k-essence emergent gravity metric resembles closely to the new type of generalized Vaidya massive gravity metric with the rainbow deformations for null fluid collapse where we consider the k-essence scalar field as a function solely of the advanced or the retarded time. The k-essence emergent Vaidya massive gravity rainbow mass function is also different. This new type k-essence emergent Vaidya massive gravity rainbow metric has satisfied the required energy conditions. The existence of the locally naked central singularity, the strength and the strongness of the singularities for the rainbow deformations of the k-essence emergent Vaidya massive gravity metric are the interesting outcomes of the present work.

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arXiv2020

Gravitational Collapse for the K-essence Emergent Vaidya Spacetime

In this paper, we study the gravitational collapse in the {\bf k-}essence emergent gravity using a generalized Vaidya-type metric as a background. We also analyze the cosmic censorship hypothesis for this system. We show that the emergent gravity metric resembles closely to the new type of the generalized Vaidya metrics for null fluid collapse with the {\bf k-}essence emergent mass function, where we consider the {\bf k-}essence scalar field being a function solely of the advanced or the retarded time. This new type of {\bf k-}essence emergent Vaidya metric has satisfied the required energy conditions. The existence of the locally naked central singularity, the strength and the strongness of the singularities for the {\bf k-}essence emergent Vaidya metric are the interesting outcomes of the present work.

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arXiv2020

K-essence Emergent Spacetime as Generalized Vaidya Geometry

We establish a formal connection between the {\bf K}-essence emergent gravity scenario and generalizations of Vaidya spacetime. Choosing the {\bf K}-essence action to be of the Dirac-Born-Infeld variety, the physical spacetime to be a general static spherically symmetric black hole and restricting the {\bf K}-essence scalar field to be a function solely of the advanced or the retarded time, we show that the emergent gravity metric resembles closely the generalized Vaidya metrics for null fluid collapse proposed by Husain. Imposing null energy conditions on the emergent energy-momentum tensor derived from the emergent Einstein equation, restrictions are obtained on the functions characterizing the emergent metric for consistent identification with generalized Vaidya spacetimes. We discuss the possibility of dynamical horizons in the {\bf K-}essence emergent Vaidya spacetime. Admissible explicit black hole background metrics are discussed as examples.

gr-qc↗

arXiv2020

Time-like geodesic structure for the K-essence Emergent Barriola-Vilenkin type spacetime

For a particular type of {\bf k-}essence scalar field, the {\bf k-}essence emergent gravity metric is exactly mapped on to the Barriola-Vilenkin (BV) type metric for Schwarzschild background established by Gangopadhyay and Manna. Based on the S. Chandrasekhar, we report the exciting features of the time-like geodesic structure in the presence of dark energy in an emergent gravity scenario for this Barriola-Vilenkin type metric. We trace the different kinds of trajectories for time-like geodesic in the presence of dark energy for the {\bf k-}essence emergent Barriola-Vilenkin spacetime, which is same as the Schwarzchild spacetime in view of the basic orientation, but the allowed ranges of the aphelion and perihelion distances are much more different. The bound and unbound orbits are plotted for a fixed value of the dark energy density.

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arXiv2019

Thermodynamics for the k-essence Emergent Reissner-Nordstrom-de Sitter Spacetime

The {\bf k-}essence emergent Reissner-Nordstrom-de Sitter spacetime has exactly mapped on to the Robinson-Trautman (RT) type spacetime with cosmological constant $Ł$ for certain configuration of {\bf k-}essence scalar field. Theoretically, we evaluated that the thermodynamical quantities for the RT type emergent black hole is different from the usual one in the presence of kinetic energy of the {\bf k-}essence scalar field i.e., the dark energy density. We restrict ourselves into the fact that the dark energy density (K) is to be unity, then the effective temperature and pressure both are negative for the RT type emergent black hole which implies that the system is thermodynamically unstable when the charge $Q\neq 0$ and the emergent spacetime is only dark energy dominated and it does not radiate when $Q=0$. The thermodynamically unstable situation is physically plausible only when we consider spin degrees of freedom of a system. We have made this analysis in the context of dark energy in an emergent gravity scenario having {\bf k-}essence scalar fields $ϕ$ with a Dirac-Born-Infeld type lagrangian. The scalar field also satisfies the emergent equation of motion at $r\rightarrow\infty$.

gr-qc↗

arXiv2019

The Hawking temperature in the context of dark energy for Kerr-Newman and Kerr-Newman-AdS backgrounds

We show that the Hawking temperature is modified in the presence of dark energy in an emergent gravity scenario for Kerr-Newman(KN) and Kerr-Newman-AdS(KNAdS) background metrics. The emergent gravity metric is not conformally equivalent to the gravitational metric. We calculate the Hawking temperatures for these emergent gravity metrics along $θ=0$. Also we show that the emergent black hole metrics are satisfying Einstein's equations for large $r$ and $θ=0$. Our analysis is done in the context of dark energy in an emergent gravity scenario having $k-$essence scalar fields $ϕ$ with a Dirac-Born-Infeld type lagrangian. In KN and KNAdS background, the scalar field $ϕ(r,t)=ϕ_{1}(r)+ϕ_{2}(t)$ satisfies the emergent gravity equations of motion at $r\rightarrow\infty$ for $θ=0$.

