Results for "Dimitrios Katsinis"

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Area Law Behaviour of Mutual Information at Finite TemperatureJul 10 2019Entanglement entropy in free scalar field theory at its ground state is dominated by an area law term. However, when mixed states are considered this property ceases to exist. We show that in such cases the mutual information obeys an "area law". The ... More
An Inverse Mass Expansion for Entanglement Entropy in Free Massive Scalar Field TheoryNov 07 2017We extend the entanglement entropy calculation performed in the seminal paper by Srednicki for free real massive scalar field theories in 1+1, 2+1 and 3+1 dimensions. We show that the inverse of the scalar field mass can be used as an expansion parameter ... More
Stability Analysis of Classical String Solutions and the Dressing MethodMar 04 2019The dressing method is a technique to construct new solutions in non-linear sigma models under the provision of a seed solution. This is analogous to the use of autoBacklund transformations for systems of the sine-Gordon type. In a recent work, this method ... More
Salient Features of Dressed Elliptic String Solutions on $\mathbb{R}\times$S$^2$Mar 04 2019We analyse several physical aspects of the dressed elliptic strings propagating on $\mathbb{R} \times \mathrm{S}^2$ and of their counterparts in the Pohlmeyer reduced theory, i.e. the sine-Gordon equation. The solutions are divided into two wide classes; ... More
Dressed Elliptic String Solutions on RxS^2Jun 20 2018We obtain classical string solutions on RxS^2 by applying the dressing method on string solutions with elliptic Pohlmeyer counterparts. This is realized through the use of the simplest possible dressing factor, which possesses just a pair of poles lying ... More
Elliptic String Solutions on RxS^2 and Their Pohlmeyer ReductionMay 23 2018We study classical string solutions on RxS^2 that correspond to elliptic solutions of the sine-Gordon equation. In this work, these solutions are systematically derived inverting Pohlmeyer reduction and classified with respect to their Pohlmeyer counterparts. ... More
Testing General Metric Theories of Gravity with Bursting Neutron StarsApr 18 2007Jan 10 2008I show that several observable properties of bursting neutron stars in metric theories of gravity can be calculated using only conservation laws, Killing symmetries, and the Einstein equivalence principle, without requiring the validity of the general ... More
Constraints on Braneworld Gravity Models from a Kinematic Limit on the Age of the Black Hole XTE J1118+480Dec 20 2006In braneworld gravity models with a finite AdS curvature in the extra dimension, the AdS/CFT correspondence leads to a prediction for the lifetime of astrophysical black holes that is significantly smaller than the Hubble time, for asymptotic curvatures ... More
Hydrodynamic Effects on the QPO Frequencies of Accreting Compact ObjectsOct 16 2000The variability properties of accreting compact objects predicted by dynamical models are characterized by a number of distinct frequencies that are specific to each model. Because the accretion disks around neutron stars and black holes are hydrodynamic ... More
UHECRs from magnetic reconnection in relativistic jetsJul 09 2010Aug 16 2010Ultra-high energy cosmic rays (UHECRs) may be produced in active galactic nuclei (AGN) or gamma-ray burst (GRB) jets. I argue that magnetic reconnection in jets can accelerate UHECRs rather independently of physical processes in the magnetic dissipation ... More
Powerful GeV emission from a gamma-ray-burst shock wave scattering stellar photonsMay 02 2008Sep 04 2008The gamma-ray bursts (GRBs) of long duration are very likely to be connected to the death of massive stars. The gamma-ray emission is believed to come from energy released internally in a flow that moves at ultrarelativistic speed. The fast flow drives ... More
Reconnection-driven plasmoids in blazars: fast flares on a slow envelopeNov 01 2012Mar 13 2013Minute-timescale TeV flares have been observed in several blazars. The fast flaring requires compact regions in the jet that boost their emission towards the observer at an extreme Doppler factor of delta>50. For TeV photons to avoid annihilation in the ... More
Superflares from magnetars revealing the GRB central engineJan 07 2010Aug 16 2010Long-duration gamma-ray bursts (GRBs) may be powered by the rotational energy of a millisecond magnetar. I argue that the GRB-driving magnetars lie at the high end of the distribution of magnetic field strengths of magnetars. The field of GRB magnetars ... More
Spectra of black-hole binaries in the low/hard state: from radio to X-raysApr 07 2005We propose a jet model for the low/hard state of Galactic black-hole X-ray sources that can explain the energy spectra from radio to X-rays. The model assumes that i) there is a magnetic field along the axis of the jet; ii) the electron density in the ... More
