Showing papers by "Tata Institute of Fundamental Research published in 2007"

An Index for 4 dimensional super conformal theories

Abstract: We present a trace formula for an index over the spectrum of four dimensional superconformal field theories on S 3 × time. Our index receives contributions from states invariant under at least one supercharge and captures all information – that may be obtained purely from group theory – about protected short representations in 4 dimensional superconformal field theories. In the case of the $${\mathcal N}=4$$ theory our index is a function of four continuous variables. We compute it at weak coupling using gauge theory and at strong coupling by summing over the spectrum of free massless particles in AdS 5 × S 5 and find perfect agreement at large N and small charges. Our index does not reproduce the entropy of supersymmetric black holes in AdS 5, but this is not a contradiction, as it differs qualitatively from the partition function over supersymmetric states of the $${\mathcal N}=4$$ theory. We note that entropy for some small supersymmetric AdS 5 black holes may be reproduced via a D-brane counting involving giant gravitons. For big black holes we find a qualitative (but not exact) agreement with the naive counting of BPS states in the free Yang Mills theory. In this paper we also evaluate and study the partition function over the chiral ring in the $${\mathcal N}=4$$ Yang Mills theory.

CMS physics technical design report, volume II: Physics performance

Abstract: CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider (LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This volume demonstrates the physics capability of the CMS experiment. The prime goals of CMS are to explore physics at the TeV scale and to study the mechanism of electroweak symmetry breaking--through the discovery of the Higgs particle or otherwise. To carry out this task, CMS must be prepared to search for new particles, such as the Higgs boson or supersymmetric partners of the Standard Model particles, from the start-up of the LHC since new physics at the TeV scale may manifest itself with modest data samples of the order of a few fb−1 or less. The analysis tools that have been developed are applied to study in great detail and with all the methodology of performing an analysis on CMS data specific benchmark processes upon which to gauge the performance of CMS. These processes cover several Higgs boson decay channels, the production and decay of new particles such as Z' and supersymmetric particles, Bs production and processes in heavy ion collisions. The simulation of these benchmark processes includes subtle effects such as possible detector miscalibration and misalignment. Besides these benchmark processes, the physics reach of CMS is studied for a large number of signatures arising in the Standard Model and also in theories beyond the Standard Model for integrated luminosities ranging from 1 fb−1 to 30 fb−1. The Standard Model processes include QCD, B-physics, diffraction, detailed studies of the top quark properties, and electroweak physics topics such as the W and Z0 boson properties. The production and decay of the Higgs particle is studied for many observable decays, and the precision with which the Higgs boson properties can be derived is determined. About ten different supersymmetry benchmark points are analysed using full simulation. The CMS discovery reach is evaluated in the SUSY parameter space covering a large variety of decay signatures. Furthermore, the discovery reach for a plethora of alternative models for new physics is explored, notably extra dimensions, new vector boson high mass states, little Higgs models, technicolour and others. Methods to discriminate between models have been investigated. This report is organized as follows. Chapter 1, the Introduction, describes the context of this document. Chapters 2-6 describe examples of full analyses, with photons, electrons, muons, jets, missing ET, B-mesons and τ's, and for quarkonia in heavy ion collisions. Chapters 7-15 describe the physics reach for Standard Model processes, Higgs discovery and searches for new physics beyond the Standard Model

CMS physics technical design report: Addendum on high density QCD with heavy ions

Abstract: This report presents the capabilities of the CMS experiment to explore the rich heavy-ion physics programme offered by the CERN Large Hadron Collider (LHC). The collisions of lead nuclei at energies , will probe quark and gluon matter at unprecedented values of energy density. The prime goal of this research is to study the fundamental theory of the strong interaction ? Quantum Chromodynamics (QCD) ? in extreme conditions of temperature, density and parton momentum fraction (low-x).This report covers in detail the potential of CMS to carry out a series of representative Pb-Pb measurements. These include bulk observables, (charged hadron multiplicity, low pT inclusive hadron identified spectra and elliptic flow) which provide information on the collective properties of the system, as well as perturbative probes such as quarkonia, heavy-quarks, jets and high pT hadrons which yield tomographic information of the hottest and densest phases of the reaction.

