480 research outputs found
Twisted mass lattice QCD with non-degenerate quark masses
Quantum Chromodynamics on a lattice with Wilson fermions and a chirally
twisted mass term is considered in the framework of chiral perturbation theory.
For two and three numbers of quark flavours, respectively, with non-degenerate
quark masses the pseudoscalar meson masses and decay constants are calculated
in next-to-leading order including lattice effects quadratic in the lattice
spacing a.Comment: 9 pages, LaTeX2e, reference adde
Twisted mass chiral perturbation theory for 2+1+1 quark flavours
We present results for the masses of pseudoscalar mesons in twisted mass
lattice QCD with a degenerate doublet of u and d quarks and a non-degenerate
doublet of s and c quarks in the framework of next-to-leading order chiral
perturbation theory, including lattice effects up to O(a^2). The masses depend
on the two twist angles for the light and heavy sectors. For maximal twist in
both sectors, O(a)-improvement is explicitly exhibited. The mixing of
flavour-neutral mesons is also discussed, and results in the literature for the
case of degenerate s and c quarks are corrected.Comment: LaTeX2e, 12 pages, corrected typo
The supersymmetric Ward identities on the lattice
Supersymmetric (SUSY) Ward identities are considered for the N=1 SU(2) SUSY
Yang Mills theory discretized on the lattice with Wilson fermions (gluinos).
They are used in order to compute non-perturbatively a subtracted gluino mass
and the mixing coefficient of the SUSY current. The computations were performed
at gauge coupling =2.3 and hopping parameter =0.1925, 0.194,
0.1955 using the two-step multi-bosonic dynamical-fermion algorithm. Our
results are consistent with a scenario where the Ward identities are satisfied
up to O(a) effects. The vanishing of the gluino mass occurs at a value of the
hopping parameter which is not fully consistent with the estimate based on the
chiral phase transition. This suggests that, although SUSY restoration appears
to occur close to the continuum limit of the lattice theory, the results are
still affected by significant systematic effects.Comment: 34 pages, 7 figures. Typo corrected, last sentence reformulated,
reference added. To appear in Eur. Phys. J.
Chiral perturbation theory for partially quenched twisted mass lattice QCD
Partially quenched Quantum Chromodynamics with Wilson fermions on a lattice
is considered in the framework of chiral perturbation theory. Two degenerate
quark flavours are associated with a chirally twisted mass term. The pion
masses and decay constants are calculated in next-to-leading order including
terms linear in the lattice spacing .Comment: 7 pages, LaTeX2e, final published versio
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
Correlations around an interface
We compute one-loop correlation functions for the fluctuations of an
interface using a field theory model. We obtain them from Feynman diagrams
drawn with a propagator which is the inverse of the Hamiltonian of a
Poschl-Teller problem. We derive an expression for the propagator in terms of
elementary functions, show that it corresponds to the usual spectral sum, and
use it to calculate quantities such as the surface tension and interface
profile in two and three spatial dimensions. The three-dimensional quantities
are rederived in a simple, unified manner, whereas those in two dimensions
extend the existing literature, and are applicable to thin films. In addition,
we compute the one-loop self-energy, which may be extracted from experiment, or
from Monte Carlo simulations. Our results may be applied in various scenarios,
which include fluctuations around topological defects in cosmology,
supersymmetric domain walls, Z(N) bubbles in QCD, domain walls in magnetic
systems, interfaces separating Bose-Einstein condensates, and interfaces in
binary liquid mixtures.Comment: RevTeX, 13 pages, 6 figure
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