Results for "Piero Lionello"

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Multivariate statistical modelling of future marine stormsMar 13 2019Extreme events, such as wave-storms, need to be characterized for coastal infrastructure design purposes. Such description should contain information on both the univariate behaviour and the joint-dependence of storm-variables. These two aspects have ... More
Statistical thermodynamic basis in drug-receptor interactions: double annihilation and double decoupling alchemical theories, revisitedJul 13 2016Alchemical theory is emerging as a promising tool in the context of molecular dynamics simulations for drug discovery projects. In this theoretical contribution, I revisit the statistical mechanics foundation of non covalent interactions in drug-receptor ... More
The Evolution of Luminous Matter in the UniverseSep 15 1997I review a technique for interpreting faint galaxy data which traces the evolution with cosmic time of the galaxy luminosity density, as determined from several deep spectroscopic samples and the HDF. The method relies on the rest frame UV and near-IR ... More
The Hubble Deep Field and the Early Evolution of GalaxiesJul 12 1997I review some recent progress made in our understanding of galaxy evolution and the cosmic history of star formation. The Hubble Deep Field (HDF) imaging survey has achieved the sensitivity to capture the bulk of the extragalactic background light from ... More
Star Formation at High Redshift: A Population of Early Dwarfs?Jul 20 1998The history of the transition from a neutral intergalactic medium (IGM) to one that is almost fully ionized can reveal the character of cosmological ionizing sources and set important constraints on the stellar birthrate at high redshifts. The hydrogen ... More
A closure model for intermittency in three dimensional incompressible turbulenceNov 15 1994A simplified Lagrangean closure for the Navier-Stokes equation is used to study the production of intermittency in the inertial range of three dimensional turbulence. This is done using localized wavepackets following the fluid rather than a standard ... More
Noncommutative Black Holes, The Final Appeal To Quantum Gravity: A ReviewJul 11 2008Feb 09 2009We present the state of the art regarding the relation between the physics of Quantum Black Holes and Noncommutative Geometry. We start with a review of models proposed in the literature for describing deformations of General Relativity in the presence ... More
A model of radiating black hole in noncommutative geometryJul 27 2005The phenomenology of a radiating Schwarzschild black hole is analyzed in a noncommutative spacetime. It is shown that noncommutativity does not depend on the intensity of the curvature. Thus we legitimately introduce noncommutativity in the weak field ... More
The faintest star forming galaxiesNov 14 2002I briefly report on the X-ray detection of 10 radio sub-mJy sources in the 2 Ms Chandra observation of the Hubble Deep Field North region. These sources follow the same radio/X-ray luminosities relation which holds for nearby galaxies. Making use of this ... More
I. Dissociation free energies in drug-receptor systems via non equilibrium alchemical simulations: theoretical frameworkApr 27 2016In this contribution I critically revise the alchemical reversible approach in the context of the statistical mechanics theory of non covalent bonding in drug receptor systems. I show that most of the pitfalls and entanglements for the binding free energies ... More
First Light and the Reionization of the UniverseOct 11 2002The development of primordial inhomogeneities into the non-linear regime and the formation of the first bound objects mark the transition from a simple cooling universe -- described by just a few parameters -- to a very messy hot one -- the realm of radiative, ... More
The Intergalactic MediumMay 05 2000About half a million years after the Big Bang, the ever-fading cosmic blackbody radiation cooled below 3000 K and shifted first into the infrared and then into the radio, and the smooth baryonic plasma that filled the Universe became neutral. The Universe ... More
Cosmic Star Formation HistoryDec 17 1996I review some recent progress made in our understanding of galaxy evolution and the cosmic history of star formation. Like bookends, the results obtained from deep ground-based spectroscopy and from the Hubble Deep Field imaging survey put brackets around ... More
Cosmological ReionizationMar 07 2000May 10 2000In popular cosmological scenarios, some time beyond a redshift of 10, stars within protogalaxies created the first heavy elements; these systems, together perhaps with an early population of quasars, generated the ultraviolet radiation and mechanical ... More
