251 research outputs found
Metastable Supersymmetry Breaking In A Cooling Universe
I put metastable supersymmetry breaking in a cosmological context. I argue that under reasonable assumptions, the cooling down early Universe favors metastable SUSY-breaking vacua over the stable supersymmetric vacua. To illustrate the general argument I analyze the early-Universe history of the Intriligator-Seiberg-Shih model.Physic
On Heterotic Orbifolds, M Theory and Type I' Brane Engineering
Horava--Witten M theory -- heterotic string duality poses special problems
for the twisted sectors of heterotic orbifolds. In [1] we explained how in M
theory the twisted states couple to gauge fields apparently living on M9 branes
at both ends of the eleventh dimension at the same time. The resolution
involves 7D gauge fields which live on fixed planes of the (T^4/Z_N) x
(S^1/Z_2) x R^{5,1} orbifold and lock onto the 10D gauge fields along the
intersection planes. The physics of such intersection planes does not follow
directly from the M theory but there are stringent kinematic constraints due to
duality and local consistency, which allowed us to deduce the local fields and
the boundary conditions at each intersection. In this paper we explain various
phenomena at the intersection planes in terms of duality between HW and type I'
superstring theories. The orbifold fixed planes are dual to stacks of D6
branes, the M9 planes are dual to O8 orientifold planes accompanied by D8
branes, and the intersections are dual to brane junctions. We engineer several
junction types which lead to distinct patterns of 7D/10D gauge field locking,
7D symmetry breaking and/or local 6D fields. Another aspect of brane
engineering is putting the junctions together; sometimes, the combined effect
is rather spectacular from the HW point of view and the quantum numbers of some
twisted states have to `bounce' off both ends of the eleventh dimension before
their heterotic identity becomes clear. Some models involve D6/O8 junctions
where the string coupling diverges towards the orientifold plane. We use the
heterotic-HW-I' duality to predict what should happen at such junctions.Comment: 118 pages, uses phyzzx, color printer advice
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
Naturally small Dirac neutrino masses in supergravity
We show that Dirac neutrino masses of the right size can arise from the
Kahler potential of supergravity. They are proportional to the supersymmetry
and the electroweak breaking scales. We find that they have the experimentally
observed value provided that the ultraviolet cut-off of the Minimal
Supersymmetric Standard Model (MSSM) is between the Grand Unification (GUT)
scale and the heterotic string scale. If lepton number is not conserved, then
relatively suppressed Majorana masses can also be present, resulting in
pseudo-Dirac neutrino masses.Comment: 6 pages, Revtex 4, published versio
Spontaneous R-Symmetry Breaking in O'Raifeartaigh Models
We study the question of whether spontaneous U(1)_R breaking can occur in
O'Raifeartaigh-type models of spontaneous supersymmetry breaking. We show that
in order for it to occur, there must be a field in the theory with R-charge
different from 0 or 2. We construct the simplest O'Raifeartaigh model with this
property, and we find that for a wide range of parameters, it has a meta-stable
vacuum where U(1)_R is spontaneously broken. This suggests that spontaneous
U(1)_R breaking actually occurs in generic O'Raifeartaigh models.Comment: 19 pages; v2: reference added, minor changes; v3: important typo
fixe
Supersymmetry Breaking, R-Symmetry Breaking and Metastable Vacua
Models of spontaneous supersymmetry breaking generically have an R-symmetry,
which is problematic for obtaining gaugino masses and avoiding light R-axions.
The situation is improved in models of metastable supersymmetry breaking, which
generically have only an approximate R-symmetry. Based on this we argue, with
mild assumptions, that metastable supersymmetry breaking is inevitable. We also
illustrate various general issues regarding spontaneous and explicit R-symmetry
breaking, using simple toy models of supersymmetry breaking.Comment: 23 page
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
The Ubiquitous Inflaton in String-Inspired Models
A string theory based inflationary model is developed where the inflaton
interacts with a multitude of massive string level states causing dissipation
of vacuum energy. Inflation terminates in a warm Universe without the need for
reheating.Comment: In Press Physical Review Letters 1999, modified titl
Constraints on LVS Compactifications of IIB String Theory
We argue that once all theoretical and phenomenological constraints are
imposed on the different versions of the Large Volume Scenario (LVS)
compactifications of type IIB string theory, one particular version is favored.
This is essentially a sequestered one in which the soft terms are generated by
Weyl anomaly and RG running effects. We also show that arguments questioning
sequestering in LVS models are not relevant in this case.Comment: 14 pages, additional discussion of D7 brane case and mSUGRA,
reference adde
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