Results for "Soumik Mukhopadhyay"

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Negative longitudinal magnetoresistance in the density wave phase of Y$_2$Ir$_2$O$_7$Feb 08 2018The ground state of nanowires of single crystalline Pyrochlore Y$_2$Ir$_2$O$_7$ is a density wave. Application of a {\it transverse} magnetic field increases the threshold electric field for the collective de-pinning of the density wave state at low temperature, ... More
Field-tunable stochasticity in the magnetization reversal of a cylindrical nanomagnetNov 05 2010The nature of magnetization reversal in an isolated cylindrical nanomagnet has been studied employing time-resolved magnetoresistance measurement. We find that the reversal mode is highly stochastic, occurring either by multimode or single-step switching. ... More
Inversion of magnetoresistance in magnetic tunnel junctions : effect of pinhole nanocontactsJul 29 2005Jan 19 2006Inverse magnetoresistance has been observed in magnetic tunnel junctions with pinhole nanocontacts over a broad temperature range. The tunnel magnetoresistance undergoes a change of sign at higher bias and temperature. This phenomenon is attributed to ... More
Enhancement of low field magnetoresistance at room temperature in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Al$_{2}$O$_{3}$ nanocompositeApr 19 2005Magnetotransport properties in a nanocrystalline La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/micron sized Al$_{2}$O$_{3}$ granular composite with different concentrations of Al$_{2}$O$_{3}$ have been studied. The resistivity curves in absence of magnetic field and ... More
Colossal enhancement of magnetoresistance in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ / Pr$_{0.67}$Ca$_{0.33}$MnO$_{3}$ multilayers: reproducing the phase-separation scenarioJun 23 2010Colossal enhancement of magnetoresistance has been achieved over a broad temperature range which extends upto the room temperature, in ferromagnetic metal-charge ordered insulator manganite multi-layers. The artificially created phase coexistence in the ... More
Giant enhancement of room temperature magnetoresistance in La_{0.67}Sr_{0.33}MnO_{3}/Nd_{0.67}Sr_{0.33}MnO_{3} multilayersMay 06 2005Jan 19 2006The metal-insulator transition temperature in CMR manganites has been altered and brought close to the room temperature by preparing La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO)/ Nd$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (NSMO) multilayers with ultra thin individual ... More
Pinhole and tunneling conduction channels superimposed in magnetic tunnel junction: results and inferencesMar 31 2006The influence of ballistic channels superimposed on tunneling conduction channels in magnetic tunnel junctions has been studied in a manganese oxide based tunneling device. Inversion of magnetoresistance has been observed in magnetic tunnel junctions ... More
Concentration for multidimensional diffusions and their boundary local timesMay 12 2010Apr 21 2011We prove that probability laws of certain multidimensional semimartingales which includes time-inhomogenous diffusions, under suitable assumptions, satisfy Quadratic Transportation Cost Inequality under the uniform metric. From this we derive concentration ... More
On a conjectured sharpness principle for probabilistic forecasting with calibrationFeb 02 2009This note proves a weak type of the sharpness principle as conjectured by Gneiting, Balabdaoui, and Raftery in 2007 in connection with probabilistic forecasting subject to calibration constraints. A strong version of such a principle still awaits a proper ... More
Anomalous ferroelectric switching dynamics in single crystalline SrTiO3Oct 18 2016Pure SrTiO3 in bulk form is known to be an incipient ferroelectric where the quantum fluctuations of lattice positions prevent long range ferroelectric ordering at a finite temperature. We show evidence and identify the origin of ferroelectric relaxation ... More
Emergence of ferroelectric switching in self organized Pr0.67Ca0.33MnO3 nanocrystal arrayOct 18 2016We discuss the emergence of low dimensional ferroelectricity in self-organized Pr0.67Ca0.33MnO3 nanocrystalline arrays deposited on Si substrate. We observe sharp switching of electric polarization under external electric eld with nearly rectangular hysteresis ... More
Analysis of market weights under volatility-stabilized market modelsApr 03 2009Nov 12 2012We derive the joint density of market weights, at fixed times and suitable stopping times, of the volatility-stabilized market models introduced by Fernholz and Karatzas in [Ann. Finan. 1 (2005) 149-177]. The argument rests on computing the exit density ... More
Symmetrization of BernoulliJan 26 2006Let X be a random variable. We shall call an independent random variable Y to be a symmetrizer for X, if X+Y is symmetric around zero. A random variable is said to be symmetry resistant if the variance of any symmetrizer Y, is never smaller than the variance ... More
Wright-Fisher diffusion with negative mutation ratesJan 31 2010Mar 14 2013We study a family of n-dimensional diffusions, taking values in the unit simplex of vectors with nonnegative coordinates that add up to one. These processes satisfy stochastic differential equations which are similar to the ones for the classical Wright-Fisher ... More
