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Sukanta Panda

Publications and source records attributed to Sukanta Panda.

At least 55 records · Page 3Linked to original sources
arXiv2020

Covariant quantum corrections to a scalar field model inspired by nonminimal natural inflation

We calculate the covariant one-loop quantum gravitational effective action for a scalar field model inspired by the recently proposed nonminimal natural inflation model. Our calculation is perturbative, in the sense that the effective action is evaluated in orders of background field, around a Minkowski background. The effective potential has been evaluated taking into account the finite corrections. An order-of-magnitude estimate of the one-loop corrections reveals that gravitational and non-gravitational corrections have same or comparable magnitudes.

gr-qc↗
arXiv2019

Avoiding instabilities in antisymmetric tensor field driven inflation

Models of inflation with antisymmetric tensor studied in the past are plagued with ghost instability even in an unperturbed FRW background. We show that it is possible to avoid ghosts in an unperturbed FRW background by considering the most general kinetic term for antisymmetric tensor field. The kinetic part acquires a new gauge symmetry violating term whose effect on perturbed modes is to prevent the appearance of nondynamical modes, and thus avoid ghosts. For completeness, we perform a check for gradient instability and derive the conditions for perturbations to be free of gradient instability.

gr-qc↗
arXiv2019

Hamiltonian Formalism for Nonlocal Gravity Models

Nonlocal gravity models are constructed to explain the current acceleration of the universe. These models are inspired by the infrared correction appearing in Einstein Hilbert action. Here we develop the Hamiltonian formalism of a nonlocal model by considering only terms to quadratic order in Ricci tensor and Ricci scalar. We also show how to count the degree of freedom using Hamiltonian formalism in this model.

gr-qc↗
arXiv2019

Quantum aspects of antisymmetric tensor field with spontaneous Lorentz violation

We study the quantization of a simple model of antisymmetric tensor field with spontaneous Lorentz violation in curved spacetime. We evaluate the 1-loop corrections at first order of metric perturbation, using a general covariant effective action approach. We revisit the issue of quantum equivalence, and find that it holds for non-Lorentz-violating modes but breaks down for Lorentz violating modes.

gr-qc↗
arXiv2019

Geodetic Motion Around Rotating Blackhole in Nonlocal Gravity

Recently the non-local gravity theory has come out to be a good candidate for an effective field theory of quantum gravity and also it can provide rich phenomenology to understand late-time accelerating expansion of the universe. For any valid theory of gravity, it has to surmount solar system tests as well as strong field tests. Having motivations to prepare the framework for the strong field test of the modified gravity using Extreme Mass Ratio Inspirals(EMRIs), here we try to obtain the metric for Kerr-like blackhole for a non-local gravity model known as RR model and calculate the shift in orbital frequencies of a test particle moving around the blackhole. We also derive the metric for a rotating object in the weak gravity regime for the same model.

gr-qc↗
arXiv2019

Higher Derivative Theory For Curvature Term Coupling With Scalar Field

Higher order derivative theories, generally suffer from instabilities, known as Ostrogradsky instabilities. This issue can be resolved by removing any existing degeneracy present in such theories. We consider a model involving at most second order derivatives of scalar field non-minimally coupled to curvature terms. Here we perform (3+1) decomposition of Lagrangian to separate second order time derivative form the rest. This is useful to check the degeneracy hidden in the Lagrangian will help us to find conditions under which Ostrogradsky instability do not appear. In our case, we find no such non trivial conditions which can stop the appearance of the Ostrogradsky ghost.

gr-qc↗
arXiv2019

One-Loop Effective Action for Nonminimal Natural Inflation Model

Recent and upcoming experimental data as well as the possibility of rich phenomenology has spiked interest in studying the quantum gravitational effects in cosmology at low (inflation-era) energy scales. While Planck scale physics is under development, it is still possible to incorporate quantum gravity effects at relatively low energies using quantum field theory in curved spacetime, which serves as a low-energy limit of planck scale physics. We use the Vilkovisky-DeWitt's covariant effective action formalism to study quantum gravitational corrections to a recently proposed Natural Inflation model with periodic nonminimal coupling. We present the 1-loop effective action for this theory valid in the flat-potential region, considering perturbative corrections upto quadratic order in background scalar fields.

gr-qc↗
arXiv2018

Inflation with an antisymmetric tensor field

We investigate the possibility of inflation with models of antisymmetric tensor field having minimal and nonminimal couplings to gravity. Although the minimal model does not support inflation, the nonminimal models, through the introduction of a nonminimal coupling to gravity, can give rise to stable de-Sitter solutions with a bound on the coupling parameters. The values of field and coupling parameters are sub-planckian. Slow roll analysis is performed and slow-roll parameters are defined which can give the required number of e-folds for sufficient inflation. Stability analysis has been performed for perturbations to antisymmetric field while keeping the metric unperturbed, and it is found that only the sub-horizon modes are free of ghost instability for de-Sitter space.

gr-qc↗
arXiv2018

Spherically symmetric static solutions, newtonian potential and degrees of freedom of a Nonlocal action

