Harish Chandra Research Institute

www.hri.res.in
Jhunsi, India

The Harish-Chandra Research Institute is an institution dedicated to research in Mathematics and Theoretical Physics, located in Allahabad, Uttar Pradesh in India. Established in 1965, HRI offers a doctoral program in affiliation with the Homi Bhabha National Institute.HRI has a residential campus in Jhusi town near Allahabad on the banks of the River Ganges. The institute has over 30 faculty, 50 doctoral students and 25 post-doctoral visiting research fellows and scientists. HRI is funded by the Department of Atomic Energy of the Government of India. Wikipedia.

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Nii K.,Harish Chandra Research Institute
Journal of High Energy Physics | Year: 2016

Motivated by a recent paper by Rychkov-Tan [1], we calculate the anomalous dimensions of the composite operators at the leading order in various models including a ϕ3-theory in (6 − ϵ) dimensions. The method presented here relies only on the classical equation of motion and the conformal symmetry. In case that only the leading expressions of the critical exponents are of interest, it is sufficient to reduce the multiplet recombination discussed in [1] to the classical equation of motion. We claim that in many cases the use of the classical equations of motion and the CFT constraint on two- and three-point functions completely determine the leading behavior of the anomalous dimensions at the Wilson-Fisher fixed point without any input of the Feynman diagrammatic calculation. The method developed here is closely related to the one presented in [1] but based on a more perturbative point of view. © 2016, The Author(s).


Bagchi A.,Harish Chandra Research Institute
Physical Review Letters | Year: 2010

We find a surprising connection between asymptotically flat spacetimes and nonrelativistic conformal systems in one lower dimension. The Bondi-Metzner-Sachs (BMS) group is the group of asymptotic isometries of flat Minkowski space at null infinity. This is known to be infinite dimensional in three and four dimensions. We show that the BMS algebra in 3 dimensions is the same as the 2D Galilean conformal algebra (GCA) which is of relevance to nonrelativistic conformal symmetries. We further justify our proposal by looking at a Penrose limit on a radially infalling null ray inspired by nonrelativistic scaling and obtain a flat metric. The BMS4 algebra is also discussed and found to be the same as another class of GCA, called semi-GCA, in three dimensions. We propose a general BMS-GCA correspondence. Some consequences are discussed. © 2010 The American Physical Society.


Raju S.,Harish Chandra Research Institute
Physical Review Letters | Year: 2011

We show that a generalization of the Britto-Cachazo-Feng-Witten recursion relations gives a new and efficient method of computing correlation functions of the stress tensor or conserved currents in conformal field theories with an (d+1)-dimensional anti-de Sitter space dual, for d 4, in the limit where the bulk theory is approximated by tree-level Yang-Mills theory or gravity. In supersymmetric theories, additional correlators of operators that live in the same multiplet as a conserved current or stress tensor can be computed by these means. © 2011 American Physical Society.


Basu A.,Harish Chandra Research Institute
Classical and Quantum Gravity | Year: 2015

The structure of one, two and three loop counterterms imposes strong constraints on several non-BPS interactions in the low momentum expansion of the three loop, four graviton amplitude in maximal supergravity. The constraints are imposed by demanding consistency with string amplitudes. We analyze these constraints imposed on the D8R4 interaction in 11-dimensional supergravity compacti fied on T2. We also discuss partial contributions from counterterms to interactions at higher orders in the momentum expansion. © 2015 IOP Publishing Ltd.


Raju S.,Harish Chandra Research Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We consider correlation functions of the stress-tensor or a conserved current in AdS d+1/CFT d computed using the Hilbert or the Yang-Mills action in the bulk. We introduce new recursion relations to compute these correlators at tree-level. These relations have an advantage over the Britto-Cachazo-Feng-Witten (BCFW)-like relations described in arXiv:1102.4724 and arXiv:1011.0780 because they can be used in all dimensions including d=3. We also introduce a new method of extracting flat-space S-matrix elements from AdS/CFT correlators in momentum space. We show that the (d+1)-dimensional flat-space amplitude of gravitons or gluons can be obtained as the coefficient of a particular singularity of the d-dimensional correlator of the stress-tensor or a conserved current; this technique is valid even at loop-level in the bulk. Finally, we show that our recursion relations automatically generate correlators that are consistent with this observation: they have the expected singularity and the flat-space gluon, or graviton amplitude appears as its coefficient. © 2012 American Physical Society.


