Results for "Spyros Basilakos"

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Shape Statistics of Sloan Digital Survey superclustersFeb 28 2003Jun 03 2003We study the supercluster shape properties of the recently compiled SDSS cluster catalog using an approach based on differential geometry. We detect superclusters by applying the percolation algorithm to observed cluster populations, extended out to $z_{\rm ... More
Cosmological parameters from the clustering of AGNJul 23 2001We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ($z\le 0.1$) and distant universe ($z\sim 1$).
Solving the main cosmological puzzles with a generalized time varying vacuum energyJan 21 2009Oct 12 2009We study the dynamics of the FLRW flat cosmological models in which the vacuum energy density varies with time, $\Lambda(t)$. In particular, we investigate the dynamical properties of a generalized vacuum model and we find that under certain conditions ... More
Cosmic expansion and structure formation in running vacuum cosmologiesJan 15 2015Jan 16 2015We investigate the dynamics of the FLRW flat cosmological models in which the vacuum energy varies with redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which both kind of terms $H^{2}$ and constant ... More
Testing Eistein's gravity and dark energy with growth of matter perturbations: Indications for new Physics?Oct 01 2016The growth index of matter fluctuations is computed for ten distinct accelerating cosmological models and confronted to the latest growth rate data via a two-step process. First, we implement a joint statistical analysis in order to place constraints ... More
Effective equation of state for running vacuum: "mirage" quintessence and phantom dark energyJul 17 2013Nov 04 2013Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with a phantom phase near our time. This has been the case in the years of WMAP observations, in combination with the remaining cosmological observables. Such situation ... More
Growth index of matter perturbations in running vacuum modelsSep 22 2015Nov 21 2015We derive for the first time the growth index of matter perturbations of the FLRW flat cosmological models in which the vacuum energy depends on redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which ... More
Tachyon warm-intermediate inflation in the light of Planck dataApr 19 2016Sep 17 2016We study the main properties of the warm inflationary model based on Barrow's solution for the scale factor of the universe. Within this framework we calculate analytically the basic slow roll parameters for different versions of warm inflation. We test ... More
Quantum Gravity Corrections and Entropy at the Planck timeSep 02 2010Sep 27 2010We investigate the effects of Quantum Gravity on the Planck era of the universe. In particular, using different versions of the Generalized Uncertainty Principle and under specific conditions we find that the main Planck quantities such as the Planck ... More
Do we Come from a Quantum Anomaly?May 12 2019We present a string-based picture of the cosmological evolution in which (CP-violating) gravitational anomalies acting during the inflationary phase of the universe cause the vacuum energy density to "run" with the effective Hubble parameter squared, ... More
Starobinsky-like inflation and running vacuum in the context of SupergravityMay 17 2015Jul 21 2016We describe the primeval inflationary phase of the early Universe within a quantum field theoretical (QFT) framework that can be viewed as the effective action of vacuum decay in the early times. Interestingly enough, the model accounts for the "graceful ... More
Generalizing the running vacuum energy model and comparing with the entropic-force modelsApr 21 2012Jul 19 2012We generalize the previously proposed running vacuum energy model by including a term proportional to \dot{H}, in addition to the existing H^2 term. We show that the added degree of freedom is very constrained if both low redshift and high redshift data ... More
Scalar Field Theory Description of the Running Vacuum Model: from the scalaron to the "vacuumon"Jan 20 2019Jan 23 2019We investigate the running vacuum model (RVM) in the framework of scalar field theory.This dynamical vacuum model provides an elegant global explanation of the cosmic history, namely the universe starts from a non-singular initial de Sitter vacuum stage, ... More
Quantum Anomalies, Running Vacuum and Leptogenesis: an InterplayMay 14 2019We discuss a connection between gravitational-wave physics, quantum theory anomalies, right-handed (sterile) neutrinos, (spontaneous) CPT Violation and Leptogenesis, within the framework of string-inspired cosmological models. In particular, we present ... More
Constraints on Cosmological and Biasing models using AGN clusteringApr 27 2001We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ($z\le 0.1$) and distant universe ($z\sim 1$). To this end we compare the measured angular correlation ... More