Visibility Algorithms in the Plane

Abstract: A human observer can effortlessly identify visible portions of geometric objects present in the environment. However, computations of visible portions of objects from a viewpoint involving thousands of objects is a time consuming task even for high speed computers. To solve such visibility problems, efficient algorithms have been designed. This book presents some of these visibility algorithms in two dimensions. Specifically, basic algorithms for point visibility, weak visibility, shortest paths, visibility graphs, link paths and visibility queries are all discussed. Several geometric properties are also established through lemmas and theorems. With over 300 figures and hundreds of exercises, this book is ideal for graduate students and researchers in the field of computational geometry. It will also be useful as a reference for researchers working in algorithms, robotics, computer graphics and geometric graph theory, and some algorithms from the book can be used in a first course in computational geometry.

Observation of two resonant structures in e+ e- → π+π- ψ(2S) via initial-state radiation at belle

Abstract: Reference EPFL-ARTICLE-154576doi:10.1103/PhysRevLett.99.142002View record in Web of Science Record created on 2010-11-05, modified on 2017-12-10

Observation of a new charmonium state in double charmonium production in e+ e- annihilation at s**(1/2) ~ 10.6-GeV

Abstract: We report the first observation of a charmoniumlike state recoiling from the $J/\ensuremath{\psi}$ in the inclusive process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}+\mathrm{\text{anything}}$ at a mass of $(3.943\ifmmode\pm\else\textpm\fi{}0.006\ifmmode\pm\else\textpm\fi{}0.006)\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. We also observe the decay of this state into ${D}^{*}\overline{D}$ and determine its intrinsic width to be less than $52\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ at the 90% C.L. These results are obtained from a $357\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data sample collected with the Belle detector near the $\ensuremath{\Upsilon}(4S)$ resonance, at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider.

Experimental constraints on the spin and parity of the Z(4430)

Abstract: We report the results of several studies of the Λc+π+π-X final state in continuum e+e- annihilation data collected by the Belle detector. An analysis of angular distributions in Λc(2880)+→Σc(2455)0, ++π+,- decays strongly favors a Λc(2880)+ spin assignment of 52 over 32 or 12. We find evidence for Λc(2880)+→Σc(2520)0,++π+,- decay and measure the ratio of Λc(2880)+ partial widths Γ(Σc(2520)π)/Γ(Σc(2455)π)=0.225±0. 062±0.025. This value favors the Λc(2880)+ spin-parity assignment of 52+ over 52-. We also report the first observation of Λc(2940) +→Σc(2455)0,++π+,- decay and measure Λc(2880)+ and Λc(2940)+ mass and width parameters. These studies are based on a 553fb-1 data sample collected at or near the Υ(4S) resonance at the KEKB collider. © 2007 The American Physical Society.

Supersymmetric states of N=4 Yang-Mills from giant gravitons

Abstract: Mikhailov has constructed an infinite family of 1 BPS D3-branes in AdS5 × S 5 . We regulate Mikhailov's solution space by focussing on finite dimensional submani- folds. Our submanifolds are topologically complex projective spaces with symplectic form cohomologically equal to 2πN times the Fubini-Study Kahler class. Upon quan- tization and removing the regulator we find the Hilbert Space of N noninteracting Bose particles in a 3d Harmonic oscillator, a result previously conjectured by Beasley. This Hilbert Space is isomorphic to the classical chiral ring of 1 BPS states in N = 4 Yang-Mills theory. We view our result as evidence that the spectrum of 1 BPS states in N = 4 Yang Mills theory, which is known to jump discontinuously from zero to infinitesimal coupling, receives no further renormalization at finite values of the 't Hooft coupling.

