Titles and Abstracts of Contributed Talks

1. Name: Abdulla Al Mamon

Institution: Visva-Bharati University
Designation: Ph.D Student (JRF)
Title: Study of non-canonical scalar field model using CPL parameterization
Abstract: In this present work, we try to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space-time. We have considered CPL parameterization for the equation of state parameter of the non-canonical scalar field as w_{\phi} = w_{0} + w_{1}(1-a). Under this scenario an analytical solution for the various cosmological parameters have been found out. It has been found that the deceleration parameter shows a smooth transition from a positive value to some negative value, which indicates that the universe was undergoing an early deceleration followed by late time acceleration, which is essential for the structure formation of the universe. We have also studied the observational constraints on the equation of state of the non-canonical scalar field considering the Hubble and SN Ia datasets. For both the datasets, it has been found that the values of w_0 and w_1 of the model which were chosen for analytical results are well fitted in the 1 sigma and 2 sigma confidence contours.

2. Name: Ritabrata Biswas

Institution: Indian Institution of Engineering Science and technology, Shibpur
Designation: Post-Doctoral Research Fellow
Title: Chaplygin gas Accretion Flow: Towards Preprescribed Limit of eta over s
Abstract: Modified Chaplygin gas is one of the best candidates for a combined model of dark matter and dark energy. In addition, from a field theoretical point of view the modified Chaplygin gas model is equivalent to that of a scalar field having a self-interacting potential. We formulate the equations related to both spherical accretion and disk accretion, and respective winds. The corresponding numerical solutions of the flow, particularly of velocity, are presented and are analyzed. We show that the accretion-wind system of modified Chaplygin gas dramatically alters the wind solutions, producingfaster winds, upon changes in physical parameters, while accretion solutions qualitatively remain unaffected. This implies that modified Chaplygin gas is more prone to produce outflow which is the natural consequence of the dark energy into the system. The ratio of shear viscosity ($\eta$) to entropy density ($s$), according to the string theory and gauge duality, does have a lower limit for any physical incident and the limit is approximately equal to $\mu \hbar / 4\pi k_B$ , $\mu

3. Name: Nilok Bose

Institution: S. N. Bose National Centre for Basic Sciences
Designation: Ph.D. Student
Title: Effect of Cosmic Backreaction on an Accelerating Universe
Abstract: : We investigate the effect of backreaction due to inhomogeneities on the evolution of the present universe by considering a two-scale model within the Buchert framework. Taking the observed present acceleration of the universe as an essential input, we study the effect of inhomogeneities in the future evolution. We find that the backreaction from inhomogeneities causes the acceleration to slow down in the future for a range of initial configurations and model parameters. The present acceleration ensures formation of the cosmic event horizon, and our analysis brings out how the effect of the event horizon could further curtail the global acceleration, and even lead in certain cases to the emergence of a future decelerating epoch.

4. Name: Rajesh Mondal

Institution: Indian Institute of Technology, Kharagpur
Designation: Ph.D. Student
Title: 21-cm signal from the epoch of reionization: observation and semi-numerical simulations
Abstract: : It is generally believed that reionization of hydrogen extends over wide redshift range (6<z<15). We model the distribution of neutral hydrogen (HI) in that epoch. Observations of the redshifted 21-cm emission of neutral hydrogen (HI) from this epoch are challenging because of foregrounds and noise, and also difficulties in dealing with such a wide redshift range. Foreground removal is a biggest challenge for a statistical detection of the redshifted 21cm signal. The two major foreground components are extra-galactic point sources and galactic synchrotron radiation. They have strength 4-5-order magnitude larger than the HI signal.

To generate the ionization field, we use a set of semi-numerical approaches which involve three main steps: (a) N-body simulation, (b) friends-of-friends (FoF) algorithm, and (c) an excursion set formalism to generate reionization map. We have developed a parallelize and efficient particle mesh (PM) code to generate the dark matter density field. To identify the haloes within the simulation box, we have written a code using standard FoF algorithm.

5. Name: Abhijit Mandal

Institution: Indian Institution of Engineering Science and technology, Shibpur
Designation: Research Fellow
Title: Effect of Cosmic Acceleration on Black Hole Thermodynamics
Abstract: : Direct local impacts of cosmic acceleration upon a black hole is a matter of interest. A charged de Sitter black hole solution surrounded by quintessence field is studied for this purpose. Different thermodynamic parameters are been analysed for different values of quintessence EoS parameter. Nature of phase transitions and the situations at which these transitions are occurring is noted. Before quintessence starts to work ($\omega_q=-0.33>-\frac{1}{3}$), it was preferable to have a small unstable BH followed by a large stable one. But in quintessence ($-\frac{1}{3}>\omega_q>-1$) BHs are destined to be unstable large one pre-quelled by stable/ unstable small/ intermediate mass BHs.

6. Name: Rudrani Kar Chowdhury

Institution: Presidency University
Designation: MSc Student
Title: X-ray Surface Brightness Profile of Simulated Galaxy Groups
Abstract: : Galaxies that have active super massive black holes in their centres are called active galactic nuclei (AGN). From several observations it has been seen that AGN, residing at the centres of galaxy clusters are pouring huge amount of energy on the surrounding X-ray gas and are displacing the hot X-ray gas outward. The same phenomenon has been observed in galaxy groups too. This phenomenon is referred as “AGN feedback” in the literature. Feedback from AGN has a very profound effect on structure formation. By studying the X-ray surface brightness profiles of simulated galaxy groups we now theoretically evaluate the effect of AGN feedback on the gas in the intra-cluster (group) medium.

7. Name:Sayantan Choudhury

Institution: Indian Statistical Institute, Kolkata
Designation: PhD Student (Final year)
Title: Inflationary model building, reconstruction and observational limits
Abstract: : In this talk I will speak on various cosmological consequences from sub-Planckian inflationary paradigm. I will start with a very brief introduction to inflation and its connection with various observational probes (WMAP, Planck, BICEP2 etc.) through Cosmic Microwave Background (CMB). Next I will comment on CMB B mode and its various components and their significance in the context of the detection of primordial gravity waves. Further I will discuss the top down approach of inflation in which I will focus on various physical aspects of low and high scale framework and cosmological parameter estimations from these class of models. Next I will discuss an accurate analytical bound on generating primordial gravitational waves from inflation, where inflation occurs below the Planck (sub-Planckian) scale. If inflation has to make connection with the real particle physics it must be explained within an effective field theory description where it can be trustable below the UV cut-off of the scale of gravity. Further using this input I will discuss the procedure of reconstructing inflationary potential and observational constraints. Finally I will mention the various possibilities through which it is possible to generate sub-Planckian field excursion and large (detectable) value of tensor-to-scalar ratio simultaneously in a model independent fashion.

8. Name:Dr. Sarbari Guha

Institution: : St. Xavier’s College, Kolkata
Designation: Associate Professor
Title: An interesting feature of perfect fluid collapse
Abstract: : We consider a class of spherically symmetric dynamic perfect fluid models with the purpose of examining the end state of a continual gravitational collapse. We find that for certain values of the pressure of the collapsing matter, a bounce develops within the cloud. The result is quite generic and can be achieved for a wider class of mass functions for type I matter fields, given the choice of regular initial data from which the collapse develops. The results agree with some existing models of supernova core collapse.