Faint galaxies, extragalactic background light, and the reionization of the UniverseJan 18 1999I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Largely due to a combination of deep HST imaging, Keck spectroscopy, and COBE far-IR background measurements, new constraints have ... More
X-ray Surveys of Distant Galaxy ClustersOct 04 1998I review recent observational progress in the search for and study of distant galaxy clusters in the X-ray band, with particular emphasis on the evolution of the abundance of X-ray clusters out to z~1. Several on-going deep X-ray surveys have led to the ... More
Nonlocal and generalized uncertainty principle black holesFeb 09 2012Feb 21 2012In this paper we study the issue of the role of nonlocality as a possible ingredient to solve long standing problems in the physics of black holes. To achieve this goal we analytically derive new black hole metrics improved by corrections from nonlocal ... More
Entropic force, noncommutative gravity and ungravityMay 17 2010Aug 13 2010After recalling the basic concepts of gravity as an emergent phenomenon, we analyze the recent derivation of Newton's law in terms of entropic force proposed by Verlinde. By reviewing some points of the procedure, we extend it to the case of a generic ... More
A black box method for solving the complex exponentials approximation problemMay 28 2009May 02 2012A common problem, arising in many different applied contexts, consists in estimating the number of exponentially damped sinusoids whose weighted sum best fits a finite set of noisy data and in estimating their parameters. Many different methods exist ... More
The State of the Solar Wind, Magnetosphere, and Ionosphere During the Maunder MinimumMar 19 2018Both direct observations and reconstructions from various datasets, suggest that conditions were radically different during the Maunder Minimum (MM) than during the space era. Using an MHD model, we develop a set of feasible solutions to infer the properties ... More
Formation of the current sheet in a coronal streamerNov 11 2011The present work is on the study of a coronal streamer observed in March 2008 at high spectral and spatial resolution by the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO. On the basis of a spectroscopic analysis of the O VI doublet, the solar ... More
Formation and early evolution of massive black holesJan 12 2007The astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at redshift 6 are poorly understood. In standard LCDM hierarchical cosmologies, the earliest ... More
Astronomy: Trouble at first lightApr 20 2006The question of how much light the first stars produced is fundamental to models of the Universe's development. But observations have so far failed to agree: is the answer a lot, or not very much at all?
Early Structure Formation and the Epoch of First LightAug 01 2002In popular cold dark matter cosmological scenarios, stars may have first appeared in significant numbers around a redshift of 10 or so, as the gas within protogalactic halos with virial temperatures in excess of 20,000 K (corresponding to masses comparable ... More
Probing the End of the Dark AgesOct 13 2000In currently popular cosmological scenarios -- all variants of the cold dark matter (CDM) cosmogony -- some time beyond a redshift of 15, stars within the numerous small halos that condense with virial temperatures ~1e4 K created the first heavy elements; ... More
Probing The High Redshift Universe with the NGSTAug 14 1998Through a combination of deep wide-field imaging and multi-object spectroscopy, the Next Generation Space Telescope will be able to chart with unprecedented accuracy the evolution of cosmic structures after the `dark ages' (z<5), when galaxies are thought ... More
Galaxy Evolution and the Cosmic Rate of SupernovaeJan 02 1998Ongoing searches for supernovae (SNe) at cosmological distances have recently started to provide a link between SN Ia statistics and galaxy evolution. In this talk I will use recent estimates of the global history of star formation to compute the theoretical ... More
Antimatter, just a `semantic' questionMay 23 2011In the attempt of including leptons in the scheme of a matter-antimatter asymmetry originated from CP violation in the primordial Universe, it is proposed of re-christening e-, muon-, tau- and their associated neutrinos as 'antiparticles' and e+, muon+, ... More
A simplified model for red cell dynamics in small blood vesselsMay 07 1998Nov 20 1998A simple mechanism for the confinement of red cells in the middle of narrow blood vessels is proposed. In the presence of a quadratic shear, red cells deform in such a way to loose fore-aft symmetry and to achieve a fixed orientation with respect to the ... More
Forces and torques on non-spherical particles in viscous shear flowsAug 27 1998Jun 02 1999The behavior of a non-spherical particle in a viscous, plane channel flow is studied by means of a combination of analytical technique and geometrical reasoning. An efficient implementation of Lamb's general solution is adopted, allowing rapid calculation, ... More
