6,479 research outputs found
When is the deconfinement phase transition universal?
Pure Yang-Mills theory has a finite-temperature phase transition, separating
the confined and deconfined bulk phases. Svetitsky and Yaffe conjectured that
if this phase transition is of second order, it belongs to the universality
class of transitions for particular scalar field theories in one lower
dimension. We examine Yang-Mills theory with the symplectic gauge groups Sp(N).
We find new evidence supporting the Svetitsky-Yaffe conjecture and make our own
conjecture as to which gauge theories have a universal second order
deconfinement phase transition.Comment: 5 pages, 4 figures; Contribution to Confinement 2003, Tokyo, Japan,
July 21-24, 200
Rotor Spectra, Berry Phases, and Monopole Fields: from Antiferromagnets to QCD
The order parameter of a finite system with a spontaneously broken continuous
global symmetry acts as a quantum mechanical rotor. Both antiferromagnets with
a spontaneously broken spin symmetry and massless QCD with a broken
chiral symmetry have rotor spectra when considered in
a finite volume. When an electron or hole is doped into an antiferromagnet or
when a nucleon is propagating through the QCD vacuum, a Berry phase arises from
a monopole field and the angular momentum of the rotor is quantized in
half-integer units.Comment: 4 page
Drastic Reduction of Cutoff Effects in 2-d Lattice O(N) Models
We investigate the cutoff effects in 2-d lattice O(N) models for a variety of
lattice actions, and we identify a class of very simple actions for which the
lattice artifacts are extremely small. One action agrees with the standard
action, except that it constrains neighboring spins to a maximal relative angle
delta. We fix delta by demanding that a particular value of the step scaling
function agrees with its continuum result already on a rather coarse lattice.
Remarkably, the cutoff effects of the entire step scaling function are then
reduced to the per mille level. This also applies to the theta-vacuum effects
of the step scaling function in the 2-d O(3) model. The cutoff effects of other
physical observables including the renormalized coupling and the mass in the
isotensor channel are also reduced drastically. Another choice, the mixed
action, which combines the standard quadratic with an appropriately tuned large
quartic term, also has extremely small cutoff effects. The size of cutoff
effects is also investigated analytically in 1-d and at N = infinity in 2-d.Comment: 39 pages, 18 figure
Color Screening, Casimir Scaling, and Domain Structure in G(2) and SU(N) Gauge Theories
We argue that screening of higher-representation color charges by gluons
implies a domain structure in the vacuum state of non-abelian gauge theories,
with the color magnetic flux in each domain quantized in units corresponding to
the gauge group center. Casimir scaling of string tensions at intermediate
distances results from random spatial variations in the color magnetic flux
within each domain. The exceptional G(2) gauge group is an example rather than
an exception to this picture, although for G(2) there is only one type of
vacuum domain, corresponding to the single element of the gauge group center.
We present some numerical results for G(2) intermediate string tensions and
Polyakov lines, as well as results for certain gauge-dependent projected
quantities. In this context, we discuss critically the idea of projecting link
variables to a subgroup of the gauge group. It is argued that such projections
are useful only when the representation-dependence of the string tension, at
some distance scale, is given by the representation of the subgroup.Comment: 24 pages, 14 figures; v2: references added; v3: published version
containing some additional introductory discussio
Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet
We have constructed a systematic low-energy effective theory for hole- and
electron-doped antiferromagnets, where holes reside in momentum space pockets
centered at and where electrons live in
pockets centered at or . The effective
theory is used to investigate the magnon-mediated binding between two holes or
two electrons in an otherwise undoped system. We derive the one-magnon exchange
potential from the effective theory and then solve the corresponding
two-quasiparticle Schr\"odinger equation. As a result, we find bound state wave
functions that resemble -like or -like symmetry. We also
study possible ground states of lightly doped antiferromagnets.Comment: 2 Pages; Proc. of SCES'07, Housto
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