4,148 research outputs found
The pseudo-Goldstone spectrum of 2-colour QCD at finite density
We examine the spectrum of 2-colour lattice QCD with 4 continuum flavours at
a finite chemical potential () for quark-number, on a
lattice. First we present evidence that the system undergoes a transition to a
state with a diquark condensate, which spontaneously breaks quark number at
, and that this transition is mean field in nature. We then
examine the 3 states that would be Goldstone bosons at for zero Dirac
and Majorana quark masses. The predictions of chiral effective Lagrangians give
a good description of the behaviour of these masses for . Except
for the heaviest of these states, these predictions diverge from our
measurements, once is significantly greater than . However, the
qualitative behaviour of these masses, indicates that the physics is very
similar to that predicted by these effective Lagrangians, and there is some
indication that at least part of these discrepancies is due to saturation, a
lattice artifact.Comment: 32 pages LaTeX/Revtex, 8 Postscript figure
Heavy Dynamical Fermions in Lattice QCD
It is expected that the only effect of heavy dynamical fermions in QCD is to
renormalize the gauge coupling. We derive a simple expression for the shift in
the gauge coupling induced by flavors of heavy fermions. We compare this
formula to the shift in the gauge coupling at which the
confinement-deconfinement phase transition occurs (at fixed lattice size) from
numerical simulations as a function of quark mass and . We find remarkable
agreement with our expression down to a fairly light quark mass. However,
simulations with eight heavy flavors and two light flavors show that the eight
flavors do more than just shift the gauge coupling. We observe
confinement-deconfinement transitions at induced by a large number of
heavy quarks. We comment on the relevance of our results to contemporary
simulations of QCD which include dynamical fermions.Comment: COLO-HEP-311, 26 pages and 6 postscript figures; file is a shar file
and all macros are (hopefully) include
Universality class for bootstrap percolation with on the cubic lattice
We study the bootstrap percolation model on a cubic lattice, using
Monte Carlo simulation and finite-size scaling techniques. In bootstrap
percolation, sites on a lattice are considered occupied (present) or vacant
(absent) with probability or , respectively. Occupied sites with less
than occupied first-neighbours are then rendered unoccupied; this culling
process is repeated until a stable configuration is reached. We evaluate the
percolation critical probability, , and both scaling powers, and
, and, contrarily to previous calculations, our results indicate that the
model belongs to the same universality class as usual percolation (i.e.,
). The critical spanning probability, , is also numerically
studied, for systems with linear sizes ranging from L=32 up to L=480: the value
we found, , is the same as for usual percolation with
free boundary conditions.Comment: 11 pages; 4 figures; to appear in Int. J. Mod. Phys.
ARCADE: Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission
The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission
(ARCADE) is a balloon-borne instrument designed to measure the temperature of
the cosmic microwave background at centimeter wavelengths. ARCADE searches for
deviations from a blackbody spectrum resulting from energy releases in the
early universe. Long-wavelength distortions in the CMB spectrum are expected in
all viable cosmological models. Detecting these distortions or showing that
they do not exist is an important step for understanding the early universe. We
describe the ARCADE instrument design, current status, and future plans.Comment: 12 pages, 6 figures. Proceedings of the Fundamental Physics With CMB
workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy
Review
The Phase Diagram of Compact QED Coupled to a Four-Fermi Interaction
Compact lattice Quantum Electrodynamics (QED) with four species of fermions
is simulated with massless quarks by using the QED scheme of adding a
four-fermi interaction to the action. Simulations directly in the chiral limit
of massless quarks are done with high statistics on , and lattices,
and the phase diagram, parameterized by the gauge and the four-fermi couplings,
is mapped out. The line of monopole condensation transitions is separate from
the line of chiral symmetry restoration. The simulation results indicate that
the monopole condensation transition is first order while the chiral transition
is second order. The challenges in determining the Universality class of the
chiral transition are discussed. If the scaling region for the chiral
transition is sufficiently wide, the simulations predict critical
indices far from mean field values. We discuss a speculative scenario in which
anti-screening provided by double-helix strands of monopole and anti-monopole
loops are the agent that balances the screening of fermion anti-fermion pairs
to produce an ultra-violet fixed point in the electric coupling.Comment: 29 pages, 8 figures and 2 table
Thermodynamics of two-colour QCD and the Nambu Jona-Lasinio model
We investigate two-flavour and two-colour QCD at finite temperature and
chemical potential in comparison with a corresponding Nambu and Jona-Lasinio
model. By minimizing the thermodynamic potential of the system, we confirm that
a second order phase transition occurs at a value of the chemical potential
equal to half the mass of the chiral Goldstone mode. For chemical potentials
beyond this value the scalar diquarks undergo Bose condensation and the diquark
condensate is nonzero. We evaluate the behaviour of the chiral condensate, the
diquark condensate, the baryon charge density and the masses of scalar diquark,
antidiquark and pion, as functions of the chemical potential. Very good
agreement is found with lattice QCD (N_c=2) results. We also compare with a
model based on leading-order chiral effective field theory.Comment: 24 pages, 12 figure
The QCD Phase Diagram at Nonzero Temperature, Baryon and Isospin Chemical Potentials in Random Matrix Theory
We introduce a random matrix model with the symmetries of QCD at finite
temperature and chemical potentials for baryon number and isospin. We analyze
the phase diagram of this model in the chemical potential plane for different
temperatures and quark masses. We find a rich phase structure with five
different phases separated by both first and second order lines. The phases are
characterized by the pion condensate and the chiral condensate for each of the
flavors. In agreement with lattice simulations, we find that in the phase with
zero pion condensate the critical temperature depends in the same way on the
baryon number chemical potential and on the isospin chemical potential. At
nonzero quark mass, we remarkably find that the critical end point at nonzero
temperature and baryon chemical potential is split in two by an arbitrarily
small isospin chemical potential. As a consequence, there are two crossovers
that separate the hadronic phase from the quark-gluon plasma phase at high
temperature. Detailed analytical results are obtained at zero temperature and
in the chiral limit.Comment: 13 pages, 5 figures, REVTeX
Phase structure of lattice QCD at finite temperature for 2+1 flavors of Kogut-Susskind quarks
We report on a study of the finite-temperature chiral transition on an
lattice for 2+1 flavors of Kogut-Susskind quarks. We find the point of
physical quark masses to lie in the region of crossover, in agreement with
results of previous studies. Results of a detailed examination of the
case indicate vanishing of the screening mass of meson
at the end point of the first-order transition.Comment: LATTICE98(hightemp), 3 pages, 4 figure
String Theory and the Fuzzy Torus
We outline a brief description of non commutative geometry and present some
applications in string theory. We use the fuzzy torus as our guiding example.Comment: Invited review for IJMPA rev1: an imprecision corrected and a
reference adde
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