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Sep 21, 2013
09/13

by
R. Narayanan; Thomas Vojta; D. Belitz; T. R. Kirkpatrick

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The effects of quenched disorder on the critical properties of itinerant quantum antiferromagnets and ferromagnets are considered. Particular attention is paid to locally ordered spatial regions that are formed in the presence of quenched disorder even when the bulk system is still in the paramagnetic phase. These rare regions or local moments are reflected in the existence of spatially inhomogeneous saddle points of the Landau-Ginzburg-Wilson functional. We derive an effective theory that...

Source: http://arxiv.org/abs/cond-mat/9905047v2

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36

Sep 21, 2013
09/13

by
A. Hietanen; R. Narayanan; R. Patel; C. Prays

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The vector meson mass is computed as a function of quark mass in the large N limit of QCD. We use continuum reduction and directly compute the vector meson propagator in momentum space. Quark momentum is inserted using the quenched momentum prescription.

Source: http://arxiv.org/abs/0901.3752v2

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Sep 21, 2013
09/13

by
A. Hietanen; R. Narayanan

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We use a single site lattice in four dimensions to study the scaling of large N Yang-Mills field coupled to a single massless Dirac fermion in the adjoint representation. We use the location of the strong to weak coupling transition defined through the eigenvalues of the folded Wilson loop operator to set a scale. We do not observe perturbative scaling in the region studied in this paper. Instead, we observe that the scale changes very slowly with the bare coupling. The lowest eigenvalue of the...

Source: http://arxiv.org/abs/1204.0331v2

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Sep 20, 2013
09/13

by
Phong S. Nguyen; Henry D. Pfister; Krishna R. Narayanan

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Algorithms based on multiple decoding attempts of Reed-Solomon (RS) codes have recently attracted new attention. Choosing decoding candidates based on rate-distortion (R-D) theory, as proposed previously by the authors, currently provides the best performance-versus-complexity trade-off. In this paper, an analysis based on the rate-distortion exponent (RDE) is used to directly minimize the exponential decay rate of the error probability. This enables rigorous bounds on the error probability for...

Source: http://arxiv.org/abs/1002.0043v2

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Jul 19, 2013
07/13

by
R. Narayanan; H. Neuberger

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Dirac fermions in the fundamental representation of SU(N) live on the surface of a cylinder embedded in $R^3$ and interact with a three dimensional SU(N) Yang Mills vector potential preserving a global chiral symmetry at finite $N$. As the circumference of the cylinder is varied from small to large, the chiral symmetry gets spontaneously broken in the infinite $N$ limit at a typical bulk scale. Replacing three dimensional YM by four dimensional YM introduces non-trivial renormalization effects.

Source: http://arxiv.org/abs/1005.0576v2

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Sep 20, 2013
09/13

by
Jing Jiang; Krishna R. Narayanan

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An iterative algorithm is presented for soft-input-soft-output (SISO) decoding of Reed-Solomon (RS) codes. The proposed iterative algorithm uses the sum product algorithm (SPA) in conjunction with a binary parity check matrix of the RS code. The novelty is in reducing a submatrix of the binary parity check matrix that corresponds to less reliable bits to a sparse nature before the SPA is applied at each iteration. The proposed algorithm can be geometrically interpreted as a two-stage gradient...

Source: http://arxiv.org/abs/cs/0506073v2

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Sep 20, 2013
09/13

by
R. Narayanan; H. Neuberger

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Some physical results in four dimensional large N gauge theories on a periodic torus are summarized.

Source: http://arxiv.org/abs/hep-th/0607149v1

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8.0

Feb 13, 2020
02/20

by
K R Narayanan

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4
4.0

Jun 30, 2018
06/18

by
Nihat Engin Tunali; Yu-Chih Huang; Joseph J. Boutros; Krishna R. Narayanan

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In this paper, we consider the use of lattice codes over Eisenstein integers for implementing a compute-and-forward protocol in wireless networks when channel state information is not available at the transmitter. We extend the compute-and-forward paradigm of Nazer and Gastpar to decoding Eisenstein integer combinations of transmitted messages at relays by proving the existence of a sequence of pairs of nested lattices over Eisenstein integers in which the coarse lattice is good for covering...

