25,485 research outputs found
On Vector Bundles and Chiral Matter in N=1 Heterotic Compactifications
In this note we derive the net number of generations of chiral fermions in
heterotic string compactifications on Calabi-Yau threefolds with certain SU(n)
vector bundles, for n odd, using the parabolic approach for bundles. We compare
our results with the spectral cover construction for bundles and make a comment
on the net number interpretation in F-theory.Comment: 8pp,latex,minor changes,note adde
Standard Model bundles of the heterotic string
We show how to construct supersymmetric three-generation models with gauge
group and matter content of the Standard Model in the framework of
non-simply-connected elliptically fibered Calabi-Yau manifolds Z. The elliptic
fibration on a cover Calabi-Yau, where the model has 6 generations of SU(5) and
the bundle is given via the spectral cover description, has a second section
leading to the needed free involution. The relevant involution on the defining
spectral data of the bundle is identified for a general Calabi-Yau of this type
and invariant bundles are generally constructible.Comment: 23 pp; minor remarks adde
Extension Bundles and the Standard Model
We construct a new class of stable vector bundles suitable for heterotic
string compactifications. Using these we describe a novel way to derive the
fermionic matter content of the Standard Model from the heterotic string. For
this we compactify on an elliptically fibered Calabi-Yau threefold X with two
sections, the B-fibration, a variant of the ordinary Weierstrass fibration,
which allows X to carry a free involution. We construct rank five vector
bundles, invariant under this involution, such that turning on a Wilson line we
obtain the Standard Model gauge group and find various three generation models.
This rank five bundle is derived from a stable rank four bundle that arises as
an extension of bundles pulled-back from the base and twisted by suitable line
bundles. We also give an account of various previous results and put the
present construction into perspective.Comment: 31 pages, harvmac, references adde
Top Quark Properties
Recent measurements of top-quark properties at the LHC and at the Tevatron
are presented. The results include precision measurements of standard model
parameters, such as the top-quark mass, the measurement of angular
distributions as well as the search for anomalous couplings.Comment: Conference proceedings for Lepton Photon, Ljubljana, 17-22 August
2015, 12 pages, 10 figure
Top Quark Production
Recent measurements of top quark pair and single top production are
presented. The results include inclusive cross sections as well as studies of
differential distributions. Evidence for single top quark production in
association with a W-boson in the final state is reported for the first time.
Calculations in perturbative QCD up to approximate next-to-next-to-leading
order show very good agreement with the data.Comment: Physics in Collision, Slovakia, 2012 PSNUM 0
Three-Branes and Five-Branes in N=1 Dual String Pairs
In this note we show that in dual N=1 string vacua provided by the heterotic
string on an elliptic Calabi-Yau together with a vector bundle respectively
F-theory on Calabi-Yau fourfold the number of heterotic fivebranes necessary
for anomaly cancellation matches the number of F-theory threebranes necessary
for tadpole cancellation. This extends to the general case the work of
Friedman, Morgan and Witten, who treated the case of embedding a heterotic
bundle, leaving no unbroken gauge group, where one has a smooth
Weierstrass model on the F-theory side.Comment: 22 pages, latex, minor chang
SU(5) Heterotic Standard Model Bundles
We construct a class of stable SU(5) bundles on an elliptically fibered
Calabi-Yau threefold with two sections, a variant of the ordinary Weierstrass
fibration, which admits a free involution. The bundles are invariant under the
involution, solve the topological constraint imposed by the heterotic anomaly
equation and give three generations of Standard Model fermions after symmetry
breaking by Wilson lines of the intermediate SU(5) GUT-group to the Standard
Model gauge group. Among the solutions we find some which can be perturbed to
solutions of the Strominger system. Thus these solutions provide a step toward
the construction of phenomenologically realistic heterotic flux
compactifications via non-Kahler deformations of Calabi-Yau geometries with
bundles. This particular class of solutions involves a rank two hidden sector
bundle and does not require background fivebranes for anomaly cancellation.Comment: 17 page
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