AR_final file_2018-19

( R c ) δ tic) magnetized shocks, a novel approach to con- sistently model particle energization due to diffu- sive shock acceleration is presented. Our approach relies on a refined shock-detection algorithm and updates the particle energy distribution based on the shock compression ratio, magnetic field orien- tation, and amount of (parameterized) turbulence. The evolved distribution from each Lagrangian par- ticle is further used to produce observational sig- natures like emission maps and polarization sig- nals, accounting for proper relativistic corrections. We further demonstrate the validity of this hy-brid framework using standard numerical bench-marks and evaluate the applicability of such a tool to study high-energy emission from extra-galactic jets. This work has been done in collaboration with Andrea Mignone, Gianluigi Bodo, Poola Rossi, and Silvano Massaglia. Murli Manohar Verma Dark matter as scalaron in f ( R ) gravity models We explore the scalar field obtained under the con- formal transformation of the spacetime metric g µν from the Jordan frame to the Einstein frame in f ( R ) gravity. This scalar field is the result of the modification in the gravitational part of the Ein- stein’s general relativistic theory of gravity. For 1+ δ f ( R ) = R , we find the effective potential of the scalar field and calculate the mass of the scalar field particle “scalaron”. It is shown that the mass of the scalaron depends upon the energy density of stan- dard matter in the background (in solar system, m φ ∼ 10 − 16 eV). The interaction between standard matter, and scalaron is weak in the high curva-ture regime. This linkage between the mass of the scalaron and the background leads to the physi-cal effects of dark matter and is expected to reflect the anisotropic propagation of scalaron in moving baryonic matter fields as in merging clusters (Bullet cluster, the Abell 520 system, MACS, etc.). Such scenario also satisfies the local gravity constraints of f ( R ) gravity. We further calculate the equation of state of the scalar field in the action-angle vari-able formalism, and show its distinct features as the dark matter and dark energy with respect to energy density of the scalar field at different val-ues of the model parameter δ . This study has been done in collaboration with Bal Krishna Yadav. Cosmological wheel of time: A classical perspective of f(R) gravity It is shown that the structures in the universe can be interpreted to show a closed wheel of time, rather than a straight arrow. An analysis in f(R) gravity model has been carried out to show that due to local observations, a small arc at any given spacetime point would invariably indicate an arrow of time from past to future, though on a quantum scale, it is not a linear flow but a closed loop, a fact that can be examined through future observations. This study has been done in collaboration with Bal Krishna Yadav. ( 220 )