arXiv subjects

Narayan Banerjee

Publications and source records attributed to Narayan Banerjee.

At least 73 records · Page 4Linked to original sources

arXiv2016

Dynamical systems study of Chameleon scalar field

The present work is an extensive study of the viable stable solutions of chameleon scalar field models leading to possibilities of an accelerated expansion of the universe. It is found that for various combinations of the chameleon field potential $V(ϕ)$ and the coupling $f(ϕ)$ of the chameleon field with matter, a stable solution for an accelerated expansion is quite possible. The investigation provides a diagnostics for the stability criteria for all sorts of combinations of $V(ϕ)$ and $f(ϕ)$.

gr-qc↗

arXiv2016

A Reconstruction of Quintessence Dark Energy

With a parametric form of the equation of state parameter of dark energy, a quintessence potential has been reconstructed. The potential is found to be a generalization of a double exponential potential. The constraints on the parameters are obtained by maximum likelihood analysis using observational Hubble data, type Ia supernova data, baryon acoustic oscillation data and the CMB shift parameter data. Th emodel shows preference towards the phantom behaviour of dark energy.

gr-qc↗

arXiv2016

Anisotropic models are unitary: A rejuvenation of standard quantum cosmology

The present work proves that the folk-lore of the pathology of non-conservation of probability in quantum anisotropic models is wrong. It is shown in full generality that all operator ordering can lead to a Hamiltonian with a self-adjoint extension as long as it is constructed to be a symmetric operator, thereby making the problem of non-unitarity in context of anisotropic homogeneous model a ghost. Moreover, it is indicated that the self-adjoint extension is not unique and this non-uniqueness is suspected not to be a feature of Anisotropic model only, in the sense that there exists operator orderings such that Hamiltonian for an isotropic homogeneous cosmological model does not have unique self-adjoint extension, albeit for isotropic model, there is a special unique extension associated with quadratic form of Hamiltonian i.e {\it Friedrichs extension}. Details of calculations are carried out for a Bianchi III model.

gr-qc↗

arXiv2015

Unitary evolution for a quantum Kantowski-Sachs cosmology

It is shown that like Bianchi I, V and IX models, a Kantowski-Sachs cosmological model also allows a unitary evolution on quantization. It has also been shown that this unitarity is not at the expense of the anisotropy. Non-unitarity, if there is any, cannot escape notice in this as the evolution is studied against a properly oriented time parameter fixed by the evolution of the fluid. Furthermore, we have constructed a wave-packet by superposing different energy eigenstates, thereby establishing unitarity in a non-trivial way, which is a stronger result than an energy eigenstate trivially giving time independent probability density. For $α\neq1$, we have proved that the Hamiltonian upon suitable operator ordering admits a self-adjoint extension under reasonable assumption, using a standard theorem. This consolidates the recently shown fact that the problem of non-unitarity cannot be a generic problem of anisotropy.

gr-qc↗

arXiv2015

Restoring unitarity in anisotropic quantum cosmological models

The present work shows that a properly chosen ordering of operators can restore unitarity in anisotropic quantum cosmological models. Bianch V and Bianchi IX models with a perfect fluid are worked out. It has been shown that a transformation of coordinates takes the Hamiltonian to that of an inverse square potential which has equal deficiency indices and a self-adjoint extension is thus possible. It is also shown, although not detected clearly before, that isotropic models are also apt to violate the conservation of probability for a careless operator ordering.

gr-qc↗

arXiv2014

Phase space analysis of a holographic dark energy model

The stability of interacting holographic dark energy model is discussed. It is found that for some class of the rate of interaction between dark matter and dark energy, the system has a natural solution where the universe had been decelerating in the begnning but finally settles down to an acelerated phase of expansion.

gr-qc↗

arXiv2014

Addressing the issue of non-unitarity in anisotropic quantum cosmology

In the present work we show that the widely believed pathology of the non-unitarity of anisotropic quantum cosmological models cannot be a generic problem. We exhibit a non trivial example, a Bianchi-I model with an ultrarelativistic fluid, that has a well behaved time independent norm. We also show that a suitable operator ordering should produce time independent norms for the wave packets in the case of other more realistic fluids as well.

gr-qc↗

arXiv2014

Acceleration of the Universe in f(R) Gravity Models

A general formalism for the investigation of the late time dynamics of the universe for any analytic f(R) gravity model, along with a cold dark matter, has been discussed in the present work. The formalism is then elucidated with two examples. The values of the parameters of the models are chosen in such a way that they are consistent with the basic observational requirement.

