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C. Pittori

Publications and source records attributed to C. Pittori.

105 records · Page 6Linked to original sources
arXiv2007

GRB 070724B: the first Gamma Ray Burst localized by SuperAGILE and its Swift X-ray Afterglow

GRB 070724B is the first Gamma Ray Burst localized by SuperAGILE, the hard X-ray monitor aboard the AGILE satellite. The coordinates of the event were published $\sim 19$ hours after the trigger. The Swift X-Ray Telescope pointed at the SuperAGILE location and detected the X-ray afterglow inside the SuperAGILE error circle. The AGILE gamma-ray Tracker and Minicalorimeter did not detect any significant gamma ray emission associated with GRB 070724B in the MeV and GeV range, neither prompt nor delayed. Searches of the optical afterglow were performed by the Swift UVOT and the Palomar automated 60-inch telescopes without any significant detection. Similarly the Very Large Array did not detect a radio afterglow. This is the first GRB event with a firm upper limit in the 100 MeV -- 30 GeV energy range, associated with an X-ray afterglow.

astro-ph↗
arXiv2005

Non-thermal Cosmic Backgrounds from Blazars: the contribution to the CMB, X-ray and gamma-ray Backgrounds

We present a new assessment of the contribution of Blazars to the extragalactic background radiation across the e.m. spectrum. Our calculations rely on deep Blazar radio counts that we derived combining several multifrequency surveys. The integrated Blazar emission yields a broad-band non-thermal background that in some parts of the e.m. spectrum dominates the extragalactic brightness. Blazars are the main point-like contributors to the CMB. Their integrated emission causes an apparent T increase of 5-50 muK in the 50-250 GHz range. The CMB fluctuation spectrum is sensibly contaminated at l>300, for a Poissonian source distribution, or at lower l values if spatial clustering is present. We estimate that well over 100,000 Blazars will produce a significant signal in the PLANCK CMB anisotropy maps. Because of the microwave-Xray flux correlation, these sources are expected to have flux > a few 10^{-15} erg/s in the soft X-ray band. Thus, a large fraction of the foreground sources in CMB anisotropy maps could be identified and removed using a multi frequency approach, provided that a sufficiently deep all sky X-ray survey will be available. We further show that Blazars are a major constituent of all high-E extragalactic backgrounds. Their contribution is 11-12% at X-ray frequencies and possibly 100% in the 0.5-50 MeV band. At E>100 MeV, the Blazar collective emission, obtained extrapolating their integrated micro-wave flux to the gamma-ray band using the SED of EGRET detected sources, over-predicts the extragalactic background by a large factor, implying that Blazars not only dominate the gamma-ray sky but also that their average duty cycle at these frequencies must be rather low. We also find that Blazars of the HBL type may produce a significant amount of flux at TeV energies.

astro-ph↗
arXiv2005

Simulating the High Energy Gamma-ray sky seen by the GLAST Large Area Telescope

This paper presents the simulation of the GLAST high energy gamma-ray telescope. The simulation package, written in C++, is based on the Geant4 toolkit, and it is integrated into a general framework used to process events. A detailed simulation of the electronic signals inside Silicon detectors has been provided and it is used for the particle tracking, which is handled by a dedicated software. A unique repository for the geometrical description of the detector has been realized using the XML language and a C++ library to access this information has been designed and implemented. A new event display based on the HepRep protocol was implemented. The full simulation was used to simulate a full week of GLAST high energy gamma-ray observations. This paper outlines the contribution developed by the Italian GLAST software group.

astro-ph↗
arXiv2001

Large pion pole in Z_{S}^{MOM}/Z_{P}^{MOM} from Wilson action data

We show that, contrarily to recent claims, data from the Wilson (unimproved) fermionic action at three different beta values demonstrate the presence of a large Goldstone boson contribution in the quark pseudoscalar vertex, quantitatively close to our previous estimate based on the SW action with c_{SW}=1.769. We show that discretisation errors on Z_{S}^{MOM}/Z_{P}^{MOM} seem to be much smaller than the Goldstone pole contribution over a very large range of momenta. The subtraction of this non perturbative contribution leads to numbers close to one-loop BPT.

hep-lat↗
arXiv2000

Lattice calculation of $1/p^2$ corrections to $α_s$ and of $Λ_{\rm {QCD}}$ in the $\widetilde{MOM}$ scheme