Linear growth in power law $f(T)$ gravityMar 31 2016Apr 06 2016We provide for the first time the growth index of linear matter fluctuations of the power law $f(T) \propto (-T)^{b}$ gravity model. We find that the asymptotic form of this particular $f(T)$ model is $\gamma \approx \frac{6}{11-6b}$ which obviously extends ... More
The $Λ$CDM growth rate of structure revisitedFeb 08 2012Jun 26 2012We re-examine the growth index of the concordance $\Lambda$ cosmology in the light of the latest 6dF and {\em WiggleZ} data. In particular, we investigate five different models for the growth index $\gamma$, by comparing their cosmological evolution using ... More
The Physical Properties of the Cosmic AccelerationJan 12 2010Jan 21 2010The observed late-time acceleration of the cosmic expansion constitutes a fundamental problem in modern theoretical physics and cosmology. In an attempt to weight the validity of a large number of dark energy models, I use the recent measurements of the ... More
The growth index of matter perturbations using the clustering of dark energyDec 06 2014Feb 23 2015We have put forward a new unified framework which provides a consistent and rather complete account of the growth index of matter perturbations in the regime where the dark energy is allowed to have clustering. In particular, we find that the growth index ... More
Cosmological implications and structure formation from a time varying vacuumMar 03 2009We study the dynamics of the FLRW flat cosmological models in which the vacuum energy varies with time, $\Lambda(t)$. In this model we find that the main cosmological functions such as the scale factor of the universe and the Hubble flow are defined in ... More
Dynamical system analysis at background and perturbation levels: Quintessence in severe disadvantage comparing to $Λ$CDMApr 02 2019We perform for the first time a dynamical system analysis of both the background and perturbation equations, of $\Lambda$CDM and quintessence scenarios. In the former case the perturbations do not change the stability of the late-time attractor of the ... More
Dark energy and dark matter unification from dynamical space time: observational constraints and cosmological implicationsApr 11 2019May 13 2019A recently proposed Dynamical Space-time Cosmology (DSC) that unifies dark energy and dark matter is studied. The general action of this scenario includes a Lagrange multiplier, which is coupled to the energy momentum tensor and a scalar field which is ... More
Thermodynamical aspects of running vacuum modelsSep 01 2015Apr 28 2016The thermal history of a large class of running vacuum models in which the effective cosmological term is described by a truncated power series of the Hubble rate, whose dominant term is $\Lambda (H) \propto H^{n+2}$, is discussed in detail. Specifically, ... More
The growth index of matter perturbations and modified gravityMar 30 2012May 08 2012We place tight constraints on the growth index $\gamma$ by using the recent growth history results of 2dFGRS, SDSS-LRG, VIMOS-VLT deep Survey (VVDS) and {\em WiggleZ} datasets. In particular, we investigate several parametrizations of the growth index ... More
Cosmology from XMM High-Z AGN ClusteringJan 24 2007We review the high-redshift X-ray selected AGN clustering, based on the XMM/2dF survey, and compare it with other recent XMM-based results. Using the recent Hasinger et al. (2005) and La Franca et al. (2005) luminosity functions we find that the spatial ... More
Precision Cosmology from X-ray AGN clusteringSep 22 2009We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM-{\it Newton} soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009a), which have a redshift distribution ... More
Entropic-force dark energy reconsideredFeb 26 2014May 21 2014We reconsider the entropic-force model in which both kind of Hubble terms ${\dot H}$ and $H^{2}$ appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely the scale factor, deceleration parameter, ... More
Constraining the CDM spectrum normalization in flat dark energy cosmologiesJul 05 2006Aug 28 2006We study the relation between the rms mass fluctuations on 8$h^{-1}$Mpc scales and $\Omega_{\rm m}$ using the recent clustering results of XMM-{\it Newton} soft (0.5-2 keV) X-ray sources, which have a median redshift of $z\sim 1.2$. The relation can be ... More
The PSCz Dipole RevisitedSep 18 2006We re-examine the gravitational acceleration (dipole) induced on the Local Group of galaxies by the Infrared Astronomical Satellite (IRAS) galaxy distribution of the Point Source Catalogue redshift survey (PSCz). We treat the cirrus-affected low galactic ... More
Cosmological Implications of the PSCz PDF and its MomentsSep 07 2001Oct 17 2001We compare the {\em pdf} and its low-order moments (variance and skewness) of the smoothed PSCz galaxy density field and of the corresponding simulated PSCz look-alikes, generated from N-body simulations of 6 different DM models; four structure normalized ... More
