Centro Fermi

Rome, Italy

Centro Fermi

Rome, Italy
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Del Pozzo W.,University of Birmingham | Del Pozzo W.,University of Pisa | Nagar A.,Centro Fermi | Nagar A.,National Institute of Nuclear Physics, Italy | Nagar A.,Institute des Hautes Etudes Scientifiques
Physical Review D | Year: 2017

Building on the analytical description of the post-merger (ringdown) waveform of coalescing, nonprecessing, spinning binary black holes introduced by Damour and Nagar [Phys. Rev. D 90, 024054 (2014)PRVDAQ1550-799810.1103/PhysRevD.90.024054], we propose an analytic, closed form, time-domain, representation of the =m=2 gravitational radiation mode emitted after merger. This expression is given as a function of the component masses and dimensionless spins (m1,2,χ1,2) of the two inspiraling objects, as well as of the mass MBH and (complex) frequency σ1 of the fundamental quasinormal mode of the remnant black hole. Our proposed template is obtained by fitting the post-merger waveform part of several publicly available numerical relativity simulations from the Simulating eXtreme Spacetimes (SXS) catalog and then suitably interpolating over (symmetric) mass ratio and spins. We show that this analytic expression accurately reproduces (∼0.01 rad) the phasing of the post-merger data of other data sets not used in its construction. This is notably the case of the spin-aligned run SXS:BBH:0305, whose intrinsic parameters are consistent with the 90% credible intervals reported in the parameter-estimation followup of GW150914 by B.P. Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.241102]. Using SXS waveforms as "experimental" data, we further show that our template could be used on the actual GW150914 data to perform a new measure of the complex frequency of the fundamental quasinormal mode so as to exploit the complete (high signal-to-noise-ratio) post-merger waveform. We assess the usefulness of our proposed template by analyzing, in a realistic setting, SXS full inspiral-merger-ringdown waveforms and constructing posterior probability distribution functions for the central frequency damping time of the first overtone of the fundamental quasinormal mode as well as for the physical parameters of the systems. We also briefly explore the possibility opened by our waveform model to test the second law of black hole dynamics. Our model will help improve current tests of general relativity, in particular the general-relativistic no-hair theorem, and allow for novel tests, such as that of the area theorem. © 2017 American Physical Society.

Rossi G.C.,University of Rome Tor Vergata | Rossi G.C.,Centro Fermi | Testa M.,University of Rome La Sapienza
Physical Review D | Year: 2017

We show that a recent interesting idea to circumvent the difficulties with the continuation of parton distribution functions to the Euclidean region, which consists in looking at equal time correlators between proton states of infinite momentum, encounters some problems related to the power divergent mixing pattern of deep inelastic scattering operators, when implemented within the lattice regularization. © 2017 American Physical Society.

Hatada K.,University of Zaragoza | Hatada K.,National Institute of Nuclear Physics, Italy | Hayakawa K.,National Institute of Nuclear Physics, Italy | Hayakawa K.,Centro Fermi | Palumbo F.,National Institute of Nuclear Physics, Italy
Physical Review C - Nuclear Physics | Year: 2011

Scissors modes were predicted in the framework of the two-rotor model. This model has an intrinsic harmonic spectrum, so that the level above the scissors mode, the first overtone, has excitation energy twice that of the scissors mode. Because the latter is of the order of 3 MeV in the rare-earth region, the energy of the overtone is below threshold for nucleon emission, and its width should remain small enough for the overtone to be observable. We find that B(E2)'overtone=164θ02B(E2)'scissors, where θ0 is the zero-point oscillation amplitude, which in the rare-earth region is of order 10-1. © 2011 American Physical Society.

