851 research outputs found
Risk Factors for Hospital Malpractice Exposure: Implications for Managers and Insurers
The possibility of identifying certain variables that might serve as predictors of above- or below-average medical malpractice claims experience was explored. Results showed that it is possible to identify significant risk factors
The Minimal Moose for a Little Higgs
Recently a new class of theories of electroweak symmetry breaking have been
constructed. These models, based on deconstruction and the physics of theory
space, provide the first alternative to weak-scale supersymmetry with naturally
light Higgs fields and perturbative new physics at the TeV scale. The Higgs is
light because it is a pseudo-Goldstone boson, and the quadratically divergent
contributions to the Higgs mass are cancelled by new TeV scale ``partners'' of
the {\em same} statistics. In this paper we present the minimal theory space
model of electroweak symmetry breaking, with two sites and four link fields,
and the minimal set of fermions. There are very few parameters and degrees of
freedom beyond the Standard Model. Below a TeV, we have the Standard Model with
two light Higgs doublets, and an additional complex scalar weak triplet and
singlet. At the TeV scale, the new particles that cancel the 1-loop quadratic
divergences in the Higgs mass are revealed. The entire Higgs potential needed
for electroweak symmetry breaking--the quartic couplings as well as the
familiar negative mass squared--can be generated by the top Yukawa coupling,
providing a novel link between the physics of flavor and electroweak symmetry
breaking.Comment: 15 pages. References added. Included clarifying comments on the
origin of quartic couplings, and on power-counting. More elegant model for
generating Higgs potential from top Yukawa coupling presente
Flavour from partially resolved singularities
In this letter we study topological open string field theory on D--branes in
a IIB background given by non compact CY geometries on with a singular point at which an extra fiber sits. We wrap
D5-branes on and effective D3-branes at singular points, which
are actually D5--branes wrapped on a shrinking cycle. We calculate the
holomorphic Chern-Simons partition function for the above models in a deformed
complex structure and find that it reduces to multi--matrix models with
flavour. These are the matrix models whose resolvents have been shown to
satisfy the generalized Konishi anomaly equations with flavour. In the
case, corresponding to a partial resolution of the singularity, the
quantum superpotential in the unitary SYM with one adjoint and
fundamentals is obtained. The case is also studied and shown to give rise
to two--matrix models which for a particular set of couplings can be exactly
solved. We explicitly show how to solve such a class of models by a quantum
equation of motion technique
Elliptic models and M-theory
We give a unified analysis of four-dimensional elliptic models with N=2
supersymmetry and a simple gauge group, and their relation to M-theory.
Explicit calculations of the Seiberg-Witten curves and the resulting
one-instanton prepotential are presented. The remarkable regularities that
emerge are emphasized. In addition, we calculate the prepotential in the
Coulomb phase of the (asymptotically-free) Sp(2N) gauge theory with N_f
fundamental hypermultiplets of arbitrary mass.Comment: 52 pages, latex, one eps figure, uses psfig.tex; revised version:
typos corrected and references adde
Coisotropic D8-branes and Model-building
Up to now chiral type IIA vacua have been mostly based on intersecting
D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue
that there are additional BPS D-branes which have so far been neglected, and
which seem to have interesting model-building features. They are coisotropic
D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional
submanifolds of the CY which are trivial in homology, but contain a worldvolume
flux that induces D6-brane charge on them. This induced D6-brane charge not
only renders the D8-brane BPS, but also creates D=4 chirality when two
D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2
orientifold, where we provide explicit examples of coisotropic D8-branes. We
study the chiral spectrum, SUSY conditions, and effective field theory of
different systems of D8-branes in this orientifold, and show how the magnetic
fluxes generate a superpotential for untwisted Kahler moduli. Finally, using
both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like
type IIA vacua.Comment: 63 pages, 11 figures. Typos corrected and comments adde
One-Instanton Test of a Seiberg-Witten Curve from M-theory: the Antisymmetric Representation of SU(N)
One-instanton predictions are obtained from the Seiberg-Witten curve derived
from M-theory by Landsteiner and Lopez for the Coulomb branch of N=2
supersymmetric SU(N) gauge theory with a matter hypermultiplet in the
antisymmetric representation. Since this cubic curve describes a Riemann
surface that is non-hyperelliptic, a systematic perturbation expansion about a
hyperelliptic curve is developed, with a comparable expansion for the
Seiberg-Witten differential. Calculation of the period integrals of the SW
differential by the method of residues of D'Hoker, Krichever, and Phong enables
us to compute the prepotential explicitly to one-instanton order. It is shown
that the one-instanton predictions for SU(2), SU(3), and SU(4) agree with
previously available results. For SU(N), N > 4, our analysis provides explicit
predictions of a curve derived from M-theory at the one-instanton level in
field theory.Comment: 37 pages, latex, no figure
Two antisymmetric hypermultiplets in N=2 SU(N) gauge theory: Seiberg-Witten curve and M-theory interpretation
The one-instanton contribution to the prepotential for N=2 supersymmetric
gauge theories with classical groups exhibits a universality of form. We
extrapolate the observed regularity to SU(N) gauge theory with two
antisymmetric hypermultiplets and N_f \leq 3 hypermultiplets in the defining
representation. Using methods developed for the instanton expansion of
non-hyperelliptic curves, we construct an effective quartic Seiberg-Witten
curve that generates this one-instanton prepotential. We then interpret this
curve in terms of an M-theoretic picture involving NS 5-branes, D4-branes,
D6-branes, and orientifold sixplanes, and show that for consistency, an
infinite chain of 5-branes and orientifold sixplanes is required, corresponding
to a curve of infinite order.Comment: 30 pages; 3 figures; LaTeX; minor typos correcte
Open string instantons and superpotentials
We study the F-terms in N=1 supersymmetric, d=4 gauge theories arising from
D(p+3)-branes wrapping supersymmetric p-cycles in a Calabi-Yau threefold. If p
is even the spectrum and superpotential for a single brane are determined by
purely classical () considerations. If p=3,
superpotentials for massless modes are forbidden to all orders in
and may only be generated by open string instantons. For this
latter case we find that such instanton effects are generically present. Mirror
symmetry relates even and odd p and thus perturbative and nonperturbative
superpotentials; we provide a preliminary discussion of a class of examples of
such mirror pairs.Comment: 22 pages, harvmac big; v2, corrected some typo
Supersymmetric (non-)Abelian Bundles in the Type I and SO(32) Heterotic String
We discuss perturbative four-dimensional compactifications of both the SO(32)
heterotic and the Type I string on smooth Calabi-Yau manifolds endowed with
general non-abelian and abelian bundles. We analyse the generalized
Green-Schwarz mechanism for multiple anomalous U(1) factors and derive the
generically non-universal one-loop threshold corrections to the gauge kinetic
function as well as the one-loop corrected Fayet-Iliopoulos terms. The latter
can be interpreted as a stringy one-loop correction to the
Donaldson-Uhlenbeck-Yau condition. Applying S-duality, for the Type I string we
obtain the perturbative Pi-stability condition for non-abelian bundles on
curved spaces. Some simple examples are given, and we qualitatively discuss
some generic phenomenological aspects of this kind of string vacua. In
particular, we point out that in principle an intermediate string scale
scenario with TeV scale large extra dimensions might be possible for the
heterotic string.Comment: LaTeX, 32 pages, v2: refs adde
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