Passive swimming in low Reynolds number flowsMar 05 2010Jul 14 2010The possibility of microscopic swimming by extraction of energy from an external flow is discussed, focusing on the migration of a simple trimer across a linear shear flow. The geometric properties of swimming, together with the possible generalization ... More
Charge-exchange emission in the starburst galaxies M82 and NGC3256Mar 05 2012Charge-exchange (CE) emission produces features which are detectable with the current X-ray instrumentation in the brightest near galaxies. We describe these aspects in the observed X-ray spectra of the star forming galaxies M82 and NGC 3256, from the ... More
High energy emission from starburst galaxiesJul 07 2004The star formation (SF) can be regarded as an engine powering the light emission of spiral galaxies at several wavelengths. SF activity also plays a significant role in the evolution of galaxies. In this thesis we focus on the X-ray emission from processes ... More
A diffusion equation for the density of the ratio of two jointly distributed Gaussian variables and the numerical inversion of Laplace transformFeb 11 2011May 24 2011It is shown that the density of the ratio of two random variables with the same variance and joint Gaussian density satisfies a non stationary diffusion equation. Implications of this result for kernel density estimation of the condensed density of the ... More
Planckian charged black holes in ultraviolet self-complete quantum gravityDec 14 2017Jan 08 2018We present an analysis of the role of the charge within the self-complete quantum gravity paradigm. By studying the classicalization of generic ultraviolet improved charged black hole solutions around the Planck scale, we showed that the charge introduces ... More
On the condensed density of the generalized eigenvalues of pencils of Hankel Gaussian random matrices and applicationsJan 22 2008Sep 07 2010Pencils of Hankel matrices whose elements have a joint Gaussian distribution with nonzero mean and not identical covariance are considered. An approximation to the distribution of the squared modulus of their determinant is computed which allows to get ... More
The behavior of closed inextensible membranes in linear and quadratic shear flowsJun 01 1999The dynamics of a spheroidal vesicle, bounded by an inextensible membrane, is analyzed in function of the enclosed fluid viscosity, and of the membrane mechanical properties. The two situations in which a bending rigidity and a shear elasticity are the ... More
The antimatter gravitational fieldJun 22 2015Nov 11 2015In this work the author derives the Galilean limit of the gravitational field of antimatter by using the equations of the quantum gravity obtained by using the hydrodynamic approach. The result shows that, even if the antimatter mass is positive, it generates ... More
After the Dark Ages: the Evolution of Luminous Sources at z<5Dec 04 1998Dec 04 1998I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Through a combination of deep imaging, Keck spectroscopy, and COBE background measurements, important constraints have emerged on ... More
The Astrophysics of Early Galaxy FormationJun 01 2007These lectures summarize our basic understanding of the emergence of cosmic structures, the epoch of first light, the survival of early substructure in present-day galaxy halos.
From the Earliest Seeds to Today's Supermassive Black HolesOct 22 2004I review scenarios for the assembly of supermassive black holes (MBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark matter halo "merger tree". Monte Carlo realizations of the merger hierarchy in a LCDM cosmology, ... More
On the condensed density of the zeros of the Cauchy transform of a complex atomic random measure with Gaussian momentsJan 10 2012An atomic random complex measure defined on the unit disk with Normally distributed moments is considered. An approximation to the distribution of the zeros of its Cauchy transform is computed. Implications of this result for solving several moments problems ... More
Robust Causality Check for Sampled Scattering Parameters via a Filtered Fourier TransformJul 05 2013Aug 13 2014We introduce a robust numerical technique to verify the causality of sampled scattering parameters given on a finite bandwidth. The method is based on a filtered Fourier transform and includes a rigorous estimation of the errors caused by missing out-of-band ... More
Noncommutative nonsingular black holesOct 24 2005Adopting noncommutative spacetime coordinates, we determined a new solution of Einstein equations for a static, spherically symmetric matter source. The limitations of the conventional Schwarzschild solution, due to curvature singularities, are overcome. ... More