k-Strings as Fundamental StringsMar 31 2015It has been noticed that the k-string observables can be expressed in terms of the fundamental string ones. We identify a sufficient condition for a generic gravity dual background which when satisfied the mapping can be done. The condition is naturally ... More
Semi-classical Strings in Sasaki-Einstein ManifoldsApr 20 2009We find point-like and classical string solutions on the AdS_5 x X^5, where X^5 are the 5-dimensional Sasaki-Einstein manifolds Ypq and Lpqr. The number of acceptable solutions is limited drastically in order to satisfy the constraints on the parameters ... More
Massive IIA supergravitiesAug 29 2005We perform a systematic search for all possible massive deformations of IIA supergravity in ten dimensions. We show that there exist exactly two possibilities: Romans supergravity and Howe-Lambert-West supergravity. Along the way we give the full details ... More
Nahm Equations and Boundary ConditionsApr 10 1998Jun 01 1998We derive certain boundary conditions in Nahm's equations by considering a system of N parallel D1-branes perpendicular to a D3-brane in type IIB string theory.
Quantum mechanics and data assimilationMar 02 2019A framework for data assimilation combining aspects of operator-theoretic ergodic theory and quantum mechanics is developed. This framework adapts the Dirac-von Neumann formalism of quantum dynamics and measurement to perform data assimilation (filtering) ... More
Quantum mechanics and data assimilationMar 02 2019May 31 2019A framework for data assimilation combining aspects of operator-theoretic ergodic theory and quantum mechanics is developed. This framework adapts the Dirac--von Neumann formalism of quantum dynamics and measurement to perform sequential data assimilation ... More
Non-removability of Sierpinski carpetsSep 14 2018We prove that all Sierpi\'nski carpets in the plane are non-removable for (quasi)conformal maps. More precisely, we show that for any two Sierpi\'nski carpets $S,S'\subset \widehat{\mathbb{C}}$ there exists a homeomorphism $f\colon \widehat{\mathbb{C}}\to ... More
A removability theorem for Sobolev functions and detour setsJun 23 2017Jun 26 2019We study the removability of compact sets for continuous Sobolev functions. In particular, we focus on sets with infinitely many complementary components, called "detour sets", which resemble the Sierpi\'nski gasket. The main theorem is that if $K\subset ... More
Non-removability of the Sierpinski GasketApr 26 2018Dec 13 2018We prove that the Sierpi\'nski gasket is non-removable for quasiconformal maps, thus answering a question of Bishop. The proof involves a new technique of constructing an exceptional homeomorphism from $\mathbb R^2$ into some non-planar surface $S$, and ... More
Two approaches to testing general relativity in the strong-field regimeJul 16 2009Observations of compact objects in the electromagnetic spectrum and the detection of gravitational waves from them can lead to quantitative tests of the theory of general relativity in the strong-field regime following two very different approaches. In ... More
Radiative Transfer in Obliquely Illuminated Accretion DisksJan 09 2001Mar 25 2002The illumination of an accretion disk around a black hole or neutron star by the central compact object or the disk itself often determines its spectrum, stability, and dynamics. The transport of radiation within the disk is in general a multi-dimensional, ... More
The peak energy of dissipative GRB photospheresNov 18 2011Mar 19 2012The radiation released at the transparency radius of an ultrarelativistic flow can account for the observed properties of gamma-ray bursts (GRBs) provided that sufficient energy is dissipated in the sub-photospheric region. Here, I investigate how the ... More
Observables in Strongly Coupled Anisotropic TheoriesJun 06 2013Dec 30 2013We review certain anisotropic gauge/gravity dualities, focusing more on a theory with space dependent axion term. Then we discuss and also present some new results for several observables: the static potential and force, the imaginary part of the static ... More
11D supergravity at ${\cal O}(l^3)$Jul 30 2004Aug 30 2004We compute certain spinorial cohomology groups controlling possible supersymmetric deformations of eleven-dimensional supergravity up to order $l^3$ in the Planck length. At ${\cal O}(l)$ and ${\cal O}(l^2)$ the spinorial cohomology groups are trivial ... More
Instanton interaction in de Sitter spacetimeFeb 09 2013Because of the presence of a cosmological horizon the dilute instanton gas approximation used for the derivation of the Coleman-De Luccia tunneling rate in de Sitter spacetime receives additional contributions due to the finite instanton separation. Here ... More
