Results for "Massimo Mecella"

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Cognitive Business Process Management for Adaptive Cyber-Physical ProcessesFeb 08 2018In the era of Big Data and Internet-of-Things (IoT), all real-world environments are gradually becoming cyber-physical (e.g., emergency management, healthcare, smart manufacturing, etc.), with the presence of connected devices and embedded ICT systems ... More
X-ray Twinkles and Pop III StarsJul 14 2016Pop III stars are typically massive stars of primordial composition forming at the centers of the first collapsed dark matter structures. Here we estimate the optimal X-ray emission in the early universe for promoting the formation of Pop III stars. This ... More
On Landau's eigenvalue theorem and information cut-setsMay 07 2014A variation of Landau's eigenvalue theorem describing the phase transition of the eigenvalues of a time-frequency limiting, self adjoint operator is presented. The total number of degrees of freedom of square-integrable, multi-dimensional, bandlimited ... More
Color superconductivity and dense quark matterDec 15 2008Dec 26 2008The properties of cold and dense quark matter have been the subject of extensive investigation, especially in the last decade. Unfortunately, we still lack of a complete understanding of the properties of matter in these conditions. One possibility is ... More
The amazing properties of crystalline color superconductorsJan 29 2014This paper is a brief journey into the amazing realm of crystalline color superconductors. Starting from a qualitative description of superfluids, superconductors and supersolids, we show how inhomogeneous phases may arise when the system is under stress. ... More
Trapped phononsJan 25 2013We analyze the effect of restricted geometries on the contribution of Nambu-Goldstone bosons (phonons) to the shear viscosity, $\eta$, of a superfluid. For illustrative purpose we examine a simplified system consisting of a circular boundary of radius ... More
From Twists and Shifts to L-R asymmetric D-branesFeb 04 2009In the first part of the talk, we discuss non-geometric twists and shifts and briefly review asymmetric orbifolds and free fermion constructions. These allow us to build Type IIB models with N = 1_L + 1_R and N = 1_L + 0_R models having few or no moduli. ... More
Recent Trends in Superstring PhenomenologySep 09 2009We review for non-experts possible phenomenological scenari in String Theory. In particular we focus on vacuum configurations with intersecting and/or magnetized unoriented D-branes. We will show how a TeV scale tension may be compatible with the existence ... More
Bound-states of D-branes in L-R asymmetric superstring vacuaMay 21 2008We discuss bound-states of D-branes in truly L-R asymmetric and thus non-geometric Type II vacuum configurations with extended supersymmetry. We argue for their stability as a result of residual supersymmetry and coupling to R-R potentials surviving in ... More
(Non-)perturbative tests of the AdS/CFT correspondenceMar 14 2001Apr 04 2001I summarize perturbative and non-perturbative field theory tests of the holographic correspondence between type IIB superstring on AdS_5xS^5 and N=4 SYM theory. The holographic duality between D-instantons and YM instantons is briefly described. Non renormalization ... More
Open Strings and DualitiesDec 02 1997In the fruitful interplay between gauge fields and strings and in many conjectured M-theory dualities, open strings play a prominent role. We review the construction of open-string descendants (un-orientifolds) of closed-string theories admitting a generalized ... More
A Note on Toroidal Compactifications of the Type I Superstring and Other Superstring Vacuum Configurations with 16 SuperchargesNov 28 1997Aug 07 1998We show that various disconnected components of the moduli space of superstring vacua with 16 supercharges admit a rationale in terms of BPS un-orientifolds, i.e. type I toroidal compactifications with constant non-vanishing but quantized vacuum expectation ... More
The emergence of power-law distributions of inter-spike intervals characterizes status epilepticus induced by pilocarpine administration in ratsJan 07 2015Objective. To ascertain the existence of power-law distributions of inter-spike intervals (ISI) occurring during the progression of status epilepticus (SE), so that the emergence of critical states could be reasonably hypothesized as being part of the ... More
Weak matrix elements and K-meson physicsOct 14 2000An overview is presented about old and recent methods to compute the $K\to \pi \pi$ decay amplitude.
