1,206 research outputs found
Open String on Symmetric Product
We develop some basic properties of the open string on the symmetric product
which is supposed to describe the open string field theory in discrete
lightcone quantization (DLCQ). After preparing the consistency conditions of
the twisted boundary conditions for Annulus/M\"obius/Klein Bottle amplitudes in
generic non-abelian orbifold, we classify the most general solutions of the
constraints when the discrete group is . We calculate the corresponding
orbifold amplitudes from two viewpoints -- from the boundary state formalism
and from the trace over the open string Hilbert space. It is shown that the
topology of the world sheet for the short string and that of the long string in
general do not coincide. For example the annulus sector for the short string
contains all the sectors (torus, annulus, Klein bottle, M\"obius strip) of the
long strings. The boundary/cross-cap states of the short strings are classified
into three categories in terms of the long string, the ordinary boundary and
the cross-cap states, and the ``joint'' state which describes the connection of
two short strings. We show that the sum of the all possible boundary conditions
is equal to the exponential of the sum of the irreducible amplitude -- one body
amplitude of long open (closed) strings. This is typical structure of DLCQ
partition function. We examined that the tadpole cancellation condition in our
language and derived the well-known gauge group .Comment: 56 pages, 11 figures, Late
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
Physical mechanisms generating spontaneous symmetry breaking and a hierarchy of scales
We discuss the phase transition in 3+1 dimensional lambda Phi^4 theory from a
very physical perspective. The particles of the symmetric phase (`phions')
interact via a hard-core repulsion and an induced, long-range -1/r^3
attraction. If the phion mass is sufficiently small, the lowest-energy state is
not the `empty' state with no phions, but is a state with a non-zero density of
phions Bose-Einstein condensed in the zero-momentum mode. The condensate
corresponds to the spontaneous-symmetry-breaking vacuum with neq 0 and
its excitations ("phonons" in atomic-physics language) correspond to Higgs
particles. The phase transition happens when the phion's physical mass m is
still positive; it does not wait until m^2 passes through zero and becomes
negative. However, at and near the phase transition, m is much, much less than
the Higgs mass M_h. This interesting physics coexists with `triviality;' all
scattering amplitudes vanish in the continuum limit, but the vacuum condensate
becomes infinitely dense. The ratio m/M_h, which goes to zero in the continuum
limit, can be viewed as a measure of non-locality in the regularized theory. An
intricate hierarchy of length scales naturally arises. We speculate about the
possible implications of these ideas for gravity and inflation.Comment: 27 pages plus 2 files of figure
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
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
Substituting the main group element in cobalt - iron based Heusler alloys: CoFeAlSi
This work reports about electronic structure calculations for the Heusler
compound CoFeAlSi. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series CoFeAlSi is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for .Comment: J. Phys. D (accepted
DLCQ Strings, Twist Fields and One-Loop Correlators on a Permutation Orbifold
We investigate some aspects of the relationship between matrix string theory
and light-cone string field theory by analysing the correspondence between the
two-loop thermal partition function of DLCQ strings in flat space and the
integrated two-point correlator of twist fields in a symmetric product orbifold
conformal field theory at one-loop order. This is carried out by deriving
combinatorial expressions for generic twist field correlation functions in
permutation orbifolds using the covering surface method, by deriving the
one-loop modification of the twist field interaction vertex, and by relating
the two-loop finite temperature DLCQ string theory to the theory of Prym
varieties for genus two covers of an elliptic curve. The case of bosonic Z(2)
orbifolds is worked out explicitly and precise agreement between both
amplitudes is found. We use these techniques to derive explicit expressions for
Z(2) orbifold spin twist field correlation functions in the Type II and
heterotic string theories.Comment: 48 pages, 1 figure; v2: typos correcte
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
High energy, high resolution photoelectron spectroscopy of Co2Mn(1-x)Fe(x)Si
This work reports on high resolution photoelectron spectroscopy for the
valence band of Co2Mn(1-x)Fe(x)Si (x=0,0.5,1) excited by photons of about 8 keV
energy. The measurements show a good agreement to calculations of the
electronic structure using the LDA+U scheme. It is shown that the high energy
spectra reveal the bulk electronic structure better compared to low energy XPS
spectra. The high resolution measurements of the valence band close to the
Fermi energy indicate the existence of the gap in the minority states for all
three alloys.Comment: 14 pages, 5 figures, submitted to J. Phys. D: Appl. Phy
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