17,143 research outputs found
Finite-size scaling and the deconfinement transition in gauge theories
We introduce a new method for determining the critical indices of the
deconfinement transition in gauge theories. The method is based on the finite
size scaling behavior of the expectation value of simple lattice operators,
such as the plaquette. We test the method for the case of SU(3) pure gauge
theory in (2+1) dimensions and obtain a precise determination of the critical
index , in agreement with the prediction of the Svetitsky-Yaffe
conjecture.Comment: 6 pages. Several comments and one reference added, results unchange
q-Deformed quaternions and su(2) instantons
We have recently introduced the notion of a q-quaternion bialgebra and shown
its strict link with the SO_q(4)-covariant quantum Euclidean space R_q^4.
Adopting the available differential geometric tools on the latter and the
quaternion language we have formulated and found solutions of the
(anti)selfduality equation [instantons and multi-instantons] of a would-be
deformed su(2) Yang-Mills theory on this quantum space. The solutions depend on
some noncommuting parameters, indicating that the moduli space of a complete
theory should be a noncommutative manifold. We summarize these results and add
an explicit comparison between the two SO_q(4)-covariant differential calculi
on R_q^4 and the two 4-dimensional bicovariant differential calculi on the bi-
(resp. Hopf) algebras M_q(2),GL_q(2),SU_q(2), showing that they essentially
coincide.Comment: Latex file, 18 page
The spectrum of massive excitations of 3d 3-state Potts model and universality
We consider the mass spectrum of the 3 3-state Potts model in the broken
phase (a) near the second order Ising critical point in the temperature -
magnetic field plane and (b) near the weakly first order transition point at
zero magnetic field. In the case (a), we compare the mass spectrum with the
prediction from universality of mass ratios in the 3 Ising class; in the
case (b), we determine a mass ratio to be compared with the corresponding one
in the spectrum of screening masses of the (3+1) SU(3) pure gauge theory at
finite temperature in the deconfined phase near the transition. The agreement
in the comparison in the case (a) would represent a non-trivial test of
validity of the conjecture of spectrum universality. A positive answer to the
comparison in the case (b) would suggest the possibility to extend this
conjecture to weakly first order phase transitions.Comment: 20 pages, 12 figures; uses axodraw.st
Triggering Active Galactic Nuclei in Hierarchical Galaxy Formation: Disk instability vs. Interactions
Using a semi analytic model for galaxy formation we investigate the effects
of Black Hole accretion triggered by disk instabilities (DI) in isolated
galaxies on the evolution of AGN. Specifically, we took on, developed and
expanded the Hopkins & Quataert (2011) model for the mass inflow following disk
perturbations, and compare the corresponding evolution of the AGN population
with that arising in a scenario where galaxy interactions trigger AGN (IT
mode). We extended and developed the DI model by including different disk
surface density profiles, to study the maximal contribution of DI to the
evolution of the AGN population. We obtained the following results: i) for
luminosities corresponding to the DI mode can provide the
BH accretion needed to match the observed AGN luminosity functions up to ; in such a luminosity range and redshift, it can compete with the
IT scenario as the main driver of cosmological evolution of AGN; ii) The DI
scenario cannot provide the observed abundance of high-luminosity QSO with
AGN, as well as the abundance of high-redhshift QSOs with , while the IT scenario provides
an acceptable match up to , as found in our earliest works; iii)
The dispersion of the distributions of Eddington ratio for low- and
intermediate-luminosity AGN (bolometric = -
erg/s) is predicted to be much smaller in the DI scenario compared to the IT
mode; iv) The above conclusions are robust with respect to the explored
variants of the Hopkins & Quataert (2011) model. We discuss the physical origin
of our findings, and how it is possible to pin down the dominant fueling
mechanism in the low-intermediate luminosity range where
both the DI and the IT modes are viable candidates as drivers for the AGN
evolution.Comment: Accepted for publication in Astronomy & Astrophysics, 24 pages, 8
figures; updated reference
q-Quaternions and q-deformed su(2) instantons
We construct (anti)instanton solutions of a would-be q-deformed su(2)
Yang-Mills theory on the quantum Euclidean space R_q^4 [the SO_q(4)-covariant