The evolution of star forming galaxies with the Wide Field X-ray TelescopeApr 30 2010Star forming galaxies represent a small yet sizable fraction of the X-ray sky (1%-20%, depending on the flux). X-ray surveys allow to derive their luminosity function and evolution, free from uncertainties due to absorption. However, much care must be ... More
Bivariate one-sample optimal location test for spherical stable densities by Pade' methodsApr 15 2014Complex signal detection in additive noise can be performed by a one-sample bivariate location test. Spherical symmetry is assumed for the noise density as well as closedness with respect to linear transformation. Therefore the noise is assumed to have ... More
Computational aspects and applications of a new transform for solving the complex exponentials approximation problemJan 28 2008Many real life problems can be reduced to the solution of a complex exponentials approximation problem which is usually ill posed. Recently a new transform for solving this problem, formulated as a specific moments problem in the plane, has been proposed ... More
On the universality of the distribution of the generalized eigenvalues of a pencil of Hankel random matricesSep 28 2012Universality properties of the distribution of the generalized eigenvalues of a pencil of random Hankel matrices, arising in the solution of the exponential interpolation problem of a complex discrete stationary process, are proved under the assumption ... More
Effective swimming strategies in low Reynolds number flowsApr 23 2010Apr 06 2011The optimal strategy for a microscopic swimmer to migrate across a linear shear flow is discussed. The two cases, in which the swimmer is located at large distance, and in the proximity of a solid wall, are taken into account. It is shown that migration ... More
Quantum Corrections to the Newton LawOct 19 2016In this work the author derives the Galilean limit of the gravity obtained by using the quantum hydrodynamic approach. The result shows that the quantum interaction generates, in the weak gravity limit, a non zero contribution. The work calculates the ... More
Cosmic Star Formation History and the Brightness of the Night SkyJul 20 1999I review the constraints imposed by the observed extragalactic background light (EBL) on the history of the stellar birthrate in galaxies. At faint magnitudes, the logarithmic slope of the galaxy counts is flatter than 0.4 in all seven UBVIJHK optical ... More
Starlight in the UniverseFeb 16 1999There has been remarkable progress recently in both observational and theoretical studies of galaxy formation and evolution. Largely due to a combination of deep Hubble Space Telescope imaging, Keck spectroscopy, and COBE far-IR background measurements, ... More
What Keeps the Universe Ionized at z=5?Apr 27 1998The history of the transition from a neutral intergalactic medium to one that is almost fully ionized can reveal the character of cosmological ionizing sources. In this talk I will discuss the implications for rival reionization scenarios of the rapid ... More
The Era of ReionizationDec 27 2002In popular cold dark matter cosmological scenarios, stars may have first appeared in significant numbers around a redshift of 10 or so, as the gas within protogalactic halos with virial temperatures in excess of 20,000 K (corresponding to masses comparable ... More
A new transform for solving the noisy complex exponentials approximation problemJan 11 2008The problem of estimating a complex measure made up by a linear combination of Dirac distributions centered on points of the complex plane from a finite number of its complex moments affected by additive i.i.d. Gaussian noise is considered. A random measure ... More
Kernel density estimation via diffusion and the complex exponentials approximation problemJun 05 2012A kernel method is proposed to estimate the condensed density of the generalized eigenvalues of pencils of Hankel matrices whose elements have a joint noncentral Gaussian distribution with nonidentical covariance. These pencils arise when the complex ... More
Log-concavity of Lucas Sequences of first kindJan 10 2011Mar 07 2011In these notes we address the study of the log-concave operator acting on Lucas Sequences of first kind. We will find for which initial values a generic Lucas sequence is log-concave, and using this we show when the same sequence is infinite log-concave. ... More
Advancing parabolic operators in thermodynamic MHD models: Explicit super time-stepping versus implicit schemes with Krylov solversOct 05 2016We explore the performance and advantages/disadvantages of using unconditionally stable explicit super time-stepping (STS) algorithms versus implicit schemes with Krylov solvers for integrating parabolic operators in thermodynamic MHD models of the solar ... More
