AR-2019-2020

Suresh Chandra H 2 SiO IRASERs in a warm region in interstellar medium Out of the silicon bearing molecules, found in cos- mic objects, the H 2 SiO is one of them. Considering that kinetic temperature in some molecular regions is found up to 300 K, for each of the ortho and para H 2 SiO, we have extended our investigation to 200 rotational levels having energy up to 540 cm − 1 . Performing LVG calculations, we have found 5 or- tho and 4 para transitions having frequencies in THz, and radiative life-time of upper level more than 10 times larger than that of the lower level. These transitions, may be called IRASERs (Infra- Red Amplification by Stimulated Emission of Ra- diation), having emission feature and may play im- portant role in identification of H 2 SiO in a warm region in the interstellar medium. This work has been done in collaboration with Mohit K. Sharma, and Monika Sharma. Electron cyclotron waves in plasma in magneto- sphere of a planet having perpendicular DC electric field Scientists have always been interested in the study of electron cyclotron waves in plasma in magneto- sphere of a planet. Series of papers are published, where AC electric field is taken perpendicular to magnetic field in the magnetosphere. Some scien- tists have claimed to consider DC electric field, but they are found not to have any electric field. We have discussed propagation of electron cyclotron waves when constant electric field is perpendicu- lar to magnetic field in megnetosphere of a planet. Using bi-Maxwellian distribution function, we have found that for the known value of electron cyclotron frequency ω c , the real oscillation frequency ω r de- pends only on the temperature anisotropy. We have also found that the growth rate γ increases continuously with the increase of the wavevector k . It is interesting to note that the dispersion relation used in series of papers is erroneous, and it has been taken as universal relation. This studey has been done in collaboration with Mohit K. Sharma. Ayan Chatterjee Effective quantum theory of black hole horizons We develop an effective quantum theory of black hole horizons using only the local horizon geome- try. On the covariant phase space of the Holst ac- tion admitting Weak Isolated Horizon as an inner boundary, we construct Hamiltonian charges cor- responding to Lorentz symmetries. We show that horizon area is the Hamiltonian charge correspond- ing to Lorentz boosts as well as that for Lorentz ro- tation, which acts on 2-sphere cross-sections of the horizon. Using this expression of area as a genera- tor of Lorentz rotation, and the fact that quantum states residing on the horizon cross-sections carry a representation of ISO (2), we derive the spectrum of area operator on the horizon. The eigenstates of this area operator are shown to be labelled by integers or half integers. The entropy is obtained completely in terms of these area quanta residing on the horizon, and is shown to have exponentially suppressing corrections to the area law. The for- malism is also extended to non-minimally coupled scalar fields, where the area operator gets modi- fied due to the value of the scalar field on the hori- zon. This work has been done in collaboration with Amit Ghosh. Marginally trapped surfaces in spherical gravita- tional collapse This work deals with a detailed study of gravita- tional collapse of dust and viscous fluids under the assumptions of spherical symmetry. Our main goal is to closely analyze the horizons which arise dur- ing this gravitational phenomenon. To this end, we examine the formation and evolution of trapped surfaces in these spacetimes, with special atten- tion to trapped regions and cylinders foliated by marginally trapped surfaces. The time evolution of trapped surfaces, collapsing shell as well as the event horizon are identified analytically as well as numerically. Using different density profiles of mat- ter, we analyze, how the nature of the marginally trapped surfaces modify as we change the energy momentum tensor. These studies reveal that de- pending on the mass function and the mass profile, it is possible to envisage situations where dynam- ical horizons, timelike tubes or isolated horizons may arise. This work has been done in collabora- tion with Amit Ghosh, and Suresh Jaryal. Ritaban Chatterjee The accretion disk-jet connection in blazars The power spectral density (PSD) of the X-ray emission variability from the accretion disk-corona