The tension of cosmological magnetic fields as a contribution to dark energyMay 14 2007We propose that cosmological magnetic fields generated in regions of finite spatial dimensions may manifest themselves in the global dynamics of the Universe as `dark energy'. We test our model in the context of spatially flat cosmological models by assuming ... More
The Substructure-Alignment ConnectionNov 16 2001Nov 20 2001Using a sample of 903 APM clusters we investigate whether their dynamical status, as evidenced by the presence of significant substructures, is related to the large-scale structure of the Universe. We find that the cluster dynamical activity is strongly ... More
Interacting Dark Matter as an Alternative to Dark EnergyNov 12 2009We investigate the global dynamics of the universe within the framework of the Interacting Dark Matter (IDM) scenario. Considering that the dark matter obeys the collisional Boltzmann equation, we can obtain analytical solutions of the global density ... More
Cosmological Evolution of Linear BiasNov 14 2000Using linear perturbation theory and the Friedmann-Lemaitre solutions of the cosmological field equations, we derive analytically a second-order differential equation for the evolution of the linear bias factor, b(z), between the background matter and ... More
Virialization of cosmological structures in models with time varying equation of stateOct 06 2006We study the virialization of the cosmic structures in the framework of flat cosmological models where the dark energy component plays an important role in the global dynamics of the universe. In particular, our analysis focuses on the study of the spherical ... More
Cosmological equivalence between the Finsler-Randers space-time and the DGP gravity modelJan 18 2013Jan 27 2013We perform a detailed comparison between the Finsler-Randers cosmological model and the Dvali, Gabadadze and Porrati braneworld model. If we assume that the spatial curvature is strictly equal to zero then we prove the following interesting proposition: ... More
Cosmological constrains from X-ray AGN clustering and SNIa dataMar 11 2005We put constraints on the main cosmological parameters of different spatially flat cosmological models by combining the recent clustering results of XMM-Newton soft (0.5-2 keV) X-ray sources, which have a redshift distribution with median redshift $z\sim ... More
The Richness-Shape Relation of the 2dFGRS GroupsFeb 26 2004We estimate the group shape of the recently compiled Pecolation-Inferred Galaxy Group (2PIGG) catalogue. Using a set of integral equations we invert the projected distribution of group axial ratios and recover the corresponding intrinsic distribution ... More
Angular distribution of cosmological parameters as a probe of inhomogeneities: a kinematic parametrisationMar 24 2016Jul 12 2016We use a kinematic parametrisation of the luminosity distance to measure the angular distribution on the sky of time derivatives of the scale factor, in particular the Hubble parameter H_0, the deceleration parameter q_0, and the jerk parameter j_0. We ... More
Growth index of matter perturbations in the light of Dark Energy SurveyMar 26 2019May 01 2019We study how the cosmological constraints from growth data are improved by including the measurements of bias from Dark Energy Survey (DES). In particular, we utilize the biasing properties of the DES Luminous Red Galaxies (LRGs) and the growth data provided ... More
Hyperbolic Inflation in the Light of Planck 2015 dataApr 14 2015May 21 2015Rubano and Barrow have discussed the emergence of a dark energy, with late-time cosmic acceleration arising from a self-interacting homogeneous scalar field with a potential of hyperbolic power type. Here, we study the evolution of this scalar field potential ... More
Growth index of matter perturbations in the light of Dark Energy SurveyMar 26 2019We study how the cosmological constraints from growth data are improved by including the measurements of bias from Dark Energy Survey (DES). In particular, we utilize the biasing properties of the DES Luminous Red Galaxies (LRGs) and the growth data provided ... More
The Apparent and Intrinsic Shape of the APM Galaxy ClustersFeb 24 2000We estimate the distribution of intrinsic shapes of APM galaxy clusters from the distribution of their apparent shapes. We measure the projected cluster ellipticities using two alternative methods. The first method is based on moments of the discrete ... More
Galaxy Cluster ShapesDec 28 1999We estimate the distribution of intrinsic shapes of the APM galaxy clusters from their corresponding distribution of projected shapes. We smooth the discrete galaxy distribution and define the cluster shape by fitting the best ellipse to the different ... More
