621 research outputs found
Dielectric strength of rigid urethane foam
Dielectric strength of rigid urethane foam for electronic packaging in space applicatio
Abelian Gauge Theory in de Sitter Space
Quantization of spinor and vector free fields in 4-dimensional de Sitter
space-time, in the ambient space notation, has been studied in the previous
works. Various two-points functions for the above fields are presented in this
paper. The interaction between the spinor field and the vector field is then
studied by the abelian gauge theory. The U(1) gauge invariant spinor field
equation is obtained in a coordinate independent way notation and their
corresponding conserved currents are computed. The solution of the field
equation is obtained by use of the perturbation method in terms of the Green's
function. The null curvature limit is discussed in the final stage.Comment: 10 pages, typos corrected, reference adde
Fluctuation effects of gauge fields in the slave-boson t-J model
We present a quantitative study of the charge-spin separation(CSS) phenomenon
in a U(1) gauge theory of the t-J model of high-Tc superconductures. We
calculate the critical temperature of confinement-deconfinement phase
transition below which the CSS takes place.Comment: Latex, 9 pages, 3 figure
On Infrared Effects in de~Sitter Background
We have estimated higher order quantum gravity corrections to de~Sitter
spacetime. Our results suggest that, while the classical spacetime metric may
be distorted by the graviton self-interactions, the corrections are relatively
weaker than previously thought, possibly growing like a power rather than
exponentially in time.Comment: 17, UM-TH-94-11, (1 postscript fig. at end
Effective gauge field theory of the t-J model in the charge-spin separated state and its transport properties
We study the slave-boson t-J model of cuprates with high superconducting
transition temperatures, and derive its low-energy effective field theory for
the charge-spin separated state in a self-consistent manner. The phase degrees
of freedom of the mean field for hoppings of holons and spinons can be regarded
as a U(1) gauge field, . The charge-spin separation occurs below certain
temperature, , as a deconfinement phenomenon of the dynamics of
. Below certain temperature , the spin-gap
phase develops as the Higgs phase of the gauge-field dynamics, and
acquires a mass . The effective field theory near takes the
form of Ginzburg-Landau theory of a complex scalar field coupled with
, where represents d-wave pairings of spinons. Three
dimensionality of the system is crucial to realize a phase transition at
.
By using this field theory, we calculate the dc resistivity . At , is proportional to . At , it deviates
downward from the -linear behavior as . When the system is near (but not) two dimensional, due to the compactness
of the phase of the field , the exponent deviates from its
mean-field value 1/2 and becomes a nonuniversal quantity which depends on
temperature and doping. This significantly improves the comparison with the
experimental data
Phase Structure of d=2+1 Compact Lattice Gauge Theories and the Transition from Mott Insulator to Fractionalized Insulator
Large-scale Monte Carlo simulations are employed to study phase transitions
in the three-dimensional compact abelian Higgs model in adjoint representations
of the matter field, labelled by an integer q, for q=2,3,4,5. We also study
various limiting cases of the model, such as the lattice gauge theory,
dual to the spin model, and the 3DXY spin model which is dual to the
lattice gauge theory in the limit . We have computed the
first, second, and third moments of the action to locate the phase transition
of the model in the parameter space , where is the
coupling constant of the matter term, and is the coupling constant of
the gauge term. We have found that for q=3, the three-dimensional compact
abelian Higgs model has a phase-transition line which
is first order for below a finite {\it tricritical} value
, and second order above. We have found that the
first order phase transition persists for finite and
joins the second order phase transition at a tricritical point
. For
all other integer we have considered, the entire phase transition
line is critical.Comment: 17 pages, 12 figures (new Fig. 2), new Section IVB, updated
references, submitted to Physical Review
Higher twists in the pion structure function
We calculate the QCD moments of the pion structure function using Drell-Yan
data on the quark distributions in the pion and a phenomenological model for
the resonance region. The extracted higher twist corrections are found to be
larger than those for the nucleon, contributing around 50% of the lowest moment
at Q^2=1 GeV^2.Comment: 8 pages, 3 figures, to appear in Phys. Rev.
Deconfinement transition in three-dimensional compact U(1) gauge theories coupled to matter fields
It is shown that permanent confinement in three-dimensional compact U(1)
gauge theory can be destroyed by matter fields in a deconfinement transition.
This is a consequence of a non-trivial infrared fixed point caused by matter,
and an anomalous scaling dimension of the gauge field. This leads to a
logarithmic interaction between the defects of the gauge-fields, which form a
gas of magnetic monopoles. In the presence of logarithmic interactions, the
original electric charges are unconfined. The confined phase which is permanent
in the absence of matter fields is reached at a critical electric charge, where
the interaction between magnetic charges is screened by a pair unbinding
transition in a Kosterlitz-Thouless type of phase-transition.Comment: RevTex4, 4 pages, no figures; version accepted for publication in PR
Grand Unification with Three Generations in Free Fermionic String Models
We examine the problem of constructing three generation free fermionic string
models with grand unified gauge groups. We attempt the construction of models, where is a grand unified group realized at level 1. This
structure allows those Higgs representations to appear which are necessary to
break the symmetry down to the standard model gauge group. For , we
find only models with an even number of generations. However, for we
find a number of 3 generation models.Comment: 22 pages, latex. References added to original versio
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