arXiv subjects

Ashmita

Publications and source records attributed to Ashmita.

5 recordsLinked to original sources

arXiv2024

Constructing Viable Interacting Dark Matter and Dark Energy Models: A Dynamical Systems Approach

We study the evolution of $k=-1$ FLRW cosmological models for two interacting Dark Matter-Dark Energy Models using dynamical system analysis. Since we are interested in late time evolution, the sign of the interaction term is chosen such that it facilitates the transfer of energy from dark matter to dark energy. We also explore the $k=0$ invariant subspace of these models. We find that both these models have sectors which have a stable fixed point where we can recover an accelerating universe with a negative equation of state. This indicates these can be viable models for our universe. We also rule out certain sectors of these models because they do not give the correct late time observational features. We observe that although we start with a dust-like Dark Matter, its effective equation of state evolves due to its interaction with Dark Energy. As a result, the Dark Matter can display features of stiff matter and exotic matter in the course of evolution.

gr-qc↗

arXiv2022

Inflationary Cosmology in a non-minimal $f(R,T)$ gravity theory using a $RT$ mixing term

We investigate a class of inflationary models in modified gravity theories which contain a non-minimal coupling between gravity and a scalar field $\phi$ (inflaton) as $f(R,T)=R \bigl(1+\alpha+ \kappa^4 \beta T \bigr)+\kappa^2\gamma T $ where $\kappa^2=8\pi G$ where $G$ is the Newton's constant. We consider two inflaton potentials of the form (i) $V = V_0 \bigl(1 +\ln{\phi} \bigr)$ and (ii) $V_0\frac{\lambda \phi^p}{1+\lambda\phi^p}$. For a range of potential parameters, we explored the constraints on modified gravity parameters i.e. ($\alpha$, $\beta$ and $\gamma$) in three categories -- (i) $\beta \neq0$, $\alpha=\gamma=0$ (considering $R$ and $RT$ mixing terms), (ii) $\alpha=0$, $\gamma\neq0$, $\beta\neq 0$ ($RT$ mixing term along with $T$ and $R$ terms) and (iii) $\gamma=0$, $\alpha\neq0$, $\beta\neq0$ ($RT$ mixing term along with $R$ term) for the above two potentials. The inclusion of $RT$ mixing term provides the scalar spectral index $n_s$ up to $3\sigma$ limit of PLANCK data, which is $n_s=0.9649\pm0.0042$ as well as the tensor-to-scalar ratio $r<0.106$ and the e-fold parameter $40<N<70$ for both the potentials.

gr-qc↗

arXiv2022

Observational Constraints on the $f(\phi,T)$ gravity theory

We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $\phi$ and the trace of the energy momentum tensor $T$ as $f(\phi,T) = 2 \phi( \kappa^{1/2} \alpha T + \kappa^{5/2} \beta T^2) $ to the Einstein-Hilbert action. We consider a class of inflaton potentials (i) $V_0 \phi^p e^{-\lambda\phi}$, (ii) $V_0\frac{ \lambda \phi^p}{1+\lambda\phi^p}$ and investigate the sensitivity of the modified gravity parameters $\alpha$ and $\beta$ on the inflaton dynamics. We derive the potential slow-roll parameters, scalar spectral index $n_s$, and tensor-to-scalar ratio $r$ in the above $f(\phi,T)$ gravity theory and analyze the following three choices of modified gravity parameters~(i) Case I:~ $\alpha \neq 0, ~\beta=0$ i.e. neglecting higher order terms, (ii) Case II:~ $\alpha=0$, $\beta \neq 0$~ and do the analysis for $T^2$ term, (iii) Case III:~ $\alpha \neq 0$ and $\beta \neq 0$ i.e. keeping all terms. For a range of potential parameters, we obtain constraints on $\alpha$ and $\beta$ in each of the above three cases using the WMAP and the PLANCK data.

gr-qc↗

arXiv2022

Inflationary Cosmology in the Modified $f(R, T)$ Gravity

In this work, we study the inflationary cosmology in modified gravity theory $f(R, T) = R + 2 \lambda T$ ($\lambda$ is the modified gravity parameter) with three distinct class of inflation potentials (i) $\phi^p e^{-\alpha\phi}$, (ii) $(1-\phi^p)e^{-\alpha\phi}$ and (iii) $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ where $\alpha$, $p$ are the potential parameters. We have derived the Einstein equation, potential slow-roll parameters, the scalar spectral index $n_s$, tensor to scalar ratio $r$, and tensor spectral index $n_T$ in modified gravity theory. We obtain the range of $\lambda$ using the spectral index constraints in the parameter space of the potentials. Comparing our results with PLANCK 2018 data and WMAP data, we found out the modified gravity parameter $\lambda$ lies between $-0.37<\lambda<1.483$.

gr-qc↗

arXiv2022

Non-Minimal Inflation with a scalar-curvature mixing term $\frac{1}{2} \xi R \phi^2$

We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $\phi$ in the presence of the non-minimal scalar-curvature mixing term $\frac{1}{2}\xi R \phi^2$. We consider four distinct scalar field potentials $\phi^p e^{-\lambda\phi},~(1 - \phi^{p})e^{-\lambda\phi},~(1-\lambda\phi)^p$ and $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ to study inflation in the non-minimal gravity theory. We calculate the potential slow-roll parameters and predict the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$, in the parameters ($\lambda, p, \alpha$) space of the potentials. We have compared our results with the ones existing in the literature, and this indicates the present status of non-minimal inflation after the release of the PLANCK 2018 data.

astro-ph.CO↗