504 research outputs found
First results from a parametrized Fixed-Point QCD action
We have constructed a new fermion action which is an approximation to the
(chirally symmetric) Fixed-Point action, containing the full Clifford algebra
with couplings inside a hypercube and paths built from renormalization group
inspired fat links. We present an exploratory study of the light hadron
spectrum and the energy-momentum dispersion relation.Comment: Lattice2001(improvement), 3 pages, based on a talk by S.H; reference
update
Progress using generalized lattice Dirac operators to parametrize the Fixed-Point QCD action
We report on an ongoing project to parametrize the Fixed-Point Dirac operator
for massless quarks, using a very general construction which has arbitrarily
many fermion offsets and gauge paths, the complete Clifford algebra and
satisfies all required symmetries. Optimizing a specific construction with
hypercubic fermion offsets, we present some preliminary results.Comment: Lattice 2000 (Improvement), 9 pages, based on a talk by K.H. and a
poster by T.J. References adde
The construction of generalized Dirac operators on the lattice
We discuss the steps to construct Dirac operators which have arbitrary
fermion offsets, gauge paths, a general structure in Dirac space and satisfy
the basic symmetries (gauge symmetry, hermiticity condition, charge
conjugation, hypercubic rotations and reflections) on the lattice. We give an
extensive set of examples and offer help to add further structures.Comment: 19 pages, latex, maple code attache
Gauged O(n) spin models in one dimension
We consider a gauged O(n) spin model, n >= 2, in one dimension which contains
both the pure O(n) and RP(n-1) models and which interpolates between them. We
show that this model is equivalent to the non-interacting sum of the O(n) and
Ising models. We derive the mass spectrum that scales in the continuum limit,
and demonstrate that there are two universality classes, one of which contains
the O(n) and RP(n-1) models and the other which has a tuneable parameter but
which is degenerate in the sense that it arises from the direct sum of the O(n)
and Ising models.Comment: 9 pages, no figures, LaTeX sourc
Operator improvement for Ginsparg-Wilson fermions
The improvement of fermionic operators for Ginsparg-Wilson fermions is
investigated. We present explicit formulae for improved Green's functions,
which apply both on-shell and off-shell.Comment: 13 pages, Latex, 4 postscript figure
Multiferroicity in the generic easy-plane triangular lattice antiferromagnet RbFe(MoO4)2
RbFe(MoO4)2 is a quasi-two-dimensional (quasi-2D) triangular lattice
antiferromagnet (TLA) that displays a zero-field magnetically-driven
multiferroic phase with a chiral spin structure. By inelastic neutron
scattering, we determine quantitatively the spin Hamiltonian. We show that the
easy-plane anisotropy is nearly 1/3 of the dominant spin exchange, making
RbFe(MoO4)2 an excellent system for studying the physics of the model 2D
easy-plane TLA. Our measurements demonstrate magnetic-field induced
fluctuations in this material to stabilize the generic finite-field phases of
the 2D XY TLA. We further explain how Dzyaloshinskii-Moriya interactions can
generate ferroelectricity only in the zero field phase. Our conclusion is that
multiferroicity in RbFe(MoO4)2, and its absence at high fields, results from
the generic properties of the 2D XY TLA.Comment: 5 pages, 5 figures, accepted in PRB as a Rapid Communicatio
Chiral measurements with the Fixed-Point Dirac operator and construction of chiral currents
In this preliminary study, we examine the chiral properties of the
parametrized Fixed-Point Dirac operator D^FP, see how to improve its chirality
via the Overlap construction, measure the renormalized quark condensate Sigma
and the topological susceptibility chi_t, and investigate local chirality of
near zero modes of the Dirac operator. We also give a general construction of
chiral currents and densities for chiral lattice actions.Comment: Lattice2001(chiral), based on a talk by T.J. and a poster by K.H., 6
page
Opening a nodal gap by fluctuating spin-density-wave in lightly doped LaSrCuO
We investigate whether the spin or charge degrees of freedom are responsible
for the nodal gap in underdoped cuprates by performing inelastic neutron
scattering and x-ray diffraction measurements on LaSrCuO, which
is on the edge of the antiferromagnetic phase. We found that fluctuating
incommensurate spin-density-wave (SDW) with a the bottom part of an hourglass
dispersion exists even in this magnetic sample. The strongest component of
these fluctuations diminishes at the same temperature where the nodal gap
opens. X-ray scattering measurements on the same crystal show no signature of
charge-density-wave (CDW). Therefore, we suggest that the nodal gap in the
electronic band of this cuprate opens due to fluctuating SDW with no
contribution from CDW
Exploring the fragile antiferromagnetic superconducting phase in CeCoIn5
CeCoIn5 is a heavy fermion Type-II superconductor which exhibits clear
indications of Pauli-limited superconductivity. A variety of measurements give
evidence for a transition at high magnetic fields inside the superconducting
state, when the field is applied either parallel to or perpendicular to the c
axis. When the field is perpendicular to the c axis, antiferromagnetic order is
observed on the high-field side of the transition, with a magnetic wavevector
of (q q 0.5), where q = 0.44 reciprocal lattice units. We show that this order
remains as the magnetic field is rotated out of the basal plane, but the
associated moment eventually disappears above 17 degrees, indicating that the
anomalies seen with the field parallel to the c axis are not related to this
magnetic order. We discuss the implications of this finding.Comment: Accepted Physical Review Letters, September 2010. 4 pages, 4 figure
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