4,692 research outputs found
Can the Electroweak Interaction Break Itself?
I examine the possibility that the electroweak interaction breaks itself via
the condensation of fermions in large representations of the weak SU(2)_L gauge
group.Comment: 10 pages, Latex, no figures. Published in Phys. Lett. B340, 236
(1994)
Lattice QCD at finite isospin density at zero and finite temperature
We simulate lattice QCD with dynamical and quarks at finite chemical
potential, , for the third component of isospin (), at both zero
and at finite temperature. At zero temperature there is some ,
say, above which and parity are spontaneously broken by a charged pion
condensate. This is in qualitative agreement with the prediction of effective
(chiral) Lagrangians which also predict . This transition appears
to be second order, with scaling properties consistent with the mean-field
predictions of such effective Lagrangian models. We have also studied the
restoration of symmetry at high temperature for . For
sufficiently large, this finite temperature phase transition appears to
be first order. As is decreased it becomes second order connecting
continuously with the zero temperature transition.Comment: 23 pages, Revtex, 9 figures. Major revision of sections 3 and 4 to
include new analyses of critical scaling which we now find to be in the
universality class of mean-field theor
On the Triviality of Textbook Quantum Electrodynamics
By adding a small, irrelevant four fermi interaction to the action of lattice
Quantum Electrodynamics (QED), the theory can be simulated with massless quarks
in a vacuum free of lattice monopoles. This allows an ab initio high precision,
controlled study of the existence of "textbook" Quantum Electrodynamics with
several species of fermions. The lattice theory possesses a second order chiral
phase transition which we show is logarithmically trivial. The logarithms of
triviality, which modify mean field scaling laws, are pinpointed in several
observables. The result supports Landau's contention that perturbative QED
suffers from complete screening and would have a vanishing fine structure
constant in the absence of a cutoff.Comment: reference to Phys. Rev. Lett.80, 4119(1998) adde
Singular Structure in 4D Simplicial Gravity
We show that the phase transition previously observed in dynamical
triangulation models of quantum gravity can be understood as being due to the
creation of a singular link. The transition between singular and non-singular
geometries as the gravitational coupling is varied appears to be first order.Comment: 9 pages, 5 figures, 3 references adde
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
Polarization Properties of A Multi-Moded Concentrator
We present the design and performance of a non-imaging concentrator for use
in broad-band polarimetry at millimeter through submillimeter wavelengths. A
rectangular geometry preserves the input polarization state as the concentrator
couples f/2 incident optics to a 2 pi sr detector. Measurements of the co-polar
and cross-polar beams in both the few-mode and highly over-moded limits agree
with a simple model based on mode truncation. The measured co-polar beam
pattern is nearly independent of frequency in both linear polarizations. The
cross-polar beam pattern is dominated by a uniform term corresponding to
polarization efficiency 94%. After correcting for efficiency, the remaining
cross-polar response is -18 dB.Comment: 9 pages including 8 figures. Accepted for publication in the Journal
of the Optical Society of America
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
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