gr-qc↗

arXiv2014

Quintessence Scalar Field: A Dynamical Systems Study

The present work deals with a dynamical systems study of quintessence potentials leading to the present accelerated expansion of the universe. The principal interest is to check for late time attractors which give an accelerated expansion for the universe. Two examples are worked out, namely the exponential and the power-law potentials.

gr-qc↗

arXiv2013

Towards a characterization of fields leading to black hole hair

In the present work, it is shown that an asymptotically flat spherical black hole can have a nontrivial signature of any field for an exterior observer if the energy momentum tensor of the corresponding field is either tracefree or if the trace falls off at least as rapidly as inverse cube of the radial distance. In the absence of a general No Hair Theorem, this result can provide a characterization of the fields leading to black hole hair.

gr-qc↗

arXiv2013

Modified Ricci flow and asymptotically non-flat spaces

The present work extends the application of a modified Ricci flow equation to an asymptotically non flat space, namely Marder's cylindrially symmetric space. It is found that the flow equation has a solution at least in a particular case.

gr-qc↗

arXiv2012

Spherically symmetric scalar field collapse

It is shown that a scalar field, minimally coupled to gravity may have collapsing modes even when the energy condition is violated, that is, for $(ρ+3p)<0$. This result may be useful in the investigation of the possible clustering of dark energy. All the examples dealt with have apparent horizons which form before the formation of the singularity. The singularities formed are shell focusing in nature. The density of the scalar field distribution is seen to diverge at singularity. The Ricci scalar also diverges at the singularity. The interior spherically symmetric metric is matched with exterior Vaidya metric at the hypersurface and the appropriate junction conditions are obtained.

gr-qc↗

arXiv2012

Perfect Fluid Quantum Anisotropic Universe: Merits and Challenges

The present paper deals with quantization of perfect fluid anisotropic cosmological models. Bianchi type V and IX models are discussed following Schutz's method of expressing fluid velocities in terms of six potentials. The wave functions are found for several examples of equations of state. In one case a complete wave packet could be formed analytically. The initial singularity of a zero proper volume can be avoided in this case, but it is plagued by the usual problem of non-unitarity of anisotropic quantum cosmological models. It is seen that a particular operator ordering alleviates this problem.

gr-qc↗

arXiv2011

Cosmology and large mass hierarchy in multiply warped braneworld scenario

Hubble expansion in warped braneworld model is addressed in presence of more than one warped extra dimensions. It is shown that while the expansion depends on all the moduli, an exponential nature of the expansion of the scale factor emerges as a generic feature which is independent of the number of extra dimensions. Expression for the effective brane cosmological constant in such model has been derived. It is shown that similar to the 5-dimensional Randall-Sundrum model a fine tuning between the bulk cosmological constant and brane tension is required to obtain the desired cosmological constant on the brane. The length of the extra dimensions are determined in such scenario. Finally introduing pressureless matter in the bulk an observationally consistent cosmology was obtained on the visible brane.

hep-th↗

arXiv2011

Collapse of non-spherically symmetric scalar field distributions

In the present work the collapse scenario of some exact non-spherical models with a minimally coupled scalar field is studied. Scalar field collapse with planar as well as toroidal, cylindrical and pseudoplanar symmetries have been investigated. It is shown that the scalar field may have collapsing modes even if it has the equation of state corresponding to that of a dark energy.

gr-qc↗

arXiv2008

Generalised scalar-tensor theory and the cosmic acceleration

In this paper it has been shown that a simple functional form of $ω(ϕ)$ in a generalised scalar tensor theory can drive the present cosmic acceleration without any quintessence field or the cosmological constant $Λ$. Furthermore, it ensures a smooth transition from a decelerated to an accelerated phase of expansion in the matter dominated regime.

gr-qc↗

arXiv2008

Brans-Dicke Scalar Field as a Chameleon

In this paper it is shown that in Brans - Dicke theory, if one considers a non-minimal coupling between the matter and the scalar field, it can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans - Dicke parameter $ω$.

gr-qc↗

arXiv2008

Can neutrino viscosity drive the late time cosmic acceleration?

In this paper it has been shown that the neutrino bulk viscous stresses can give rise to the late time acceleration of the universe. It is found that a number of spatially flat FRW models with a negative deceleration parameter can be constructed using neutrino viscosity and one of them mimics a $Λ$CDM model. This does not require any exotic dark energy component or any modification of gravity.

gr-qc↗