259 research outputs found
String corrections to gauge couplings from a field theory approach
An effective field theory approach is introduced to compute one-loop
radiative corrections to the gauge couplings due to Kaluza-Klein states
associated with a two-torus compactification. The results are compared with
those of the string in the field theory ``limit'' alpha'-> 0. The whole U and
the leading T moduli dependence of the gauge dependent part of the string
corrections to gauge couplings can be recovered using the effective field
theory approach.Comment: 8 pages, Late
Supergravity Radiative Effects on Soft Terms and the Term
We compute quadratically divergent supergravity one-loop effects on soft
supersymmetry-breaking parameters and the term in generic hidden sector
supergravity models. These effects can significantly modify the matching
condition for soft parameters at the Planck scale and also provide several new
sources of the term which are naturally of order the weak scale. We also
discuss some phenomenological implications of these effects, particularly the
violation of the scalar mass universality which may lead to dangerous FCNC
phenomena, and apply the results to superstring effective supergravity models.Comment: 12 pages, REVTEX. One reference is adde
A natural solution to the -problem in dynamical supergravity model
The Higgs mixing term coefficient is calculated in the supersymmetric
theory which possesses a non-anomalous symmetry in the limit of
global supersymmetry. In this model, supersymmetry is assumed to be broken by
gaugino condensation in the hidden sector when the supergravity effects are
turned on. The soft breaking terms in the visible sector and the term of
order the weak scale are produced in a simple manner.Comment: 6 pages, Latex, accepted for publication in Phys.Rev.
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
Threshold Corrections and Gauge Symmetry in Twisted Superstring Models
Threshold corrections to the running of gauge couplings are calculated for
superstring models with free complex world sheet fermions. For two N=1
models, the threshold corrections lead to a small increase
in the unification scale. Examples are given to illustrate how a given particle
spectrum can be described by models with different boundary conditions on the
internal fermions. We also discuss how complex twisted fermions can enhance the
symmetry group of an N=4 model to the gauge group
. It is then shown how a mixing angle analogous
to the Weinberg angle depends on the boundary conditions of the internal
fermions.Comment: easier to Tex version, figures to be sent separatel
Surveying Pseudomoduli: the Good, the Bad and the Incalculable
We classify possible types of pseudomoduli which arise when supersymmetry is
dynamically broken in infrared-free low-energy theories. We show that, even if
the pseudomoduli potential is generated only at higher loops, there is a regime
where the potential can be simply determined from a combination of one-loop
running data. In this regime, we compute whether the potential for the various
types of pseudomoduli is safe, has a dangerous runaway to the UV cutoff of the
low-energy theory, or is incalculable. Our results are applicable to building
new models of supersymmetry breaking. We apply the results to survey large
classes of models.Comment: 34 page
Quantum Deconstruction of 5D SQCD
We deconstruct the fifth dimension of 5D SCQD with general numbers of colors
and flavors and general 5D Chern-Simons level; the latter is adjusted by adding
extra quarks to the 4D quiver. We use deconstruction as a non-stringy UV
completion of the quantum 5D theory; to prove its usefulness, we compute
quantum corrections to the SQCD_5 prepotential. We also explore the
moduli/parameter space of the deconstructed SQCD_5 and show that for |K_CS| <
N_F/2 it continues to negative values of 1/(g_5)^2. In many cases there are
flop transitions connecting SQCD_5 to exotic 5D theories such as E0, and we
present several examples of such transitions. We compare deconstruction to
brane-web engineering of the same SQCD_5 and show that the phase diagram is the
same in both cases; indeed, the two UV completions are in the same universality
class, although they are not dual to each other. Hence, the phase structure of
an SQCD_5 (and presumably any other 5D gauge theory) is inherently
five-dimensional and does not depends on a UV completion.Comment: LaTeX+PStricks, 108 pages, 41 colored figures. Please print in colo
Detecting and Studying in the MSSM: Implications of Supersymmetric Decays and Discriminating GUT Scenarios
We demonstrate that supersymmetric decays, as typified by the predictions of
several GUT-scale boundary condition choices, do not prevent detection of , at a TeV or collider operating
at anticipated luminosity. For much of parameter space the relative branching
ratios for various SUSY and non-SUSY decays can be measured with sufficient
accuracy that different GUT-scale boundary condition choices can be
distinguished from one another at a very high confidence level.Comment: 54 pages, full postscript file also available via anonymous ftp at
ftp://ucdhep.ucdavis.edu/gunion/pair.p
Effects of Extra Space-time Dimensions on the Fermi Constant
Effects of Kaluza-Klein excitations associated with extra dimensions with
large radius compactifications on the Fermi constant are explored. It is shown
that the current precision determinations of the Fermi constant, of the fine
structure constant, and of the W and Z mass put stringent constraints on the
compactification radius. The analysis excludes one extra space time dimension
below TeV, and excludes 2, 3 and 4 extra space dimensions opening
simultaneously below 3.5 TeV, 5.7 TeV and 7.8 TeV at the .
Implications of these results for future collider experiments are discussed.Comment: 12 pages including one figur
MQCD, ('Barely') G_2 Manifolds and (Orientifold of) a Compact Calabi-Yau
We begin with a discussion on two apparently disconnected topics - one
related to nonperturbative superpotential generated from wrapping an M2-brane
around a supersymmetric three cycle embedded in a G_2-manifold evaluated by the
path-integral inside a path-integral approach of [1], and the other centered
around the compact Calabi-Yau CY_3(3,243) expressed as a blow-up of a degree-24
Fermat hypersurface in WCP^4[1,1,2,8,12]. For the former, we compare the
results with the ones of Witten on heterotic world-sheet instantons [2]. The
subtopics covered in the latter include an N=1 triality between Heterotic, M-
and F-theories, evaluation of RP^2-instanton superpotential, Picard-Fuchs
equation for the mirror Landau-Ginsburg model corresponding to CY_3(3,243),
D=11 supergravity corresponding to M-theory compactified on a `barely' G_2
manifold involving CY_3(3,243) and a conjecture related to the action of
antiholomorphic involution on period integrals. We then show an indirect
connection between the two topics by showing a connection between each one of
the two and Witten's MQCD [3]. As an aside, we show that in the limit of
vanishing "\zeta", a complex constant that appears in the Riemann surfaces
relevant to definining the boundary conditions for the domain wall in MQCD, the
infinite series of [4] used to represent a suitable embedding of a
supersymmetric 3-cycle in a G_2-mannifold, can be summed.Comment: 37 pages, LaTex; PARTLY based on talks given at ``Seventh Workshop on
QCD" [session on "Strings, Branes and (De-)Construction"], Jan 6-10, 2003, La
Cittadelle, Villefranche-sur-Mer, France; Fourth Workshop on ``Gauge Fields
and Strings", Feb 25-Mar 1, 2003, Jena, Germany; ``XII Oporto Meeting on
Geometry, Topology and Strings", July 17-20, 2003, Oporto, Portugal; "SQS03"
- International Workshop on "Supersymmetries and Quantum Symmetries', July
24-29, 2003, JINR, Dubna, Russia; poster presented at ``XIV International
Congress on Mathematical Physics", July 28-Aug 2, 2003, Lisbon, Portuga
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