20,691 research outputs found
Chaotic Dynamics of SU(2) Gauge Fields in the Presence of Static Charges
We have found in numerical simulations that the chaoticity of the classical
hamiltonian lattice SU(2) gauge theory is reduced in the presence of static
charges at the same total energy. The transition from strongly to weakly
chaotic behavior is rather sudden at a critical charge strength.Comment: LaTeX, 10 pages, 2 figs as .PS in ym_figs.uu Submitted to Chaos,
Solitons and Fractal
Effects of methamphetamine abuse and serotonin transporter gene variants on aggression and emotion-processing neurocircuitry.
Individuals who abuse methamphetamine (MA) exhibit heightened aggression, but the neurobiological underpinnings are poorly understood. As variability in the serotonin transporter (SERT) gene can influence aggression, this study assessed possible contributions of this gene to MA-related aggression. In all, 53 MA-dependent and 47 control participants provided self-reports of aggression, and underwent functional magnetic resonance imaging while viewing pictures of faces. Participants were genotyped at two functional polymorphic loci in the SERT gene: the SERT-linked polymorphic region (SERT-LPR) and the intron 2 variable number tandem repeat polymorphism (STin2 VNTR); participants were then classified as having high or low risk for aggression according to individual SERT risk allele combinations. Comparison of SERT risk allele loads between groups showed no difference between MA-dependent and control participants. Comparison of self-report scores showed greater aggression in MA-dependent than control participants, and in high genetic risk than low-risk participants. Signal change in the amygdala was lower in high genetic risk than low-risk participants, but showed no main effect of MA abuse; however, signal change correlated negatively with MA use measures. Whole-brain differences in activation were observed between MA-dependent and control groups in the occipital and prefrontal cortex, and between genetic high- and low-risk groups in the occipital, fusiform, supramarginal and prefrontal cortex, with effects overlapping in a small region in the right ventrolateral prefrontal cortex. The findings suggest that the investigated SERT risk allele loads are comparable between MA-dependent and healthy individuals, and that MA and genetic risk influence aggression independently, with minimal overlap in associated neural substrates
A More Improved Lattice Action for Heavy Quarks
We extend the Fermilab formalism for heavy quarks to develop a more improved
action. We give results of matching calculations of the improvement couplings
at tree level. Finally, we estimate the discretization errors associated with
the new action.Comment: 3 pages, 1 figure, Lattice 2003 Tsukuba Japa
Test of Universality in Anisotropic 3D Ising Model
Chen and Dohm predicted theoretically in 2004 that the widely believed
universality principle is violated in the Ising model on the simple cubic
lattice with more than only six nearest neighbours. Schulte and Drope by Monte
Carlo simulations found such violation, but not in the predicted direction.
Selke and Shchur tested the square lattice. Here we check only this
universality for the susceptibility ratio near the critical point. For this
purpose we study first the standard Ising model on a simple cubic lattice with
six nearest neighbours, then with six nearest and twelve next-nearest
neighbours, and compare the results with the Chen-Dohm lattice of six nearest
neighbours and only half of the twelve next-nearest neighbours. We do not
confirm the violation of universality found by Schulte and Drope in the
susceptibility ratio.Comment: 6 pages including 4 figures, Physica A, in pres
Cavity optomechanics with stoichiometric SiN films
We study high-stress SiN films for reaching the quantum regime with
mesoscopic oscillators connected to a room-temperature thermal bath, for which
there are stringent requirements on the oscillators' quality factors and
frequencies. Our SiN films support mechanical modes with unprecedented products
of mechanical quality factor and frequency reaching Hz. The SiN membranes exhibit a low optical absorption
characterized by Im at 935 nm, representing a 15 times
reduction for SiN membranes. We have developed an apparatus to simultaneously
cool the motion of multiple mechanical modes based on a short, high-finesse
Fabry-Perot cavity and present initial cooling results along with future
possibilities.Comment: 4 pages, 5 figure
Flavor SU(4) breaking between effective couplings
Using a framework in which all elements are constrained by Dyson-Schwinger
equation studies in QCD, and therefore incorporates a consistent, direct and
simultaneous description of light- and heavy-quarks and the states they
constitute, we analyze the accuracy of SU(4)-flavor symmetry relations between
{\pi}{\rho}{\pi}, K{\rho}K and D{\rho}D couplings. Such relations are widely
used in phenomenological analyses of the interactions between matter and
charmed mesons. We find that whilst SU(3)-flavor symmetry is accurate to 20%,
SU(4) relations underestimate the D{\rho}D coupling by a factor of five.Comment: 5 pages, two figure
Scale without Conformal Invariance: An Example
We give an explicit example of a model in D=4-epsilon space-time dimensions
that is scale but not conformally invariant, is unitary, and has finite
correlators. The invariance is associated with a limit cycle renormalization
group (RG) trajectory. We also prove, to second order in the loop expansion, in
D=4-epsilon, that scale implies conformal invariance for models of any number
of real scalars. For models with one real scalar and any number of Weyl spinors
we show that scale implies conformal invariance to all orders in perturbation
theory.Comment: 13 pages, 2 figures, Erratum adde
The Thirring interaction in the two-dimensional axial-current-pseudoscalar derivative coupling model
The authors reexamine the two-dimensional model of massive fermions
interacting with a massless pseudoscalar field via axial-current-pseudoscalar
derivative coupling. Performing a canonical field transformation on the Bose
field algebra the model is mapped into the Thirring model with an additional
vector-current-scalar-derivative interaction (Schroer-Thirring model). The
complete bosonized version of the model is presented. The bosonized composite
operators of the quantum Hamiltonian are obtained as the leading operators in
the Wilson short distance expansion.Comment: 13 page
Aggregation of Votes with Multiple Positions on Each Issue
We consider the problem of aggregating votes cast by a society on a fixed set
of issues, where each member of the society may vote for one of several
positions on each issue, but the combination of votes on the various issues is
restricted to a set of feasible voting patterns. We require the aggregation to
be supportive, i.e. for every issue the corresponding component of
every aggregator on every issue should satisfy . We prove that, in such a set-up, non-dictatorial
aggregation of votes in a society of some size is possible if and only if
either non-dictatorial aggregation is possible in a society of only two members
or a ternary aggregator exists that either on every issue is a majority
operation, i.e. the corresponding component satisfies , or on every issue is a minority operation, i.e.
the corresponding component satisfies We then introduce a notion of uniformly non-dictatorial
aggregator, which is defined to be an aggregator that on every issue, and when
restricted to an arbitrary two-element subset of the votes for that issue,
differs from all projection functions. We first give a characterization of sets
of feasible voting patterns that admit a uniformly non-dictatorial aggregator.
Then making use of Bulatov's dichotomy theorem for conservative constraint
satisfaction problems, we connect social choice theory with combinatorial
complexity by proving that if a set of feasible voting patterns has a
uniformly non-dictatorial aggregator of some arity then the multi-sorted
conservative constraint satisfaction problem on , in the sense introduced by
Bulatov and Jeavons, with each issue representing a sort, is tractable;
otherwise it is NP-complete
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