374 research outputs found
On Schwinger Pair Creation in Gravity and in Closed Superstring Theory
We investigate the Schwinger pair creation process in the context of
gravitational models with the back reaction of the electric field included in
the geometry. The background is also an exact solution of type II superstring
theory, where the electric field arises by Kaluza-Klein reduction. We obtain a
closed formula for the pair creation rate that incorporates the gravitational
back reaction. At weak fields it has the same structure as the general
Schwinger formula, albeit pairs are produced by a combination of Schwinger and
Unruh effect, the latter due to the presence of a Rindler horizon. In four
spacetime dimensions, the rate becomes constant at strong electric fields. For
states with mass of Kaluza-Klein origin, the rate has a power-like dependence
in the electric field, rather than the familiar (non-perturbative) exponential
dependence. We also reproduce the same formula from the string partition
function for winding string states. Finally, we comment on the generalization
to excited string states.Comment: 21 page
A D=4 N=1 Orbifold of Type I Strings
We consider the propagation of Type I open superstrings on orbifolds with
four non-compact dimensions and supersymmetry. In this paper, we
concentrate on a non-trivial Z_2xZ_2 example. We show that consistency
conditions, arising from tadpole cancellation and algebraic sources, require
the existence of three sets of Dirichlet 5-branes. We discuss fully the
enhancements of the spectrum when these 5-branes intersect. An amusing
attribute of these models is the importance of the tree-level (in Type I
language) superpotential to the consistent relationship between Higgsing and
the motions of 5-branes.Comment: 24 pages, uses LaTeX and epsf.st
A Note on Six-Dimensional Gauge Theories
We study the new ``gauge'' theories in 5+1 dimensions, and their
non-commutative generalizations. We argue that the -term and the
non-commutative torus parameters appear on an equal footing in the non-critical
string theories which define the gauge theories. The use of these theories as a
Matrix description of M-theory on , as well as a closely related
realization as 5-branes in type IIB string theory, proves useful in studying
some of their properties.Comment: Minor changes, Final version to appear in Physics Letters
The Large N Limit of the (2,0) Superconformal Field Theory
We discuss the large N limit of the (2,0) field theory in six dimensions. We
do this by assuming the validity of Maldacena's conjecture of the
correspondence between large N gauge theories and supergravity backgrounds,
here . We review the spectrum of the supergravity theory and
compute the spectrum of primary operators of the conformal algebra of arbitrary
spin.Comment: Minor changes, version to appear in Physics Letters
Three-Family Supersymmetric Standard-like Models from Intersecting Brane Worlds
We construct the first three family N=1 supersymmetric string model with
Standard Model gauge group SU(3)_C x SU(2)_L x U(1)_Y from an orientifold of
type IIA theory on T^6/(Z_2 x Z_2) and D6-branes intersecting at angles. In
addition to the minimal supersymmetric Standard Model particles, the model
contains right-handed neutrinos, a chiral (but anomaly-free) set of exotic
multiplets, and extra vector-like multiplets. We discuss some phenomenological
features of this model.Comment: 4 pages, minor typos correcte
A Chiral N=1 Type I Vacuum in Four Dimensions and Its Heterotic Dual
In this paper we consider Type I string theory compactified on a Z_7
orbifold. The model has N=1 supersymmetry, a U(4) \otimes U(4) \otimes U(4)
\otimes SO(8) gauge group, and chiral matter. There are only D9-branes (for
which we discuss tadpole cancellation conditions) in this model corresponding
to a perturbative heterotic description in a certain region of the moduli
space. We construct the heterotic dual, match the perturbative type I and
heterotic tree-level massless spectra via giving certain scalars appropriate
vevs, and point out the crucial role of the perturbative superpotential (on the
heterotic side) for this matching. The relevant couplings in this
superpotential turn out to be non-renormalizable (unlike the Z-orbifold case
discussed in Ref [1], where Yukawa couplings sufficed for duality matching). We
also discuss the role of the anomalous U(1) gauge symmetry present in both type
I and heterotic models. In the perturbative regime we match the (tree-level)
moduli spaces of these models. We point out possible generalizations of the Z_3
and Z_7 cases to include D5-branes which would help in understanding
non-perturbative five-brane dynamics on the heterotic side.Comment: Revtex 3.0, 23 pages, 1 eps figure (to appear in Phys. Rev. D
Tensors from K3 Orientifolds
Recently Gimon and Johnson (hep-th/9604129) and Dabholkar and Park
(hep-th/9604178) have constructed Type I theories on K3 orbifolds. The spectra
differ from that of Type I on a smooth K3, having extra tensors. We show that
the orbifold theories cannot be blown up to smooth K3's, but rather
orbifold singularities always remain. Douglas's recent proposal to use D-branes
as probes is useful in understanding the geometry. The singularities are
of a new type, with a different orientifold projection from those previously
considered. We also find a new world-sheet consistency condition that must be
satisfied by orientifold models.Comment: References added. 16 pages, LaTe
Unity of Supersymmetry Breaking Models
We examine the models with gauge group U(1)^{k-1}\times\prod_{i=1}^k SU(n_i),
which are obtained from decomposing the supersymmetry breaking model of
Affleck, Dine and Seiberg containing an antisymmetric tensor field. We note
that all of these models are distinct vacua of a single SU(N) gauge theory with
an adjoint superfield. The dynamics of this model may be analyzed using the
duality of Kutasov and Schwimmer and the deconfinement trick of Berkooz. This
analysis leads to a simple picture for supersymmetry breaking for k=2,
complementing that of previous work. We examine the flat directions of these
models, and give straightforward criteria for lifting them, explaining the
requisite peculiar form of the superpotential. For all cases with k>2, the
duality argument fails to give supersymmetry breaking dynamics, and we identify
a class of problematic flat directions, which we term 2m-baryons. We study in
some detail the requirements for lifting these directions, and uncover some
surprising facts regarding the relationship between R-symmetry and
supersymmetry breaking in models with several gauge groups.Comment: harvmac, 40 page
D=4, N=1, Type IIA Orientifolds
We study D=4, N=1, type IIA orientifold with orbifold group and . We calculate one-loop vacuum amplitudes for Klein bottle, cylinder
and Mobius strip and extract the tadpole divergences. We find that the tadpole
cancellation conditions thus obtained are satisfied by the , ,
, orientifolds while there is no solution for , ,
, , . The type IIA orientifold is also
constructed by introducing four different configurations of 6-branes. We argue
about perturbative versus non-perturbative orientifold vacua under T- duality
between the type IIA and the type IIB orientifolds in four dimensions.Comment: 32 pages, LaTe
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