Results for "Soumik Mukhopadhyay"

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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
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
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
Suppression of long range magnetic ordering and electrical conduction in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$ thin filmApr 18 2019We find that the long-range magnetic ordering is absent and electrical conduction suppressed in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$/YSZ(100) thin film prepared by pulsed laser deposition. The sharp down-turn of inverse magnetic susceptibility X-1(T) from the ... More
Influence of electronic structure parameters on the electrical transport and magnetic properties of $Y_{2-x}Bi_xIr_2O_7$ pyrochlore iridatesMay 07 2019We report the systematic study of structural, magnetic and electrical transport properties of $Y_{2-x}Bi_xIr_2O_7$ (x = 0.0, 0.1, 0.2, 0.3) pyrochlore iridates. The chemical doping enhances electrical conductivity and antiferromagnetic correlation substantially. ... More
Coexistence of high electrical conductivity and weak ferromagnetism in Cr doped Y$_2$Ir$_2$O$_7$ pyrochlore iridateApr 11 2019We report the structural, magnetic and electrical transport properties of Y$_2$Ir$_{2-x}$Cr$_x$O$_7$ pyrochlore iridates. The chemical doping leads to order of magnitude enhancement of electrical conductivity. The introduction of Cr3+ at Ir4+ site tends ... 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
Transverse spin relaxation and magnetic correlation in $Pr_{1-x}Ca_{x}MnO_{3}$ : influence of particle size variation and chemical dopingMar 03 2017The short ranged magnetic correlations and dynamics of hole doped $Pr_{1-x}Ca_{x}MnO_{3}$ (0.33 < x < 0.5) of different crystallite sizes have been investigated using electron spin resonance spectroscopy (ESR). The major contribution to the temperature ... More
Antiferromagnetic rare region effect in $Pr_{0.5}Ca_{0.5}MnO_3$Jan 29 2018We present evidence of coexistence of electron paramagnetic resonance signal and anti-ferromagnetic resonance signals above the anti-ferromagnetic (AFM) transition ($T_N$) in $Pr_{0.5}Ca_{0.5}MnO_3$. We identify the latter with AFM rare regions within ... 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
Capital Requirement for Achieving AcceptabilityJan 25 2006Consider an agent who enters a financial market on day t = 0 with an initial capital amount x. He invests this amount on stocks and the money market, and by day t = T, has generated a wealth W . He is given a convex class of probability measures (called ... 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
Evidence of density waves in single crystalline nanowires of Pyrochlore IridatesMar 03 2017We present experimental evidence of emergent density wave instability in single crystalline low dimensional wires of Yittrium based Pyrochlore Iridates. We demonstrate electric field induced nonlinear hysteretic switching of the density wave 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
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
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
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
Floodings of metric graphsAug 12 2017We consider random labelings of finite graphs conditioned on a small fixed number of peaks. We introduce a continuum framework where a combinatorial graph is associated with a metric graph and edges are identified with intervals. Next we consider a sequence ... More
A Note on Transportation Cost Inequalities for Diffusions with ReflectionsAug 07 2018Feb 08 2019We prove that reflected Brownian motion with normal reflections in a convex domain satisfies a dimension free Talagrand type transportation cost-information inequality. The result is generalized to other reflected diffusions with suitable drifts and diffusions. ... More
Shuffling cards by spatial motionAug 27 2017Nov 03 2017We propose a model of card shuffling where a pack of cards, spread as points on a rectangular table, are repeatedly gathered locally at random spots and then spread towards a random direction. A shuffling or permutation of the cards is then obtained by ... 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
Role of p-induced population of medium mass(A $\sim$ 150) neutron rich nucleiDec 24 2014Excitation functions were measured by stacked-foil activation technique for the $^{150}$Nd(p, xpyn) reaction using 97.65$%$ enriched $^{150}$Nd target. Measurement up to $\sim$50$%$ above barrier and down to 18$%$ below the barrier was performed using ... 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
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
Twin peaksJun 26 2016Feb 23 2017We 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
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
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
DeWitt-Virasoro constructionOct 05 2010We study a particular approach for analyzing worldsheet conformal invariance for bosonic string propagating in a curved background using hamiltonian formalism. We work in the Schrodinger picture of a single particle description of the problem where the ... More