Precision growth index using the clustering of cosmic structures and growth dataFeb 05 2014Aug 20 2014We use the clustering properties of Luminous Red Galaxies (LRGs) and the growth rate data provided by the various galaxy surveys in order to constrain the growth index ($\gamma$) of the linear matter fluctuations. We perform a standard $\chi^2$-minimization ... More
Dynamical symmetries and observational constraints in scalar field cosmologyOct 18 2014Nov 14 2014We propose to use dynamical symmetries of the field equations, in order to classify the dark energy models in the context of scalar field (quintessence or phantom) FLRW cosmologies. Practically, symmetries provide a useful mathematical tool in physical ... More
Confronting the relaxation mechanism for a large cosmological constant with observationsSep 22 2011Jan 03 2012In order to deal with a large cosmological constant a relaxation mechanism based on modified gravity has been proposed recently. By virtue of this mechanism the effect of the vacuum energy density of a given quantum field/string theory (no matter how ... More
Dynamical vacuum energy in the expanding Universe confronted with observations: a dedicated studySep 24 2014Nov 27 2014Despite the many efforts, our theoretical understanding of the ultimate nature of the dark energy component of the universe still lags well behind the astounding experimental evidence achieved from the increasingly sophisticated observational tools at ... More
Spherical collapse model and cluster number counts in power law $f(T)$ gravitySep 03 2016Dec 22 2016We study the spherical collapse model (SCM) in the framework of spatially flat power law $f(T) \propto (-T)^{b}$ gravity model. We find that the linear and non-linear growth of spherical overdensities of this particular $f(T)$ model are affected by the ... More
Black hole spin down in GRB observations and CosmologyJul 24 2014Mar 03 2015According to Blandford & Znajek (1977), energy can be extracted electromagnetically from a rotating black hole, should the latter be endowed with a magnetic field supported by electric currents in a surrounding disk. We show that exact models of black ... More
Measuring the effects of Loop Quantum Cosmology in the CMB dataMay 16 2017In this Essay we investigate the observational signatures of Loop Quantum Cosmology (LQC) in the CMB data. First, we concentrate on the dynamics of LQC and we provide the basic cosmological functions. We then obtain the power spectrum of scalar and tensor ... More
Halo Shapes, Dynamics and EnvironmentApr 07 2006In the hierarchical structure formation model cosmic halos are supposed to form by accretion of smaller units along anisotropic direction, defined by large-scale filamentary structures. After the epoch of primary mass aggregation (which depend on the ... More
Dynamics and chaos in the unified scalar field CosmologyJan 08 2008Feb 15 2008We study the dynamics of the closed scalar field FRW cosmological models in the framework of the so called Unified Dark Matter (UDM) scenario. Performing a theoretical as well as a numerical analysis we find that there is a strong indication of chaos ... More
Observational constraints on viable f(R) parametrizations with geometrical and dynamical probesFeb 25 2013Jul 02 2013We demonstrate that a wide range of viable f(R) parameterizations (including the Hu & Sawicki and the Starobinsky models) can be expressed as perturbations deviating from the LCDM Lagrangian. We constrain the deviation parameter b using a combination ... More
Comment on "A study of phantom scalar field cosmology using Lie and Noether symmetries" [Int. J. Mod. Phys. D 25 (2016) 1650051]May 17 2016We show that the recent results of \ [Int. J. Mod. Phys. D 25 (2016) 1650051] on the application of Lie/Noether symmetries in scalar field cosmology are well-known in the literature while the problem could have been solved easily under a coordinate transformation. ... More
CMB lensing reconstruction from the WMAP 7-year dataDec 29 2012Sep 07 2013We attempt to make a direct measurement of the weak lensing signal from the WMAP 7-year data. We apply the real-space implementation of the optimal quadratic estimator on the maps produced by the W-band Differencing Assemblies. We obtain a weak lensing ... More
Cluster Formation Rate in Models with Dark EnergyMar 05 2003Apr 21 2003Based on flat Friedmann-Robertson Walker cold dark matter (CDM) type models driven by non-relativistic matter and an exotic fluid (quintessence) with an equation of state: $p_{Q}=w\rho_{Q}$ ($-1\le w<0$), we investigate whether or not the large scale ... More
Tachyon warm inflation with the effects of Loop Quantum Cosmology in the light of Planck 2015Mar 04 2017Jan 14 2018We investigate the observational signatures of quantum cosmology in the Cosmic Microwave Background data provided by Planck collaboration. We apply the warm inflationary paradigm with a tachyon scalar field to the loop quantum cosmology. In this context, ... More