Chiappini A.,CNR Institute for Photonics and Nanotechnologies | Armellini C.,CNR Institute for Photonics and Nanotechnologies | Carpentiero A.,CNR Institute for Photonics and Nanotechnologies | Minati L.,CNR Institute for Photonics and Nanotechnologies | And 3 more authors.
Optical Materials | Year: 2013

In this paper we describe a composite system based on polystyrene colloidal nanoparticles assembled and embedded in an elastomeric matrix (polymer colloidal crystal, PCC), in the specific we have designed a PCC structure which displays an iridescent green color that can be attributed to the photonic crystal effect. This effect has been exploited to create a chemical sensor, in fact optical measurements have evidenced that the composite structure presents a different optical response as a function of the solvent applied on the surface. In particular we have demonstrated that the PCC possess, for specific solvents: (i) high sensitivity, (ii) fast response (less than 1s), and (iii) reversibility of the signal change. Finally preliminary results on the PCC have shown that this system can be also used as optical writing substrate using a specific solvent as ink, moreover an erasing procedure is also reported and discussed. © 2013 Elsevier B.V. All rights reserved.

Valligatla S.,CNR Institute for Photonics and Nanotechnologies | Valligatla S.,University of Trento | Valligatla S.,University of Hyderabad | Chiasera A.,CNR Institute for Photonics and Nanotechnologies | And 6 more authors.
Optics Express | Year: 2012

Rare earth-activated 1-D photonic crystals were fabricated by RF-sputtering technique. The cavity is constituted by an Er3+-doped SiO 2 active layer inserted between two Bragg reflectors consisting of ten pairs of SiO2/TiO2 layers. Scanning electron microscopy is employed to put in evidence the quality of the sample, the homogeneities of the layers thickness and the good adhesion among them. Near infrared transmittance and variable angle reflectance spectra confirm the presence of a stop band from 1500 nm to 2000 nm with a cavity resonance centered at 1749 nm at 0° and a quality factor of 890. The influence of the cavity on the 4I13/2 → 4I15/2 emission band of Er3+ ion is also demonstrated. © 2012 Optical Society of America.

Hatada K.,University of Zaragoza | Hatada K.,National Institute of Nuclear Physics, Italy | Hayakawa K.,National Institute of Nuclear Physics, Italy | Hayakawa K.,Centro Fermi | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2010

We present a rigorous derivation of a real-space full-potential multiple scattering theory (FP-MST) that is free from the drawbacks that up to now have impaired its development (in particular the need to expand cell shape functions in spherical harmonics and rectangular matrices), valid both for continuum and bound states, under conditions for space partitioning that are not excessively restrictive and easily implemented. In this connection we give a new scheme to generate local basis functions for the truncated potential cells that is simple, fast, efficient, valid for any shape of the cell and reduces to the minimum the number of spherical harmonics in the expansion of the scattering wavefunction. The method also avoids the need for saturating 'internal sums' due to the re-expansion of the spherical Hankel functions around another point in space (usually another cell center). Thus this approach provides a straightforward extension of MST in the muffin-tin (MT) approximation, with only one truncation parameter given by the classical relation lmax = kRb, where k is the electron wavevector (either in the excited or ground state of the system under consideration) and Rb is the radius of the bounding sphere of the scattering cell. Moreover, the scattering path operator of the theory can be found in terms of an absolutely convergent procedure in the limit. Consequently, this feature provides a firm ground for the use of FP-MST as a viable method for electronic structure calculations and makes possible the computation of x-ray spectroscopies, notably photo-electron diffraction, absorption and anomalous scattering among others, with the ease and versatility of the corresponding MT theory. Some numerical applications of the theory are presented, both for continuum and bound states. © 2010 IOP Publishing Ltd.

De Gruttola D.,Centro Fermi | De Gruttola D.,National Institute of Nuclear Physics, Italy
Nuclear Physics A | Year: 2014

The photoproduction of vector mesons in Ultra-Peripheral Collisions (UPC) is a powerful tool to probe the nuclear gluon distribution, for which there is considerable uncertainty in the low-x region. We present the first measurements in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV, performed with the ALICE detector. The J / ψ is identified via its dimuon decay in the forward rapidity region and via dimuon and dielectron decay at midrapidity. The results are compared to theoretical models for coherent J / ψ production and found to be in good agreement with models which include nuclear gluon shadowing. The cross section measurement for incoherent J / ψ and γ γ → e+ e- at mid-rapidity is reported. Finally we present the first results on p-Pb UPC at sqrt(sNN) = 5.02 TeV. © 2014 CERN.