The path integral measure, constraints and ghosts for massive gravitons with a cosmological constantJul 24 2009Dec 06 2009For massive gravity in a de Sitter background one encounters problems of stability when the curvature is larger than the graviton mass. I analyze this situation from the path integral point of view and show that it is related to the conformal factor problem ... More
Effects of the cosmological expansion on the bubble nucleation rate for relativistic first-order phase transitionsApr 07 2008Sep 01 2008I calculate the first corrections to the dynamical pre-exponential factor of the bubble nucleation rate for a relativistic first-order phase transition in an expanding cosmological background by estimating the effects of the Hubble expansion rate on the ... More
A removability theorem for Sobolev functions and detour setsJun 23 2017We study the removability of compact sets for continuous Sobolev functions. In particular, we focus on sets with infinitely many complementary components, called "detour sets", which resemble the Sierpi\'nski gasket. The main theorem is that if $K\subset ... More
One dimensional diffusion in an asymmetric random environmentOct 02 2006According to a theorem of S. Schumacher, for a diffusion X in an environment determined by a stable process that belongs to an appropriate class and has index a, it holds that X_t/(log t)^a converges in distribution, as t goes to infinity, to a random ... More
Semi-hyperbolic rational maps and size of Fatou componentsFeb 15 2017Nov 06 2017Recently Merenkov and Sabitova introduced the notion of a homogeneous planar set. Using this notion they proved a result for Sierpi${\'n}$ski carpet Julia sets of hyperbolic rational maps that relates the diameters of the peripheral circles to the Hausdorff ... More
Dynamics-Adapted Cone KernelsMar 03 2014We present a family of kernels for analysis of data generated by dynamical systems. These so-called cone kernels feature an explicit dependence on the dynamical vector field operating in the phase-space manifold, estimated empirically through finite-differences ... More
A secret sharing scheme using groupsAug 31 2010In this paper a secret sharing scheme based on the word problem in groups is introduced. The security of the scheme and possible variations are discussed in section 2. The article concludes with the suggestion of two categories of platform groups for ... More
Feynman rules for Gauss's lawApr 18 2016Jun 26 2016I work on a set of Feynman rules that were derived in order to incorporate the constraint of Gauss's law in the perturbation expansion of gauge field theories and calculate the interaction energy of two static sources. The constraint is implemented via ... More
Graviton mass and cosmological constant: a toy modelOct 01 2010Oct 25 2010I consider a simple model where the graviton mass and the cosmological constant depend on a scalar field with appropriate couplings and I calculate the graviton propagator and the resulting effective action for the scalar field.
Fivebrane instantons and Calabi-Yau fourfolds with fluxJan 31 2007Feb 15 2007Using recent results on eleven-dimensional superspace, we compute the contribution of fivebrane instantons with four fermionic zeromodes in M-theory compactifications on Calabi-Yau fourfolds with flux. We find that no superpotential is generated in this ... More
M-theory on eight-manifolds revisited: N=1 supersymmetry and generalized Spin(7) structuresNov 04 2005Apr 10 2006The requirement of ${\cal N}=1$ supersymmetry for M-theory backgrounds of the form of a warped product ${\cal M}\times_{w}X$, where $X$ is an eight-manifold and ${\cal M}$ is three-dimensional Minkowski or AdS space, implies the existence of a nowhere-vanishing ... More
Generalized geometry lectures on type II backgroundsJun 28 2016The first part of these notes is a self-contained introduction to generalized complex geometry. It is intended as a `user manual' for tools used in the study of supersymmetric backgrounds of supergravity. In the second part we review some past and recent ... More
Curved 11D SupergeometryJul 28 2004Dec 01 2004We examine the theta-expansion of the eleven-dimensional supervielbein. We outline a systematic procedure which can be iterated to any order. We give explicit expressions for the vielbein and three-form potential components up to order ${\cal O}(\th^5)$. ... More
Probes and Tests of Strong-Field Gravity with Observations in the Electromagnetic SpectrumJun 09 2008Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of probing with observations of such compact objects some of the most intriguing General Relativistic ... More
