Chennai Mathematical Institute
Chennai, India

Chennai Mathematical Institute is a research and education institute in Chennai, India. It was founded by the SPIC Science Foundation in 1989, and offers undergraduate as well as postgraduate programmes in Physics, Mathematics and Computer Science, besides its key strength in the form of high-end research in Mathematics. CMI is noted for its research in the field of algebraic geometry, in particular in the area of moduli of bundles.CMI was earlier located in T. Nagar in the heart of Chennai in an office complex. It moved to a new 5-acre campus in Siruseri in October 2005.In December 2006, CMI was recognized as a university under Section 3 of the UGC Act 1956, making it a deemed university. Until then, the teaching program was offered in association with Bhoj Open University, as it offered more flexibility. Wikipedia.

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Ma E.,University of California at Riverside | Srivastava R.,Chennai Mathematical Institute
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Many studies have been made on extensions of the standard model with B-L gauge symmetry. The addition of three singlet (right-handed) neutrinos renders it anomaly-free. It has always been assumed that the spontaneous breaking of B-L is accomplished by a singlet scalar field carrying two units of B-L charge. This results in a very natural implementation of the Majorana seesaw mechanism for neutrinos. However, there exists in fact another simple anomaly-free solution which allows Dirac or inverse seesaw neutrino masses. We show for the first time these new possibilities and discuss an application to neutrino mixing with S3 flavor symmetry. © 2015 The Authors.

Hassan S.R.,Chennai Mathematical Institute | Senechal D.,Université de Sherbrooke
Physical Review Letters | Year: 2013

The question of the existence of a spin liquid state in the half-filled Hubbard model on the honeycomb (also known as graphene) lattice is revisited. The variational cluster approximation, the cluster dynamical mean field theory, and the cluster dynamical impurity approximation are applied to various cluster systems. Assuming that the spin liquid phase coincides with the Mott insulating phase in this nonfrustrated system, we find that the Mott transition is preempted by a magnetic transition occurring at a lower value of the interaction U, and therefore the spin liquid phase does not occur. This conclusion is obtained using clusters with two bath orbitals connected to each boundary cluster site. We argue that using a single bath orbital per boundary site is insufficient and leads to the erroneous conclusion that the system is gapped for all nonzero values of U. © 2013 American Physical Society.

Ponmurugan M.,Chennai Mathematical Institute
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

It has been shown recently that the Jarzynski equality is generalized under nonequilibrium feedback control. The presence of feedback control in physical systems should modify both the Jarzynski equality and the detailed fluctuation theorem. However, the generalized Jarzynski equality under forward feedback control has been proved by considering that the physical systems under feedback control should locally satisfy the detailed fluctuation theorem. We use the same formalism and derive the generalized detailed fluctuation theorem for nonequilibrium driven systems under feedback control. We find that the feedback control in a physical system should preserve the detailed fluctuation theorem if the system has the same feedback information measure in forward and reverse directions. © 2010 The American Physical Society.

Chandrashekar C.M.,Chennai Mathematical Institute
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We present an approach to induce localization of a Bose-Einstein condensate in a one-dimensional lattice under the influence of unitary quantum-walk evolution using disordered quantum coin operation. We introduce a discrete-time quantum-walk model in which the interference effect is modified to diffuse or strongly localize the probability distribution of the particle by assigning a different set of coin parameters picked randomly for each step of the walk, respectively. Spatial localization of the particle or state is explained by comparing the variance of the probability distribution of the quantum walk in position space using disordered coin operation to that of the walk using an identical coin operation for each step. Due to the high degree of control over quantum coin operation and most of the system parameters, ultracold atoms in an optical lattice offer opportunities to implement a disordered quantum walk that is unitary and induces localization. Here we present a scheme to use a Bose-Einstein condensate that can be evolved to the superposition of its internal states in an optical lattice and control the dynamics of atoms to observe localization. This approach can be adopted to any other physical system in which controlled disordered quantum walk can be implemented. © 2011 American Physical Society.

Narayan K.,Chennai Mathematical Institute
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

Following Narayan (2012) [4] and Narayan et al. (2013) [8], we study non-conformal brane plane wave backgrounds dual to strongly coupled gauge theories with constant energy flux and holographic entanglement entropy for strip subsystems in them. We find that for the strip direction along the direction of the energy flux, the finite cutoff-independent part of entanglement entropy can be estimated in terms of a dimensionless combination of the energy density and the strip dimensions, alongwith an effective scale-dependent number of degrees of freedom. For the strip orthogonal to the flux direction, there are indications of phase transitions. We also briefly discuss NS5-brane backgrounds corresponding to plane wave states in little string theories. © 2013 Elsevier B.V.