String worldsheet theory in hamiltonian framework and background independenceMar 31 2010We analyze exact conformal invariance of string worldsheet theory in non-trivial backgrounds using hamiltonian framework. In the first part of this talk we consider the example of type IIB superstrings in Ramond-Ramond pp-wave background. In particular, ... More
Tachyon Condensation and Non-BPS D-branes in a Ramond-Ramond Plane Wave BackgroundNov 13 2006Jan 30 2008We consider string theory in maximally supersymmetric type IIB plane wave background with constant five form Ramond-Ramond flux (RR plane wave). It is argued that there exists a universal sector of string configurations independent of the null coordinate ... More
On D-Brane Boundary State Analysis in Pure-Spinor FormalismMay 17 2005Mar 20 2006We explore a particular approach to study D-brane boundary states in Berkovits' pure spinor formalism of superstring theories. In this approach one constructs the boundary states in the relevant conformal field theory by relaxing the pure spinor constraints. ... More
On The Problem of Particle Production in c=1 Matrix ModelJun 02 2004Aug 28 2004We reconsider and analyze in detail the problem of particle production in the time dependent background of $c=1$ matrix model where the Fermi sea drains away at late time. In addition to the moving mirror method, which has already been discussed in hep-th/0403169 ... More
Dynamical supersymmetry analysis of conformal invariance for superstrings in type IIB R-R plane-waveJul 13 2009Aug 24 2009In a previous work (arXiv:0902.3750 [hep-th]) we studied the world-sheet conformal invariance for superstrings in type IIB R-R plane-wave in semi-light-cone gauge. Here we give further justification to the results found in that work through alternative ... More
Non-BPS D-Branes in Light-Cone Green-Schwarz FormalismNov 10 2004Feb 03 2005Non-BPS D-branes are difficult to describe covariantly in a manifestly supersymmetric formalism. For definiteness we concentrate on type IIB string theory in flat background in light-cone Green-Schwarz formalism. We study both the boundary state and the ... More
$φ$ meson production in Au - Au collisions at $\sqrt{s_{NN}}$ = 200 GeVSep 28 2002A simultaneous measurement of the $\phi$ meson via its $K^{+} K^{-} $ and $e^{+} e^{-}$ decay channels was performed in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at mid-rapidity by the PHENIX experiment. The preliminary minimum bias yields $dN_{\phi}/dy$ ... 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
Large Scale Signal Detection: A Unified PerspectiveJul 31 2015Aug 23 2015There is an overwhelmingly large literature and algorithms already available on `large scale inference problems' based on different modeling techniques and cultures. Our primary goal in this paper is \emph{not to add one more new methodology} to the existing ... 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
A Mixture of g-priors for Variable Selection when the Number of Regressors Grows with the Sample SizeApr 15 2015We consider variable selection problem in linear regression using mixture of $g$-priors. A number of mixtures are proposed in the literature which work well, especially when the number of regressors $p$ is fixed. In this paper, we propose a mixture of ... More
A cut-off tubular geometry of loop spaceJul 28 2014Jan 22 2017Motivated 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
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
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
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
Decentralized Nonparametric Multiple TestingMay 05 2018Consider a big data multiple testing task, where, due to storage and computational bottlenecks, one is given a very large collection of p-values by splitting into manageable chunks and distributing over thousands of computer nodes. This paper is concerned ... 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
To understand deep learning we need to understand kernel learningFeb 05 2018Jun 14 2018Generalization performance of classifiers in deep learning has recently become a subject of intense study. Deep models, typically over-parametrized, tend to fit the training data exactly. Despite this "overfitting", they perform well on test data, a phenomenon ... 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
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
Multiplicative Schrödinger problem and the Dirichlet transportJul 16 2018We consider an optimal transport problem on the unit simplex whose solutions are given by gradients of exponentially concave functions and prove two main results. One, we show that the optimal transport is the large deviation limit of a particle system ... More
Systems of Brownian particles with asymmetric collisionsSep 30 2012We study systems of Brownian particles on the real line, which interact by splitting the local times of collisions among themselves in an asymmetric manner. We prove the strong existence and uniqueness of such processes and identify them with the collections ... More