13,791 research outputs found
Unequal Intra-layer Coupling in a Bilayer Driven Lattice Gas
The system under study is a twin-layered square lattice gas at half-filling,
being driven to non-equilibrium steady states by a large, finite `electric'
field. By making intra-layer couplings unequal we were able to extend the phase
diagram obtained by Hill, Zia and Schmittmann (1996) and found that the
tri-critical point, which separates the phase regions of the stripped (S) phase
(stable at positive interlayer interactions J_3), the filled-empty (FE) phase
(stable at negative J_3) and disorder (D), is shifted even further into the
negative J_3 region as the coupling traverse to the driving field increases.
Many transient phases to the S phase at the S-FE boundary were found to be
long-lived. We also attempted to test whether the universality class of D-FE
transitions under a drive is still Ising. Simulation results suggest a value of
1.75 for the exponent gamma but a value close to 2.0 for the ratio gamma/nu. We
speculate that the D-FE second order transition is different from Ising near
criticality, where observed first-order-like transitions between FE and its
"local minimum" cousin occur during each simulation run.Comment: 29 pages, 19 figure
S=1 kagom\'e Ising model with triquadratic interactions, single-ion anisotropy and magnetic field: exact phase diagrams
We consider a S=1 kagom\'e Ising model with triquadratic interactions around
each triangular face of the kagom\'e lattice, single-ion anisotropy and an
applied magnetic field. A mapping establishes an equivalence between the
magnetic canonical partition function of the model and the grand canonical
partition function of a kagom\'e lattice-gas model with localized
three-particle interactions. Since exact phase diagrams are known for
condensation in the one-parameter lattice-gas model, the mapping directly
provides the corresponding exact phase diagrams of the three-parameter S=1
Ising model. As anisotropy competes with interactions, results include the
appearance of confluent singularities effecting changes in the topology of the
phase diagrams, phase boundary curves (magnetic field vs temperature) with
purely positive or negative slopes as well as intermediate cases showing
nonmonotonicity, and coexistence curves (magnetization vs temperature) with
varying shapes and orientations, in some instances entrapping a homogeneous
phase.Comment: 14 pages plus 11 figures; to be published in Physica
Toward the minimal realization of a light composite Higgs
Work in progress is reported on a particularly interesting gauge theory with
a fermion doublet in the two-index symmetric (sextet) representation of the
SU(3) color gauge group. Extending previous studies we outline our strategy as
we investigate Goldstone dynamics and Electroweak scale setting from chiral
symmetry breaking ( SB), test the GMOR relation from the spectrum of the
Dirac operator and the related chiral condensate, begin to develop and test
mixed action based improved analysis of SB with new run plans at fixed
topology to cross over from the p-regime to the epsilon-regime of SB,
continue to pursue the light scalar and its relation to the dilaton,
and probe the scale-dependent running coupling from the perturbative UV scale
to the scale of chiral symmetry breaking. Our observations suggest that the
model is very close to the conformal window and a light composite scalar,
perhaps the Higgs impostor with or without dilaton-like interpretation, appears
to emerge with quantum numbers. The lightest baryon of the model on
the 3 TeV scale has intriguing implications.Comment: 14 pages, 7 figures, The 32nd International Symposium on Lattice
Field Theory,23-28 June, 2014 Columbia University, New York, NY, US
Updated analysis of meson-nucleon sigma terms in the perturbative chiral quark model
We present an updated analysis of meson-baryon sigma terms in the
perturbative chiral quark model, which is based on effective chiral Lagrangian.
The new feature concerns the inclusion of excited states in the quark
propagator. Its influence on meson loops is shown to lead in particular for the
pion-nucleon sigma term to an enhancement relevant for the current evaluation
of this quantity. We also determine various flavor combinations of the scalar
nucleon form factors and their respective low-momentum transfer limits.Comment: 26 pages, 10 figures, to be published in Phys Rev
Chiral loop corrections to weak decays of B mesons to positive and negative parity charmed mesons
We determine chiral loop corrections to the B meson decay amplitudes to
positive and negative parity charmed mesons within a framework which combines
heavy quark and chiral symmetries. Then we investigate the impact of the
lowest-lying positive parity heavy mesons on the determination of the
Isgur-Wise functions. The corrections due to these states are competitive with
the contributions arising from K and eta meson loops. Since lattice studies
rely on the chiral behavior of the amplitudes we discuss the chiral limit of
our results. We find that the determination of the slope at zero recoil of the
Isgur-Wise function xi for the B transition to negative parity charm mesons is
moderately affected by the inclusion of new states, while the slope of
tau_{1/2} is affected significantly more.Comment: 10 pages, 4 figure
First lattice calculation of the QED corrections to leptonic decay rates
The leading-order electromagnetic and strong isospin-breaking corrections to
the ratio of and decay rates are evaluated for the
first time on the lattice, following a method recently proposed. The lattice
results are obtained using the gauge ensembles produced by the European Twisted
Mass Collaboration with dynamical quarks. Systematics effects
are evaluated and the impact of the quenched QED approximation is estimated.
Our result for the correction to the tree-level decay
ratio is to be compared to the estimate based
on Chiral Perturbation Theory and adopted by the Particle Data Group.Comment: 5 pages, 6 figures; extended supplemental material with 1 table and 1
figure, results unchange
Hadron Spectrum in a Two-Colour Baryon-Rich Medium
The hadron spectrum of SU(2) lattice gauge theory with two flavours of Wilson
quark is studied on an 8^3x16 lattice using all-to-all propagators, with
particular emphasis on the dependence on quark chemical potential mu. As mu is
increased from zero the diquark states with non-zero baryon number B respond as
expected, while states with B=0 remain unaffected until the onset of non-zero
baryon density at mu=m_pi/2. Post onset the pi-meson mass increases in
accordance with chiral perturbation theory while the rho becomes lighter. In
the diquark sector a Goldstone state associated with a superfluid ground state
can be identified. A further consequence of superfluidity is an approximate
degeneracy between mesons and baryons with the same spacetime and isospin
quantum numbers. Finally we find tentative evidence for the binding of states
with kaon quantum numbers within the baryonic medium.Comment: 14 pages, 5 figure
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