512 research outputs found
The Stefan-Boltzmann law in a small box and the pressure deficit in hot SU(N) lattice gauge theory
The blackbody radiation in a box L^3 with periodic boundary conditions in
thermal equilibrium at a temperature T is affected by finite-size effects.
These bring about modifications of the thermodynamic functions which can be
expressed in a closed form in terms of the dimensionless parameter LT. For
instance, when LT~4 - corresponding to the value where the most reliable SU(N)
gauge lattice simulations have been performed above the deconfining temperature
T_c - the deviation of the free energy density from its thermodynamic limit is
about 5%. This may account for almost half of the pressure deficit observed in
lattice simulations at T~ 4 T_c.Comment: 9 pages, 2 figures v2:a side remark on the final result and
references adde
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
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.
String effects and the distribution of the glue in mesons at finite temperature
The distribution of the gluon action density in mesonic systems is
investigated at finite temperature. The simulations are performed in quenched
QCD for two temperatures below the deconfinment phase. Unlike the gluonic
profiles displayed at T=0, the action density iso-surfaces display a
prolate-spheroid like shape. The curved width profile of the flux-tube is found
to be consistent with the prediction of the free Bosonic string model at large
distances.Comment: 14 pages,10 figure
Non-Perturbative Green's Functions in Theories with Extended Superconformal Symmetry
The multiplets that occur in four dimensional rigidly supersymmetric theories
can be described either by chiral superfields in Minkowski superspace or
analytic superfields in harmonic superspace. The superconformal Ward identities
for Green's functions of gauge invariant operators of these types are derived.
It is shown that there are no chiral superconformal invariants. It is further
shown that the Green's functions of analytic operators are severely restricted
by the superconformal Ward when analyticity is taken into account.Comment: 17 pages, plain tex. Some conjectures that were in the original paper
are clarifed in the light of more recent work to which we give references.
See Note added for detail
A novel approach to the analysis of human growth
OBJECTIVES: Several formulations have been proposed in order to model human growth from birth to maturity. They are usually based on âad hocâ heuristic assumptions. In the present contribution we adopt, as an alternative, a completely general (interdisciplinary) approach, based on the formalism of the Phenomenological Universalities (PUN). METHODS: The main PUN class investigated to date, i.e. UN, can only account for the overall growth pattern. For a realistic description it is necessary to add to it one or more âspurtsâ, as expected on biological grounds, due to the stimulation of growth and sex hormones. RESULTS: A new PUN class (UNâ+âFM) is generated and shown to be able to provide excellent agreement with standard auxological datasets. The accuracy of the fitting and reliability of the model suggest applications both at the diagnostic and therapeutic level. CONCLUSIONS: The developed formalism can be suitably related to the biological description of bone plate growth under selective hormonal stimulation on the bone epiphysis; i.e., the additional increase of stature is the âmacroscopicâ response to a well defined biological signal
Tricritical Points in Random Combinatorics: the (2+p)-SAT case
The (2+p)-Satisfiability (SAT) problem interpolates between different classes
of complexity theory and is believed to be of basic interest in understanding
the onset of typical case complexity in random combinatorics. In this paper, a
tricritical point in the phase diagram of the random -SAT problem is
analytically computed using the replica approach and found to lie in the range
. These bounds on are in agreement with previous
numerical simulations and rigorous results.Comment: 7 pages, 1 figure, RevTeX, to appear in J.Phys.
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
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