Entropy of null surfaces and dynamics of spacetime

Abstract: The null surfaces of a spacetime act as oneway membranes and can block information for a corresponding family of observers (timelike curves). Since lack of information can be related to entropy, this suggests the possibility of assigning an entropy to the null surfaces of a spacetime. We motivate and introduce such an entropy functional for any vector field in terms of a fourth-rank divergence-free tensor ${P}_{ab}^{cd}$ with the symmetries of the curvature tensor. Extremizing this entropy for all the null surfaces then leads to equations for the background metric of the spacetime. When ${P}_{ab}^{cd}$ is constructed from the metric alone, these equations are identical to Einstein's equations with an undetermined cosmological constant (which arises as an integration constant). More generally, if ${P}_{ab}^{cd}$ is allowed to depend on both metric and curvature in a polynomial form, one recovers the Lanczos-Lovelock gravity. In all these cases: (a) We only need to extremize the entropy associated with the null surfaces; the metric is not a dynamical variable in this approach. (b) The extremal value of the entropy agrees with standard results, when evaluated on shell for a solution admitting a horizon. The role of the full quantum theory of gravity will be to provide the specific form of ${P}_{ab}^{cd}$ which should be used in the entropy functional. With such an interpretation, it seems reasonable to interpret the Lanczos-Lovelock type terms as quantum corrections to classical gravity.

Black hole microstates and attractor without supersymmetry

Abstract: Due to the attractor mechanism, the entropy of an extremal black hole does not vary continuously as we vary the asymptotic values of various moduli fields. Using this fact we argue that the entropy of an extremal black hole in string theory, calculated for a range of values of the asymptotic moduli for which the microscopic theory is strongly coupled, should match the statistical entropy of the same system calculated for a range of values of the asymptotic moduli for which the microscopic theory is weakly coupled. This argument does not rely on supersymmetry and applies equally well to nonsupersymmetric extremal black holes. We discuss several examples which support this argument and also several caveats which could invalidate this argument.

Oral mucosal lesions associated with betel quid, areca nut and tobacco chewing habits: consensus from a workshop held in Kuala Lumpur, Malaysia, November 25-27, 1996.

Abstract: A variety of betel/areca nut/tobacco habits have been reviewed and categorized because of their possible causal association with oral cancer and various oral precancerous lesions and conditions, and on account of their widespread occurrence in different parts of the world. At a recent workshop in Kuala Lumpur it was recommended that "quid" be defined as "a substance, or mixture of substances, placed in the mouth or chewed and remaining in contact with the mucosa, usually containing one or both of the two basic ingredients, tobacco and/or areca nut, in raw or any manufactured or processed form." Clear delineations on contents of the quid (areca nut quid, tobacco quid, and tobacco and areca nut quid) are recommended as absolute criteria with finer subdivisions to be added if necessary. The betel quid refers to any quid wrapped in betel leaf and is therefore a specific variety of quid. The workshop proposed that quid-related lesions should be categorized conceptually into two categories: first, those that are diffusely outlined and second, those localized at the site where a quid is regularly placed. Additional or expanded criteria and guidelines were proposed to define, describe or identify lesions such as chewer's mucosa, areca nut chewer's lesion, oral submucous fibrosis and other quid-related lesions. A new clinical entity, betel-quid lichenoid lesion, was also proposed to describe an oral lichen planus-like lesion associated with the betel quid habit.