On the number of rational points of a plane algebraic curveNov 07 2002The number of rational points of a plane non-singular algebraic curve X defined over a finite field is computed, provided that the generic point of X is not an inflexion and that X is Frobenius non-classical with respect to conics.
No-hair conjectures, primordial shear and protoinflationary initial conditionsDec 17 2013Anisotropic inflationary background geometries are analyzed in the context of an extended gauge action where the electric and magnetic susceptibilities are not bound to coincide and depend on the inflaton field. After deriving various classes of solutions ... More
Fluid phonons, protoinflationary dynamics and large-scale gravitational fluctuationsApr 17 2013We explore what can be said on the effective temperature and sound speed of a statistical ensemble of fluid phonons present at the onset of a conventional inflationary phase. The phonons are the actual normal modes of the gravitating and irrotational ... More
Bootstrapping from inflationary magnetogenesis to CMB initial conditionsMar 15 2013The temperature and polarization anisotropies of the Cosmic Microwave Background are analyzed under the hypothesis that the same inflationary seed accounting for protogalactic magnetism also affects the Einstein-Boltzmann hierarchy whose initial conditions ... More
Count response model for the CMB spotsOct 28 2010The statistics of the curvature quanta generated during a stage of inflationary expansion is used to derive a count response model for the large-scale phonons determining, in the concordance lore, the warmer and the cooler spots of the large-scale temperature ... More
Secondary graviton spectra and waterfall-like fieldsAug 06 2010The secondary spectra of the gravitons induced by a waterfall-like field are computed and the general bounds on the spectral energy density of the tensor modes of the geometry are translated into explicit constraints on the amplitude and slope of the ... More
A circular polarimeter for the Cosmic Microwave BackgroundMar 30 2010A primordial degree of circular polarization of the Cosmic Microwave Background is not observationally excluded. The hypothesis of primordial dichroism can be quantitatively falsified if the plasma is magnetized prior to photon decoupling since the initial ... More
Estimating relic magnetic fields from CMB temperature correlationsFeb 25 2009The temperature and polarization inhomogeneities of the Cosmic Microwave Background might bear the mark of pre-decoupling magnetism. The parameters of a putative magnetized background are hereby estimated from the observed temperature autocorrelation ... More
Anomalous magnetohydrodynamics in the extreme relativistic domainJun 27 2016The evolution equations of anomalous magnetohydrodynamics are derived in the extreme relativistic regime and contrasted with the treatment of hydromagnetic nonlinearities pioneered by Lichnerowicz in the absence of anomalous currents. In particular we ... More
Faraday scaling and the Bicep2 observationsApr 15 2014As repeatedly speculated in the past, the linear polarization of the Cosmic Microwave Background can be rotated via the Faraday effect. An economic explanation of the recent Bicep2 observations, not relying on long-wavelength tensor modes of the geometry, ... More
Anomalous MagnetohydrodynamicsJul 09 2013Anomalous symmetries induce currents which can be parallel rather than orthogonal to the hypermagnetic field. Building on the analogy with charged liquids at high magnetic Reynolds numbers, the persistence of anomalous currents is scrutinized for parametrically ... More
Primordial Magnetic Fields and Stochastic GW BackgroundsDec 20 2002Dec 21 2002Operating resonant mass detectors set interesting bounds on diffused backgrounds of gravitational radiation and in the next five years the wide-band interferometers will also look for stochastic sources. In this lecture the interplay among relic GW backgrounds ... More
Magnetogenesis, variation of gauge couplings and inflationDec 16 2002The interplay among the possible variation of gauge coupling and the inflationary dynamics is investigated in a simplified toy model. Depending upon various parameters (scalar mass, curvature scale at the end of inflation and at the onset of the radiation ... More
Homogeneous magnetic fields in fully anisotropic string cosmological backgroundsMar 30 2000We present new solutions of the string cosmological effective action in the presence of a homogeneous Maxwell field with pure magnetic component. Exact solutions are derived in the case of space-independent dilaton and vanishing torsion background. In ... More
Primordial Hypermagnetic KnotsMay 16 1999Topologically non-trivial configurations of the hypermagnetic flux lines lead to the formation of hypermagnetic knots (HK) whose decay might seed the Baryon Asymmetry of the Universe (BAU).HK can be dynamically generated provided a topologically trivial ... More
Production and detection of relic gravitons in quintessential inflationary modelsFeb 27 1999A large class of quintessential inflationary models, recently proposed by Peebles and Vilenkin, leads to post-inflationary phases whose effective equation of state is stiffer than radiation. The expected gravitational waves logarithmic energy spectra ... More
