Kolkata, India

The Saha Institute of Nuclear Physics is an institution of basic research and training in physical and biophysical science located in Bidhannagar, Kolkata, India. The institute is named after the famous Indian physicist Meghnad Saha. Wikipedia.

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Pradhan S.,Norwegian University of Science and Technology | Pradhan S.,Sintef | Hansen A.,Norwegian University of Science and Technology | Chakrabarti B.K.,Saha Institute of Nuclear Physics
Reviews of Modern Physics | Year: 2010

The fiber bundle model describes a collection of elastic fibers under load. The fibers fail successively and, for each failure, the load distribution among the surviving fibers changes. Even though very simple, this model captures the essentials of failure processes in a large number of materials and settings. A review of the fiber bundle model is presented with different load redistribution mechanisms from the point of view of statistics and statistical physics rather than materials science, with a focus on concepts such as criticality, universality, and fluctuations. The fiber bundle model is discussed as a tool for understanding phenomena such as creep and fatigue and how it is used to describe the behavior of fiber-reinforced composites as well as modeling, e.g., network failure, traffic jams, and earthquake dynamics. © 2010 The American Physical Society.

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.

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.

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.

Agrawal B.K.,Saha Institute of Nuclear Physics
Physical Review C - Nuclear Physics | Year: 2010

The density dependence of the symmetry energy, instrumental in understanding the behavior of the asymmetric nuclear matter, is investigated within the extended relativistic mean-field (ERMF) model, which includes the contributions from the self- and mixed-interaction terms for the scalar-isoscalar (σ), vector-isoscalar (ω), and vector-isovector (ρ) mesons up to the quartic order. Each of the 26 different parametrizations of the ERMF model employed is compatible with the bulk properties of the finite nuclei. The behavior of the symmetry energy for several parameter sets is found to be consistent with the empirical constraints on them as extracted from the analyses of the isospin diffusion data. The neutron-skin thickness in the Pb208 nucleus for these parameter sets of the ERMF model lies in the range of ~0.20-0.24fm, which is in harmony with the thickness predicted by the Skyrme Hartree-Fock model. We also investigate the role of various mixed-interaction terms that are crucial for the density dependence of the symmetry energy. © 2010 The 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.

Singh H.,Saha Institute of Nuclear Physics
Journal of High Energy Physics | Year: 2012

We extend our earlier study of special double limits of 'boosted' AdS 5black hole solutions to include all black Dp-branes of type II strings. We find that Lifshitz solutions can be obtained in generality, with varied dynamical exponents, by employing these limits. We then study such double limits for 'boosted' Dp-brane bubble solutions and find that the resulting non-relativistic solutions instead describe Schrödinger like spacetimes, having varied dynamical exponents. We get a simple map between these Lifshitz & Schrödinger solutions and a relationship between two types of dynamical exponents. We also discuss about the singularities of the Lifshitz solutions and an intriguing thermodynamic duality. © SISSA 2012.

Banik A.D.,Saha Institute of Nuclear Physics | Majumdar D.,Saha Institute of Nuclear Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Recent study of gamma rays originating from the region of galactic centre has confirmed an anomalous γ-ray excess within the energy range 1-3 GeV. This can be explained as the consequence of pair annihilation of a 31-40 GeV dark matter into bb- with thermal annihilation cross-section σv~1.4-2.0×10-26cm3/s. In this work we revisit the Inert Doublet Model (IDM) in order to explain this gamma ray excess. Taking the lightest inert particle (LIP) as a stable DM candidate we show that a 31-40 GeV dark matter derived from IDM will fail to satisfy experimental limits on dark matter direct detection cross-section obtained from ongoing direct detection experiments and is also inconsistent with LHC findings. We show that a singlet extended inert doublet model can easily explain the reported γ-ray excess which is as well in agreement with Higgs search results at LHC and other observed results like DM relic density and direct detection constraints. © 2015 The Authors.

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).

Agrawal B.K.,Saha Institute of Nuclear Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

The stable configurations of nonrotating and rotating hybrid stars composed of color-superconducting quark matter cores are constructed using several equations of state (EOSs). We use a set of diverse EOSs for the nuclear matter which represents the low density phase. The EOSs at higher densities correspond to the quark matter in the color-superconducting phase and are computed within the Nambu-Jona-Lasinio-like model for different values of the scalar diquark and vector current couplings strengths. The phase transition to the quark matter is computed by a Maxwell construction. We find that the stability of the hybrid stars are mainly governed by the behavior of the EOSs for the color-superconducting quark matter. However the compositions of hybrid stars are sensitive to the EOS of the nuclear matter. The value of the critical rotation frequency for the hybrid star depends strongly on the EOS of the nuclear matter as well as that for the color-superconducting quark matter. Our results indicate that the EOS for the color-superconducting quark matter can be obtained, by adjusting the parameters of the Nambu-Jona-Lasinio model, to yield the stable configurations of the hybrid star having the maximum mass ∼1.5M in the nonrotating limit and the critical rotation frequency ∼1kHz. © 2010 The American Physical Society.

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