We report on very strong evidence of the occurrence of power terms in $\as(p)$, the QCD running coupling constant in the $\widetilde{MOM}$ scheme, by analyzing non-perturbative measurements from the lattice three-gluon vertex between 2.0 and 10.0 GeV at zero flavor. While putting forward the caveat that this definition of the coupling is a gauge dependent one, the general relevance of such an occurrence is discussed. We fit $Λ_{\bar{\rm MS}}^{(n_f=0)}= 237 \pm 3 ^{+ 0}_{-10}$ MeV in perfect agreement with the result obtained by the ALPHA group with a totally different method. The power correction to $\as(p)$ is fitted to $(0.63\pm 0.03 ^{+ 0.0}_{- 0.13}) {\rm GeV}^2/p^2$.

hep-ph↗
arXiv1999

Pseudoscalar Vertex and Quark Masses

We analyse available data on the quark pseudoscalar vertex and extract the contribution og the Goldstone boson pole. The strength of the pole is found to be quite large at presently accessible scales. We draw the important consequences of this finding for the various definitions of quark masses.

hep-lat↗
arXiv1999

Pseudoscalar Vertex, Goldstone Boson and Quark Masses on the Lattice

We analyse the Structure Function collaboration data on the quark pseudoscalar vertex and extract the Goldstone boson pole contribution, in 1/p2. The strength of the pole is found to be quite large at presently accessible scales. We draw the important consequences of this finding for the various definitions of quark masses, and point out potential problems with the operator product expansion.

hep-lat↗
arXiv1998

Search for 1/p^2 Corrections to the Running QCD Coupling

We investigate the occurrence of power terms in the running QCD coupling by analysing non-perturbative measurements of alpha_s (p) at low momenta obtained from the lattice three-gluon vertex. Our exploratory study provides some evidence for power contributions to alpha_s (p) proportional to 1/p^2. Possible implications for physical observables are discussed.

hep-ph↗
arXiv1998

Search for Lambda^2/p^2 corrections to the QCD running coupling

We investigate the occurrence of power terms $(Lambda^2/p^2$ in the running QCD coupling by analysing non-perturbative measurements of $α_s(p)$ at quite low momenta obtained from the lattice three-gluon vertex. Our study provides some evidence for such a contribution. The phenomenological implications of such a presence are reviewed.

hep-lat↗
arXiv1998

The running QCD coupling in the pre-asymptotic region

We study deviations from the perturbative asymptotic behaviour in the running QCD coupling by analysing non-perturbative measurements of alpha_s (p) at low momenta as obtained from the lattice three-gluon vertex. Our exploratory study provides some evidence for power corrections to the perturbative running proportional to 1/p^2.

hep-ph↗
arXiv1997

Alpha_s from the non-perturbatively renormalised lattice three-gluon vertex

We compute the running QCD coupling on the lattice by evaluating two-point and three-point off-shell gluon Green's functions in a fixed gauge and imposing non-perturbative renormalisation conditions on them. Our exploratory study is performed in the quenched approximation at beta=6.0 on 16^4 and 24^4 lattices. We show that, for momenta in the range 1.8-2.3 Gev, our coupling runs according to the two-loop asymptotic formula, allowing a precise determination of the corresponding Lambda parameter. The role of lattice artifacts and finite-volume effects is carefully analysed and these appear to be under control in the momentum range of interest. Our renormalisation procedure corresponds to a momentum subtraction scheme in continuum field theory, and therefore lattice perturbation theory is not needed in order to match our results to the MSbar scheme, thus eliminating a major source of uncertainty in the determination of alpha_MSbar. Our method can be applied directly to the unquenched case.

hep-lat↗
arXiv1995

The Strong Coupling Constant from the Lattice 3-Gluon Vertex

We compute the QCD running coupling on the lattice as defined from the 3-gluon vertex. We present the results of an exploratory study at $β=6.0$ on a $16^4$ lattice, which show that for momenta larger than 2 \Gev, the coupling runs according to the 2-loop asymptotic formula, allowing a precise determination of the $Λ$ parameter. Our renormalization procedure corresponds to a momentum subtraction scheme in the continuum and, most remarkably, one does not need lattice perturbation theory to match the results to MSbar scheme. We obtain $α^{\MSB}(M_Z) = 0.115 \pm 0.003 \pm 0.008$.

hep-lat↗
arXiv1994

A General Method for Non-Perturbative Renormalization of Lattice Operators

We propose a non-perturbative method for computing the renormalization constants of generic composite operators. This method is intended to reduce some systematic errors, which are present when one tries to obtain physical predictions from the matrix elements of lattice operators. We also present the results of a calculation of the renormalization constants of several two-fermion operators, obtained, with our method, by numerical simulation of $QCD$, on a $16^3 \times 32$ lattice, at $β=6.0$. The results of this simulation are encouraging, and further applications to four-fermion operators and to the heavy quark effective theory are proposed.

hep-lat↗