Topics: Mathematics, Computing Research Repository, Information Theory

Source: http://arxiv.org/abs/1404.1312

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2.0

Jun 30, 2018
06/18

by
Yu-Chih Huang; Krishna R. Narayanan

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In this paper, using compute-and-forward as an example, we provide an overview of constructions of lattices from codes that possess the right algebraic structures for harnessing interference. This includes Construction A, Construction D, and Construction $\pi_A$ (previously called product construction) recently proposed by the authors. We then discuss two generalizations where the first one is a general construction of lattices named Construction $\pi_D$ subsuming the above three constructions...

Topics: Mathematics, Computing Research Repository, Information Theory

Source: http://arxiv.org/abs/1406.3368

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4.0

Jun 29, 2018
06/18

by
Ying Wang; Minghai Qin; Krishna R. Narayanan; Anxiao Jiang; Zvonimir Bandic

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We exploit the redundancy of the language-based source to help polar decoding. By judging the validity of decoded words in the decoded sequence with the help of a dictionary, the polar list decoder constantly detects erroneous paths after every few bits are decoded. This path-pruning technique based on joint decoding has advantages over stand-alone polar list decoding in that most decoding errors in early stages are corrected. In order to facilitate the joint decoding, we first propose a...

Topics: Information Theory, Computing Research Repository, Mathematics

Source: http://arxiv.org/abs/1601.06184

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6.0

Jun 26, 2018
06/18

by
Yu-Chih Huang; Krishna R. Narayanan; Ping-Chung Wang

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We consider the compute-and-forward paradigm with limited feedback. Without feedback, compute-and-forward is typically realized with lattice codes over the ring of integers, the ring of Gaussian integers, or the ring of Eisenstein integers, which are all principal ideal domains (PID). A novel scheme called adaptive compute-and-forward is proposed to exploit the limited feedback about the channel state by working with the best ring of imaginary quadratic integers. This is enabled by generalizing...

Topics: Information Theory, Mathematics, Computing Research Repository

Source: http://arxiv.org/abs/1501.07740

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2.0

Jun 30, 2018
06/18

by
Nagaraj T. Janakiraman; Avinash Vem; Krishna R. Narayanan; Jean-Francois Chamberland

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We consider the problem of querying a string (or, a database) of length $N$ bits to determine all the locations where a substring (query) of length $M$ appears either exactly or is within a Hamming distance of $K$ from the query. We assume that sketches of the original signal can be computed off line and stored. Using the sparse Fourier transform computation based approach introduced by Pawar and Ramchandran, we show that all such matches can be determined with high probability in sub-linear...

Topics: Information Theory, Data Structures and Algorithms, Computing Research Repository, Mathematics

Source: http://arxiv.org/abs/1704.07852

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5.0

Jun 30, 2018
06/18

by
Yu-Chih Huang; Krishna R. Narayanan; Nihat Engin Tunali

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A novel construction of lattices is proposed. This construction can be thought of as Construction A with codes that can be represented as the Cartesian product of $L$ linear codes over $\mathbb{F}_{p_1},\ldots,\mathbb{F}_{p_L}$, respectively; hence, is referred to as the product construction. The existence of a sequence of such lattices that are good for quantization and Poltyrev-good under multistage decoding is shown. This family of lattices is then used to generate a sequence of nested...

Topics: Mathematics, Computing Research Repository, Information Theory

Source: http://arxiv.org/abs/1401.2228

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Sep 22, 2013
09/13

by
J. Kiskis; R. Narayanan

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We numerically compute the spatial string tension in the deconfined phase of three dimensional QCD in the large N limit. Our results clearly show that the string tension grows linearly with temperature.

Source: http://arxiv.org/abs/0906.3015v1

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Sep 22, 2013
09/13

by
R. Narayanan

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Overlap formalism deals with the construction of chiral gauge theories on the lattice. These set of lectures provide a pedagogical introduction to the subject with emphasis on chiral anomalies and gauge field topology. Subtleties associated with the generating functional for gauge theories coupled to chiral fermions are discussed.