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arXiv2015

Cosmology in presence of dark energy in an emergent gravity scenario

We obtain the analogues of the Friedman equations in an emergent gravity scenario in the presence of dark energy. The background metric is taken to be Friedman-Lemaitre-Robertson-Walker (FLRW). We show that if $\dotϕ^{2}$ is the dark energy density (in units of the critical density) then (a) for total energy density greater than the pressure (non-relativistic scenario, matter domination) the deceleration parameter $q(t)\approx\frac {1}{2} [1 + 27 \dotϕ^{2}+...] > \frac{1}{2}$ (b) for total energy density equal to 3 times the pressure (relativistic case, radiation domination), the deceleration parameter $q(t)\approx 1 + 18\dotϕ^{2} +... > 1$ and (c) for total energy density equal to the negative of the pressure (dark energy scenario), the deceleration parameter $q(t)< -1$. Our results indicate that many aspects of standard cosmology can be accommodated with the presence of dark energy right from the beginning of the universe where the time parameter $t\equiv \frac{t}{t_{0}}$, $t_{0}$ being the present epoch.

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arXiv2014

The Hawking Temperature in the context of Dark Energy for Reissner-Nordstrom and Kerr background

For emergent gravity metrics, presence of dark energy modifies the Hawking temperature. We show that for the spherically symmetric Reissner-Nordstrom (RN) background metric, the emergent metric can be mapped into a Robinson-Trautman blackhole. Allowed values of the dark energy density follow from rather general conditions. For some allowed value of the dark energy density this blackhole can have zero Hawking temperature i.e. the blackhole does not radiate. For a Kerr background along $θ=0$, the emergent blackhole metric satisfies Einstein's equations for large $r$ and always radiates. Our analysis is done in the context of emergent gravity metrics having $k-$essence scalar fields $ϕ$ with a Born-Infeld type lagrangian. In both cases the scalar field $ϕ(r,t)=ϕ_{1}(r)+ϕ_{2}(t)$ also satisfies the emergent gravity equations of motion for $r\rightarrow\infty$ and $θ=0$. \keywords{dark energy, k-essence, Reissner-Nordstrom and Kerr blackholes} \pacs{98.80.-k ;95.36.+x}

physics.gen-ph↗

arXiv2012

The Hawking temperature in the context of dark energy

An emergent gravity metric incorporating $k-$essence scalar fields $ϕ$ having a Born-Infeld type lagrangian is mapped into a metric whose structure is similar to that of a blackhole of large mass $M$ that has swallowed a global monopole. However, here the field is not that of a monopole but rather that of a $k-$essence scalar field. If $ϕ_{emergent}$ be solutions of the emergent gravity equations of motion under cosmological boundary conditions at $\infty$, then for $r\rightarrow\infty$ the rescaled field $\frac {ϕ_{emergent}}{2GM-1}$ has exact correspondence with $ϕ$ with $ϕ(r,t)=ϕ_{1}(r)+ϕ_{2}(t)$. The Hawking temperature of this metric is $T_{\mathrm emergent}= \frac{\hbar c^{3}}{8πGM k_{\mathrm B}}(1-K)^{2}\equiv \frac{\hbar}{8πGM k_{\mathrm B}}(1-K)^{2}$, taking the speed of light $c=1$. Here $K=\dotϕ_{2}^{2}$ is the kinetic energy of the $k-$essence field $ϕ$ and $K$ is always less than unity, $k_{\mathrm B}$ is the Boltzmann constant. This is phenomenologically interesting in the context of Belgiorno {\it et al's} gravitational analogue experiment.

physics.gen-ph↗

arXiv2011

Masking singularities with $k-$essence fields in an emergent gravity metric

It is known that dynamical solutions of the $k$-essence equation of motion change the metric for the perturbations around these solutions and the perturbations propagate in an emergent spacetime with metric $\tilde G^{μν}$ different from the gravitational metric $g^{μν}$. We show that for observers travelling with the perturbations, there exist homogeneous field configurations for the lagrangian $L=[{1\over 2}g^{μν}\nabla_μϕ\nabla_νϕ]^{2}$ for which a singularity in the gravitational metric $g^{μν}$ can be masked or hidden for such observers. This is shown for the Schwarzschild and the Reissner-Nordstrom metrics.

gr-qc↗

arXiv2011

Hawking temperature for a global monopole metric in the context of k- essence and emergent gravity

The Hawking temperature for the Barriola-Vilenkin global monopole metric is shown to be $T_{\mathrm BV}= {\hbar (1-α) ^{2}\over8πGM k_{\mathrm B}}$, where $α$ is the global monopole charge,$M$ the mass of the black hole, $k_{\mathrm B}$ is the Boltzmann constant and speed of light $c=1$. We then show that a similar metric can also be obtained for certain $k-$ essence field configurations in an emergent gravity situation. Therefore, in the context of Belgiorno {\it et al's} recent demonstration of spontaneous emission of photons in a gravitational analogue experiment, any future observation of $T_{\mathrm BV}$ need not necessarily imply the existence of global monopoles. An alternative implication might as well be a very indirect signature of dark energy in an emergent gravity scenario. This should lead to effects that may be detectable in refined and modified versions of Belgiorno {\it et al's} experiment.

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