Frezzotti R.,University of Rome Tor Vergata | Rossi G.C.,University of Rome Tor Vergata | Rossi G.C.,Centro Fermi
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Taking inspiration from lattice QCD data, we argue that a finite nonperturbative contribution to the quark mass is generated as a consequence of the dynamical phenomenon of spontaneous chiral symmetry breaking, in turn triggered by the explicit breaking of chiral symmetry induced by the critical Wilson term in the action. In pure lattice QCD this mass term cannot be separated from the unavoidably associated linearly divergent contribution. However, if QCD is enlarged to a theory where also a scalar field is present, coupled to an SU(2) doublet of fermions via a Yukawa and a Wilson-like term, then in the phase where the scalar field takes a nonvanishing expectation value, a dynamically generated and "naturally" light fermion mass (numerically unrelated to the expectation value of the scalar field) is conjectured to emerge at a critical value of the Yukawa coupling where the symmetry of the model is maximally enhanced. Masses dynamically generated in this way display a natural hierarchy according to which the stronger is the strongest of the interactions the fermion is subjected to, the larger will be its mass. © 2015 American Physical Society. © 2015 American Physical Society.

Paolozzi A.,University of Rome La Sapienza | Ciufolini I.,University of Salento | Ciufolini I.,Centro Fermi
Acta Astronautica | Year: 2013

On February 13th 2012, the LARES satellite of the Italian Space Agency (ASI) was launched into orbit with the qualification flight of the new VEGA launcher of the European Space Agency (ESA). The payload was released very accurately in the nominal orbit. The name LARES means LAser RElativity Satellite and summarises the objective of the mission and some characteristics of the satellite. It is, in fact, a mission designed to test Einstein's General Relativity Theory (specifically 'frame-dragging' and Lense-Thirring effect). The satellite is passive and covered with optical retroreflectors that send back laser pulses to the emitting ground station. This allows accurate positioning of the satellite, which is important for measuring the very small deviations from Galilei-Newton's laws. In 2008, ASI selected the prime industrial contractor for the LARES system with a heavy involvement of the universities in all phases of the programme, from the design to the construction and testing of the satellite and separation system. The data exploitation phase started immediately after the launch under a new contract between ASI and those universities. Tracking of the satellite is provided by the International Laser Ranging Service. Due to its particular design, LARES is the orbiting object with the highest known mean density in the solar system. In this paper, it is shown that this peculiarity makes it the best proof particle ever manufactured. Design aspects, mission objectives and preliminary data analysis will be also presented. © 2013 IAA.

Rossi G.C.,University of Rome Tor Vergata | Rossi G.C.,Centro Fermi | Veneziano G.,Collège de France | Veneziano G.,CERN | Veneziano G.,University of Rome La Sapienza
Journal of High Energy Physics | Year: 2016

Abstract: We recall and update, both theoretically and phenomenologically, our (nearly) forty-years-old proposal of a string-junction as a necessary complement to the conventional classification of hadrons based just on their quark-antiquark constituents. In that proposal single (though in general metastable) hadronic states are associated with “irreducible” gauge-invariant operators consisting of Wilson lines (visualized as strings of color flux tubes) that may either end on a quark or an antiquark, or annihilate in triplets at a junction J or an anti-junction J¯. For the junction-free sector (ordinary qq¯ mesons and glueballs) the picture is supported by large-N (number of colors) considerations as well as by a lattice strong-coupling expansion. Both imply the famous OZI rule suppressing quark-antiquark annihilation diagrams. For hadrons with J and/or J¯ constituents the same expansions support our proposal, including its generalization of the OZI rule to the suppression of J− J¯ annihilation diagrams. Such a rule implies that hadrons with junctions are “mesophobic” and thus unusually narrow if they are below threshold for decaying into as many baryons as their total number of junctions (two for a tetraquark, three for a pentaquark). Experimental support for our claim, based on the observation that narrow multiquark states typically lie below (well above) the relevant baryonic (mesonic) thresholds, will be presented. © 2016, The Author(s).

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