Colossal enhancement of electrical conductivity in Y2Ir2O7 nanoparticlesNov 17 2016We present a comparative study of the magnetic and electrical properties of polycrystalline and nanocrystalline Y2Ir2O7, the latter prepared using a new chemical route. We find that reduction in particle size leads to enhanced ferromagnetism and orders ... More
Tracking random walk of individual domain walls in cylindrical nanomagnets with resistance noiseJun 30 2010The stochasticity of domain wall (DW) motion in magnetic nanowires has been probed by measuring slow fluctuations, or noise, in electrical resistance at small magnetic fields. By controlled injection of DWs into isolated cylindrical nanowires of nickel, ... More
Brownian approximation to counting graphsJan 27 2012Jun 01 2012Let C(n,k) denote the number of connected graphs with n labeled vertices and n+k-1 edges. For any sequence (k_n), the limit of C(n,k_n) as n tends to infinity is known. It has been observed that, if k_n=o(\sqrt{n}), this limit is asymptotically equal ... More
On the Aldous diffusion on Continuum Trees. IApr 21 2011Consider a Markov chain on the space of rooted real binary trees that randomly removes leaves and reinserts them on a random edge and suitably rescales the lengths of edges. This chain was introduced by David Aldous who conjectured a diffusion limit of ... More
Exponentially concave functions and high dimensional stochastic portfolio theoryMar 06 2016Mar 12 2016We consider the following problem in stochastic portfolio theory. Are there portfolios that are relative arbitrages with respect to the market portfolio over very short periods of time under realistic assumptions? We answer a slightly relaxed question ... More
An Excursion-Theoretic Approach to Stability of Discrete-Time Stochastic Hybrid SystemsJan 15 2009Aug 29 2010We address stability of a class of Markovian discrete-time stochastic hybrid systems. This class of systems is characterized by the state-space of the system being partitioned into a safe or target set and its exterior, and the dynamics of the system ... More
Markov processes on time-like graphsDec 02 2009Nov 15 2012We study Markov processes where the "time" parameter is replaced by paths in a directed graph from an initial vertex to a terminal one. Along each directed path the process is Markov and has the same distribution as the one along any other directed path. ... More
Intertwining diffusions and wave equationsJun 04 2013Dec 19 2015We develop a general theory of intertwined diffusion processes of any dimension. Our main result gives an SDE characterization of all possible intertwinings of diffusion processes and shows that they correspond to nonnegative solutions of hyperbolic partial ... More
Twin peaksJun 26 2016We study random labelings of graphs conditioned on a small number (typically one or two) peaks, i.e., local maxima. We show that the boundaries of level sets of a random labeling of a square with a single peak have dimension 2, in a suitable asymptotic ... More
Anomalous bias dependence of tunnel magnetoresistance in a magnetic tunnel junctionJul 12 2004Apr 07 2005We have fabricated a spin-polarized tunneling device based on half metallic manganites incorporating $Ba_{2}LaNbO_{6}$ as insulating barrier. An anomalous bias dependence of tunnel magnetoresistance (TMR) has been observed, the first of its kind in a ... More
A phase transition behavior for Brownian motions interacting through their ranksJun 25 2007Oct 05 2009Consider a time-varying collection of n points on the positive real axis, modeled as exponentials of n Brownian motions whose drift vector at every time point is determined by the relative ranks of the coordinate processes at that time. If at each time ... More
One-dimensional Brownian particle systems with rank dependent driftsApr 06 2007Jan 22 2008We study interacting systems of linear Brownian motions whose drift vector at every time point is determined by the relative ranks of the coordinate processes at that time. Our main objective has been to study the long range behavior of the spacings between ... More
Concentration of measure for systems of Brownian particles interacting through their ranksNov 10 2010We consider a finite or countable collection of one-dimensional Brownian particles whose dynamics at any point in time is determined by their rank in the entire particle system. Using Transportation Cost Inequalities for stochastic processes we provide ... More
Analysis of continuous strict local martingales via h-transformsNov 07 2007Jun 02 2010We study strict local martingales via h-transforms, a method which first appeared in Delbaen-Schachermayer. We show that strict local martingales arise whenever there is a consistent family of change of measures where the two measures are not equivalent ... More
Cycles and eigenvalues of sequentially growing random regular graphsMar 06 2012Jul 28 2014Consider the sum of $d$ many i.i.d. random permutation matrices on $n$ labels along with their transposes. The resulting matrix is the adjacency matrix of a random regular (multi)-graph of degree $2d$ on $n$ vertices. It is known that the distribution ... More