Coronal Pseudo-Streamer and Bipolar Streamer Observed by SOHO/UVCS in March 2008May 21 2015The last solar minimum is characterized by several peculiar aspects and by the presence of a complex magnetic topology with two different kinds of coronal streamers: pseudo-streamers and bipolar streamers. Pseudo-streamers or unipolar streamer are coronal ... More
Sextonions, Zorn Matrices, and e_{71/2}Jun 15 2015Oct 27 2015By exploiting suitably constrained Zorn matrices, we present a new construction of the algebra of sextonions (over the algebraically closed field C). This allows for an explicit construction, in terms of Jordan pairs, of the non-semisimple Lie algebra ... More
He II absorption and the sawtooth spectrum of the cosmic far-UV backgroundDec 03 2008Jan 26 2009Cosmic ultraviolet background radiation between 3 and 4 Ryd is reprocessed by resonant line absorption in the Lyman series of intergalactic He II. This process results in a sawtooth modulation of the radiation spectrum from the He II Lya frequency to ... More
A novel determination of the local dark matter densityJul 01 2009Jul 30 2009We present a novel study on the problem of constructing mass models for the Milky Way, concentrating on features regarding the dark matter halo component. We have considered a variegated sample of dynamical observables for the Galaxy, including several ... More
The local dark matter phase-space density and impact on WIMP direct detectionNov 15 2011Jun 29 2012We present a new determination of the local dark matter phase-space density. This result is obtained implementing, in the limit of isotropic velocity distribution and spherical symmetry, Eddington's inversion formula, which links univocally the dark matter ... More
Relativistic Winds from Compact Gamma-ray Sources: I. Radiative Acceleration in the Klein-Nishina RegimeSep 03 1999Nov 30 1999We consider the radiative acceleration to relativistic bulk velocities of a cold, optically thin plasma which is exposed to an external source of gamma-rays. The flow is driven by radiative momentum input to the gas, the accelerating force being due to ... More
Gravitational Lensing of Distant Supernovae in Cold Dark Matter UniversesOct 25 1998Oct 20 1999Ongoing searches for supernovae (SNe) at cosmological distances have recently started to provide large numbers of events with measured redshifts and apparent brightnesses. Compared to quasars or galaxies, Type Ia SNe represent a population of sources ... More
Connecting horizon pixels and interior voxels of a black holeSep 17 2014Oct 03 2014In this paper we discuss to what extent one can infer details of the interior structure of a black hole based on its horizon. Recalling that black hole thermal properties are connected to the non-classical nature of gravity, we circumvent the restrictions ... More
Minimal Scales from an Extended Hilbert SpaceMay 18 2010Nov 30 2010We consider an extension of the conventional quantum Heisenberg algebra, assuming that coordinates as well as momenta fulfil nontrivial commutation relations. As a consequence, a minimal length and a minimal mass scale are implemented. Our commutators ... More
Generalized canonical approach to gyrokinetic theoryJun 17 2004We face the well-known gyrokinetic problem, which arises in the description of the dynamics of a charged particle subject to fast gyration for the presence of a strong electromagnetic field. The customary approach to gyrokinetic theory, using canonical ... More
Fuzziness at the horizonJan 07 2010Aug 03 2010We study the stability of the noncommutative Schwarzschild black hole interior by analysing the propagation of a massless scalar field between the two horizons. We show that the spacetime fuzziness triggered by the field higher momenta can cure the classical ... More
Kinetic description of classical matter infalling in black holesNov 16 2006A popular aspect of black holes physics is the mathematical analogy between their laws, coming from general relativity and the laws of thermodynamics. The analogy is achieved by identifying a suitable set of observables, precisely: \emph{(a)} $E=M$ (being ... More
The Dawn of GalaxiesMar 26 2003The development of primordial inhomogeneities into the non-linear regime and the formation of the first astrophysical objects within dark matter halos mark the transition from a simple, neutral, cooling universe -- described by just a few parameters -- ... More
Hausdorff dimension of a particle path in a quantum manifoldSep 16 2010Jan 14 2011After recalling the concept of the Hausdorff dimension, we study the fractal properties of a quantum particle path. As a novelty we consider the possibility for the space where the particle propagates to be endowed with a quantum-gravity-induced minimal ... More
Some relations between Lagrangian models and synthetic random velocity fieldsJul 25 2003Oct 15 2004We propose an alternative interpretation of Markovian transport models based on the well-mixedness condition, in terms of the properties of a random velocity field with second order structure functions scaling linearly in the space time increments. This ... More