The Influence of Gas Dynamics on Measuring the Properties of the Black Hole in the Center of the Milky Way with Stellar Orbits and PulsarsNov 30 2011Observations of stars and pulsars orbiting the black hole in the center of the Milky Way offer the potential of measuring not only the mass of the black hole but also its spin and quadrupole moment, thereby providing observational verification of the ... More
Measurements of Black Hole Spins and Tests of Strong-Field General RelativityFeb 10 2004Fast variability studies of accreting black holes in the Galaxy offer us a unique opportunity to measure the spins of black holes and test the strong-field behavior of general relativity. In this review, I summarize the arguments often used in attempts ... More
Models of Quasi-Periodic Variability in Neutron Stars and Black HolesDec 12 2000Black holes and weakly-magnetic accreting neutron stars show strong quasi-periodic variability over timescales that span a very wide range. This property offer us a unique opportunity to improve our understanding of basic physical processes in strong ... More
Neutrino-cooled accretion and GRB variabilityApr 12 2007For accretion rates Mdot~0.1 Msun/s to a few solar mass black hole the inner part of the disk is expected to make a transition from advection dominance to neutrino cooling. This transition is characterized by sharp changes of the disk properties. I argue ... More
On the non-BPS string solutions in Sasaki-Einstein gauge/gravity dualityDec 18 2009We present an extensive analysis on several string solutions in AdS_5 x Ypq and find some interesting properties of their energy-spin relations. Their energy depends always on the parameter a(p,q) which characterizes these manifolds. The range of this ... More
Semiclassical strings in marginally deformed toric AdS/CFTOct 07 2010We study string solutions in the beta-deformed Sasaki-Einstein gauge/gravity dualities. We find that the BPS point-like strings move in the submanifolds where the two U(1) circles shrink to zero size. In the corresponding T^3 fibration description, the ... More
The Generic Expansion in Analytic Modified GravityMay 30 2019In this Thesis, we treat the problem of the existence of generic perturbations of the regular and singular state in higher-order gravity in cases of vacuum and radiation models that derives from the lagrangian $R+\epsilon R^2$. We show that there is a ... More
Localization of favorite points for diffusion in random environmentDec 18 2006For a diffusion X_t in a one-dimensional Wiener medium W, it is known that there is a certain process b_x(W) that depends only on the environment W, so that X_t-b_{logt}(W) converges in distribution as t goes to infinity. We prove that, modulo a relatively ... More
Minimization of Constrained Quadratic forms in Hilbert SpacesMar 29 2010A common optimization problem is the minimization of a symmetric positive definite quadratic form $< x,Tx >$ under linear constrains. The solution to this problem may be given using the Moore-Penrose inverse matrix. In this work we extend this result ... More
Accreting Neutron Stars and Black Holes: A Decade of DiscoveriesOct 22 2004This is a review of recent observational and theoretical developments related to accreting neutron stars and black holes in binary systems.
Data-driven spectral decomposition and forecasting of ergodic dynamical systemsJul 08 2015Sep 28 2016We develop a framework for dimension reduction, mode decomposition, and nonparametric forecasting of data generated by ergodic dynamical systems. This framework is based on a representation of the Koopman and Perron-Frobenius groups of unitary operators ... More
Prompt GRB emission from gradual energy dissipationNov 16 2007Sep 04 2008I calculate the emission expected from a Poynting-flux-dominated gamma-ray burst (GRB) flow in which energy is dissipated gradually by magnetic reconnection. In this picture, the energy of the radiating particles is determined by heating and cooling balance ... More
Prompt emission spectra from the photosphere of a GRBFeb 17 2006Sep 08 2006I explore the observational appearance of the photosphere of an ultrarelativistic flow with internal dissipation of energy (``dissipative'' GRB models). As a case study, I use the magnetic reconnection model (AC model) that makes robust predictions on ... More
Mean value results and $Ω$-results for the hyperbolic lattice point problem in conjugacy classesOct 05 2016Oct 12 2016For $\Gamma$ a Fuchsian group of finite covolume, we study the lattice point problem in conjugacy classes on the Riemann surface $\Gamma \backslash \mathbb{H}$. Let $\mathcal{H}$ be a hyperbolic conjugacy class in $\Gamma$ and $\ell$ the $\mathcal{H}$-invariant ... More