Sparse regular random graphs: Spectral density and eigenvectorsOct 28 2009Oct 12 2012We examine the empirical distribution of the eigenvalues and the eigenvectors of adjacency matrices of sparse regular random graphs. We find that when the degree sequence of the graph slowly increases to infinity with the number of vertices, the empirical ... More
The Random Transposition Dynamics on Random Regular Graphs and the Gaussian Free FieldSep 27 2014Dec 29 2014A single permutation, seen as union of disjoint cycles, represents a regular graph of degree two. Consider $d$ many independent random permutations and superimpose their graph structures. It is a common model of a random regular (multi-) graph of degree ... More
A combinatorial analysis of interacting diffusionsFeb 27 2009We consider a particular class of n-dimensional homogeneous diffusions all of which have an identity diffusion matrix and a drift function that is piecewise constant and scale invariant. Abstract stochastic calculus immediately gives us general results ... More
Is non-locality stronger in higher dimensions?Aug 18 2016A critique of a prescription of non-locality in [Phys. Rev. Lett. 85, 4418 (2000)], [Phys. Rev. Lett. 88, 040404 (2002)], [Phys. Rev. Lett. 92, 130404 (2004)] that appears to be stronger and more general than the Bell-CHSH formulation is presented. It ... More
Direct experimental evidence of multiferroicity in a nanocrystalline Zener polaron ordered manganiteDec 24 2014We discuss the particle size driven tunability of the coexistence of ferromagnetism and ferroelectricity in Pr0.67Ca0.33MnO3(PCMO) with the help of x ray diffraction, magnetization, impedance spectroscopy, and remanent polarization measurements. The remanent ... More
Gravity induced neutrino-antineutrino oscillation: CPT and lepton number non-conservation under gravityFeb 10 2007We introduce a new effect in the neutrino oscillation phase which shows the neutrino-antineutrino oscillation is possible under gravity even if the rest masses of the corresponding eigenstates are same. This is due to CPT violation and possible to demonstrate ... More
Route of hydrodynamic turbulence in rotating shear flow: Secondary perturbation triggers growing eigenmodes through the elliptical instabilityAug 31 2005Origin of hydrodynamic turbulence in rotating shear flow, e.g. plane Couette flow including the Coriolis force, is a big puzzle. While the flow often exhibits turbulence in laboratory experiments, according to the linear perturbation theory it should ... More
Stability of accretion disk around rotating black holes: a pseudo-general-relativistic fluid dynamical studyDec 07 2002We discuss the solution of accretion disk when the black hole is chosen to be rotating. We study, how the fluid properties get affected for different rotation parameters of the black hole. We know that no cosmic object is static in Universe. Here the ... More
Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black HolesJul 10 1998We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier ... More
Model of a disk-outflow coupled system: disk-outflow symbiosisFeb 13 2013Several observational evidences and deeper theoretical insights reveal that accretion and outflow/jet are strongly correlated. We model an advective disk-outflow coupled dynamics. We investigate the properties of the disk-outflow surface and how is it ... More
Two temperature accretion flows around rotating black holes and determining the kerr parameter of sourcesJan 24 2011We model two temperature viscous accretion flows in the sub-Keplerian, optically thin, regime around rotating black holes including important radiation effects self-consistently. The model successfully explains observed luminosities from ultra-luminous ... More
Stability of accretion disk around rotating black holesFeb 08 2004I discuss the stability of accretion disks when the black hole is considered to be rotating. I show, how the fluid properties get changed for different choices of angular momentum of black holes. I treat the problem in pseudo-Newtonian approach with a ... More
Description of Pseudo-Newtonian Potential for the Relativistic Accretion Disk around Kerr Black HolesMay 28 2002Aug 16 2002We present a pseudo-Newtonian potential for accretion disk modeling around the rotating black holes. This potential can describe the general relativistic effects on accretion disk. As the inclusion of rotation in a proper way is very important at an inner ... More
Dynamics of electromagnetic waves in Kerr geometryFeb 14 2002Here we are interested to study the spin-1 particle i.e., electro-magnetic wave in curved space-time, say around black hole. After separating the equations into radial and angular parts, writing them according to the black hole geometry, say, Kerr black ... More
Significantly super-Chandrasekhar limiting mass white dwarfs as progenitors for peculiar over-luminous type Ia supernovaeSep 30 2015Since 2012, we have initiated developing systematically the simplistic to rigorous models to prove that highly super-Chandrasekhar, as well as highly sub-Chandrasekhar, limiting mass white dwarfs are possible to exist. We show that the mass of highly ... More