Raju S.,Harish Chandra Research Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We compute four-point functions of the stress tensor and conserved currents in AdS 4/CFT 3 using bulk perturbation theory. We work at tree-level in the bulk theory, which we take to be either pure gravity or Yang-Mills theory in AdS. We bypass the tedious evaluation of Witten diagrams using recently developed recursion relations for these correlators. In this approach, the four-point function is obtained as the sum of residues of a rational function at easily identifiable poles. We write down an explicit formula for the four-point correlator with arbitrary external helicities and momenta. We verify that, precisely as conjectured in a companion paper, the Maximally Helicity Violating (MHV) amplitude of gravitons or gluons appears as the coefficient of a specified singularity in the MHV stress-tensor or current correlator. We comment on the remarkably simple analytic structure of our answers in momentum space. © 2012 American Physical Society.


Bhattacharyya S.,Harish Chandra Research Institute
Journal of High Energy Physics | Year: 2012

In this note we have tried to determine how the existence of a local entropy current with non-negative divergence constrains the second order transport coefficients of an uncharged fluid, following the procedure described in [1]. Just on symmetry ground the stress tensor of an uncharged fluid can have 15 transport coefficients at second order in derivative expansion. The condition of entropy-increase gives five relations among these 15 coefficients. So finally the relativistic stress tensor of an uncharged fluid can have 10 independent transport coefficients at second order. © SISSA 2012.


Sen A.,Harish Chandra Research Institute
General Relativity and Gravitation | Year: 2012

We compute logarithmic corrections to the entropy of rotating extremal black holes using quantum entropy function i. e. Euclidean quantum gravity approach. Our analysis includes five dimensional supersymmetric BMPV black holes in type IIB string theory on T 5 and K3 × S 1 as well as in the five dimensional CHL models, and also non-supersymmetric extremal Kerr black hole and slowly rotating extremal Kerr-Newmann black holes in four dimensions. For BMPV black holes our results are in perfect agreement with the microscopic results derived from string theory. In particular we reproduce correctly the dependence of the logarithmic corrections on the number of U(1) gauge fields in the theory, and on the angular momentum carried by the black hole in different scaling limits. We also explain the shortcomings of the Cardy limit in explaining the logarithmic corrections in the limit in which the (super)gravity description of these black holes becomes a valid approximation. For non-supersymmetric extremal black holes, e. g. for the extremal Kerr black hole in four dimensions, our result provides a stringent testing ground for any microscopic explanation of the black hole entropy, e. g. Kerr/CFT correspondence. © 2012 Springer Science+Business Media, LLC.


Sen A.,Harish Chandra Research Institute
Journal of High Energy Physics | Year: 2013

Euclidean gravity method has been successful in computing logarithmic corrections to extremal black hole entropy in terms of low energy data, and gives results in perfect agreement with the microscopic results in string theory. Motivated by this success we apply Euclidean gravity to compute logarithmic corrections to the entropy of various non-extremal black holes in different dimensions, taking special care of integration over the zero modes and keeping track of the ensemble in which the computation is done. These results provide strong constraint on any ultraviolet completion of the theory if the latter is able to give an independent computation of the entropy of non-extremal black holes from microscopic description. For Schwarzschild black holes in four space-time dimensions the macroscopic result seems to disagree with the existing result in loop quantum gravity. © 2013, SISSA.


Raju S.,Harish Chandra Research Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We expand on the results of our recent letter, where we presented new recursion relations for correlation functions of the stress-tensor and conserved currents in conformal field theories with an AdS d+1 dual for d 4. These recursion relations are derived by generalizing the Britto-Cachazo-Feng- Witten (BCFW) relations to amplitudes in anti-de Sitter space (AdS) that are dual to boundary correlators, and are usually computed perturbatively by Witten diagrams. Our results relate vacuum-correlation functions to integrated products of lower-point transition amplitudes, which correspond to correlators calculated between states dual to certain normalizable modes. We show that the set of "polarization vectors" for which amplitudes behave well under the BCFW extension is smaller than in flat-space. We describe how transition amplitudes for more general external polarizations can be constructed by combining answers obtained by different pairs of BCFW shifts. We then generalize these recursion relations to supersymmetric theories. In AdS, unlike flat-space, even maximal supersymmetry is insufficient to permit the computation of all correlators of operators in the same multiplet as a stress-tensor or conserved current. Finally, we work out some simple examples to verify our results. © 2011 American Physical Society.

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