Coherence, space non-locality and lacunarity in a cascade model of turbulenceApr 16 1998We use multiscale-multispace correlations and Fourier transform techniques, to study some intermittent random field properties, which escape analysis by structure function scaling. These properties are parametrized in terms of a set of scale ratios, giving ... More
Kinematics of hypervelocity stars in the triaxial halo of the Milky WayMay 24 2007Hypervelocity stars (HVSs) ejected by the massive black hole at the Galactic center have unique kinematic properties compared to other halo stars. Their trajectories will deviate from being exactly radial because of the asymmetry of the Milky Way potential ... More
Rush the inspiral: efficient Effective One Body time-domain gravitational waveformsMay 10 2018Computationally efficient waveforms are of central importance for gravitational wave data analysis of inspiralling and coalescing compact binaries. We show that the post-adiabatic (PA) approximation to the effective-one-body (EOB) description of the binary ... More
On a Class of Parameters Estimators in Linear Models Dominating the Least Squares one, Based on Compressed Sensing TechniquesMay 05 2014The estimation of parameters in a linear model is considered under the hypothesis that the noise, with finite second order statistics, can be represented in a given deterministic basis by random coefficients. An extended underdetermined design matrix ... More
Some Asymptotic Results for Fiducial and Confidence DistributionsDec 13 2016Oct 17 2017Under standard regularity assumptions, we provide simple approximations for specific classes of fiducial and confidence distributions and discuss their connections with objective Bayesian posteriors. For a real parameter the approximations are accurate ... More
Multi-wavelength signals of dark matter annihilations at the Galactic centerFeb 02 2008Aug 04 2008We perform a systematic study of the multi-wavelength signal induced by weakly interacting massive particle (WIMP) annihilations at the Galactic Center (GC). Referring to a generic WIMP dark matter (DM) scenario and depending on astrophysical inputs, ... More
Deep Galaxy Counts, Extragalactic Background Light, and the Stellar Baryon BudgetJul 22 1999Nov 04 1999We assess the constraints imposed by the observed extragalactic background light (EBL) on the cosmic history of star formation and the stellar mass density today. The logarithmic slope of the galaxy number-magnitude relation from the Southern Hubble Deep ... More
Carbon-Enhanced Metal-Poor Stars: Relics from the Dark AgesMay 28 2014Jul 24 2014We use detailed nucleosynthesis calculations and a realistic prescription for the environment of the first stars to explore the first episodes of chemical enrichment that occurred during the dark ages. Based on these calculations, we propose a novel explanation ... More
An open-system approach for the characterization of spatio-temporal chaosJan 05 2003We investigate the structure of the invariant measure of space-time chaos by adopting an "open-system" point of view. We consider large but finite windows of formally infinite one-dimensional lattices and quantify the effect of the interaction with the ... More
Compton Heating of the Intergalactic Medium by the Hard X-ray BackgroundFeb 04 1999Mar 15 1999High-resolution hydrodynamics simulations of the Ly-alpha forest in cold dark matter dominated cosmologies appear to predict line widths that are substantially narrower than those observed. Here we point out that Compton heating of the intergalactic gas ... More
Radiative Transfer in a Clumpy Universe: II. The Utraviolet Extragalactic BackgroundSep 19 1995We present a detailed calculation of the propagation of AGN-like ionizing radiation through the intergalactic space. We model the ionization state of absorbing clouds, and show that the universe will be more opaque above $4\,$Ryd than previously estimated. ... More
Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact BinariesJun 25 2016We compute the expected X-ray diffuse background and radiative feedback on the intergalactic medium (IGM) from X-ray binaries prior and during the epoch of reionization. The cosmic evolution of compact binaries is followed using a population synthesis ... More
On the Association of Gamma-ray Bursts with Massive Stars: Implications for Number Counts and Lensing StatisticsAug 18 2000Oct 18 2000Recent evidence appears to link gamma-ray bursts (GRBs) to star-forming regions in galaxies at cosmological distances. If short-lived massive stars are the progenitors of GRBs, the rate of events per unit cosmological volume should be an unbiased tracer ... More
