708 research outputs found
Two flavor QCD and Confinement
We argue that the order of the chiral transition for N_f=2 is a sensitive
probe of the QCD vacuum, in particular of the mechanism of color confinement. A
strategy is developed to investigate the order of the transition by use of
finite size scaling analysis. An in-depth numerical investigation is performed
with staggered fermions on lattices with N_t=4 and N_s=12,16,20,24,32 and quark
masses am_q ranging from 0.01335 to 0.307036. The specific heat and a number of
susceptibilities are measured and compared with the expectations of an O(4)
second order and of a first order phase transition. A second order transition
in the O(4) and O(2) universality classes are excluded. Substantial evidence
emerges for a first order transition. A detailed comparison with previous works
is performed.Comment: 46 pages, 20 eps figures, 9 tables, REVTeX
Direct numerical computation of disorder parameters
In the framework of various statistical models as well as of mechanisms for
color confinement, disorder parameters can be developed which are generally
expressed as ratios of partition functions and whose numerical determination is
usually challenging. We develop an efficient method for their computation and
apply it to the study of dual superconductivity in 4d compact U(1) gauge
theory.Comment: 5 pages, 6 figures. Final revised version published in PR
Chiral Transition of N=4 Super Yang-Mills with Flavor on a 3-Sphere
We use the AdS/CFT correspondence to perform a numerical study of a phase
transition in strongly-coupled large-Nc N = 4 Super-Yang-Mills theory on a
3-sphere coupled to a finite number Nf of massive N = 2 hypermultiplets in the
fundamental representation of the gauge group. The gravity dual system is a
number Nf of probe D7-branes embedded in AdS_5 x S^5. We draw the phase diagram
for this theory in the plane of hypermultiplet mass versus temperature and
identify for temperatures above the Hawking-Page deconfinement temperature a
first-order phase transition line across which the chiral condensate jumps
discontinuously.Comment: 23 pages, 15 figures, minor corrections, reference added, nine
figures improved, no change in results or conclusions; expanded discussion of
fixing finite counterterms in section 3.3, figures updated, no changes to
conclusion
SXP 7.92: A Recently Rediscovered Be/X-ray Binary in the Small Magellanic Cloud, Viewed Edge On
We present a detailed optical and X-ray study of the 2013 outburst of the Small Magellanic Cloud Be/X-ray binary SXP 7.92, as well as an overview of the last 18 years of observations from OGLE (Optical Gravitational Lensing Experiment), RXTE, Chandra and XMM-Newton. We revise the position of this source to RA(J2000) = 00:57:58.4, Dec(J2000) = â72:22:29.5 with a 1Ï uncertainty of 1.5 arcsec, correcting the previously reported position by Coe et al. by more than 20 arcmin. We identify and spectrally classify the correct counterpart as a B1Ve star. The optical spectrum is distinguished by an uncharacteristically deep narrow Balmer series, with the Hα line in particular having a distinctive shell profile, i.e. a deep absorption core embedded in an emission line. We interpret this as evidence that we are viewing the system edge on and are seeing self-obscuration of the circumstellar disc. We derive an optical period for the system of 40.0 ±â0.3 d, which we interpret as the orbital period, and present several mechanisms to describe the X-ray/optical behaviour in the recent outburst, in particular the âflares'and âdipsâ seen in the optical light curve, including a transient accretion disc and an elongated precessing disc
Holographic Roberge-Weiss Transitions
We investigate N=4 SYM coupled to fundamental flavours at nonzero imaginary
quark chemical potential in the strong coupling and large N limit, using
gauge/gravity duality applied to the D3-D7 system, treating flavours in the
probe approximation. The interplay between Z(N) symmetry and the imaginary
chemical potential yields a series of first-order Roberge-Weiss transitions. An
additional thermal transition separates phases where quarks are bound/unbound
into mesons. This results in a set of Roberge-Weiss endpoints: we establish
that these are triple points, determine the Roberge-Weiss temperature, give the
curvature of the phase boundaries and confirm that the theory is analytic in
mu^2 when mu^2~0.Comment: 37 pages, 13 figures; minor comments added, to appear in JHE
Motor Current Cyclic-Non-Stationary Analysis for Bearing Diagnostic
The Motor Current Signature Analysis (MCSA) is a research area focused on the diagnosis of components of
electric motors based on post-processing of the current signal mainly. In particular, the bearing diagnostics
is based on two different assumptions: the fault on the bearing causes a vibration of the shaft it supports,
so there is an air gap variation between stator and rotor causing a modulation in the current signal; the fault
on the bearing hinders the rotation of the shaft, so it can be modeled as an additional loading torque that
the motor satisfies increasing the current signal. In this paper, a cyclic-non-stationarity analysis of the motor
current is used to assess the status of ball-bearings in servomotors, running at variable speed. Both speed of
the motor and motor current are provided by the control loop of the servomotor, that is no external sensors
are used. The cyclic nature of the application allows an average of the cyclic-cyclic order maps to increase
the signal-to-noise ratio. The proposed technique is successfully applied to both healthy and faulty bearings
Dynamical Symmetry Breaking in Models with the Yukawa Interaction
We discuss models with a massless fermion and a self-interacting massive
scalar field with the Yukawa interaction. The chiral condensate and the fermion
mass are calculated analytically. It is shown that the models have a phase
transition as a function of the squared mass of the scalar field.Comment: 7 pages, no figures, in Eqs. (7) and (11) one coefficient was change
Low-energy theorems of QCD and bulk viscosity at finite temperature and baryon density in a magnetic field
The nonperturbative QCD vacuum at finite temperature and a finite baryon
density in an external magnetic field is studied. Equations relating
nonperturbative condensates to the thermodynamic pressure for , and are obtained, and low-energy theorems are derived. A bulk
viscosity is expressed in terms of basic thermodynamical
quantities describing the quark-gluon matter at , , and
. Various limiting cases are also considered.Comment: 12 pages; v2: title changed, new section about bulk viscosity and new
references added; v3: new discussion adde
Topological susceptibility in Yang-Mills theory in the vacuum correlator method
We calculate the topological susceptibility of the Yang-Mills vacuum using
the field correlator method. Our estimate for the SU(3) gauge group, \chi^{1/4}
= 196(7) MeV, is in a very good agreement with the results of recent numerical
simulations of the Yang-Mills theory on the lattice.Comment: 5 pages (JETP Letters style
Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD
We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.Comment: 14 pages, LaTeX file, + 6 PS figure
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