noncommutative space] by reinterpreting the function algebra on the latter as a
q-quaternion bialgebra. Since the (anti)selfduality equations are covariant
under the quantum group of deformed rotations, translations and scale change,
by applying the latter we can generate new solutions from the one centered at
the origin and with unit size. We also construct multi-instanton solutions. As
they depend on noncommuting parameters playing the roles of `sizes' and
`coordinates of the centers' of the instantons, this indicates that the moduli
space of a complete theory will be a noncommutative manifold. Similarly, gauge
transformations should be allowed to depend on additional noncommutative
parameters.Comment: Latex file, 39 pages. Final version appeared in JM
Influence of disordered porous media in the anomalous properties of a simple water model
The thermodynamic, dynamic and structural behavior of a water-like system
confined in a matrix is analyzed for increasing confining geometries. The
liquid is modeled by a two dimensional associating lattice gas model that
exhibits density and diffusion anomalies, in similarity to the anomalies
present in liquid water. The matrix is a triangular lattice in which fixed
obstacles impose restrictions to the occupation of the particles. We show that
obstacules shortens all lines, including the phase coexistence, the critical
and the anomalous lines. The inclusion of a very dense matrix not only suppress
the anomalies but also the liquid-liquid critical point
The spectrum of screening masses near T_c: predictions from universality
We discuss the spectrum of screening masses in a pure gauge theory near the
deconfinement temperature from the point of view of the dimensionally reduced
model describing the spontaneous breaking of the center symmetry. Universality
arguments can be used to predict the values of the mass ratios in the scaling
region of the deconfined phase when the transition is of second order. One such
prediction is that the scalar sector of the screening spectrum in SU(2) pure
gauge theory contains a bound state of the fundamental excitation,
corresponding through universality to the bound state found in the 3D Ising
model and phi^4 theory in the broken symmetry phase. A Monte Carlo evaluation
of the screening masses in the gauge theory confirms the validity of the
prediction. We briefly discuss the possibility of using similar arguments for
first order deconfinement transitions, and in particular for the physically
relevant case of SU(3).Comment: 12 pages, 3 figures. Some changes in the discussion, added
references, results unchanged. Version to appear in Phys. Rev.
Quark-antiquark contribution to the BFKL kernel
The quark-antiquark contribution to the BFKL kernel is calculated. Using the
effective vertex for the pair production in the Reggeon-Reggeon
collision we find this contribution by integrating the square of this vertex
over relative transverse momenta and fractions of longitudinal momenta of
produced particles.Comment: 12 pages, Late
Multiphase gas flows in the nearby Seyfert galaxy ESO428-G14
We present ALMA rest-frame 230 GHz continuum and CO(2-1) line observations of
the nearby Compton-thick Seyfert galaxy ESO428-G14, with angular resolution 0.7
arcsec (78 pc). We detect CO(2-1) emission from spiral arms and a
circum-nuclear ring with 200 pc radius, and from a transverse gas lane with
size of pc, which crosses the nucleus and connects the two portions
the circumnuclear ring. The molecular gas in the host galaxy is distributed in
a rotating disk with intrinsic circular velocity km/s,
inclination deg, and dynamical mass within a radius of kpc. In the inner 100 pc region CO is
distributed in a equatorial bar, whose kinematics is highly perturbed and
consistent with an inflow of gas towards the AGN. This inner CO bar overlaps
with the most obscured, Compton-thick region seen in X-rays. We derive a column
density of in this region,
suggesting that molecular gas may contribute significantly to the AGN
obscuration. We detect a molecular outflow with a total outflow rate , distributed along a bi-conical structure with
size of pc on both sides of the AGN. The bi-conical outflow is also
detected in the emission line at 2.12 m, which traces a warmer
nuclear outflow located within 170 pc from the AGN. This suggests that the
outflow cools with increasing distance from the AGN. We find that the hard
X-ray emitting nuclear region mapped with Chandra is CO-deprived, but filled
with warm molecular gas traced by - thus confirming that the hard
(3-6 keV) continuum and Fe K emission are due to scattering from dense
neutral clouds in the ISM.Comment: Submitted to Ap
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