Secondary Perturbation Effects in Keplerian Accretion Disks: Elliptical InstabilityMar 09 2007Origin of turbulence in cold accretion disks, particularly in 3D, which is expected to be hydrodynamic but not magnetohydrodynamic, is a big puzzle. While the flow must exhibit some turbulence in support of the transfer of mass inward and angular momentum ... More
Nucleosynthesis in Advective Accretion Disk around Compact ObjectMar 12 2001We study the nucleosynthesis in accretion disk around compact object. When matter falls towards the compact object, due to interactions in nuclear species nuclear energy is released in the high temperature. In some region of parameter space nuclear energy ... More
Nucleosynthesis Around Black HolesOct 05 1999Study of nucleosynthesis in accretion disks around black holes was initiated by Chakrabarti et al. (1987). In the present work we do the similar analysis using the state-of-the-art disk model, namely, Advective Accretion Disks. During the infall, matter ... More
Non-equilibrium fluctuation-dissipation relation from holographyJun 14 2012Feb 25 2013We derive a non-equilibrium fluctuation-dissipation relation for bosonic correlation functions from holography in the classical gravity approximation at strong coupling. This generalizes the familiar thermal fluctuation-dissipation relation in absence ... More
A cut-off tubular geometry of loop spaceJul 28 2014Aug 17 2016Motivated by the computation of loop space quantum mechanics as indicated in [7], here we seek a better understanding of the tubular geometry of loop space ${\cal L}{\cal M}$ corresponding to a Riemannian manifold ${\cal M}$ around the submanifold of ... More
Oscillator Representation of the BCFT Construction of D-branes in Vacuum String Field TheoryOct 15 2001Nov 14 2001Starting from the boundary CFT definition for the D-branes in vacuum string field theory (VSFT) given in hep-th/0105168, we derive the oscillator expression for the D24-brane solution in the VSFT on D25-brane. We show that the state takes the form of ... More
Transonic properties of the accretion disk around compact objectsNov 13 2008An accretion flow is necessarily transonic around a black hole. However, around a neutron star it may or may not be transonic, depending on the inner disk boundary conditions influenced by the neutron star. I will discuss various transonic behavior of ... More
Neutrino asymmetry around black holes: Neutrinos interact with gravityMay 21 2005Propagation of a fermion in curved space-time generates a gravitational interaction due to coupling of its spin with the space-time curvature connection. This gravitational interaction, which is an axial-four-vector multiplied by a four gravitational ... More
Neutrino oscillations under gravity: mass independent oscillationJul 12 2003Aug 04 2003I discuss the possibility of neutrino oscillation in presence of gravity. In this respect I consider the propagation of neutrinos in the early phase of universe and around black holes. It is seen that whether the rest masses of a neutrino and corresponding ... More
Exploring a missing link between peculiar, sub- and super-Chandrasekhar type Ia supernovae by modifying Einstein's gravityMar 01 2016Observations of several peculiar, under- and over-luminous type Ia supernovae (SNeIa) argue for exploding masses widely different from the Chandrasekhar-limit. We explore the modification to Einstein's gravity in white dwarfs for the first time in the ... More
Behaviour of spin-1/2 particle around a charged black holeMar 15 2000Dirac equation is separable in curved space-time and its solution was found for both spherically and axially symmetric geometry. But most of the works were done without considering the charge of the black hole. Here we consider the spherically symmetric ... More
On a coordinate independent description of string worldsheet theoryDec 20 2009Mar 27 2010We study worldsheet conformal invariance for bosonic string propagating in a curved background using the hamiltonian formalism. In order to formulate the problem in a background independent manner we first rewrite the worldsheet theory in a language where ... More
DeWitt-Virasoro construction in tensor representationsApr 14 2010Apr 27 2010We generalize the DeWitt-Virasoro (DWV) construction of arXiv:0912.3987 [hep-th] to tensor representations of higher ranks. A rank-$n$ tensor state, which is by itself coordinate invariant, is expanded in terms of position eigenstates that transform as ... More
On the Conformal Field Theories for Bosonic Strings in PP-WavesJul 06 2008Recently Kazama and Yokoi (arXiv:0801.1561 [hep-th]) have used a phase-space method to study the Virasoro algebra of type IIB superstring theory in the maximally supersymmetric R-R plane wave background in a semi-light-cone gauge. Two types of normal ... More
The Symmetric Algebra for Certain Monomial CurvesFeb 18 2010Jan 11 2011In this article we compute a minimal Groebner basis for the symmetric algebra for certain affine Monomial Curves, as an R-module. Keywords: Monomial Curves, Groebner Basis, Symmetric Algebra. Mathematics Subject Classification 2000: 13P10, 13A30 .
Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?Feb 13 2013It is believed that jets emerging from blazars (Flat Spectrum Radio Quasars (FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually exhibit lower luminosity and harder power law spectra at gamma-ray energies than FSRQs. It was argued ... More
Higher order nonlinearity in accretion disks: QPOs of black hole and neutron star sources and their spinNov 13 2008We propose a unified model to explain Quasi-Periodic-Oscillation (QPO), particularly of high frequency, observed from black hole and neutron star systems globally. We consider accreting systems to be damped harmonic oscillators exhibiting epicyclic oscillations ... More
Growing hydrodynamic modes in Keplerian accretion disks during secondary perturbations: Elliptical vortex effectsAug 18 2006The origin of hydrodynamic turbulence, and in particular of an anomalously enhanced angular momentum transport, in accretion disks is still an unsolved problem. This is especially important for cold disk systems which are practically neutral in charge ... More
Hydrodynamical Study of Advective Accretion flow around Neutron StarsMar 25 2002Here we study the accretion process around a neutron star, especially for the cases where shock does form in the accretion disk. In case of accretion flows around a black hole, close to the horizon matter is supersonic. On the other hand for the case ... More
Possible Neutrino-Antineutrino Oscillation Under Gravity and its ConsequencesJan 15 2007Mar 07 2007We show that under gravity the effective masses for neutrino and antineutrino are different which opens a possible window of neutrino-antineutrino oscillation even if the rest masses of the corresponding eigenstates are same. This is due to CPT violation ... More
Dirac Equation in Kerr GeometryOct 06 1999We are familiar with Dirac equation in flat space by which we can investigate the behaviour of half-integral spin particle. With the introduction of general relativistic effects the form of the Dirac equation will be modified. For the cases of different ... More
Mode Identification and Data-Driven SciencesSep 21 2015Nov 12 2015Bump-hunting or mode identification is a fundamental problem that arises in almost every scientific field of data-driven discovery. Surprisingly, very few data modeling tools are available for automatic (not requiring manual case-by-base investigation), ... More
A Covariant Form of the Navier-Stokes Equation for the Galilean Conformal AlgebraAug 06 2009Dec 29 2009We demonstrate that the Navier-Stokes equation can be covariantized under the full infinite dimensional Galilean Conformal Algebra (GCA), such that it reduces to the usual Navier-Stokes equation in an inertial frame. The covariantization is possible only ... More
General Construction of Tubular GeometryAug 26 2016We consider the problem of locally describing tubular geometry around a submanifold embedded in a (pseudo)Riemannian manifold in its general form. Given the geometry of ambient space in an arbitrary coordinate system and equations determining the submanifold ... More
Superstrings in type IIB R-R plane-wave in semi-light-cone gauge and conformal invarianceFeb 21 2009We reconsider the analysis done by Kazama and Yokoi in arXiv:0801.1561 (hep-th). We find that although the right vacuum of the theory is the one associated to massless normal ordering (MNO), phase space normal ordering (PNO) plays crucial role in the ... More
Generalized protocol for distribution and concentration of Quantum informationNov 04 2003Alice can distribute a quantum state $|\phi>$ to $N$ spatially separated parties(say Bobs) by telecloning. It is possible for Charlie to reconstruct the quantum state to him if he shares same kind of telecloning quantum channel with Bobs using only LOCC. ... More
Unstable Non-BPS D-Branes of Type-II String Theories in Light-Cone Green-Schwarz FormalismNov 08 2000The problem of describing the boundary states of unstable non-BPS D-branes of type-II string theories in light-cone Green-Schwarz (GS) formalism is addressed. Regarding the type II theories in light-cone gauge as different realizations of the $\hat{SO}(8)_{k=1}$ ... More
Strength of Connections in a Random Graph: Definition, Characterization, and EstimationDec 04 2014Dec 09 2015How can the `affinity' or `strength' of ties of a random graph be characterized and compactly represented? How can concepts like Fourier and inverse-Fourier like transform be developed for graph data? To do so, we introduce a new graph-theoretic function ... More
