278 research outputs found
Large center vortices and confinement in 3D Z(2) gauge theory
We study the role of large clusters of center vortices in producing
confinement in 3D Z(2) gauge theory. First, we modify each configuration of a
Monte Carlo-generated ensemble in the confined phase by removing the largest
cluster of center vortices, and show that the ensemble thus obtained does not
confine. Conversely, we show that removing all of the small clusters of center
vortices and leaving the largest one only, confinement is preserved, albeit
with a string tension significantly smaller than the original one. Remarkably,
also the string corrections due to the quantum fluctuations of the confining
flux tube are preserved by this transformation.Comment: 8 pages,5 figure
Monopole clusters, center vortices, and confinement in a Z(2) gauge-Higgs system
We propose to use the different kinds of vacua of the gauge theories coupled
to matter as a laboratory to test confinement ideas of pure Yang-Mills
theories. In particular, the very poor overlap of the Wilson loop with the
broken string states supports the 't Hooft and Mandelstam confinement criteria.
However in the Z(2) gauge-Higgs model we use as a guide we find that the
condensation of monopoles and center vortices is a necessary, but not
sufficient condition for confinement.Comment: 13 pages, 6 figures, minor changes, version to be published on Phys.
Rev.
Random percolation as a gauge theory
Three-dimensional bond or site percolation theory on a lattice can be
interpreted as a gauge theory in which the Wilson loops are viewed as counters
of topological linking with random clusters. Beyond the percolation threshold
large Wilson loops decay with an area law and show the universal shape effects
due to flux tube quantum fluctuations like in ordinary confining gauge
theories. Wilson loop correlators define a non-trivial spectrum of physical
states of increasing mass and spin, like the glueballs of ordinary gauge
theory. The crumbling of the percolating cluster when the length of one
periodic direction decreases below a critical threshold accounts for the finite
temperature deconfinement, which belongs to 2-D percolation universality class.Comment: 20 pages, 14 figure
XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504
We present the temporal analysis of X-ray observations of the radio-loud
Narrow-Line Seyfert 1 galaxy (NLS1) PKS 0558-504 obtained during the XMM-Newton
Calibration and Performance Verification (Cal/PV) phase. The long term light
curve is characterized by persistent variability with a clear tendency for the
X-ray continuum to harden when the count rate increases. Another strong
correlation on long time scales has been found between the variability in the
hard band and the total flux. On shorter time scales the most relevant result
is the presence of smooth modulations, with characteristic time of ~ 2 hours
observed in each individual observation. The short term spectral variability
turns out to be rather complex but can be described by a well defined pattern
in the hardness ratio-count rate plane.Comment: 6 pages, 7 figures, accepted for publication in A&A special issue on
first results from XM
Some universal features of the effective string picture of pure gauge theories
The effective string describing the large distance behaviour of the quark
sources of gauge field theories in the confining phase in D=3 or D=4 space-time
dimensions can be formulated, in the infrared limit, as a suitable 2D conformal
field theory on surfaces with quark loops as boundaries. Recent results on
self-avoiding random surfaces allow to fix almost uniquely such a conformal
theory. As a consequence, some universal relationships among the string tension
, the thickness of the colour flux tube, the deconfinement temperature and a
lower bound of the glueball mass spectrum are found. The general agreement with
the data extracted from recent lattice simulations with different gauge groups
is rather impressive.(Talk held by F.Gliozzi at Lattice'92 , Amsterdam)Comment: 9 pages(LaTeX),DFTT61/9
The nature of a broad line radio galaxy: Simultaneous RXTE and Chandra HETG observations of 3C 382
We present the results from simultaneous chandra and rxte observations of the
X-ray bright Broad-Line Radio Galaxy (BLRG) 3C 382. The long (120 ks) exposure
with chandra HETG allows a detailed study of the soft X-ray continuum and of
the narrow component of the Fe Kalpha line. The rxte PCA data are used to put