The Communication Complexity of Correlation

Abstract: We examine the communication required for generating random variables remotely. One party Alice is given a distribution D, and she has to send a message to Bob, who is then required to generate a value with distribution exactly D. Alice and Bob are allowed to share random bits generated without the knowledge of D. There are two settings based on how the distribution D provided to Alice is chosen. If D is itself chosen randomly from some set (the set and distribution are known in advance) and we wish to minimize the expected communication in order for Alice to generate a value y, with distribution D, then we characterize the communication required in terms of the mutual information between the input to Alice and the output Bob is required to generate. If D is chosen from a set of distributions D, and we wish to devise a protocol so that the expected communication (the randomness comes from the shared random string and Alice's coin tosses) is small for each D isin D, then we characterize the communication required in this case in terms of the channel capacity associated with the set D. Our proofs are based on an improved rejection sampling procedure that relates the relative entropy between two distributions to the communication complexity of generating one distribution from the other. As an application of these results, we derive a direct sum theorem in communication complexity that substantially improves the previous such result shown by Jain et al. (2003).

Evidence for production of single top quarks and first direct measurement of |Vtb|

Abstract: The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron collider. Using a 0.9 fb(-1) dataset, we apply a multivariate analysis to separate sig ...

Optimal control of treatment in a mathematical model of chronic myelogenous leukemia

Abstract: We consider a mathematical model of drug therapy for chronic myelogenous leukemia for an individual patient over a fixed time horizon. The disease dynamics are given by a system of ordinary differential equations that describe the interaction between naive T cells, effector T cells and leukemic cancer cells in a hypothetical patient. We introduce two drug therapies into this model, one a targeted therapy, and the other a broad cytotoxic therapy. Our goal is to find treatment regimens that minimize the cancer cell count and the deleterious effects of the drugs for a given patient. We examine the control setting analytically, and include numerical solutions to illustrate the optimal regimens under various assumptions.

Evidence for D0-D̄0 mixing

Abstract: We present evidence for D0-D(0) mixing in D(0)-->K(+)pi(-) decays from 384 fb(-1) of e(+)e(-) colliding-beam data recorded near square root s=10.6 GeV with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. We find the mixing parameters x('2)=[-0.22+/-0.30(stat)+/-0.21(syst)] x 10(-3) and y(')=[9.7+/-4.4(stat)+/-3.1(syst)] x 10(-3) and a correlation between them of -0.95. This result is inconsistent with the no-mixing hypothesis with a significance of 3.9 standard deviations. We measure R(D), the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates, to be [0.303+/-0.016(stat)+/-0.010(syst)]%. We find no evidence for CP violation.

Measurement of D0-D̄0 mixing parameters in D0→Ksπ+π- decays

Abstract: We report a measurement of D0-D(0) mixing parameters in D(0) --> K(s)(0) pi(+) pi(-) decays using a time-dependent Dalitz-plot analysis. We first assume CP conservation and subsequently allow for CP violation. The results are based on 540 fb(-1) of data accumulated with the Belle detector at the KEKB e(+)e(-) collider. Assuming negligible CP violation, we measure the mixing parameters x = (0.80 +/- 0.29(-0.07-0.14)(+0.09+0.10))% and y = (0.33+/-0.24(-0.12-0.08)(+0.08+0.06))%, where the errors are statistical, experimental systematic, and systematic due to the Dalitz decay model, respectively. Allowing for CP violation, we obtain the CP-violating parameters |q / p| = 0.86(-0.29-0.03)(+0.30+0.06) +/- 0.08 and arg(q/p) = (-14(-18-3-4)(+16+5+2)) degrees .

Zinc lowers amyloid-β toxicity by selectively precipitating aggregation intermediates

Abstract: Soluble amyloid-β (Aβ) aggregates are suspected to play a major role in Alzheimer's disease. Zn2+ at a concentration of a few micromolar, which is too dilute to affect the precipitation equilibrium of Aβ, can destabilize these aggregates [Garai, K., Sengupta, P., Sahoo, B., and Maiti, S. (2006) Biochem. Biophys. Res. Commun. 345, 210−215]. Here we investigate the nature of these aggregates in the context of the precipitation pathway, the mechanism underlying their destabilization, and the biological consequences of this destabilization. We show that the larger soluble aggregates (size >10 nm) form only in supersaturated Aβ solutions, implying that they are intermediates in the pathway toward fibril formation. We also show that Zn2+ destabilizes these intermediates by accelerating their aggregation kinetics. The resulting change in the size distribution of the Aβ solution is sufficient to eliminate its toxicity to cultured mammalian neurons. Our results provide an explanation for the existing observations ...