Remarks on level one conformal blocks divisorsOct 20 2013We show that conformal blocks divisors of type B_r and D_r at level one are effective sums of boundary divisors of $\bar{M}_{0,n}$. We also prove that the conformal blocks divisor of type $B_r$ at level 1 with weights (\omega_1,\dots,\omega_1) scales ... More
Diagram automorphisms and Rank-Level dualityAug 08 2013We study the effect of diagram automorphisms on rank-level duality. We use it to prove new symplectic rank-level dualities on genus zero smooth curves with marked points and chosen coordinates. We also show that rank-level dualities for the pair sl(r), ... More
Unified Statistical Theory of Spectral Graph AnalysisFeb 11 2016Sep 20 2016The goal of this paper is to show that there exists a simple, yet universal statistical logic of spectral graph analysis by recasting it into a nonparametric function estimation problem. The prescribed viewpoint appears to be good enough to accommodate ... More
Large-Scale Mode Identification and Data-Driven SciencesSep 21 2015Nov 08 2016Bump-hunting or mode identification is a fundamental problem that arises in almost every scientific field of data-driven discovery. Surprisingly, very few data modeling tools are available for automatic (not requiring manual case-by-base investigation), ... More
Root-cause analysis for time-series anomalies via spatiotemporal causal graphical modelingMay 20 2016Modern distributed cyber-physical systems encounter a large variety of anomalies and in many cases, they are vulnerable to catastrophic fault propagation scenarios due to strong connectivity among the sub-systems. In this regard, root-cause analysis becomes ... More
Brownian earthwormNov 24 2010Dec 13 2013We prove that the distance between two reflected Brownian motions, driven by the same white noise, outside a sphere in a 3-dimensional flat torus does not converge to 0, a.s., if the radius of the sphere is sufficiently small, relative to the size of ... More
Exponentially concave functions and a new information geometryMay 19 2016Aug 03 2016A function is exponentially concave if its exponential is concave. We consider exponentially concave functions on the unit simplex. It is known that gradient maps of exponentially concave functions are solutions of a Monge-Kantorovich optimal transport ... More
Convergence rates for rank-based models with applications to portfolio theoryAug 01 2011We determine rates of convergence of rank-based interacting diffusions and semimartingale reflecting Brownian motions to equilibrium. Convergence rate for the total variation metric is derived using Lyapunov functions. Sharp fluctuations of additive functionals ... More
Crowding of Brownian spheresFeb 04 2010Dec 25 2010We study two models consisting of reflecting one-dimensional Brownian "particles" of positive radius. We show that the stationary empirical distributions for the particle systems do not converge to the harmonic function for the generator of the individual ... More
Archimedes' principle for Brownian liquidDec 30 2009Feb 13 2012We consider a family of hard core objects moving as independent Brownian motions confined to a vessel by reflection. These are subject to gravitational forces modeled by drifts. The stationary distribution for the process has many interesting implications, ... More
Energy, entropy, and arbitrageAug 25 2013Jan 01 2016We introduce a pathwise approach to analyze the relative performance of an equity portfolio with respect to a benchmark market portfolio. In this energy-entropy framework, the relative performance is decomposed into three components: a volatility term, ... More
Lorentz Symmetry Violation in Neutrinos in Curved Spacetime and its ConsequencesJan 24 2011The neutrino propagating in curved spacetimes, e.g. around black holes, in early curved universe, violates Lorentz and then CPT symmetry, at least in the local coordinate. This occurs due to coupling of spin of the neutrino to background spin connection ... More
Predicting spin of compact objects from their QPOs: A global QPO modelSep 19 2008We establish a unified model to explain Quasi-Periodic-Oscillation (QPO) observed from black hole and neutron star systems globally. This is based on the accreting systems thought to be damped harmonic oscillators with higher order nonlinearity. The model ... More