an upper limit on the broad line component and constrain the hard X-ray
continuum. A strong soft excess below 1 keV is observed in the time-averaged
HETG spectrum, which can be parameterized with a steep power law or a thermal
model. The flux variability at low energies indicates that the origin of the
soft excess cannot be entirely ascribed to the circumnuclear diffuse emission,
detected by chandra on scales of 20-30 arcsec (22-33 kpc). A narrow (sigma<90
eV) Fe Kalpha line (with EW< 100 eV) is observed by the chandra HEG. Similar
values for the line parameters are measured by the rxte PCA, suggesting that
the contribution from a broad line component is negligible. The fact that the
exposure is split into two observations taken three days apart allows us to
investigate the spectral and temporal evolution of the source on different
timescales. Significant flux variability associated with spectral changes is
observed on timescales of hours and days. The spectral variability is similar
to that observed in radio-quiet AGN ruling out a jet-dominated origin of the
X-rays.Comment: 19 pages, 10 figures, 3 tables, accepted for publication in Ap
A Very Radio-Loud Narrow-Line Seyfert 1: PKS 2004-447
We have discovered a very radio-loud Narrow-Line Seyfert 1 candidate: PKS
2004-447. This Seyfert is consistent with the formal definition for NLS1s,
although it does not have quite the same spectral features as some typical
members of this subclass. Only ROSAT survey data is available at X-ray
wavelengths, so it has not been possible to compare this source with other
NLS1s at these wavelengths. A full comparison of this source with other members
of the subclass will improve our physical understanding of NLS1s. In addition,
using standard calculations, we estimate the central black hole to have a mass
of . This does not agree with predictions in the
literature, that radio-loud AGN host very massive black holes.Comment: 15 pages, 4 figures, accepted for publication in ApJ, minor typos
change
Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C390.3
We present XMM and Suzaku observations of the Broad-Line Radio Galaxy (BLRG)
3C390.3. The Fe Ka line has a width FWHM ~ 8,800 km/s, consistent within a
factor two with the width of the double-peaked H_alpha line, suggesting an
origin from the Broad Line Region. The data show for the first time a weak,
broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid
energy is 6.6 keV in the source's rest-frame with FWHM of 43,000 km/s and EW of
50 eV; its most likely interpretation is emission from He-like Fe (Fe XXV),
suggesting the presence of an ionized medium in the inner regions of 3C390.3.
The broad-band 0.5-100 keV continuum is well described by a single power law
with photon index Gamma=1.6 and cutoff energy 157 keV, plus cold reflection
with strength R=0.5. In addition, ionized reflection is required to account for
the 6.6 keV bump in the broad-band continuum, yielding an ionization parameter
xi ~ 2700 ergs cm s^-1; the inner radius of the ionized reflector is
constrained to be larger than 20 r_G, although this result depends on the
assumed emissivity profile of the disk. If true, we argue that the lack of
broad Fe K emission from within 20 r_G indicates that the innermost regions of
the disk in 3C390.3 are obscured and/or poorly illuminated. While the SED of
3C390.3 is generally dominated by accretion-related continuum, during accretion
low states the jet can significantly contribute in the optical to X-ray bands
via synchrotron self-Compton emission. (Abridged)Comment: 7 figures, 5 tables, accepted for publication in Ap
Semen quality of Italian local pig breeds
From 1996 to 1999 a conservation programme was carried out within the framework of EC contract "European gene banking project for the pig genetic resources" (Ollivier et al., 2001) in the Italian local pig breeds. The aims of the program included the primary characterization of the breeds, i.e. information on the organization in charge of the breed, breeding population numbers, breed description and qualifications, and field trials on productive and reproductive performances. In this context the "Semen Bank of Italian local pig breeds" was built. A total of 30,835 straws of four Italian local pig breeds (Cinta Senese, Casertana, Mora Romagnola and Nero Siciliano), collected from 42 sires, have been stored. In this work semen quality traits, lipid composition and freezability of the four Italian local pig breeds are reported
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