Source: http://arxiv.org/abs/1103.4588v2

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Sep 19, 2013
09/13

by
R. Narayanan; H. Neuberger

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Dirac fermions in the fundamental representation of SU(N) live on a two dimensional torus flatly embedded in $R^4$. They interact with a four dimensional SU(N) Yang Mills vector potential preserving a global chiral symmetry at finite $N$. As the size of the torus in units of $\frac{1}{\Lambda_{SU(N)}}$ is varied from small to large, the chiral symmetry gets spontaneously broken in the infinite $N$ limit.

Source: http://arxiv.org/abs/0909.4066v1

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Sep 23, 2013
09/13

by
R. Narayanan

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Large N gauge theories with adjoint matter can be numerically studied using lattice techniques. Eguchi-Kawai reductions holds for this theory and one can reduce the lattice model to a single site. Hybrid Monte Carlo algorithm can be used to simulate this model. One can either perform an exact computation of the "fermionic force" or use pseudo fermions as part of the HMC algorithm. The former algorithm is slower than the latter but has the advantage that one can work with any real...

Source: http://arxiv.org/abs/1109.6890v1

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Sep 23, 2013
09/13

by
Parimal Parag; Jean-Francois Chamberland; Henry D. Pfister; Krishna R. Narayanan

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This paper considers the queueing performance of a system that transmits coded data over a time-varying erasure channel. In our model, the queue length and channel state together form a Markov chain that depends on the system parameters. This gives a framework that allows a rigorous analysis of the queue as a function of the code rate. Most prior work in this area either ignores block-length (e.g., fluid models) or assumes error-free communication using finite codes. This work enables one to...

Source: http://arxiv.org/abs/1006.2403v1

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Sep 19, 2013
09/13

by
Kapil Bhattad; Krishna R. Narayanan; Giuseppe Caire

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We consider the problem of joint source-channel coding for transmitting K samples of a complex Gaussian source over T = bK uses of a block-fading multiple input multiple output (MIMO) channel with M transmit and N receive antennas. We consider the case when we are allowed to code over L blocks. The channel gain is assumed to be constant over a block and channel gains for different blocks are assumed to be independent. The performance measure of interest is the rate of decay of the expected mean...

Source: http://arxiv.org/abs/cs/0703035v2

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Sep 18, 2013
09/13

by
F. Berruto; R. Narayanan; H. Neuberger

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We introduce a simple method to find localized exact fermionic zero modes for any local fermionic action. The zero modes are attached to specific local gauge configurations. Examples are provided for staggered and Wilson fermion actions in 2-6 dimensions, at finite and infinite lattice volumes, and for abelian and non-abelian gauge groups. One of our concrete results is that a finite density of almost zero modes must occur in quenched four dimensional lattice gauge theory simulations that use...

Source: http://arxiv.org/abs/hep-lat/0006030v2

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Jul 20, 2013
07/13

by
Phong S. Nguyen; Arvind Yedla; Henry D. Pfister; Krishna R. Narayanan

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Recently, it has been observed that terminated low-density-parity-check (LDPC) convolutional codes (or spatially-coupled codes) appear to approach capacity universally across the class of binary memoryless channels. This is facilitated by the "threshold saturation" effect whereby the belief-propagation (BP) threshold of the spatially-coupled ensemble is boosted to the maximum a-posteriori (MAP) threshold of the underlying constituent ensemble. In this paper, we consider the...

Source: http://arxiv.org/abs/1107.3253v2

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44

Sep 21, 2013
09/13

by
R. Narayanan; H. Neuberger

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Numerical studies support the conjecture that in continuum planar QCD the eigenvalue density of a Wilson loop operator undergoes a transition as the loop is dilated while keeping the loop shape fixed. A second part of the conjecture is that the transition obeys large N universality and that this universality class is the same in 2, 3 and 4 Euclidean space-time dimensions. The focus of the talk will be on clarifying precisely what the conjecture is claiming.

Source: http://arxiv.org/abs/0709.4494v1

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Sep 17, 2013
09/13

by
D. Belitz; S. L. Sessions; T. R. Kirkpatrick; M. T. Mercaldo; R. Narayanan; Thomas Vojta

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The behavior of the conductivity and the density of states, as well as the phase relaxation time, of disordered itinerant electrons across a quantum ferromagnetic transition is discussed. It is shown that critical fluctuations lead to anomalies in the temperature and energy dependence of the conductivity and the tunneling density of states, respectively, that are stronger than the usual weak-localization anomalies in a disordered Fermi liquid. This can be used as an experimental probe of the...