Singularity free dilaton-driven cosmologies and pre-little-bangJul 07 1998There are no reasons why the singularity in the growth of the dilaton coupling should not be regularised, in a string cosmological context, by the presence of classical inhomogeneities. We discuss a class of inhomogeneous dilaton-driven models whose curvature ... More
Gradient expansion(s) and dark energyJun 29 2005Sep 07 2005Motivated by recent claims stating that the acceleration of the present Universe is due to fluctuations with wavelength larger than the Hubble radius, we present a general analysis of various perturbative solutions of fully inhomogeneous Einstein equations ... More
Scalar normal modes of higher dimensional gravitating kinksJul 29 2002The scalar normal modes of higher dimensional gravitating kink solutions are derived. By perturbing to second order the gravity and matter parts of the action in the background of a five-dimensional kink, the effective Lagrangian of the scalar fluctuations ... More
Gauge field localization on Abelian vortices in six dimensionsMay 14 2002The vector and tensor fluctuations of vortices localizing gravity in the context of the six-dimensional Abelian Higgs model are studied. These string-like solutions break spontaneously six-dimensional Poincar\'e invariance leading to a finite four-dimensional ... More
Gauge-invariant fluctuations of scalar branesJun 05 2001A generalization of the Bardeen formalism to the case of warped geometries is presented. The system determining the gauge-invariant fluctuations of the metric induced by the scalar fluctuations of the brane is reduced to a set of Schr\"odinger-like equations ... More
Hedgehogs in higher dimensional gravity with curvature self-interactionsSep 21 2000Static solutions of the higher dimensional Einstein-Hilbert gravity supplemented by quadratic curvature self-interactions are discussed in the presence of hedgehog configurations along the transverse dimensions. The quadratic part of the action is parametrized ... More
Hypermagnetic Knots, Chern-Simons Waves and the Baryon AsymmetryJun 03 1999At finite hyperconductivity and finite fermionic density the flux lines of long range hypermagnetic fields may not have a topologically trivial structure. The combined evolution of the chemical potentials and of pseudoscalar fields (like the axial Higgs), ... More
Blue Spectra of Kalb-Ramond Axions and Fully Anisotropic String CosmologiesSep 25 1998The inhomogeneities associated with massless Kalb-Ramond axions can be amplified not only in isotropic (four-dimensional) string cosmological models but also in the fully anisotropic case. If the background geometry is isotropic, the axions (which are ... More
The large-N phase transition of lattice SU(N) gauge theoriesSep 11 1998We investigate the large-N phase transition of lattice SU(N) gauge theories in the Wilson formulation, by performing a Monte Carlo simulation of the twisted Eguchi-Kawai model. A variant of the multicanonical algorithm allows a detailed exploration of ... More
Improving Ranking Using Quantum ProbabilityAug 28 2011The paper shows that ranking information units by quantum probability differs from ranking them by classical probability provided the same data used for parameter estimation. As probability of detection (also known as recall or power) and probability ... More
Smooth circle actions on $S^7$ with unbounded periods and non-linearizable multicentresApr 08 2014We will give an example of a smooth free action of $S^1=U(1)$ on $S^7$ whose orbits have unbounded lenghts (equivalently: unbounded periods). As an application of this example we construct a $C^{\infty}$ vector field $X$, defined in a neighbourhood $U$ ... More
Anomalous magnetization of a carbon nanotube as an excitonic insulatorMay 13 2014Oct 28 2014We show theoretically that an undoped carbon nanotube might be an excitonic insulator---the long-sought phase of matter proposed by Keldysh, Kohn and others fifty years ago. We predict that the condensation of triplet excitons, driven by intervalley exchange ... More
Tunneling theory of two interacting atoms in a trapNov 15 2011Feb 04 2012A theory for the tunneling of one atom out of a trap containing two interacting cold atoms is developed. The quasiparticle wave function, dressed by the interaction with the companion atom in the trap, replaces the non-interacting orbital at resonance ... More
Classical electrodynamics of point chargesOct 16 2001Jun 05 2002A simple mathematical procedure is introduced which allows redefining in an exact way divergent integrals and limits that appear in the basic equations of classical electrodynamics with point charges. In this way all divergences are at once removed without ... More
SystemC Analysis of a New Dynamic Power Management ArchitectureOct 25 2007This paper presents a new dynamic power management architecture of a System on Chip. The Power State Machine describing the status of the core follows the recommendations of the ACPI standard. The algorithm controls the power states of each block on the ... More
Some Considerations on Chiral Gauge TheoriesDec 20 1999Some general considerations on the problem of non-perturbative definition of Chiral Gauge Theories are presented.
