5,590 research outputs found
On the reduction of hypercubic lattice artifacts
This note presents a comparative study of various options to reduce the
errors coming from the discretization of a Quantum Field Theory in a lattice
with hypercubic symmetry. We show that it is possible to perform an
extrapolation towards the continuum which is able to eliminate systematically
the artifacts which break the O(4) symmetry.Comment: 15 pages. 4 figures. Minor changes (Appendix and refs added
Violation of action--reaction and self-forces induced by nonequilibrium fluctuations
We show that the extension of Casimir-like forces to fluctuating fluids
driven out of equilibrium can exhibit two interrelated phenomena forbidden at
equilibrium: self-forces can be induced on single asymmetric objects and the
action--reaction principle between two objects can be violated. These effects
originate in asymmetric restrictions imposed by the objects' boundaries on the
fluid's fluctuations. They are not ruled out by the second law of
thermodynamics since the fluid is in a nonequilibrium state. Considering a
simple reaction--diffusion model for the fluid, we explicitly calculate the
self-force induced on a deformed circle. We also show that the action--reaction
principle does not apply for the internal Casimir forces exerting between a
circle and a plate. Their sum, instead of vanishing, provides the self-force on
the circle-plate assembly.Comment: 4 pages, 1 figure. V2: New title; Abstract partially rewritten;
Largely enhanced introductory and concluding remarks (incl. new Refs.
Lost and found: the radial quantum number of Laguerre-Gauss modes
We introduce an operator linked with the radial index in the Laguerre-Gauss
modes of a two-dimensional harmonic oscillator in cylindrical coordinates. We
discuss ladder operators for this variable, and confirm that they obey the
commutation relations of the su(1,1) algebra. Using this fact, we examine how
basic quantum optical concepts can be recast in terms of radial modes.Comment: Some minor typos fixed
The Nuclear Yukawa Model on a Lattice
We present the results of the quantum field theory approach to nuclear Yukawa
model obtained by standard lattice techniques. We have considered the simplest
case of two identical fermions interacting via a scalar meson exchange.
Calculations have been performed using Wilson fermions in the quenched
approximation. We found the existence of a critical coupling constant above
which the model cannot be numerically solved. The range of the accessible
coupling constants is below the threshold value for producing two-body bound
states. Two-body scattering lengths have been obtained and compared to the non
relativistic results.Comment: 15 page
An Instanton Picture O.P.E. <A^2> Condensate?
Gluon two- and three-point Green Functions computed in Landau gauge from the
lattice show the existence of power corrections to the purely perturbative
expressions, that can be explained through an Operator Product Expansion as the
influence of a non gauge invariant mass dimension two condensate. The
relationship of this condensate with topological properties of QCD, namely
instantons, will be studied, giving a first estimate of the contribution of
instantons to this condensate based in the direct lattice measure, after a
cooling process, of the instanton liquid properties.Comment: Lattice2002(topology) contribution, 3 pages, 2 figure
O.P.E. and Power Corrections to the QCD coupling constant
Lattice data seems to show that power corrections should be convoked to
describe appropriately the transition of the QCD coupling constant running from
U.V. to I.R. domains. Those power corrections for the Landau-gauge MOM coupling
constant in a pure Yang-Mills theory (N_f=0) are analysed in terms of Operator
Product Expansion (O.P.E.) of two- and three-point Green functions, the gluon
condensate emerging from this study. The semi-classical picture given by
instantons can be also used to look for into the nature of the power
corrections and gluon condensate.Comment: 5 pages, talk given at XXX International Meeting on Fundamental
Physics, Jaca 200
NMR Evidence for Antiferromagnetic Transition in the Single-Component Molecular Conductor, [Au(tmdt)_{2}] at 110 K
We present the results of a ^{1}H NMR study of the single-component molecular
conductor, [Au(tmdt)_{2}].
A steep increase in the NMR line width and a peak formation of the nuclear
spin-lattice relaxation rate, 1/T_{1}, were observed at around 110 K.
This behavior provides clear and microscopic evidences for a magnetic phase
transition at considerably high temperature among organic conductors.
The observed variation in 1/T_{1} with respect to temperature indicates the
highly correlated nature of the metallic phase.Comment: 5pages, 6figures to be published in J. Phys. Soc. Jp
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