Source: http://arxiv.org/abs/cond-mat/0108118v1

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31

Sep 19, 2013
09/13

by
J. Kiskis; R. Narayanan. H. Neuberger

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Some results in QCD_2 at large N are presented using the reduced model on the lattice. Overlap fermions are used to compute meson propagators.

Source: http://arxiv.org/abs/hep-lat/0208021v1

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38

Sep 18, 2013
09/13

by
T. R. Kirkpatrick; D. Belitz; Thomas Vojta; R. Narayanan

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It is shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of the magnons to the longitudinal magnetic susceptibility. Together with the tendency of the low-temperature ferromagnetic transition in very clean Heisenberg magnets to be of first order, this qualitatively explains the phase diagram recently observed in UGe_2.

Source: http://arxiv.org/abs/cond-mat/0105627v2

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36

Sep 21, 2013
09/13

by
R. Narayanan; H. Neuberger

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There exist chiral gauge models in two dimensions that have massless composite fermions. Two examples are presented and it is suggested that they be accepted as benchmark test-cases for generic proposals of non-perturbatively regulating chiral gauge theories in any dimension. We apply the overlap to the simpler of the two benchmarks and present the results of a numerical simulation of modest size.

Source: http://arxiv.org/abs/hep-lat/9609031v1

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3.0

Jun 30, 2018
06/18

by
V. Haefner; J. Schindler; N. Weik; T. Mayer; S. Balakrishnan; R. Narayanan; S. Bera; F. Evers

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The density of states (DoS), $\varrho(E)$, of graphene is investigated numerically and within the self-consistent T-matrix approximation (SCTMA) in the presence of vacancies within the tight binding model. The focus is on compensated disorder, where the concentration of vacancies, $n_\text{A}$ and $n_\text{B}$, in both sub-lattices is the same. Formally, this model belongs to the chiral symmetry class BDI. The prediction of the non-linear sigma-model for this class is a Gade-type singularity...

Topics: Mesoscale and Nanoscale Physics, Disordered Systems and Neural Networks, Condensed Matter

Source: http://arxiv.org/abs/1404.6138

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30

Sep 22, 2013
09/13

by
Phong S. Nguyen; Henry D. Pfister; Krishna R. Narayanan

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Recently, a number of authors have proposed decoding schemes for Reed-Solomon (RS) codes based on multiple trials of a simple RS decoding algorithm. In this paper, we present a rate-distortion (R-D) approach to analyze these multiple-decoding algorithms for RS codes. This approach is first used to understand the asymptotic performance-versus-complexity trade-off of multiple error-and-erasure decoding of RS codes. By defining an appropriate distortion measure between an error pattern and an...

Source: http://arxiv.org/abs/0908.2828v1

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37

Sep 22, 2013
09/13

by
R. Narayanan

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We study the thermodynamics of the two flavor massless Schwinger model on a torus at a finite chemical potential. We show that thermodynamic quantities only depend on the isospin chemical potential and there are marked deviations from a free fermion theory.

Source: http://arxiv.org/abs/1210.3072v2

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Sep 23, 2013
09/13

by
P. H. Damgaard; R. G. Edwards; U. M. Heller; R. Narayanan

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In the large-volume limit $V\to\infty$ with $V < < 1/m_{\pi}^4$ the mass-dependent chiral condensate is predicted to satisfy exact finite-volume scaling laws that fall into three major universality classes. We test these analytical predictions with staggered fermions and overlap fermions in gauge field sectors of fixed topological charge $\nu$.

Source: http://arxiv.org/abs/hep-lat/9909009v1

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Sep 23, 2013
09/13

by
Priyanka Mohan; R. Narayanan

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We investigate the influence of weak disorder on the fluctuation driven first order transition found in a p-wave superconductor. The flow equations for the disorder averaged effective theory is derived in an $4-\epsilon$ expansion. The fixed point structure of these flow equations and their stability is discussed.

