Ghosh A.,Saha Institute of Nuclear Physics |
Perez A.,Aix - Marseille University
Physical Review Letters | Year: 2011
We present a statistical mechanical calculation of the thermodynamical properties of (nonrotating) isolated horizons. The introduction of the Planck scale allows for the definition of a universal horizon temperature (independent of the mass of the black hole) and a well-defined notion of energy (as measured by suitable local observers) proportional to the horizon area in Planck units. The microcanonical and canonical ensembles associated with the system are introduced. Black hole entropy and other thermodynamical quantities can be consistently computed in both ensembles and results are in agreement with Hawking's semiclassical analysis for all values of the Immirzi parameter. © 2011 American Physical Society.
Mitra P.,Saha Institute of Nuclear Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
Black hole thermodynamics suggests that a black hole should have an entropy given by a quarter of the area of its horizon. Earlier calculations in U(1) loop quantum gravity have led to a dominant term proportional to the area, but there was a correction involving the logarithm of the area. We find however that SU(2) loop quantum gravity can provide an entropy that is strictly proportional to the area as expected from black hole thermodynamics. © 2012 American Physical Society.
Modak K.P.,Saha Institute of Nuclear Physics
Journal of High Energy Physics | Year: 2015
Abstract: We consider the dark matter model with radiative neutrino mass generation where the Standard Model is extended with three right-handed singlet neutrinos (N1, N2 and N3) and one additional SU(2)L doublet scalar η. One of the right-handed neutrinos (N1), being lightest among them, is a leptophilic fermionic dark matter candidate whose stability is ensured by the imposed Z2 symmetry on this model. The second lightest right-handed neutrino (N2) is assumed to be nearly degenerated in mass with the lightest one enhancing the co-annihilation between them. The effective interaction term among the lightest, second lightest right-handed neutrinos and photon containing transition magnetic moment is responsible for the decay of heavier right-handed neutrino to the lightest one and a photon (N2 → N1 + γ). This radiative decay of heavier right-handed neutrino with charged scalar and leptons in internal lines could explain the X-ray line signal ∼ 3.5 keV recently claimed by XMM-Newton X-ray observatory from different galaxy clusters and Andromeda galaxy (M31). The value of the transition magnetic moment is computed and found to be several orders of magnitude below the current reach of various direct dark matter searches. The other parameter space in this framework in the light of the observed signal is further investigated. © 2015, The Author(s).
Singh H.,Saha Institute of Nuclear Physics
Journal of High Energy Physics | Year: 2011
We uplift 5-dimensional super-Yang-Mills theory to a 6-dimensional gauge theory with the help of a space-like constant vector ?M, whose norm determines the YM coupling constant. After the localization of ?M the 6D gauge theory acquires Lorentzian invariance as well as scale invariance. We discuss KK states, instantons and the flux quantization. The theory admits extended solutions like 1/2 BPS 'strings' and monopoles. © 2011 SISSA.
Bhattacharyya G.,Saha Institute of Nuclear Physics
Reports on Progress in Physics | Year: 2011
We review different avenues of electroweak symmetry breaking explored over the years. This constitutes a timely exercise as the world's largest and the highest energy particle accelerator, namely, the Large Hadron Collider (LHC) at CERN near Geneva, has started running whose primary mission is to find the Higgs or some phenomena that mimic the effects of the Higgs, i.e. to unravel the mysteries of electroweak phase transition. In the beginning, we discuss the Standard Model Higgs mechanism. After that we review the Higgs sector of the minimal supersymmetric Standard Model. Then we take up three relatively recent ideas: little Higgs, gauge-Higgs unification and Higgsless scenarios. For the latter three cases, we first present the basic ideas and restrict our illustration to some instructive toy models to provide an intuitive feel of the underlying dynamics, and then discuss, for each of the three cases, how more realistic scenarios are constructed and how to decipher their experimental signatures. Wherever possible, we provide pedagogical details, which beginners might find useful. © 2011 IOP Publishing Ltd.