Testing for substructure in optical and X-ray clustersJan 11 2000We present a detailed study of the morphological features of 22 rich galaxy clusters. We systematically compare cluster images and morphological parameters in an attempt to reliably identify possible substructure in both optical and X-ray images. To this ... More
Resembling dark energy and modified gravity with Finsler-Randers cosmologyNov 21 2013Dec 15 2013In this article we present the cosmological equivalence between the relativistic Finsler-Randers cosmology, with dark energy and modified gravity constructions, at the background level. Starting from a small deviation from the quadraticity of the Riemannian ... More
Searching for cluster substructure using APM and ROSAT dataFeb 23 2000Aug 04 2000We present a detailed study of the morphological features of 22 rich galaxy clusters. Our sample is constructed from a cross-correlation of optical (Abell+APM) data with X-ray (0.1 - 2.4) keV ROSAT pointed observations. We systematically compare cluster ... More
Dynamical analysis in scalar field cosmologyMar 19 2015Jun 04 2015We give a general method to find exact cosmological solutions for scalar-field dark energy in the presence of perfect fluids. We use the existence of invariant transformations for the Wheeler De Witt (WdW) equation. We show that the existence of a point ... More
Growth of matter perturbations in clustered holographic dark energy cosmologiesOct 14 2015Nov 17 2015We investigate the growth of matter fluctuations in holographic dark energy cosmologies. First we use an overall statistical analysis involving the latest observational data in order to place constraints on the cosmological parameters. Then we test the ... More
Conformally related metrics and Lagrangians and their physical interpretation in cosmologyJul 25 2013Conformally related metrics and Lagrangians are considered in the context of scalar-tensor gravity cosmology. After the discussion of the problem, we pose a lemma in which we show that the field equations of two conformally related Lagrangians are also ... More
Hubble expansion and structure formation in the "running FLRW model" of the cosmic evolutionMar 23 2011Aug 07 2011A new class of FLRW cosmological models with time-evolving fundamental parameters should emerge naturally from a description of the expansion of the universe based on the first principles of quantum field theory and string theory. Within this general ... More
New integrable models and analytical solutions in $f(R)$~cosmology with an ideal gasJan 04 2018In the context of $f\left( R\right) $-gravity with a spatially flat FLRW metric containing an ideal fluid, we use the method of invariant transformations to specify families of models which are integrable. We find three families of $f(R)$ theories for ... More
Dark energy and dark matter unification from dynamical space time: observational constraints and cosmological implicationsApr 11 2019A recently proposed Dynamical Space-time Cosmology (DSC) that unifies dark energy and dark matter is studied. The general action of this scenario includes a Lagrange multiplier, which is coupled to the energy-momentum tensor and a scalar field which is ... More
Classical and Quantum Solutions in Brans-Dicke Cosmology with a Perfect FluidNov 02 2015Jan 28 2016We consider the application of group invariant transformations in order to constrain a flat isotropic and homogeneous cosmological model, containing of a Brans-Dicke scalar field and a perfect fluid with a constant equation of state parameter $w$, where ... More
Dynamics and constraints of the dissipative Liouville cosmologyJul 18 2011May 21 2012In this article we investigate the properties of the FLRW flat cosmological models in which the cosmic expansion of the Universe is affected by a dilaton dark energy (Liouville scenario). In particular, we perform a detailed study of these models in the ... More
The decomposition of Global Conformal Invariants VDec 18 2009This is the fifth in a series of papers where we prove a conjecture of Deser and Schwimmer regarding the algebraic structure of ``global conformal invariants''; these are defined to be conformally invariant integrals of geometric scalars. The conjecture ... More
The decomposition of Global Conformal Invariants I: On a conjecture of Deser and SchwimmerNov 11 2007Dec 18 2009This is the first in a series of papers where we prove a conjecture of Deser and Schwimmer regarding the algebraic structure of ``global confor- mal invariants"; these are defined to be conformally invariant integrals of geometric scalars. The conjecture ... More
An explanation of unexpected Hoxd expressions in mutant miceSep 03 2012The Hox gene collinearity enigma has often been approached using models based on biomolecular mechanisms. The biophysical model, is an alternative approach, speculating that collinearity is caused by physical forces pulling the Hox clusters from a territory ... More