Arun K.G.,Chennai Mathematical Institute
Classical and Quantum Gravity | Year: 2012

Various alternative theories of gravity predict dipolar gravitational radiation in addition to quadrupolar radiation. We show that gravitational wave (GW) observations of inspiralling compact binaries can put interesting constraints on the strengths of the dipole modes of GW polarizations. We put forward a physically motivated gravitational waveform for dipole modes, in the Fourier domain, in terms of two parameters: one which captures the relative amplitude of the dipole mode with respect to the quadrupole mode (α) and the other a dipole term in the phase (β). We then use this two-parameter representation to discuss typical bounds on their values using GW measurements. We obtain the expected bounds on the amplitude parameter and the phase parameter for advanced LIGO (AdvLIGO) and Einstein telescope (ET) noise power spectral densities using Fisher information matrix. AdvLIGO and ET may at best bound α to an accuracy of ∼10 2 and ∼10 3 and β to an accuracy of ∼10 5 and ∼10 6. © 2012 IOP Publishing Ltd.

Narayan K.,Chennai Mathematical Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We explore string and M-theory constructions of holographic theories with Lifshitz scaling exponent z and hyperscaling violation exponent θ, finding a range of z, θ values. Some of these arise as effective metrics from dimensional reduction of certain kinds of null deformations of AdS spacetimes appearing in the near-horizon geometries of extremal D3-, M2-, and M5-brane theories. The AdS 5 solution, in particular, gives rise to θ=1 in d=2 (boundary) space dimensions. Other solutions arise as the IIA D2- and D4-brane solutions with appropriate null deformations, and we discuss the phase structure of these systems. © 2012 American Physical Society.

Narayan K.,Chennai Mathematical Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We study AdS×X null deformations arising as near horizon limits of D3-brane analogs of inhomogeneous plane waves. Restricting to normalizable deformations for the AdS5 case, these generically correspond in the dual field theory to super Yang-Mills states with light cone momentum density T++ varying spatially, the homogeneous case studied in corresponding to uniform T++. All of these preserve some supersymmetry. Generically these inhomogeneous solutions exhibit analogs of horizons in the interior where a timelike Killing vector becomes null. From the point of view of x +-dimensional reduction, the circle pinches off on these horizon loci in the interior. We discuss similar inhomogeneous solutions with asymptotically Lifshitz boundary conditions, as well as aspects of Lifshitz singularities in string constructions involving anti-de Sitter null deformations. We also briefly discuss holographic entanglement entropy for some of these. © 2012 American Physical Society.

Narayan K.,Chennai Mathematical Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Following K. Balasubramanian and K. Narayan [JHEPFG1029-8479J. High Energy Phys. 08 (2010) 01410.1007/JHEP08(2010)014], we discuss certain lightlike deformations of AdS5×X5 in type IIB string theory sourced by a lightlike dilaton Φ(x+) dual to the N=4 super Yang-Mills theory with a lightlike varying gauge coupling. We argue that, in the case where the x+ direction is noncompact, these solutions describe anisotropic 3+1-dim Lifshitz-like systems with a potential in the x+ direction generated by the lightlike dilaton. We then describe solutions of this sort with a linear dilaton. This enables a detailed calculation of two-point correlation functions of operators dual to bulk scalars and helps illustrate the spatial structure of these theories. Following this, we discuss a nongeometric string construction involving a compactification along the x+ direction of this linear dilaton system. We also point out similar IIB axionic solutions. Similar bulk arguments for x+-noncompact can be carried out for deformations of AdS4×X7 in M theory. © 2011 American Physical Society.

Nautiyal A.,Chennai Mathematical Institute
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We study single field inflation in noncommutative spacetime and compute two-point and three-point correlation functions for the curvature perturbation. We find that both power spectrum and bispectrum for comoving curvature perturbation are statistically anisotropic and the bispectrum is also modified by a phase factor depending upon the noncommutative parameters. The non-linearity parameter fNL is small for small statistical anisotropic corrections to the bispectrum coming from the noncommutative geometry and is consistent with the recent PLANCK bounds. There is a scale dependence of fNL due to the noncommutative spacetime which is different from the standard single field inflation models and statistically anisotropic vector field inflation models. Deviations from statistical isotropy of CMB, observed by PLANCK can tightly constraint the effects due to noncommutative geometry on power spectrum and bispectrum. © 2013 The Author. Published by Elsevier B.V.

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