81 research outputs found
Dynamically SUSY Breaking SQCD on F-Theory Seven-Branes
We study how dynamically breaking SQCD can be obtained on two intersecting
seven-branes in F-theory. In the mechanism which we present in this paper one
of the seven-branes is responsible for producing the low-energy gauge group and
the other one is for generating vector bundle moduli. The fundamental matter
charged under the gauge group is localized on the intersection. The mass of the
matter fields is controlled by the vector bundle moduli. The analysis of under
what conditions a sufficient number of the fundamental flavors becomes light
turns out to be equivalent to the analysis of non-perturbative superpotentials
for vector bundle moduli in Heterotic M-theory. We give an example in which we
present an explicit equation in the moduli space whose zero locus corresponds
to the fundamental fields becoming light. This allows us to provide a local
F-theory realization of massive , SQCD in the free
magnetic range which dynamically breaks supersymmetry.Comment: 40 pages. v2:references added; v3:minor changes, version published in
JHE
Non-generic Couplings in Supersymmetric Standard Models
We study two phases of a heterotic standard model, obtained from a Calabi-Yau
compactification of the E8xE8 heterotic string, in the context of the
associated four-dimensional effective theories. In the first phase we have a
standard model gauge group, an MSSM spectrum, four additional U(1) symmetries
and singlet fields. In the second phase, obtained from the first by continuing
along the singlet directions, three of the additional U(1) symmetries are
spontaneously broken and the remaining one is a B-L symmetry. In this second
phase, dimension five operators inducing proton decay are consistent with all
symmetries and as such, they are expected to be present. We show that, contrary
to this expectation, these operators are forbidden due to the additional U(1)
symmetries present in the first phase of the model. We emphasize that such
'unexpected' absences of operators, due to symmetry enhancement at specific
loci in the moduli space, can be phenomenologically relevant and, in the
present case, protect the model from fast proton decay.Comment: 5 page
A Heterotic Standard Model with B-L Symmetry and a Stable Proton
We consider heterotic Calabi-Yau compactifications with S(U(4)xU(1))
background gauge fields. These models lead to gauge groups with an additional
U(1) factor which, under certain conditions, can combine with hypercharge to a
B-L symmetry. The associated gauge boson is automatically super-massive and,
hence, does not constitute a phenomenological problem. We illustrate this class
of compactifications with a model based on the monad construction, which leads
to a supersymmetric standard model with three families of quarks and leptons,
one pair of Higgs doublets, three right-handed neutrinos and no exotics charged
under the standard model group. The presence of the B-L symmetry means that the
model is safe from proton decay induced by dimension four operators. Due to the
presence of a special locus in moduli space where the bundle structure group is
Abelian and the low-energy symmetry enhances we can also show the absence of
dimension five proton-decay inducing operators.Comment: 23 pages Late
Holomorphic Yukawa Couplings for Complete Intersection Calabi-Yau Manifolds
We develop methods to compute holomorphic Yukawa couplings for heterotic
compactifications on complete intersection Calabi-Yau manifolds, generalising
results of an earlier paper for Calabi-Yau hypersurfaces. Our methods are based
on constructing the required bundle-valued forms explicitly and evaluating the
relevant integrals over the projective ambient space. We also show how our
approach relates to an earlier, algebraic one to calculate the holomorphic
Yukawa couplings. A vanishing theorem, which we prove, implies that certain
Yukawa couplings allowed by low-energy symmetries are zero due to topological
reasons. To illustrate our methods, we calculate Yukawa couplings for
SU(5)-based standard models on a co-dimension two complete intersection
manifold.Comment: 40 pages, Latex; v2: minor corrections, references adde
Non-vanishing Heterotic Superpotentials on Elliptic Fibrations
We present models of heterotic compactification on Calabi-Yau threefolds and
compute the non-perturbative superpotential for vector bundle moduli. The key
feature of these models is that the threefolds, which are elliptically fibered
over del Pezzo surfaces, have homology classes with a unique holomorphic,
isolated genus-zero curve. Using the spectral cover construction, we present
vector bundles for which we can explicitly calculate the Pfaffians associated
with string instantons on these curves. These are shown to be non-zero, thus
leading to a non-vanishing superpotential in the 4D effective action. We
discuss, in detail, why such compactifications avoid the Beasley-Witten residue
theorem.Comment: 1 + 23 page
Non-Gaussianities in New Ekpyrotic Cosmology
New Ekpyrotic Cosmology is an alternative scenario of the early universe
which relies on a phase of slow contraction before the big bang. We calculate
the 3-point and 4-point correlation functions of primordial density
perturbations and find a generically large non-Gaussian signal, just below the
current sensitivity level of CMB experiments. This is in contrast with
slow-roll inflation, which predicts negligible non-Gaussianity. The model is
also distinguishable from alternative inflationary scenarios that yield large
non-Gaussianity, such as DBI inflation and the simplest curvaton-like models,
through the shape dependence of the correlation functions. Non-Gaussianity
therefore provides a distinguishing and testable prediction of New Ekpyrotic
Cosmology.Comment: 4 pages. v2: sign convention clarified, references added; v3: minor
changes, version to appear in PR
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