AR_final file_2018-19

the inflation. Furthermore, in contrast to the stan- dard normal inflation for which only upper bound on tensor-to-scalar ratio r are possible, we obtain both upper and lower bounds for the two hybrid fields in the phantom scenario. Finally, we discuss prospects of future high precision polarization mea- surements and show that it may be possible to es- tablish the dominance of one model over the other. This work has been done in collaboration with Asif Iqbal, and Mussadig H. Qureshi. Variable Stars in M 37 The CCD photometric observations of open star cluster M 37 (NGC 2099) were carried out up to limiting magnitude of V ∼ 20 in both B and V filters to search for variable stars using 2 k × 4 k CCD and 1.3m telescope at Vainu Bapu Obser- vatory, Kavalur. A total of 314 stars have been observed in the first observing run, out of which 60 have been identified as variables. Eight out of the identified 60 variables are classified as W UMa binary stars. For model fitting, we used PHOEBE based on W-D code to estimate the physical param- eters of these newly detected W UMa binaries that theoretically best match the observed light curves. This work has been done in collaboration with Ajaz Ahmad dar, S. P. Padmakar, and Parvej Saleh. Soma Mandal The flux distribution of individual blazars as a key to understand the dynamics of particle acceleration The observed lognormal flux distributions in the high-energy emission from blazars have been inter- preted as being due to variability stemming from non-linear multiplicative processes generated dy- namically from the accretion disc. On the other hand, rapid minute scale variations in the flux point to a compact emitting region inside the jet, prob- ably disconnected from the disc. In this work, we show that linear Gaussian variations of the intrin- sic particle acceleration or escape time-scales can produce distinct non-Gaussian flux distributions, including lognormal ones. Moreover, the spectral index distributions can provide confirming evidence for the origin of the variability. Thus, modelling of the flux and index distributions can lead to quan- titative identification of the micro-physical origin of the variability in these sources. As an exam- ple, we model the X-ray flux and index distribu- tion of Mkn 421 obtained from ∼ 9 yr of MAXI observations and show that the variability in the X-ray emission is driven by Gaussian fluctuations of the particle acceleration process rather than that of the escape rate. This work has been done in col- laboration with Atreyee Sinha, Ruraiya Khatoon, Ranjeev Misra, Surender Sahayaratham, Rupjyoti Gogoi, et al. Titus K. Mathew Expansion law from first law of thermodynamics Padmanabhan, in his paper [arxiv: 1206.4916] has put forth an intriguing idea calling for the modifi- cation of Einstein’s gravity theory on cosmic scales by arguing the accelerated expansion of the uni- verse being due to the emergence of cosmic space as cosmic time progresses with the expansion be- ing triggered due to the difference in the degrees of freedom on a holographic surface and the one in its emerged bulk. Applying the first law of thermodynamics to the horizon of a Friedmann- Robertson-Walker (FRW) Universe, we obtain the modified expansion law of the universe as proposed by Sheykhi in (n+1) dimensional Einstein gravity, Gauss-Bonnet, and more general Lovelock gravity theories. We also show that the modified versions of the expansion law due to Cai and Yang, et al. in the case of Gauss-Bonnet gravity show a strong im- plicit correspondance to each other. This work has been done in collaboration with M. Mahith, and P. B. Krishna. Entropy maximaization in the emergent gravity paradigm The accelerated expansion of the universe can be interpreted as a quest for satisfying holographic equi partition. It can be expressed by a simple law, ∆ V = ∆ t ( N surf − N bulk ), which leads to the standard Friedmann equation. This novel idea sug- gested by Padmanabhan in the context of general relativity has been generalized by Cai and Yang, et al. to Gauss-Bonnet and Lovelock gravities for a spatially flat universe in different methods. We investigate the consistency of these generalizations with the constraints imposed by the maximum en- tropy principle. Interestingly, both these general- izations imply entropy maximization even if their basic assumptions are different. Further, we ana- lyze the consistency of Verlinde’s emergent gravity with the maximum entropy principle in the cos- mological context. Even though the conceptual ( 199 )