Source: http://arxiv.org/abs/0903.0245v1

Cultural Resources of India

8
8.0

Nov 15, 2020
11/20

by
Shri K. R. Narayanan and Dr. Kapila Vatsyayan

movies

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Administrative Source Indira Gandhi National Centre for the Arts, Delhi ( IGNCA ) Identifier 236 Title Coverage of UNESCO Seminar on Technology in Cultural Heritage (Vol. I) Alternative IGNCA-236-VHS Medium Video Home System; National (SP NV-E180SPX) ExtentOriginal 02:09:56 Spatial IGNCA, New Delhi Temporal Seminar Created 24.02.1993 and 28.02.1993 Relation 1 of 2 Rights IGNCA Descriptive Subject Cultural Heritage and Technology Keywords UNESCO, Seminar, Technology, Cultural Heritage, IGNCA,...

Topic: Cultural Heritage and Technology

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42

Sep 18, 2013
09/13

by
A. Gonzalez-Arroyo; R. Narayanan; H. Neuberger

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We consider SU(N) lattice gauge theory at infinite N defined on a torus with a CP invariant twist. Massless fermions are incorporated in an elegant way, while keeping them quenched. We present some numerical results which suggest that twisting can make numerical simulations of planar QCD more efficient.

Source: http://arxiv.org/abs/hep-lat/0509074v1

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36

Sep 20, 2013
09/13

by
Krishna R. Narayanan; Kapil Bhattad

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We consider the problem of compression of two memoryless binary sources, the correlation between which is defined by a Hidden Markov Model (HMM). We propose a Decision Feedback (DF) based scheme which when used with low density parity check codes results in compression close to the Slepian Wolf limits.

Source: http://arxiv.org/abs/cs/0506045v1

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40

Sep 20, 2013
09/13

by
R. Narayanan; H. Neuberger

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We present numerical evidence for the hypothesis that, in the planar limit, four dimensional Euclidean Yang-Mills theory on a finite symmetrical four-torus breaks chiral symmetry spontaneously when the length of the sides l is larger than a critical value l_c with a bilinear condensate whose value is independent of l. Therefore spontaneous symmetry breaking occurs at finite volume and infinite N_c reduction holds for the chiral condensate.

Source: http://arxiv.org/abs/hep-lat/0405025v3

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Sep 17, 2013
09/13

by
S. Bera; A. Arnold; F. Evers; R. Narayanan; P. Woelfle

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We present a calculation of the free energy, the surface free energy and the elastic constants ("Lam'e parameters" i.e, Poisson ratio, Young's modulus) of graphene flakes on the level of the density functional theory employing different standard functionals. We observe that the Lam'e parameters in small flakes can differ from the bulk values by 30% for hydrogenated zig-zag edges. The change results from the edge of the flake that compresses the interior. When including the vibrational...

Source: http://arxiv.org/abs/1003.4429v1

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32

Sep 20, 2013
09/13

by
R. Narayanan; H. Neuberger

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We define smoothed Wilson loop operators on a four dimensional lattice and check numerically that they have a finite and nontrivial continuum limit. The continuum operators maintain their character as unitary matrices and undergo a phase transition at infinite N reflected by the eigenvalue distribution closing a gap in its spectrum when the defining smooth loop is dilated from a small size to a large one. If this large N phase transition belongs to a solvable universality class one might be...

Source: http://arxiv.org/abs/hep-th/0601210v2

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2.0

Feb 1, 2021
02/21

by
K R Narayanan

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7.0

Feb 28, 2020
02/20

by
A. Raman, Chairman; T. R. Shah, Member; N. R. Kulkarni, Member; R. Narayanan, Member; A. Bagchi, Member; H. B. Shivamaggi, Member; Meenakshi Tyagarajan, Member; C. S. Ramachandran, Member; K. R. Viswanathan, Member-Secretary

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Central Secretariat Library, Government of India Source URL: http://cslrepository.nvli.in/handle/123456789/33

Topic: Central Secretariat Library

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41

Sep 22, 2013
09/13

by
R. G. Edwards; U. M. Heller; R. Narayanan

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We review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. We describe properties of the overlap Dirac operator, and methods to implement it numerically. We use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain wall and overlap fermions.

Source: http://arxiv.org/abs/hep-lat/0001013v1

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Sep 18, 2013
09/13

by
R. Narayanan; H. Neuberger; F. Reynoso

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It is established by numerical means that continuum large N QCD defined on a three dimensional torus can exist in four different phases. They are (i) confined phase; (ii) deconfined phase; (iii) small box at zero temperature and (iv) small box at high temperatures.

