19,345 research outputs found
Exact Expressions for Minor Hysteresis Loops in the Random Field Ising Model on a Bethe Lattice at Zero Temperature
We obtain exact expressions for the minor hysteresis loops in the
ferromagnetic random field Ising model on a Bethe lattice at zero temperature
in the case when the driving field is cycled infinitely slowly.Comment: Replaced with the published versio
Electron Correlations and Two-Photon States in Polycyclic Aromatic Hydrocarbon Molecules: A Peculiar Role of Geometry
We present numerical studies of one- and two-photon excited states ordering
in a number of polycyclic aromatic hydrocarbon molecules: coronene,
hexa-peri-hexabenzocoronene and circumcoronene, all possessing point
group symmetry versus ovalene with symmetry, within the
Pariser-Parr-Pople model of interacting -electrons. The calculated
energies of the two-photon states as well as their relative two-photon
absorption cross-sections within the interacting model are qualitatively
different from single-particle descriptions. More remarkably, a peculiar role
of molecular geometry is found. The consequence of electron correlations is far
stronger for ovalene, where the lowest spin-singlet two-photon state is a
quantum superposition of pairs of lowest spin triplet states, as in the linear
polyenes. The same is not true for group hydrocarbons. Our work
indicates significant covalent character, in valence bond language, of the
ground state, the lowest spin triplet state and a few of the lowest two-photon
states in ovalene but not in those with symmetry.Comment: 11 pages, 3 figures, 3 table
Augmented Superfield Approach to Nilpotent Symmetries in the Modified Version of 2D Proca Theory
We derive the complete set of off-shell nilpotent and absolutely
anticommuting Becchi-Rouet-Stora-Tyutin (BRST), anti-BRST and (anti-)co-BRST
symmetry transformations for all the fields of the modified version of two
(1+1)-dimensional (2D) Proca theory by exploiting the "augmented" superfield
formalism where the (dual-)horizontality conditions and (dual-)gauge-invariant
restrictions are exploited together. We capture the (anti-)BRST and
(anti-)co-BRST invariance of the Lagrangian density in the language of
superfield formalism. We also express the nilpotency and absolute
anticommutativity of the (anti-)BRST and (anti-)co-BRST charges within the
framework of augmented superfield formalism. This exercise leads to some novel
observations which have, hitherto, not been pointed out in the literature
within the framework of superfield approach to BRST formalism. For the sake of
completeness, we also mention, very briefly, a unique bosonic symmetry, the
ghost-scale symmetry and discrete symmetries of the theory and show that the
algebra of conserved charges captures the cohomological aspects of differential
geometry. Thus, our present modified 2D Proca theory is a model for the Hodge
Theory.Comment: LaTeX file, 32 pages, journal reference give
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