892 research outputs found
Perturbative Computation of Glueball Superpotentials for SO(N) and USp(N)
We use the superspace method of hep-th/0211017 to prove the matrix model
conjecture for N=1 USp(N) and SO(N) gauge theories in four dimensions. We
derive the prescription to relate the matrix model to the field theory
computations. We perform an explicit calculation of glueball superpotentials.
The result is consistent with field theory expectations.Comment: 24 pages, 10 figure
Note on Matrix Model with Massless Flavors
In this note, following the work of Seiberg in hep-th/0211234 for the
conjecture between the field theory and matrix model in the case with massive
fundamental flavors, we generalize it to the case with massless fundamental
flavors. We show that with a little modifications, the analysis given by
Seiberg can be used directly to the case of massless flavors. Furthermore, this
new method explains the insertion of delta functions in the matrix model given
by Demasure and Janik in hep-th/0211082.Comment: 10 pages. Type fixed. Remarks adde
The sixth Painleve equation arising from D_4^{(1)} hierarchy
The sixth Painleve equation arises from a Drinfel'd-Sokolov hierarchy
associated with the affine Lie algebra of type D_4 by similarity reduction.Comment: 14 page
Exact diagonalisation study of charge order in the quarter-filled two-leg ladder system NaV2O5
The charge ordering transition in the layer compound NaV2O5 is studied by
means of exact diagonalization methods for finite systems. The 2-leg ladders of
the V-Trellis lattice are associated with one spin variable of the vanadium
3d-electron in the rung and a pseudospin variable that describes its positional
degree of freedom. The charge ordering (CO) due to intersite Coulomb
interactions is described by an effective Ising-like Hamiltonian for the
pseudo-spins that are coupled to the spin fluctuations along the ladder. We
employ a Lanczos algortihm on 2D lattice to compute charge (pseudo-spin) and
spin-correlation functions and the energies of the low lying excited states. A
CO-phase diagram is constructed and the effect of intra-ladder exchange on the
CO transition is studied. It is shown that a phase with no-longe range order
(no-LRO) exists between the in-line and zig-zag ordered structures. We provide
a finite-size scaling analysis for the spin excitation gap and also discuss the
type of excitations. In addition we studied the effect of bond-alternation of
spin exchange and derived a scaling form for the spin gap in terms of the
dimerization parameter.Comment: 9 pages with 9 EPS figures and 1 table, To be appeared in Phys. Rev.
B (2001
Electron correlations in CoMnFeSi Heusler compounds
This study presents the effect of local electronic correlations on the
Heusler compounds CoMnFeSi as a function of the concentration
. The analysis has been performed by means of first-principles
band-structure calculations based on the local approximation to spin-density
functional theory (LSDA). Correlation effects are treated in terms of the
Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is
implemented within the Korringa-Kohn-Rostoker (KKR) Green's function method.
In good agreement with the available experimental data the magnetic and
spectroscopic properties of the compound are explained in terms of strong
electronic correlations. In addition the correlation effects have been analysed
separately with respect to their static or dynamical origin. To achieve a
quantitative description of the electronic structure of
CoMnFeSi both static and dynamic correlations must be treated
on equal footing.Comment: 12 pages, 5 figure
Exact Mesonic Vacua From Matrix Models
We investigate in detail the structure of mesonic vacua of N=1 U(Nc)
supersymmetric gauge theory with Nf flavors from the matrix model. We show that
the Witten index from the matrix model calculation agrees with a result from
field theoretical analysis. We also discuss the relationship between a
diagrammatic summation and direct matrix integration with insertion of a
variable changing delta function. Using this formalism, we obtain the quantum
moduli space and evidence of the Seiberg duality from the matrix models.Comment: 14 pages, 1 figure, typos corrected and note on the quamtum moduli
space adde
Semiclassical Strings Probing NS5 Brane Wrapped on S^5
We study little string theory on R^1 x S^5, defined by a theory which lives
on type IIA N NS5 branes wrapped on S^5, using its supergravity dual. In
particular we study semiclassical rotating closed strings in this background.
We also consider Penrose limit of this background that leads to a plane wave on
which string theory is exactly solvable.Comment: 14 pages, Latex, v2: typos corrected, Refs. added, v3: typos
correcte
New nonlinear coherent states and some of their nonclassical properties
We construct a displacement operator type nonlinear coherent state and
examine some of its properties. In particular it is shown that this nonlinear
coherent state exhibits nonclassical properties like squeezing and
sub-Poissonian behaviour.Comment: 3 eps figures. to appear in J.Opt
Charge Order Driven spin-Peierls Transition in NaV2O5
We conclude from 23Na and 51V NMR measurements in NaxV2O5(x=0.996) a charge
ordering transition starting at T=37 K and preceding the lattice distortion and
the formation of a spin gap Delta=106 K at Tc=34.7 K. Above Tc, only a single
Na site is observed in agreement with the Pmmn space group of this first
1/4-filled ladder system. Below Tc=34.7 K, this line evolves into eight
distinct 23Na quadrupolar split lines, which evidences a lattice distortion
with, at least, a doubling of the unit cell in the (a,b) plane. A model for
this unique transition implying both charge density wave and spin-Peierls order
is discussed.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
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