Unique continuation for the vacuum Einstein equationsFeb 06 2009Sep 02 2009We derive a unique continuation theorem for the vacuum Einstein equations. Our method of proof utilizes Carleman estimates (most importantly one obtained recently by Ionescu and Klainerman), but also relies strongly on certain geometric gauge constructions ... More
The Penrose inequality on perturbations of the Schwarzschild exteriorJun 21 2015We prove a version the Penrose inequality for black hole space-times which are perturbations of the Schwarzschild exterior in a slab around a null hypersurface $\underline{\mathcal{N}}_0$. $\underline{\mathcal{N}}_0$ terminates at past null infinity $\mathcal{I}^-$ ... More
Theoretical and Observational Constraints on Brane Inflation and Study of Scalar Perturbations through the Effective Field Theory FormalismJun 04 2014In this thesis, consisting of two main parts, we study observational signatures of cosmic (super)strings in the context of D-brane inflation and properties of scalar perturbations on generic homogeneous inflating backgrounds. In the first part we study ... More
Memory-preserving equilibration after a quantum quench in a 1d critical modelJul 28 2015Sep 09 2016One of the fundamental principles of statistical physics is that only partial information about a system's state is required for its macroscopic description. This is not only true for thermal ensembles, but also for the unconventional ensemble, known ... More
The decomposition of global conformal invariants VI: The proof of the proposition on local Riemannian invariantsDec 18 2009This is the last in a series of papers where we prove a conjecture of Deser and Schwimmer regarding the algebraic structure of ``global conformal invariants''; these are defined to be conformally invariant integrals of geometric scalars. The conjecture ... More
Further Connections Between Contract-Scheduling and Ray-Searching ProblemsApr 27 2015This paper addresses two classes of different, yet interrelated optimization problems. The first class of problems involves a robot that must locate a hidden target in an environment that consists of a set of concurrent rays. The second class pertains ... More
The decomposition of global conformal invariants II: The Fefferman-Graham ambient metric and the nature of the decompositionDec 18 2009This is the second in a series of papers where we prove a conjecture of Deser and Schwimmer regarding the algebraic structure of ``global conformal invariants''; these are defined to be conformally invariant integrals of geometric scalars. The conjecture ... More
Equilibration in one-dimensional quantum hydrodynamic systemsDec 01 2016We study quench dynamics and equilibration in one-dimensional quantum hydrodynamics, which provides effective descriptions of the density and velocity fields in gapless quantum gases. We show that the information content of the large time steady state ... More
On conformally invariant differential operatorsAug 31 2006Mar 29 2007We construct new families of conformally invariant differential operators acting on densities. We introduce a simple, direct approach which shows that all such operators arise via this construction when the degree is bounded by the dimension. The method ... More
On the decomposition of global conformal invariants ISep 23 2005Mar 26 2006This is the first of two papers where we address and partially confirm a conjecture of Deser and Schwimmer, originally postulated in high energy physics. The objects of study are scalar Riemannian quantities constructed out of the curvature and its covariant ... More
Testing GRBs as Standard CandlesMay 07 2008Sep 02 2008Several correlations among Gamma Ray Burst (GRB) observables with available redshifts have been recently identified. Proper evaluation and calibration of these correlations may facilitate the use of GRBs as standard candles constraining the expansion ... More
Complete Cosmic History with a dynamical Lambda(H) termJun 03 2013Sep 21 2013In the present mainstream cosmology, matter and spacetime emerged from a singularity and evolved through four distinct periods: early inflation, radiation, dark matter and late-time inflation (driven by dark energy). During the radiation and dark matter ... More
On the road to precision cosmology with high redshift HII galaxiesMay 17 2015We report the first results of a programme aimed at studying the properties of high redshift galaxies with on-going massive and dominant episodes of star formation (HII galaxies). We use the $L(\mathrm{H}\beta) - \sigma$ distance estimator based on the ... More
Determining the Hubble constant using Giant extragalactic HII regions and HII galaxiesMar 28 2012Jun 14 2012We report the first results of a long term program aiming to provide accurate independent estimates of the Hubble constant (H0) using the L-sigma distance estimator for Giant extragalactic HII regions (GEHR) and HII galaxies. We have used VLT and Subaru ... More
