1,959 research outputs found
BRST-anti-BRST Antifield formalism : The Example of the Freedman-Townsend Model
The general BRST-anti-BRST construction in the framework of the
antifield-antibracket formalism is illustrated in the case of the
Freedmann-Townsend model.Comment: 16 pages, Latex file, Latex errors corrected, otherwise unchange
Algebraic Properties of BRST Coupled Doublets
We characterize the dependence on doublets of the cohomology of an arbitrary
nilpotent differential s (including BRST differentials and classical linearized
Slavnov-Taylor (ST) operators) in terms of the cohomology of the
doublets-independent component of s. All cohomologies are computed in the space
of local integrated formal power series. We drop the usual assumption that the
counting operator for the doublets commutes with s (decoupled doublets) and
discuss the general case where the counting operator does not commute with s
(coupled doublets). The results are purely algebraic and do not rely on
power-counting arguments.Comment: Some explanations enlarged, references adde
Available energy from diffusive and reversible phase space rearrangements
Rearranging the six-dimensional phase space of particles in plasma can
release energy. The rearrangement may happen through the application of
electric and magnetic fields, subject to various constraints. The maximum
energy that can be released through a rearrangement of a distribution of
particles can be called its available or free energy. Rearrangement subject to
phase space volume conservation leads to the classic Gardner free energy. Less
free energy is available when constraints are applied, such as respecting
conserved quantities. Also, less energy is available if particles can only be
diffused in phase-space from regions of high phase-space density to regions of
lower phase-space density. The least amount of free energy is available if
particles can only be diffused in phase space, while conserved quantities still
need to be respected.Comment: 7 pages, 3 figure
Power-law correlations and orientational glass in random-field Heisenberg models
Monte Carlo simulations have been used to study a discretized Heisenberg
ferromagnet (FM) in a random field on simple cubic lattices. The spin variable
on each site is chosen from the twelve [110] directions. The random field has
infinite strength and a random direction on a fraction x of the sites of the
lattice, and is zero on the remaining sites. For x = 0 there are two phase
transitions. At low temperatures there is a [110] FM phase, and at intermediate
temperature there is a [111] FM phase. For x > 0 there is an intermediate phase
between the paramagnet and the ferromagnet, which is characterized by a
|k|^(-3) decay of two-spin correlations, but no true FM order. The [111] FM
phase becomes unstable at a small value of x. At x = 1/8 the [110] FM phase has
disappeared, but the power-law correlated phase survives.Comment: 8 pages, 12 Postscript figure
Subextensive singularity in the 2D Ising spin glass
The statistics of low energy states of the 2D Ising spin glass with +1 and -1
bonds are studied for square lattices with , and =
0.5, where is the fraction of negative bonds, using periodic and/or
antiperiodic boundary conditions. The behavior of the density of states near
the ground state energy is analyzed as a function of , in order to obtain
the low temperature behavior of the model. For large finite there is a
range of in which the heat capacity is proportional to .
The range of in which this behavior occurs scales slowly to as
increases. Similar results are found for = 0.25. Our results indicate that
this model probably obeys the ordinary hyperscaling relation , even though . The existence of the subextensive behavior is
attributed to long-range correlations between zero-energy domain walls, and
evidence of such correlations is presented.Comment: 13 pages, 7 figures; final version, to appear in J. Stat. Phy
Power-law correlated phase in random-field XY models and randomly pinned charge-density waves
Monte Carlo simulations have been used to study the Z6 ferromagnet in a
random field on simple cubic lattices, which is a simple model for randomly
pinned charge-density waves. The random field is chosen to have infinite
strength on a fraction x of the sites of the lattice, and to be zero on the
remaining sites. For x= 1/16 there are two phase transitions. At low
temperature there is a ferromagnetic phase, which is stabilized by the six-fold
nonrandom anisotropy. The intermediate temperature phase is characterized by a
|k|^(-3) decay of two-spin correlations, but no true ferromagnetic order. At
the transition between the power-law correlated phase and the paramagnetic
phase the magnetic susceptibility diverges, and the two-spin correlations decay
approximately as |k|^(-2.87).Comment: 16 pages, 8 figures, Postscrip
Topological Defects in the Random-Field XY Model and the Pinned Vortex Lattice to Vortex Glass Transition in Type-II Superconductors
As a simplified model of randomly pinned vortex lattices or charge-density
waves, we study the random-field XY model on square () and simple cubic
() lattices. We verify in Monte Carlo simulations, that the average
spacing between topological defects (vortices) diverges more strongly than the
Imry-Ma pinning length as the random field strength, , is reduced. We
suggest that for the simulation data are consistent with a topological
phase transition at a nonzero critical field, , to a pinned phase that is
defect-free at large length-scales. We also discuss the connection between the
possible existence of this phase transition in the random-field XY model and
the magnetic field driven transition from pinned vortex lattice to vortex glass
in weakly disordered type-II superconductors.Comment: LATEX file; 5 Postscript figures are available from [email protected]
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