Fidelity approach to the disordered quantum XY model

We study the random XY spin chain in a transverse field by analyzing the susceptibility of the ground state fidelity, numerically evaluated through a standard mapping of the model onto quasi-free fermions. It is found that the fidelity susceptibility and its scaling properties provide useful information about the phase diagram. In particular it is possible to determine the Ising critical line and the Griffiths phase regions, in agreement with previous analytical and numerical results.Comment: 4 pages, 3 figures; references adde

Constituent quarks, chiral symmetry, and chiral point of the constituent quark model

We construct the full axial current of the constituent quarks by a summation of the infinite number of diagrams describing constituent-quark soft interactions. By requiring that the conservation of this current is violated only by terms of order $O(M_\pi^2)$, where $M_\pi$ is the mass of the lowest pseudoscalar $\bar QQ$ bound state, we derive important constraints on (i) the axial coupling $g_A$ of the constituent quark and (ii) the $\bar QQ$ potential at large distances. We define the chiral point of the constituent quark model as those values of the parameters, such as the masses of the constituent quarks and the couplings in the $\bar QQ$ potential, for which $M_\pi$ vanishes. At the chiral point the main signatures of the spontaneously broken chiral symmetry are shown to be present, namely: the axial current of the constituent quarks is conserved, the leptonic decay constants of the excited pseudoscalar bound states vanish, and the pion decay constant has a nonzero value.Comment: 10 pages, typo in eq. (46) of the published version is correcte

SMAUG: a new technique for the deprojection of galaxy clusters

This paper presents a new technique for reconstructing the spatial distributions of hydrogen, temperature and metal abundance of a galaxy cluster. These quantities are worked out from the X-ray spectrum, modeled starting from few analytical functions describing their spatial distributions. These functions depend upon some parameters, determined by fitting the model to the observed spectrum. We have implemented this technique as a new model in the XSPEC software analysis package. We describe the details of the method, and apply it to work out the structure of the cluster A1795. We combine the observation of three satellites, exploiting the high spatial resolution of Chandra for the cluster core, the wide collecting area of XMM-Newton for the intermediate regions and the large field of view of Beppo-SAX for the outer regions. We also test the validity and precision of our method by i) comparing its results with those from a geometrical deprojection, ii) examining the spectral residuals at different radii of the cluster and iii) reprojecting the unfolded profiles and comparing them directly to the measured quantities. Our analytical method yields the parameters defining the spatial functions directly from the spectra. Their explicit knowledge allows a straightforward derivation of other indirect physical quantities like the gravitating mass, as well as a fast and easy estimate of the profiles uncertainties.Comment: 24 pages, 11 figures, 3 tables; emulateapj; accepted for publication in the Astrophysical Journa

On the Fe abundance peak formation in cool-core clusters of galaxies: hints from cluster WARPJ1415.1+3612 at z=1.03

We present a detailed study of the iron content of the core of the high-redshift cluster WARPJ1415.1+3612 (z=1.03). By comparing the central Fe mass excess observed in this system, M_Fe^exc = (1.67 +/- 0.40) x 10^9 M_sun, with those measured in local cool-core systems, we infer that the bulk of the mass excess was already in place at z=1, when the age of the Universe was about half of what it is today. Our measures point to an early and intense period of star formation most likely associated with the formation of the BCG. Indeed, in the case of the power-law delay time distribution with slope -1, which reproduces the data of WARPJ1415.1+3612 best, half of the supernovae explode within 0.4 Gyr of the formation of the BCG. Finally, while for local cool-core clusters the Fe distribution is broader than the near infrared light distribution of the BCG, in WARPJ1415.1+3612 the two distributions are consistent, indicating that the process responsible for broadening the Fe distribution in local systems has not yet started in this distant cluster.Comment: 10 pages, accepted for publication in A&A, minor language corrections added in v

Radiative cooling, heating and thermal conduction in M87

The crisis of the standard cooling flow model brought about by Chandra and XMM-Newton observations of galaxy clusters, has led to the development of several models which explore different heating processes in order to assess if they can quench the cooling flow. Among the most appealing mechanisms are thermal conduction and heating through buoyant gas deposited in the ICM by AGNs. We combine Virgo/M87 observations of three satellites (Chandra, XMM-Newton and Beppo-SAX) to inspect the dynamics of the ICM in the center of the cluster. Using the spectral deprojection technique, we derive the physical quantities describing the ICM and determine the extra-heating needed to balance the cooling flow assuming that thermal conduction operates at a fixed fraction of the Spitzer value. We assume that the extra-heating is due to buoyant gas and we fit the data using the model developed by Ruszkowski and Begelman (2002). We derive a scale radius for the model of $\sim 5$ kpc, which is comparable with the M87 AGN jet extension, and a required luminosity of the AGN of a $few \times 10^{42}$ erg s$^{-1}$, which is comparable to the observed AGN luminosity. We discuss a scenario where the buoyant bubbles are filled of relativistic particles and magnetic field responsible for the radio emission in M87. The AGN is supposed to be intermittent and to inject populations of buoyant bubbles through a succession of outbursts. We also study the X-ray cool component detected in the radio lobes and suggest that it is structured in blobs which are tied to the radio buoyant bubbles.Comment: 25 pages, 10 figures and 2 tables. Accepted for publication in Ap

Bipartite quantum states and random complex networks

We introduce a mapping between graphs and pure quantum bipartite states and show that the associated entanglement entropy conveys non-trivial information about the structure of the graph. Our primary goal is to investigate the family of random graphs known as complex networks. In the case of classical random graphs we derive an analytic expression for the averaged entanglement entropy $\bar S$ while for general complex networks we rely on numerics. For large number of nodes $n$ we find a scaling $\bar{S} \sim c \log n +g_e$ where both the prefactor $c$ and the sub-leading O(1) term $g_e$ are a characteristic of the different classes of complex networks. In particular, $g_e$ encodes topological features of the graphs and is named network topological entropy. Our results suggest that quantum entanglement may provide a powerful tool in the analysis of large complex networks with non-trivial topological properties.Comment: 4 pages, 3 figure

Validation of landslide hazard assessment by means of GPS monitoring technique ? a case study in the Dolomites (Eastern Alps, Italy)

International audienceIn the last years a research project aimed at the assessment of the landslide hazard and susceptibility in the high Cordevole river basin (Eastern Dolomites, Italy) have been carried out. The hazard map was made adopting the Swiss Confederation semi-deterministic approach that takes into account parameters such as velocity, geometry and frequency of landslides. Usually these parameters are collected by means of geological and morphological surveys, historical archive researches, aerophotogrammetric analysis etc. In this framework however the dynamics of an instable slope can be difficult to determine. This work aims at illustrating some progress in landslide hazard assessment using a modified version of the Swiss Confederation semi-deterministic approach in which the values of some parameters have been refined in order to accomplish more reliable results in hazard assessment. A validation of the accuracy of these new values, using GPS and inclinometric measurements, has been carried out on a test site located inside the high Cordevole river basin