The $L - σ$ relation for massive bursts of star formationMay 15 2014The validity of the emission line luminosity vs. ionised gas velocity dispersion ($L - \sigma$) correlation for HII galaxies (HIIGx), and its potential as an accurate distance estimator are assessed. For a sample of 128 local ($0.02\lesssim z\lesssim ... More
Constraints to dark energy using PADE parameterisationsJun 07 2017We put constraints on dark energy properties using the PADE parameterisation, and compare it to the same constraints using Chevalier-Polarski-Linder (CPL) and $\Lambda$CDM, at both the background and the perturbation levels. The dark energy equation of ... More
Validity of the GGE for quantum quenches from interacting to noninteracting modelsMar 28 2014May 28 2014In the majority of the analytical verifications of the conjecture that the Generalised Gibbs Ensemble describes the large time asymptotics of local observables in quantum quench problems, both the post-quench and the pre-quench Hamiltonians are essentially ... More
Forecasting the cost of processing multi-join queries via hashing for main-memory databases (Extended version)Jul 11 2015Jul 21 2015Database management systems (DBMSs) carefully optimize complex multi-join queries to avoid expensive disk I/O. As servers today feature tens or hundreds of gigabytes of RAM, a significant fraction of many analytic databases becomes memory-resident. Even ... More
Towards Exascale Scientific Metadata ManagementMar 29 2015Advances in technology and computing hardware are enabling scientists from all areas of science to produce massive amounts of data using large-scale simulations or observational facilities. In this era of data deluge, effective coordination between the ... More
LocNet: Improving Localization Accuracy for Object DetectionNov 24 2015Apr 07 2016We propose a novel object localization methodology with the purpose of boosting the localization accuracy of state-of-the-art object detection systems. Our model, given a search region, aims at returning the bounding box of an object of interest inside ... More
Quantum quench in interacting field theory: a self-consistent approximationFeb 01 2010Apr 14 2010We study a composite quantum quench of the energy gap and the interactions in the interacting \phi^4 model using a self-consistent approximation. Firstly we review the results for free theories where a quantum quench of the energy gap or mass leads for ... More
Generating Classification Weights with GNN Denoising Autoencoders for Few-Shot LearningMay 03 2019Given an initial recognition model already trained on a set of base classes, the goal of this work is to develop a meta-model for few-shot learning. The meta-model, given as input some novel classes with few training examples per class, must properly ... More
Attend Refine Repeat: Active Box Proposal Generation via In-Out LocalizationJun 14 2016The problem of computing category agnostic bounding box proposals is utilized as a core component in many computer vision tasks and thus has lately attracted a lot of attention. In this work we propose a new approach to tackle this problem that is based ... More
Quasi locality of the GGE in interacting-to-free quenches in relativistic field theoriesAug 02 2016We study the quench dynamics in continuous relativistic quantum field theory, more specifically the locality properties of the large time stationary state. After a quantum quench in a one-dimensional integrable model, the expectation values of local observables ... More
Cluster expansion for ground states of local HamiltoniansJan 11 2016May 13 2016A central problem in many-body quantum physics is the determination of the ground state of a thermodynamically large physical system. We construct a cluster expansion for ground states of local Hamiltonians, which naturally incorporates physical requirements ... More
Quench echo and work statistics in integrable quantum field theoriesMar 28 2014Feb 16 2015We propose a boundary thermodynamic Bethe ansatz calculation technique to obtain the Loschmidt echo and the statistics of the work done when a global quantum quench is performed on an integrable quantum field theory. We derive an analytic expression for ... More
On the profile of energy concentration at blow-up points for sub-conformal focusing nonlinear wavesDec 21 2014We consider singularities of the focusing subconformal nonlinear wave equation and some generalizations of it. At noncharacteristic points on the singularity surface, Merle and Zaag have identified the rate of blow-up of the $H^1$-norm of the solution ... More
Convex Relaxations of Probabilistic AC Optimal Power Flow for Interconnected AC and HVDC GridsMar 30 2018Jan 28 2019High Voltage Direct Current (HVDC) systems interconnect AC grids to increase reliability, connect offshore wind generation, and enable coupling of electricity markets. Considering the growing uncertainty in power infeed and the complexity introduced by ... More