Properties of Confinement in HolographyMay 26 2015We review certain properties of confinement with added focus on the ones we study with holography. Then we discuss observables whose unique behavior can indicate the presence of confinement. Using mainly the Wilson loop in the gauge/gravity formalism, ... More
Low-mass pre--main-sequence stars in the Magellanic CloudsFeb 29 2012[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar stars form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming ... More
Scalar and fermion contributions to the vacuum energyMar 03 2013I consider a theory of a real scalar and a fermion field, with a Yukawa interaction and a potential term that admits two degenerate minima at the tree level. I calculate the quantum vacuum energy difference between these two vacua and I find a finite, ... More
Quantum-classical interactions through the path integralJul 26 2006Mar 09 2007I consider the case of two interacting scalar fields, \phi and \psi, and use the path integral formalism in order to treat the first classically and the second quantum-mechanically. I derive the Feynman rules and the resulting equation of motion for the ... More
Potential theory on Sierpinski carpets with applications to uniformizationMay 31 2018This research is motivated by the study of the geometry of fractal sets and is focused on uniformization problems: transformation of sets to canonical sets, using maps that preserve the geometry in some sense. More specifically, the main question addressed ... More
Diffusion in random environment and the renewal theoremOct 20 2003Oct 23 2004According to a theorem of S. Schumacher and T. Brox, for a diffusion $X$ in a Brownian environment it holds that $(X_t-b_{\log t})/\log^2t\to 0 $ in probability, as $t\to\infty$, where $b_{\cdot}$ is a stochastic process having an explicit description ... More
Leveraging Trust and Distrust in Recommender Systems via Deep LearningMay 31 2019The data scarcity of user preferences and the cold-start problem often appear in real-world applications and limit the recommendation accuracy of collaborative filtering strategies. Leveraging the selections of social friends and foes can efficiently ... More
Constraining Brans-Dicke Gravity with Millisecond Pulsars in Ultracompact BinariesJan 12 2005The five accreting, millisecond X-ray pulsars in ultracompact binaries that were recently discovered with the Rossi X-ray Timing Explorer provide excellent candidates for constraining the deviations from general relativity described by the Brans-Dicke ... More
Compton Scattering in Static and Moving Media. II. System-Frame Solutions for Spherically Symmetric FlowsNov 29 2000Mar 23 2001I study the formation of Comptonization spectra in spherically symmetric, fast moving media in a flat spacetime. I analyze the mathematical character of the moments of the transfer equation in the system-frame and describe a numerical method that provides ... More
Probing strongly coupled anisotropic plasmaFeb 20 2012Jul 09 2012We calculate the static potential, the drag force and the jet quenching parameter in strongly coupled anisotropic N=4 super Yang-Mills plasma. We find that the jet quenching is in general enhanced in presence of anisotropy compared to the isotropic case ... More
Spherically symmetric, static spacetimes in a tensor-vector-scalar theoryFeb 28 2005Apr 27 2005Recently, a relativistic gravitation theory has been proposed [J. D. Bekenstein, Phys. Rev. D {\bf 70}, 083509 (2004)] that gives the Modified Newtonian Dynamics (or MOND) in the weak acceleration regime. The theory is based on three dynamic gravitational ... More
Flares in GRB afterglows from delayed magnetic dissipationJun 19 2006One of the most intriguing discoveries made by the Swift satellite is the flaring activity in about half of the afterglow lightcurves. Flares have been observed on both long and short duration GRBs and on time scales that range from minutes to ~1 day ... More
Supersymmetric AdS vacua and separation of scalesJun 26 2012Sep 03 2012The moduli space of the supersymmetric massive IIA AdS4xS2(B4) vacua, where S2(B4) is a two-sphere bundle over a four-dimensional Kaehler-Einstein base B4, includes three independent parameters which can be thought of as corresponding to the sizes of ... More
Gravitational effects on critical Q-ballsNov 30 2004Mar 09 2007In a cosmological phase transition in theories that admit Q-balls there is a value of the soliton charge above which the soliton becomes unstable and expands, converting space to the true vacuum, much like a critical bubble in the case of ordinary tunneling. ... More
A note on recurrent random walksOct 02 2006For any recurrent random walk (S_n)_{n>0} on R, there are increasing sequences (g_n)_{n>0} converging to infinity for which (g_n S_n)_{n>0} has at least one finite accumulation point. For one class of random walks, we give a criterion on (g_n)_{n>0} and ... More