Chaotic behavior of micro quasar GRS 1915+105Feb 10 2004Black hole binaries are variable in timescales of rang from months to milli-seconds. The origin of this variability is still not clear, it could be due to the variation of external parameters, like mass accretion rate, instabilities in the inner regions ... More
Neutrino asymmetry in presence of gravitational interactionJan 22 2004Feb 07 2004Propagation of fermions in curved space-time generates a gravitational interaction due to the coupling between spin of the fermion and space-time curvature. This gravitational interaction, which is an axial-vector appears as the CPT violating term in ... More
Unification to the "Pseudo-General-Relativistic" analysis of accretion disks around rotating black holes and neutron starsMar 05 2003I analyse the relativistic accretion phenomena around rotating black holes and neutron stars in pseudo-Newtonian approach and show both the kinds of disk can be treated in an unified manner. For this purpose, number of pseudo-Newtonian potentials are ... More
Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?Apr 09 2012Mar 01 2013String theory and gauge/gravity duality suggest the lower bound of shear viscosity (eta) to entropy density (s) for any matter to be ~ mu hbar/4pi k_B, when hbar and k_B are reduced Planck and Boltzmann constants respectively and mu <= 1. Motivated by ... More
Behaviour of spin-half particles in curved space-timeMar 12 2001We study the behaviour of spin-half particles in curved space-time. Since Dirac equation gives the dynamics of spin-half particles, we mainly study the Dirac equation in Schwarzschild, Kerr, Reissner-Nordstr\"om geometry. Due to the consideration of existence ... More
Instantaneous Reflection and Transmission Coefficients and a Special Method to Solve Wave EquationAug 07 1999People are familiar with quantum mechanical reflection and transmission coefficient. In all those cases corresponding potentials are usually assumed as of constant height and depth. For the cases of varying potential, corresponding reflection and transmission ... More
General relativity and relativistic astrophysicsSep 07 2016Einstein established the theory of general relativity and the corresponding field equation in 1915 and its vacuum solutions were obtained by Schwarzschild and Kerr for, respectively, static and rotating black holes, in 1916 and 1963, respectively. They ... More
All order covariant tubular expansionMar 06 2012Aug 17 2016We consider tubular neighborhood of an arbitrary submanifold embedded in a (pseudo-)Riemannian manifold. This can be described by Fermi normal coordinates (FNC) satisfying certain conditions as described by Florides and Synge in \cite{FS}. By generalizing ... More
On a semi-classical limit of loop space quantum mechanicsFeb 13 2012Apr 29 2012Following earlier work, we view two dimensional non-linear sigma model with target space $\cM$ as a single particle relativistic quantum mechanics in the corresponding free loop space $\cLM$. In a natural semi-classical limit ($\hbar=\alpha' \to 0$) of ... More
A Universality in PP-WavesApr 01 2007Apr 09 2007We discuss a universality property of any covariant field theory in space-time expanded around pp-wave backgrounds. According to this property the space-time lagrangian density evaluated on a restricted set of field configurations, called universal sector, ... More
DDF Construction and D-Brane Boundary States in Pure Spinor FormalismDec 14 2005Apr 14 2006Open string boundary conditions for non-BPS D-branes in type II string theories discussed in hep-th/0505157 give rise to two sectors with integer (R sector) and half-integer (NS sector) modes for the combined fermionic matter and bosonic ghost variables ... More
CDfdr: A Comparison Density Approach to Local False Discovery Rate EstimationAug 11 2013Efron et al. (2001) proposed empirical Bayes formulation of the frequentist Benjamini and Hochbergs False Discovery Rate method (Benjamini and Hochberg,1995). This article attempts to unify the `two cultures' using concepts of comparison density and distribution ... More
Understanding the holographic principle via RG flowDec 01 2016This is a review of some recent works which demonstrate how the classical equations of gravity in AdS themselves hold the key to understanding their holographic origin in the form of a strongly coupled large $N$ QFT whose algebra of local operators can ... More