What is the sign of $\hbar$ ?Jul 02 2010We present an elementary argument showing that the sign of $\hbar$ in the basic formulation of Quantum Mechanics can be changed without incurring in any physical consequences.
Gravitational interaction of antimatterMar 08 2010Until now, there is no experimental evidence on the gravitational behaviour of antimatter. While we may be confident that antimatter attracts antimatter, we do not know anything on the interaction between matter and antimatter. We investigate this issue ... More
NoSQL DatabasesJan 09 2014In this document, I present the main notions of NoSQL databases and compare four selected products (Riak, MongoDB, Cassandra, Neo4J) according to their capabilities with respect to consistency, availability, and partition tolerance, as well as performance. ... More
On some stability results of frame atomic decompositionsFeb 10 2005This paper is concerned with the implications of sufficient conditions ensuring that a perturbation of a frame is again a frame. We emphasize how stability of frames is fundamental for numerical applications and we discuss in particular the connection ... More
Higher Spins and String InteractionsMay 17 2010May 24 2010In this Thesis we address the issue of consistent higher-spin interactions taking String Theory as a "theoretical laboratory". We thus arrive at a simple expression encompassing all three-point amplitudes for states belonging to the first Regge trajectory ... More
Statistical anisotropy from inflationary magnetogenesisJan 14 2016Provided the quantum fluctuations are amplified in the presence of a classical gauge field configuration the resulting curvature perturbations exhibit a mild statistical anisotropy which should be sufficiently weak not to conflict with current observational ... More
Hypermagnetic gyrotropy, inflation and the baryon asymmetry of the UniverseOct 31 2015We investigate the production of the hypermagnetic gyrotropy when the electric and magnetic gauge couplings evolve at different rates, as it happens in the the relativistic theory of the Van der Waals forces. If a pseudo-scalar interaction breaks the ... More
Inflationary magnetogenesis, derivative couplings and relativistic Van der Waals interactionsJun 12 2015Aug 20 2015When the gauge fields have derivative couplings to scalars, like in the case of the relativistic theory of Van der Waals (or Casimir-Polder) interactions, conformal invariance is broken but the magnetic and electric susceptibilities are not bound to coincide. ... More
The scalar modes of the relic gravitonsOct 20 2014In conformally flat background geometries the long wavelength gravitons can be described in the fluid approximation and they induce scalar fluctuations both during inflation and in the subsequent radiation-dominated epoch. While this effect is minute ... More
The symmetries of inflationary magnetogenesis and the plasma initial conditionsJul 27 2012As soon as the geometry expands quasi-exponentially the plasma sources are customarily tuned to zero as if the duration of the inflationary phase was immaterial for the gauge field fluctuations at large-scale. The serendipitous disappearance of the plasma ... More
Circular dichroism, magnetic knots and the spectropolarimetry of the Cosmic Microwave BackgroundSep 25 2009Jan 07 2010When the last electron-photon scattering takes place in a magnetized environment, the degree of circular polarization of the outgoing radiation depends upon the magnetic field strength. After deriving the scattering matrix of the process, the generalized ... More
Dynamical suppression of non-adiabatic modesAug 27 2008Recent analyses of the WMAP 5-year data constrain possible non-adiabatic contributions to the initial conditions of CMB anisotropies. Depending upon the early dynamics of the plasma, the amplitude of the entropic modes can experience a different suppression ... More
Magnetized initial conditions for CMB anisotropiesSep 24 2004Dec 25 2004This paper introduces a systematic treatment of the linear theory of scalar gravitational perturbations in the presence of a fully inhomogeneous magnetic field. The analysis is conducted both in the synchronous and in the conformally Newtonian gauges. ... More
The Magnetized UniverseDec 24 2003Mar 10 2004Cosmology, high-energy physics and astrophysics are converging on the study of large-scale magnetic fields. While the experimental evidence for the existence of large-scale magnetization in galaxies, clusters and superclusters is rather compelling, the ... More