Restricted Linear Constrained Minimization of quadratic functionalsSep 17 2010In this work a linearly constrained minimization of a positive semidefinite quadratic functional is examined. Our results are concerning infinite dimensional real Hilbert spaces, with a singular positive operator related to the functional, and considering ... More
Sgr A*: The Optimal Testbed of Strong-Field GravityDec 07 2010The black hole in the center of the Milky Way has been observed and modeled intensely during the last decades. It is also the prime target of a number of new experiments that aim to zoom into the vicinity of its horizon and reveal the inner working of ... More
A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. I. Quasi-Kerr Black HolesNov 17 2010We describe a new numerical algorithm for ray tracing in the external spacetimes of spinning compact objects characterized by arbitrary quadrupole moments. Such spacetimes describe non-Kerr vacuum solutions that can be used to test the no-hair theorem ... More
Gluon Scattering Amplitudes in Finite Temperature Gauge/Gravity DualitiesNov 29 2010Jun 08 2011We examine the gluon scattering amplitude in N=4 super Yang-Mills at finite temperature with nonzero R-charge densities, and in Non-Commutative gauge theory at finite temperature. The gluon scattering amplitude is defined as a light-like Wilson loop which ... More
Nodal-antinodal dichotomy from pairing disorder in d-wave superconductorsNov 27 2009We study the basic features of the local density of states (LDOS) observed in STM experiments on high-T$_c$ d-wave superconductors in the context of a minimal model of a d-wave superconductor which has {\it weakly} modulated off-diagonal disorder. We ... More
Entanglement Entropy of the N=4 SYM spin chainMar 18 2016Aug 29 2016We present a detailed study of the Entanglement Entropy (EE) of excited states in all closed rank one subsectors of N=4 SYM, namely SU(2), SU(1|1) and SL(2). Exploiting the techniques of the Coordinate and the Algebraic Bethe Ansatz we obtain the EE for ... More
Flavor Corrections in the Static Potential in Holographic QCDApr 08 2011May 02 2011We examine the static potential in the presence of flavors in the perturbative backreacted D4/D8 system from localized D8 branes, focusing in particular on the Sakai-Sugimoto model. For the case of long strings we find the flavor corrections to the static ... More
Numerical evidence of the double-Griffiths phase of the random quantum Ashkin-Teller chainJun 01 2015Jan 26 2016The random quantum Ashkin-Teller chain is studied numerically by means of time-dependent Density-Matrix Renormalization Group. The critical lines are estimated as the location of the peaks of the integrated autocorrelation times, computed from spin-spin ... More
Statistics of Measuring Neutron Star Radii: Assessing A Frequentist and A Bayesian ApproachMay 19 2015Aug 25 2015Measuring neutron star radii with spectroscopic and timing techniques relies on the combination of multiple observables to break the degeneracies between the mass and radius introduced by general relativistic effects. Here, we explore a previously used ... More
Eternal Solutions Of The Burgers EquationNov 18 2016Solutions that satisfy classically the Burgers equation except, perhaps, on a closed set S of the plane of potential singularities whose Hausdorff 1-measure is zero, $H^1(S) = 0$, are necessarily identically constant. We show this under the additional ... More
The word entropy of natural languagesJun 22 2016The average uncertainty associated with words is an information-theoretic concept at the heart of quantitative and computational linguistics. The entropy has been established as a measure of this average uncertainty - also called average information content. ... More
The action principle and the supersymmetrisation of Chern-Simons terms in eleven-dimensional supergravityDec 06 2016We develop computational tools for calculating supersymmetric higher-order derivative corrections to eleven-dimensional supergravity using the action principle approach. We show that, provided the superspace Bianchi identities admit a perturbative solution ... More
Electric dipole moment constraints on CP-violating light-quark YukawasNov 13 2018Feb 04 2019Nonstandard CP violation in the Higgs sector can play an essential role in electroweak baryogenesis. We calculate the full two-loop matching conditions of the standard model, with Higgs Yukawa couplings to light quarks modified to include arbitrary CP-violating ... More
Hopf reductions, fluxes and branesJun 28 2001Sep 19 2001We use a series of reductions, T-dualities and liftings to construct connections between fractional brane solutions in IIA, IIB and M-theory. We find a number of phantom branes that are not supported by the geometry, however materialize upon untwisting ... More
