• Parthasarathi Majumdar

      Articles written in Pramana – Journal of Physics

    • Aspects of Planckian scattering beyond the eikonal

      Saurya Das Parthasarathi Majumdar

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      We discuss an approach to compute two-particle scattering amplitudes for spinless light particles colliding at Planckian centre-of-mass energies, with increasing momentum transfer away from the eikonal limit. The leading corrections to the eikonal amplitude, in our ‘external metric’ approach, are shown to be vanishingly small in the limit of the source particle mass going to zero. For massless charged particles, the electromagnetic and gravitational interactions decouple in the eikonal limit, but mix non-trivially for the leading order corrections.

    • Quantum aspects of black hole entropy

      Parthasarathi Majumdar

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      This survey intends to cover recent approaches to black hole entropy which attempt to go beyond the standard semiclassical perspective. Quantum corrections to the semiclassical Bekenstein-Hawking area law for black hole entropy, obtained within the quantum geometry framework, are treated in some detail. Their ramification for the holographic entropy bound for bounded stationary spacetimes is discussed. Four dimensional supersymmetric extremal black holes in string-based N=2 supergravity are also discussed, albeit more briefly.

    • Workshop II — Black holes and compact objects: Quantum aspects

      Parthasarathi Majumdar

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      This is a summary of the papers presented in session W2 on a fairly wide-ranging variety of topics in the area of black hole physics and quantum aspects of gravity, including quantum field and string theory in curved spacetimes. In addition, experts in a couple of topical subjects were invited to present short surveys on the subjects of their specialization. The invited speakers were: Mitra, who surveys recent research on the very topical area of AdS black holes, and Date, who presents a comparative perspective on trapping and isolated horizons. Among the contributed papers, the first, by Jassal, is an attempt to understand the dynamics of strings near a black hole horizon. This is followed by a paper by Barve et al on a calculation of the quantum stress tensor for a background that includes a naked singularity. Following this we have Singh on radial oscillations of quark stars in strong magnetic fields. The next paper by Goyal and Dahiya, discusses chiral symmetry restoration in a linear sigma model in the presence of a magnetic field. The following paper, by Horwitz, offers new perspectives on the intriguing question of primordial black holes. Finally, Madhavan discusses issues pertaining to the classical limit of kinematical quantum gravity.

    • Universal canonical entropy for gravitating systems

      Ashok Chatterjee Parthasarathi Majumdar

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      The thermodynamics of general relativistic systems with boundary, obeying a Hamiltonian constraint in the bulk, is determined solely by the boundary quantum dynamics, and hence by the area spectrum. Assuming, for large area of the boundary, (a) an area spectrum as determined by non-perturbative canonical quantum general relativity (NCQGR), (b) an energy spectrum that bears a power law relation to the area spectrum, (c) an area law for the leading order microcanonical entropy, leading thermal fluctuation corrections to the canonical entropy are shown to be logarithmic in area with a universal coefficient. Since the microcanonical entropy also has universal logarithmic corrections to the area law (from quantum space-time fluctuations, as found earlier) the canonical entropy then has a universal form including logarithmic corrections to the area law. This form is shown to be independent of the index appearing in assumption (b). The index, however, is crucial in ascertaining the domain of validity of our approach based on thermal equilibrium.

    • Kalb–Ramond fields and the CMBR

      Parthasarathi Majumdar

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      Cosmological implications on the polarization of the cosmic microwave background radiation, of a Kalb–Ramond field interacting with gauge fields and gravity as dictated by quantum consistency of heterotic string theory are surveyed. A parity violating augmentation going beyond the dictates of string theory is shown to lead to possible appearance of a 𝐵 mode generated in the cosmic microwave background (CMB) in the post-last scattering epoch. This generation of the 𝐵 mode of CMB appears to be dramatic when the augmentation is embedded within a Randall–Sundrum braneworld scenario of the first kind.

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