Nonlocal terms in the Einstein Hilbert(EH) action appears as IR corrections in effective theory of quantum gravity. Here we have considered such an action keeping the terms which are quadratic in Ricci Scalar. We obtain the solution for a spherical symmetric. We conduct an analysis for linearised gravity action and find the Newtonian potentials of linearized gravity action and count the degrees of freedom. Finally we reproduce the results for few known examples found in literature.

gr-qc↗
arXiv2018

Local Scale Invariance and Inflation

We study the inflation and the cosmological perturbations generated during the inflation in a local scale invariant model. The local scale invariant model introduces a vector field $S_μ$ in this theory. In this paper, for simplicity, we consider the temporal part of the vector field $S_t$. We show that the temporal part is associated with the slow roll parameter of scalar field. Due to local scale invariance, we have a gauge degree of freedom. In a particular gauge, we show that the local scale invariance provides sufficient number of e-foldings for the inflation. Finally, we estimate the power spectrum of scalar perturbation in terms of the parameters of the theory.

physics.gen-ph↗
arXiv2018

Metric for Rotating object in Infrared Corrected Nonlocal Gravity Model

Here, we derive the metric for the spacetime around rotating object for the gravity action having nonlocal correction of $R\Box^{-2} R $ to the Einstein-Hilbert action. Starting with the generic stationary, axisymmetric metric, we solve the equations of motion in linearized gravity limit for the modified action including energy-momentum tensor of the rotating mass. We also derive the rotating metric from the static metric using the Demanski-Janis-Newmann algorithm. Finally, we obtain the constraint on the value of $M$ by calculating the frame dragging effect in our theory and comparing it with that of General Relativity and Gravity Probe B results, where $M$ is the mass scale of the theory.

gr-qc↗
arXiv2018

Non-local cosmological models

Nonlocal cosmological models are studied extensively in recent times because of their interesting cosmological consequences. In this paper, we have analyzed background cosmology on a class of non-local models which are motivated by the perturbative nature of gravity at infrared scale. We show that inflationary solutions are possible in all constructed non-local models. However, exit from inflation to RD era is not possible in most of the models.

gr-qc↗
arXiv2018

Covariant Effective Action for Antisymmetric Tensor Field

Covariant quantization of rank-2 antisymmetric fields is non-trivial due to additional symmetries of the gauge parameters. We present an intuitive way to deal with this additional symmetry of gauge parameters in terms of geometrical understanding of field space. We generalize the DeWitt-Vilkovisky covariant effective action formalism for quantization of such theories. As an application, we quantize a massive rank-2 antisymmetric field using the covariant effective action approach and reproduce previously obtained results.

gr-qc↗
arXiv2017

A New f(R) Model in the Light of Local Gravity Test and Late-time Cosmology

We propose a new model of f(R) gravity containing Arctan function in the lagrangian. We show here that this model satisfies fifth force constraint unlike a similar model in Kruglov 2013. In addition to this, we carry out the fixed point analysis as well as comment on the existence of curvature singularity in this model. The cosmological evolution for this f(R) gravity model is also analyzed in the Freidmann Robertson Walker(FRW) background. To understand observational significance of the model, cosmological parameters are obtained numerically and compared with those of Lambda cold dark matter (ΛCDM) model. We also scrutinize the model with supernova data. We apply Om diagnostic given by Sahni et al. 2008 to the model. Using this diagnostic, we detect the distinction between cosmic evolution caused by the f(R) model and ΛCDM. We find best-fit parameter values of the model using Baryon Acoustic Oscillations data.

physics.gen-ph↗
arXiv2016

Anisotropic universe with anisotropic sources

We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de~Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union~2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.

gr-qc↗
arXiv2016

Viability of Arctan Model of f(R) Gravity for Late-time Cosmology

$f(R)$ modifications of Einstein's gravity is an interesting possibility to explain the late time acceleration of the Universe. In this work we explore the cosmological viability of one such $f(R)$ modification proposed in (Kruglov:2013). We show that the model violates fifth-force constraints. The model is also plagued with the issue of curvature singularity in a spherically collapsing object, where the effective scalar field reaches to the point of diverging scalar curvature.

gr-qc↗
arXiv2015

Anisotropic Cyclic Universe in $F(X)-V(ϕ)$ model

We investigate the cosmology of a class of model with noncanonical scalar field and matter in an anisotropy background. We find fixed points and their stability which constraints equation of state parameter for the matter. This is done after expressing the Einstein equations in terms of dimensionless variables. Similarly we define a set of suitable dynamical variables for studying bouncing solutions. The condition for nonsingular bounce is obtained. Here we show, numerically, that solution that of a cyclic universe exist for the certain form of kinetic term of noncanonical scalar field and the time period of cycle depends on the kinetic term of noncanonical scalar field. In certain case we find that a cyclic universe can be approximated to be a single bouncing scenario for the entire evolution of the dynamical variables. Resemblling an eternal bouncing scenario, this model may also be free from BKL instability. Also, the univerese isotropize in the expansion phase and this isotropization can be delayed to some extent by tuning the the parameter of the model.

gr-qc↗