Controlling Artificial Viscosity in SPH simulations of accretion disksApr 21 2010We test the operation of two methods for selective application of Artificial Viscosity (AV) in SPH simulations of Keplerian Accretion Disks, using a ring spreading test to quantify effective viscosity, and a correlation coefficient technique to measure ... More
De Sitter space from dilatino condensates in (massive) IIADec 19 2017Dec 22 2017We use the superspace formulation of (massive) IIA supergravity to obtain the explicit form of the dilatino terms, and we find that the quartic-dilatino term is positive. The theory admits a ten-dimensional de Sitter solution, obtained by assuming a nonvanishing ... More
Training Deep Neural Networks with Different Datasets In-the-wild: The Emotion Recognition ParadigmSep 12 2018A novel procedure is presented in this paper, for training a deep convolutional and recurrent neural network, taking into account both the available training data set and some information extracted from similar networks trained with other relevant data ... More
SU(3) structures on S2 bundles over four-manifoldsJul 14 2017We construct globally-defined $SU(3)$ structures on smooth compact toric varieties (SCTV) in the class of $\mathbb{CP}^1$ bundles over $M$, where $M$ is an arbitrary SCTV of complex dimension two. The construction can be extended to the case where the ... More
Exact Lexicographic Scheduling and Approximate ReschedulingMay 09 2018Feb 06 2019In industrial scheduling, an initial planning phase may solve the nominal problem and a subsequent recovery phase may intervene to repair inefficiencies and infeasibilities, e.g. due to machine failures and job processing time variations. This work investigates ... More
Deep Learning in CardiologyFeb 22 2019The medical field is creating large amount of data that physicians are unable to decipher and use efficiently. Moreover, rule-based expert systems are inefficient in solving complicated medical tasks or for creating insights using big data. Deep learning ... More
One-loop bosonic string and De Sitter spaceOct 04 2018We calculate the bosonic string one-loop three- and four-point amplitudes to quadradic order in momentum, and we read off the one-loop low-energy two-derivative effective action for the massless fields, $S_{eff}$. Treating the renormalized one-loop vacuum ... More
Koopman spectra in reproducing kernel Hilbert spacesJan 23 2018Jun 19 2019Every invertible, measure-preserving dynamical system induces a Koopman operator, which is a linear, unitary evolution operator acting on the $L^2$ space of observables associated with the invariant measure. Koopman eigenfunctions represent the quasiperiodic, ... More
Sparsely Activated NetworksJul 12 2019Previous literature on unsupervised learning focused on designing structural priors and optimization functions with the aim of learning meaningful features, but without considering the description length of the representations. Here we present Sparsely ... More
Crepant Resolutions of Gorenstein Toric Singularities and Upper Bound TheoremOct 25 2001A necessary condition for the existence of torus-equivariant crepant resolutions of Gorenstein toric singularities can be derived by making use of a variant of the classical Upper Bound Theorem which is valid for simplicial balls.
A Metric for Rapidly Spinning Black Holes Suitable for Strong-Field Tests of the No-Hair TheoremMay 16 2011May 20 2011According to the no-hair theorem, astrophysical black holes are uniquely characterized by their masses and spins and are described by the Kerr metric. Several parametric deviations from the Kerr metric have been suggested to study observational signatures ... More
Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum: II. Black-Hole ImagesMay 11 2010Jun 01 2010According to the no-hair theorem, all astrophysical black holes are fully described by their masses and spins. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this ... More
Bounds on Neutron-Star Moments of Inertia and the Evidence for General Relativistic Frame DraggingMar 26 1999May 11 1999Recent X-ray variability observations of accreting neutron stars may provide the first evidence for frame dragging effects around spinning relativistic objects. Motivated by this possibility and its implications for neutron-star structural properties, ... More
Testing Strong-field Gravity with Quasi-Periodic OscillationsMay 04 2004The frequencies of quasi-periodic oscillations around neutron stars are believed to be related to characteristic frequencies in the gravitational fields of the compact objects. In different variability models, these include the Keplerian, epicyclic, and ... More