May-happen-in-parallel analysis of X10 programs

Abstract: X10 is a modern object-oriented programming language designed for high performance, high productivity programming of parallel and multi-core computer systems. Compared to the lower-level thread-based concurrency model in the JavaTM language, X10 has higher-level concurrency constructs such as async, atomic and finish built into the language to simplify creation, analysis and optimization of parallel programs. In this paper, we introduce a new algorithm for May-Happen-in-Parallel (MHP) analysis of X10 programs. The analysis algorithm is based on simple path traversals in the Program Structure Tree, and does not rely on pointer alias analysis of thread objects as in MHP analysis for Java programs. We introduce a more precise definition of the MHP relation than in past work by adding condition vectors that identify execution instances for which the MHP relation holds, instead of just returning a single true/false value for all pairs of executing instances. Further, MHP analysis is refined in our approach by using the observation that two statement instances which occur in atomic sections that execute at the same X10 place must have MHP = false. We expect that our MHP analysis algorithm will be applicable to any language that adopts the core concepts of places, async, finish, and atomic sections from the X10 programming model. We also believe that this approach offers the best of two worlds to programmers and parallel programming tools ---higher-level abstractions of concurrency coupled with simple and efficient analysis algorithms.

A stream of cells migrating from the caudal telencephalon reveals a link between the amygdala and neocortex

Abstract: The amygdaloid complex consists of diverse nuclei that belong to distinct functional systems, yet many issues about its development are poorly understood. Here, we identify a stream of migrating cells that form specific amygdaloid nuclei in mice. In utero electroporation showed that this caudal amygdaloid stream (CAS) originated in a unique domain at the caudal telencephalic pole that is contiguous with the dorsal pallium, which was previously thought to generate only neocortical cells. The CAS and the neocortex share mechanisms for specification (transcription factors Tbr1, Lhx2 and Emx1/2) and migration (reelin and Cdk5). Reelin, a critical cue for migration in the neocortex, and Cdk5, which is specifically required for migration along radial glia in the neocortex, were both selectively required for the normal migration of the CAS, but not for that of other amygdaloid nuclei. This is first evidence of a dorsal pallial contribution to the amygdala, demonstrating a developmental and mechanistic link between the amygdala and the neocortex.

Thermodynamics of the Polyakov-Nambu-Jona-Lasinio model with nonzero baryon and isospin chemical potentials

Abstract: We have extended the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two degenerate flavors to include the isospin chemical potential (${\ensuremath{\mu}}_{I}$). All the diagonal and mixed derivatives of pressure with respect to the quark number (proportional to baryon number) chemical potential (${\ensuremath{\mu}}_{0}$) and isospin chemical potential up to sixth order have been extracted at ${\ensuremath{\mu}}_{0}={\ensuremath{\mu}}_{I}=0$. These derivatives give the generalized susceptibilities with respect to quark and isospin numbers. Similar estimates for the flavor diagonal and off-diagonal susceptibilities are also presented. Comparison to lattice QCD (LQCD) data of some of these susceptibilities for which LQCD data are available show similar temperature dependence, though there are some quantitative deviations above the crossover temperature. We have also looked at the effects of instanton induced flavor mixing coming from the ${U}_{A}(1)$ chiral symmetry breaking 't Hooft determinantlike term in the NJL part of the model. The diagonal quark number and isospin susceptibilities are completely unaffected. The off-diagonal susceptibilities show significant dependence near the crossover. Finally we present the chemical potential dependence of specific heat and speed of sound within the limits of chemical potentials where neither diquarks nor pions can condense.