Magnetization of fluid phonons and large-scale curvature perturbationsAug 20 2014The quasinormal mode of a gravitating and magnetized fluid in a spatially flat, isotropic and homogeneous cosmological background is derived in the presence of the fluid sources of anisotropic stress and of the entropic fluctuations of the plasma. The ... More
Fluid phonons and inflaton quanta at the protoinflationary transitionApr 25 2012Quantum and thermal fluctuations of an irrotational fluid are studied across the transition regime connecting a protoinflationary phase of decelerated expansion to an accelerated epoch driven by a single inflaton field. The protoinflationary inhomogeneities ... More
Growth rate of matter perturbations as a probe of large-scale magnetismJun 24 2011The growth rate of matter perturbations is computed in a magnetized environment for the LambdaCDM and wCDM paradigms. It is argued that the baryons do not necessarily follow into the dark matter potential wells after they are released from the drag of ... More
Last scattering, relic gravitons and the circular polarization of the CMBJan 23 2010The tensor contribution to the $V$-mode polarization induced by a magnetized plasma at last scattering vanishes exactly. Conversely a polarized background of relic gravitons cannot generate a $V$-mode polarization. The reported results suggest that, in ... More
Electric-magnetic duality and the conditions of inflationary magnetogenesisNov 04 2009The magnetogenesis scenarios triggered by the early variation of the gauge coupling are critically analyzed. In the absence of sources, it is shown that the electric and magnetic power spectra can be explicitly computed by means of electric-magnetic duality ... More
The V-mode polarization of the Cosmic Microwave BackgroundSep 20 2009Jan 02 2010The V-mode polarization of the Cosmic Microwave Background is discussed in a weakly magnetized plasma. The VV and VT angular power spectra are computed for adiabatic initial conditions of the Einstein-Boltzmann hierarchy. Depending upon the frequency ... More
Large-scale magnetic fields, curvature fluctuations and the thermal history of the UniverseJul 05 2007It is shown that gravitating magnetic fields affect the evolution of curvature perturbations in a way that is reminiscent of a pristine non-adiabatic pressure fluctuation. The gauge-invariant evolution of curvature perturbations is used to constrain the ... More
Gravitating multidefects from higher dimensionsDec 12 2006Warped configurations admitting pairs of gravitating defects are analyzed. After devising a general method for the construction of multidefects, specific examples are presented in the case of higher-dimensional Einstein-Hilbert gravity. The obtained profiles ... More
Stochastic GW backgrounds and Ground based detectorsSep 28 2000The interplay between different ground based detectors and stochastic backgrounds of relic GW is described. A simultaneous detection of GW in the kHz and in the MHz--GHz region can point towards a cosmological nature of the signal. The sensitivity of ... More
Spikes in the Relic Graviton Background from Quintessential InflationMar 05 1999The energy spectra of gravitational waves (GW) produced in quintessential inflationary models increase in frequency and exhibit a sharp spike around 170 GHz where the associated fraction of critical energy density today stored in relic gravitons is of ... More
Regular Cosmological Examples of Tree-Level Dilaton-Driven ModelsDec 12 1997Mar 26 1998We construct some examples of analytic solutions of the low energy (i.e. tree-level) string cosmological effective action. We work with the ``minimal'' field content (i.e. graviton and dilaton) in the absence of any dilaton potential. Provided the metric ... More
Magnetized birefringence and CMB polarizationOct 28 2004Dec 18 2004The polarization plane of the cosmic microwave background radiation can be rotated either in a magnetized plasma or in the presence of a quintessential background with pseudoscalar coupling to electromagnetism. A unified treatment of these two phenomena ... More
Rotational inhomogeneities from pre-big bang?Oct 08 2004Dec 26 2004The evolution of the rotational inhomogeneities is investigated in the specific framework of four-dimensional pre-big bang models. While minimal (dilaton-driven) scenarios do not lead to rotational fluctuations, in the case of non-minimal (string-driven) ... More