Source: http://arxiv.org/abs/0704.2591v1

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Sep 23, 2013
09/13

by
R. Narayanan; H. Neuberger

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The main focus of this talk is the physics of large N QCD on a continuum torus. A cascade of phase transitions associated with the breaking of U(1) symmetries will be discussed. The continuum Wilson loop as a function of its area will be discussed along with its universality properties and the associated double scaling limit. Some recent progress in twisted Eguchi-Kawai is presented. Gauge field topology and $\theta$ vacuua are also discussed in the context of large N gauge theories. Phase...

Source: http://arxiv.org/abs/0710.0098v2

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44

Sep 21, 2013
09/13

by
R. Narayanan; Thomas Vojta; D. Belitz; T. R. Kirkpatrick

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The Griffiths region that is due to rare regions and the resulting local moments in disordered itinerant quantum magnets, and its influence on the critical behavior, is considered within the framework of an effective field theory. It is shown that the local moments can be described in terms of static, annealed disorder, and the physical consequences of this description are discussed.

Source: http://arxiv.org/abs/cond-mat/9907384v2

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Jul 19, 2013
07/13

by
Phong S. Nguyen; Henry D. Pfister; Krishna R. Narayanan

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One popular approach to soft-decision decoding of Reed-Solomon (RS) codes is based on using multiple trials of a simple RS decoding algorithm in combination with erasing or flipping a set of symbols or bits in each trial. This paper presents a framework based on rate-distortion (RD) theory to analyze these multiple-decoding algorithms. By defining an appropriate distortion measure between an error pattern and an erasure pattern, the successful decoding condition, for a single...

Source: http://arxiv.org/abs/1005.4461v3

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36

Sep 18, 2013
09/13

by
Arvind Yedla; Henry D. Pfister; Krishna R. Narayanan

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We consider a noisy Slepian-Wolf problem where two correlated sources are separately encoded (using codes of fixed rate) and transmitted over two independent binary memoryless symmetric channels. The capacity of each channel is characterized by a single parameter which is not known at the transmitter. The goal is to design systems that retain near-optimal performance without channel knowledge at the transmitter. It was conjectured that it may be hard to design codes that perform well for...

Source: http://arxiv.org/abs/1201.0409v1

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Sep 20, 2013
09/13

by
Kapil Bhattad; Niranjan Ratnakar; Ralf Koetter; Krishna R. Narayanan

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We give an information flow interpretation for multicasting using network coding. This generalizes the fluid model used to represent flows to a single receiver. Using the generalized model, we present a decentralized algorithm to minimize the number of packets that undergo network coding. We also propose a decentralized algorithm to construct capacity achieving multicast codes when the processing at some nodes is restricted to routing. The proposed algorithms can be coupled with existing...

Source: http://arxiv.org/abs/cs/0506044v1

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Sep 23, 2013
09/13

by
Serge Florens; Priyanka Mohan; C. Janani; T. Gupta; R. Narayanan

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Dynamics of magnetic moments near the Mott metal-insulator transition is investigated by a combined slave-rotor and Dynamical Mean-Field Theory solution of the Hubbard model with additional fully-frustrated random Heisenberg couplings. In the paramagnetic Mott state, the spinon decomposition allows to generate a Sachdev-Ye spin liquid in place of the collection of independent local moments that typically occurs in the absence of magnetic correlations. Cooling down into the spin-liquid phase,...

Source: http://arxiv.org/abs/1006.3620v3

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501

Jun 12, 2010
06/10

by
K R Narayanan Namboothiri

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This is a collection of poems in Malayalam, written, composed and sung by K. R . Narayanan Namboothiri You can visit his blog at http://karanattu.wordpress.com to see his other works. Mail him at narayanan (dot) karanattu At gmail (dot) com

Topics: Malayalam, Poems

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25

Sep 21, 2013
09/13

by
J. Kiskis; R. Narayanan; H. Neuberger

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Using quenched reduction, we propose a method for the numerical calculation of meson correlation functions in the planar limit of QCD. General features of the approach are outlined, and an example is given in the context of two-dimensional QCD.

Source: http://arxiv.org/abs/hep-lat/0203005v3