Sudipta Das

Barrow holographic dark energy model is an extension of holographic dark energy that incorporates modifications to entropy due to quantum gravitational effects. In this work we study the cosmological properties of interacting Barrow holographic dark energy model in the case of non-zero curvature universe. We construct the differential equations governing the evolution of the Barrow holographic dark energy density parameter and the dark matter density parameter in coupled form for both closed and open spatial geometry. Considering three different forms of coupling, we obtain the corresponding analytical expressions for the equation of state parameter for the dark energy component. We confront the scenario using recent observational datasets like cosmic chronometer and Pantheon data. It has been found that the strength of interaction as well as the curvature contribution come out to be nonzero which indicates that a non-flat interacting scenario is preferred by observational data.

In this work, we have proposed a simple parametrization for the pressure component [ ] of the dark energy model and have studied the cosmological implications of this model in the framework of [ ] modified gravity theory, aka, the symmetric teleparallel gravity theory, where Q is known as the nonmetricity scalar. By considering a particular parametric form of [ ], we obtained the Hubble solution for the [ ] modified gravity model. In order to see whether this model is consistent with or challenges the [ ]CDM limits, we tried to put constraints on the model parameters using the recent observational datasets like Hubble data, Cosmic Chronometer data, Type Ia Supernovae (SNIa) data, baryonic acoustic oscillations (BAO) data. We have employed the [ ] minimization technique and have carried out the Markov Chain Monte Carlo (MCMC) analysis using emcee package. We have found that the deceleration parameter shows a smooth transition from positive to negative value in recent past which is essential for the structure formation of the Universe. It has been found that the parametric form of the dark energy pressure parameter is consistent with current cosmological scenario.

Purpose of the study:: In our present work, we have considered a simple parametric form of the Hubble parameter (H) for a canonical scalar field model described within a spatially flat FRW spacetime framework. Here we have considered a well-behaved parametrization scheme of the normalized Hubble parameter to explain the expansion history of the universe. Methods:: Under this scenario, we have obtained the analytic solutions for various relevant cosmological parameters. We have also reconstructed the potential function V(φ) for the scalar field φ. Results:: It has been found that the deceleration parameter (q) shows exactly the nature which is well expected, i.e., an accelerated expansion for low z limit and deceleration for high z limit, which is essential for the structure formation of the Universe. Detailed data analysis has been carried out to check the viability of the proposed theoretical model by using combined dataset SNIa+H(z)+BAO/CMB and put constraints on the cosmological parameters, viz. the present value of the Hubble parameter H0. Conclusion:: As it has been observed that the deceleration parameter undergoes a smooth transition from an accelerating phase to decelerating expansion, this result supports the structure formation at the early time and the late time cosmic acceleration measurements. The results are found to be closer to the value obtained by the PLANCK collaboration.

The task of a telecloning protocol is to send an arbitrary qubit possessed by a sender to multiple receivers. Instead of performing Bell measurement at the sender's node, if one applies unsharp measurement, we show that the shared state can be recycled for further telecloning protocol. Specifically, in case of a single sender and two receivers, the maximal attempting number, which is defined as the maximum number of rounds used by the channel to obtain quantum advantage in the fidelity, turns out to be three both for optimal and nonoptimal shared states for telecloning while the maximal number reduces to two in case of three receivers. Although the original telecloning with quantum advantage being possible for arbitrary numbers of receivers, we report that the recycling of resources is not possible in telecloning involving a single sender and more than three receivers, thereby demonstrating a no-go theorem. We also connect the maximal achievable fidelities in each round with the bipartite entanglement content of the reduced state between the sender and one of the receivers as well as with the monogamy score of entanglement.

We construct Barrow holographic dark energy in the case of nonflat universe. In particular, considering closed and open spatial geometry we extract the differential equations that determine the evolution of the dark-energy density parameter, and we provide the analytical expression for the corresponding dark energy equation-of-state parameter. We show that the scenario can describe the thermal history of the universe, with the sequence of matter and dark energy epochs. Comparing to the flat case, where the phantom regime is obtained for relative large Barrow exponents, the incorporation of positive curvature leads the universe into the phantom regime for significantly smaller values. Additionally, in the case of negative curvature we find a reversed behavior, namely for increased Barrow exponent we acquire algebraically higher dark-energy equation-of-state parameters. Furthermore, we confront the scenario with Hubble parameter measurements and supernova type Ia data. Hence, the incorporation of slightly non-flat spatial geometry to Barrow holographic dark energy improves the phenomenology while keeping the new Barrow exponent to smaller values.