Tracking Curvaton(s)?Oct 01 2003The ratio of the curvaton energy density to that of the dominant component of the background sources may be constant during a significant period in the evolution of the Universe. The possibility of having tracking curvatons, whose decay occurs prior to ... More
Localization of metric fluctuations on scalar branesJun 15 2001The localization of metric fluctuations on scalar brane configurations breaking spontaneously five-dimensional Poincar\'e invariance is discussed. Assuming that the four-dimensional Planck mass is finite and that the geometry is regular, it is demonstrated ... More
Physical flavor neutrino statesJul 27 2011The problem of representation for flavor states of mixed neutrinos is discussed. By resorting to recent results, it is shown that a specific representation exists in which a number of conceptual problems are resolved. Phenomenological consequences of ... More
Ising spin glass models versus Ising models: an effective mapping at high temperature I. General resultJul 19 2006We show that, above the critical temperature, if the dimension D of a given Ising spin glass model is sufficiently high, its free energy can be effectively expressed through the free energy of a related Ising model. When, in a large sense, D is infinite, ... More
Fluctuations analysis in complex networks modeled by hidden variable models. Necessity of a large cut-off in hidden-variable modelsFeb 18 2014It is becoming more and more clear that complex networks present remarkable large fluctuations. These fluctuations may manifest differently according to the given model. In this paper we re-consider hidden variable models which turn out to be more analytically ... More
Semantic Ambiguity and Perceived AmbiguityMay 16 1995I explore some of the issues that arise when trying to establish a connection between the underspecification hypothesis pursued in the NLP literature and work on ambiguity in semantics and in the psychological literature. A theory of underspecification ... More
Superfluidity of 4He nanoclusters in confinementNov 20 2015Structure and superfluid response of nanoscale size helium-four clusters enclosed in spherical cavities are studied by computer simulations. The curved surface causes the formation of well-defined concentric shells, thus imparting to the system a very ... More
Complex BeautyFeb 24 2014Complex systems and their underlying convoluted networks are ubiquitous, all we need is an eye for them. They pose problems of organized complexity which cannot be approached with a reductionist method. Complexity science and its emergent sister network ... More
Theory of electron spectroscopies in strongly correlated semiconductor quantum dotsFeb 10 2006Quantum dots may display fascinating features of strong correlation such as finite-size Wigner crystallization. We here review a few electron spectroscopies and predict that both inelastic light scattering and tunneling imaging experiments are able to ... More
A Note on Field Redefinitions and Higher-Spin EquationsJul 16 2016Jul 25 2016In this note we provide some details on the quasi-local field redefinitions which map interactions extracted from Vasiliev's equations to those obtained via holographic reconstruction. Without loss of generality, we focus on the source to the Fronsdal ... More
Boosted Statistical MechanicsJul 30 2015Based on the fundamental principles of Relativistic Quantum Mechanics, we give a rigorous, but completely elementary, proof of the relation between fundamental observables of a statistical system when measured relatively to two inertial reference frames, ... More
On Near-MDS Elliptic CodesNov 06 2002The main conjecture on maximum distance separable (MDS) codes states that, execpt for some special cases, the maximum length of a q-ary linear MDS code is q+1. This conjecture does not hold true for near maximum distance separable codes because of the ... More
The first observations of wide-band interferometers and the spectra of relic gravitonsMar 30 2016Jun 14 2016Stochastic backgrounds of relic gravitons of cosmological origin extend from frequencies of the order of the aHz up to the GHz range. Since the temperature and polarization anisotropies constrain the low frequency normalization of the spectra, in the ... More
The spectrum of anomalous magnetohydrodynamicsSep 07 2015The equations of anomalous magnetohydrodynamics describe an Abelian plasma where conduction and chiral currents are simultaneously present and constrained by the second law of thermodynamics. At high frequencies the magnetic currents play the leading ... More
Uniform gradient expansionsDec 19 2014Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the ... More
Tensor B mode and stochastic Faraday mixingApr 14 2014Jun 12 2014This paper investigates the Faraday effect as a different source of B mode polarization. The E mode polarization is Faraday rotated provided a stochastic large-scale magnetic field is present prior to photon decoupling. In the first part of the paper ... More
Scaling laws and sum rules for the B-mode polarizationFeb 03 2014The formation of the microwave background polarization anisotropies is investigated when the stochastic Faraday rate is stationary, random and Markovian. The scaling properties of the polarization power spectra and of their nonlinear combinations are ... More
Inflationary susceptibilities, duality and large-scale magnetic fields generationOct 07 2013We investigate what can be said about the interaction of scalar fields with Abelian gauge fields during a quasi-de Sitter phase of expansion and under the assumption that the electric and the magnetic susceptibilities do not coincide. The duality symmetry, ... More
Reynolds numbers in the early UniverseNov 16 2011After electron-positron annihilation and prior to photon decoupling the magnetic Reynolds number is approximately twenty orders of magnitude larger than its kinetic counterpart which is, in turn, smaller than one. In this globally neutral system the large-scale ... More
Parameter dependence of magnetized CMB observablesMar 30 2009May 08 2009Pre-decoupling magnetic fields affect the scalar modes of the geometry and produce observable effects which can be constrained also through the use of current (as opposed to forthcoming) data stemming from the Cosmic Microwave Background observations. ... More
Non-topological gravitating defects in five-dimensional anti-de Sitter spaceJul 27 2006A class of five-dimensional warped solutions is presented. The geometry is everywhere regular and tends to five-dimensional anti-de Sitter space for large absolute values of the bulk coordinate. The physical features of the solutions change depending ... More
Tight coupling expansion and fully inhomogeneous magnetic fieldsJun 30 2006The tight coupling expansion, appropriately generalized to include large-scale magnetic fields, allows the estimate of the brightness perturbations of CMB anisotropies for typical wavelengths that are larger than the Hubble radius after matter-radiation ... More
Homogeneous and isotropic big rips?Jul 15 2005We investigate the way big rips are approached in a fully inhomogeneous description of the space-time geometry. If the pressure and energy densities are connected by a (supernegative) barotropic index, the spatial gradients and the anisotropic expansion ... More
Thick branes and Gauss-Bonnet self-interactionsJul 27 2001Thick branes obtained from a bulk action containing Gauss-Bonnet self-interactions are analyzed in light of the localization properties of the various modes of the geometry. The entangled system describing the localization of the tensor, vector and scalar ... More
Inflationary magnetogenesis from dynamical gauge couplingsApr 21 2001The evolution of the gauge coupling is modelled using a scalar degree of freedom whose homogeneous and inhomogeneous modes evolve from an ordinary inflationary phase to the subsequent epochs. Depending upon various parameters (scalar mass, curvature scale ... More
On the variation of the gauge couplings during inflationApr 17 2001It is shown that the evolution of the (Abelian) gauge coupling during an inflationary phase of de Sitter type drives the growth of the two-point function of the magnetic inhomogeneities. After examining the constraints on the variation of the gauge coupling ... More
Stochastic gravitational waves backgrounds: a probe for inflationary and non-inflationary cosmologyDec 22 1999Physical scenarios, leading to highly energetic stochastic gravitational waves backgrounds (for frequencies ranging from the $\mu$Hz up to the GHz) are examined. In some cases the typical amplitude of the logarithmic energy spectrum can be even eight ... More