Microscopic statistical description of classical matter around black holesAug 10 2005The problem of statistical description of classical matter, represented by a N-body system of relativistic point particles falling into a black hole, is investigated, adopting a classical framework. A covariant microscopic statistical description is developed ... More
Shilnikov Lemma for a nondegenerate critical manifold of a Hamiltonian systemAug 21 2013We prove an analog of Shilnikov Lemma for a normally hyperbolic symplectic critical manifold $M\subset H^{-1}(0)$ of a Hamiltonian system. Using this result, trajectories with small energy $H=\mu>0$ shadowing chains of homoclinic orbits to $M$ are represented ... More
An energy constrained method for the existence of layered type solutions of NLS equationsNov 28 2012We study the existence of positive solutions on $\R^{N+1}$ to semilinear elliptic equation $-\Delta u+u=f(u)$ where $N\geq 1$ and $f$ is modeled on the power case $f(u)=|u|^{p-1}u$. Denoting with $c$ the mountain pass level of $\f(u)=\tfrac 12\|u\|^{2}_{H^{1}(\R^{N})}-\int_{\R^{N}}F(u)\, ... More
Fiducial, confidence and objective Bayesian posterior distributions for a multidimensional parameterDec 06 2016We propose a way to construct fiducial distributions for a multidimensional parameter using a step-by-step conditional procedure related to the inferential importance of the components of the parameter. For discrete models, in which the non-uniqueness ... More
Sextonions, Zorn Matrices, and $\mathbf{e_{7 \frac12}}$Jun 15 2015May 20 2017By exploiting suitably constrained Zorn matrices, we present a new construction of the algebra of sextonions (over the algebraically closed field $\mathbb{C}$). This allows for an explicit construction, in terms of Jordan pairs, of the non-semisimple ... More
Exceptional Lie Algebras at the very Foundations of Space and TimeJun 29 2015While describing the results of our recent work on exceptional Lie and Jordan algebras, so tightly intertwined in their connection with elementary particles, we will try to stimulate a critical discussion on the nature of spacetime and indicate how these ... More
Radiative transfer in a clumpy universe: IV. New synthesis models of the cosmic UV/X-ray backgroundMay 10 2011Nov 26 2011We present improved synthesis models of the evolving spectrum of the UV/X-ray diffuse background, updating and extending our previous results. Five new main components are added to our radiative transfer code CUBA: (1) the sawtooth modulation of the background ... More
New Population Synthesis Models of the Cosmic UV BackgroundMar 27 2011We present improved synthesis models of the evolving spectrum of the UV/X-ray diffuse background, updating and extending our previous results. A "minimal cosmic reionization model" is presented in which the galaxy UV emissivity traces recent determinations ... More
Modelling the uv/x-ray cosmic background with CUBAJun 01 2001In this paper, I will describe the features of the numerical code CUBA, aimed at the solution of the radiative transfer equation in a cosmological context. CUBA will be soon available for public use at the URL, allowing ... More
Accurate estimate of the relic density and the kinetic decoupling in non-thermal dark matter modelsApr 18 2011Apr 20 2011Non-thermal dark matter generation is an appealing alternative to the standard paradigm of thermal WIMP dark matter. We reconsider non-thermal production mechanisms in a systematic way, and develop a numerical code for accurate computations of the dark ... More
Relativistic Winds from Compact Gamma-Ray Sources: II. Pair Loading and Radiative Acceleration in Gamma-ray BurstsSep 06 1999Feb 21 2000We consider the effects of rapid pair creation by an intense pulse of gamma-rays propagating ahead of a relativistic shock. Side-scattered photons colliding with the main gamma-ray beam amplify the density of scattering charges. The acceleration rate ... More
The Optical Extragalactic Background Light from Resolved GalaxiesNov 20 2000We discuss the ultraviolet to near-IR galaxy counts from the deepest imaging surveys, including the northern and southern Hubble Deep Fields. The logarithmic slope of the galaxy number-magnitude relation is flatter than 0.4 in all seven UBVIJHK optical ... More
The origin of intergalactic metals around Lyman-break galaxiesApr 06 2005Theoretical and observational arguments suggest that the intergalactic medium (IGM) might have been polluted with metals produced by early star formation. In this scenario, Lyman-break galaxies (LBGs) at redshift z=3 are likely to be surrounded by old ... More
Spectral dimension of a quantum universeDec 01 2009May 24 2010In this paper, we calculate in a transparent way the spectral dimension of a quantum spacetime, considering a diffusion process propagating on a fluctuating manifold. To describe the erratic path of the diffusion, we implement a minimal length by averaging ... More