AR-2019-2020

hury, and Arnab Chakrabory. Ujjal Debnath Charge gravastars in f ( T ) modified gravity We have studied the four dimensional spherically symmetric stellar system in the framework of mod- ified f ( T ) gravity theory with electro-magnetic field. The field equations have been written for two cases, either T = 0 or f TT = 0. Next, we have dis- cussed the charged gravastar model which has three regions: interior, shell and exterior. In the interior region, we have found the solutions of all physical quantities like density, pressure, electro-magnetic field and also the metric coefficients for both the cases. For T = 0, gravastar cannot form but it forms only for the case f TT = 0. In the exterior re- gion, we have obtained the exterior solution for vac- uum model. In the shell region, we have assumed that the interior and exterior regions join together at a place, so the intermediate region must be thin shell with the approximation h ( ≡ e − b ) 1. Under this approximation, we have found the analytical solutions. The proper length of the thin shell, en- tropy and energy content inside the thin shell have been found and they are directly proportional to the proper thickness of the shell under the approx- imation ( 1). According to the Darmois-Israel formalism, we have studied the matching between the surfaces of interior and exterior regions of the gravastar. The energy density, pressure, equation of state parameter on the surface and mass of the thin shell have been obtained. Parametrizations of dark energy models in the back- ground of general non-canonical scalar field in D - dimensional fractal universe We have explored non-canonical scalar field model in the background of non-flat D -dimensional frac- tal universe on the condition that the matter and scalar field are separately conserved. The poten- tial V , scalar field φ , function f , densities, Hub- ble parameter and deceleration parameter can be expressed in terms of the redshift z , and these de- pend on the equation of state parameter w φ . We have also investigated the cosmological analysis of four kinds of well known parametrization models. Graphically, we have analyzed the nature of poten- tial, scalar field, function f , densities, the Hubble parameter and deceleration parameter. As a result, the best fitted values of the unknown parameters ( w 0 , w 1 ) of the parametrization models due to the joint data analysis (SNIa+BAO+CMB+Hubble) have been found. Furthermore, the minimum val- ues of χ 2 function have been obtained. Also we have plotted the graphs for different confidence lev- els 66%, 90% and 99% contours for ( w 0 , w 1 ) by fixing the other parameters. This work has been done in collaboration with Kazuharu Bamba. Shantanu Desai Robust model comparison tests of DAMA/LIBRA annual modulation We evaluate the statistical significance of the DAMA/LIBRA claims for annual modulation using three independent model comparison techniques, viz frequentist, information theory, and Bayesian analysis. We fit the data from the DAMA/LIBRA experiment to both cosine and a constant model, and carry out model comparison by choosing the constant model as the null hypothesis. For the fre- quentist test, we invoke Wilk’s theorem and cal- culate the significance using Δ χ 2 between the two models. For information theoretical tests, we calcu- late the difference in Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) between the two models. We also compare the two models in a Bayesian context by calculating the Bayes factor. We also search for higher har- monics in the DAMA/LIBRA data using general- ized Lomb-Scargle periodogram. We finally test the sensitivity of these model comparison techniques in discriminating between pure noise and a cosine sig- nal using synthetic data. This is the first proof of principles application of AIC, BIC as well as Bayes factor to the DAMA data. This evaluation has been done in collaboration with Aditi Krishak, and Aisha Dantulurib. Looking for ancillary signals around GW150914 We replicated the procedure of Liu and Jackson who had found evidence for a low amplitude signal in the vicinity of GW150914. This was based upon the large correlation between the time integral of the Pearson cross-correlation coefficient in the off- source region of GW150914, and the Pearson cross- correlation in a narrow window around GW150914, for the same time lag between the two LIGO de- tectors as the gravitational wave signal. Our re- sults mostly agree with those of Liu and Jackson We find the statistical significance of the observed