Measurement of the Near-Threshold e+e-D(*)±D(*) Cross Section using Initial-State Radiation

Abstract: We report a measurement of the exclusive e{sup +}e{sup -}{yields}D{sup (*){+-}}D*{sup {+-}} cross section as a function of center-of-mass energy near the D{sup (*)}{+-}D*{sup {+-}} threshold with initial-state radiation. A partial reconstruction technique is used to increase the efficiency and to suppress background. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 547.8 fb{sup -1}.

Metamorphosis of an identified serotonergic neuron in the Drosophila olfactory system.

Abstract: Odors are detected by sensory neurons that carry information to the olfactory lobe where they connect to projection neurons and local interneurons in glomeruli: anatomically well-characterized structures that collect, integrate and relay information to higher centers. Recent studies have revealed that the sensitivity of such networks can be modulated by wide-field feedback neurons. The connectivity and function of such feedback neurons are themselves subject to alteration by external cues, such as hormones, stress, or experience. Very little is known about how this class of central neurons changes its anatomical properties to perform functions in altered developmental contexts. A mechanistic understanding of how central neurons change their anatomy to meet new functional requirements will benefit greatly from the establishment of a model preparation where cellular and molecular changes can be examined in an identified central neuron. In this study, we examine a wide-field serotonergic neuron in the Drosophila olfactory pathway and map the dramatic changes that it undergoes from larva to adult. We show that expression of a dominant-negative form of the ecdysterone receptor prevents remodeling. We further use different transgenic constructs to silence neuronal activity and report defects in the morphology of the adult-specific dendritic trees. The branching of the presynaptic axonal arbors is regulated by mechanisms that affect axon growth and retrograde transport. The neuron develops its normal morphology in the absence of sensory input to the antennal lobe, or of the mushroom bodies. However, ablation of its presumptive postsynaptic partners, the projection neurons and/or local interneurons, affects the growth and branching of terminal arbors. Our studies establish a cellular system for studying remodeling of a central neuromodulatory feedback neuron and also identify key elements in this process. Understanding the morphogenesis of such neurons, which have been shown in other systems to modulate the sensitivity and directionality of response to odors, links anatomy to the development of olfactory behavior.

Cosmologies with null singularities and their gauge theory duals

Abstract: We investigate backgrounds of Type IIB string theory with null singularities and their duals proposed in S. R. Das, J. Michelson, K. Narayan, S. P. Trivedi, hep-th/0602107. The dual theory is a deformed $\mathcal{N}=4$ Yang-Mills theory in $3+1$ dimensions with couplings dependent on a lightlike direction. We concentrate on backgrounds which become ${\mathrm{AdS}}_{5}\ifmmode\times\else\texttimes\fi{}{S}^{5}$ at early and late times and where the string coupling is bounded, vanishing at the singularity. Our main conclusion is that in these cases the dual gauge theory is nonsingular. We show this by arguing that there exists a complete set of gauge invariant observables in the dual gauge theory whose correlation functions are nonsingular at all times. The two-point correlator for some operators calculated in the gauge theory does not agree with the result from the bulk supergravity solution. However, the bulk calculation is invalid near the singularity where corrections to the supergravity approximation become important. We also obtain pp-waves which are suitable Penrose limits of this general class of solutions, and construct the matrix membrane theory which describes these pp-wave backgrounds.

Spectrum of CHL dyons from genus-two partition function

Abstract: We compute the genus-two chiral partition function of the left-moving heterotic string for a 2 CHL orbifold. The required twisted determinants can be evaluated explicitly in terms of the untwisted determinants and theta functions using orbifold techniques. The dependence on Prym periods cancels neatly once summation over odd charges is properly taken into account. The resulting partition function is a Siegel modular form of level two and precisely equals recently proposed dyon partition function for this model. This result provides an independent weak coupling derivation of the dyon partition function using the M-theory lift of string webs representing the dyons. We discuss generalization of this technique to general N orbifolds.

Direct observation of the strange b Baryon Ξb

Abstract: We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst).