464 research outputs found
TASI Lectures: Particle Physics from Perturbative and Non-perturbative Effects in D-braneworlds
In these notes we review aspects of semi-realistic particle physics from the
point of view of type II orientifold compactifications. We discuss the
appearance of gauge theories on spacetime filling D-branes which wrap
non-trivial cycles in the Calabi-Yau. Chiral matter can appear at their
intersections, with a natural interpretation of family replication given by the
topological intersection number. We discuss global consistency, including
tadpole cancellation and the generalized Green-Schwarz mechanism, and also the
importance of related global symmetries for superpotential couplings. We
review the basics of D-instantons, which can generate superpotential
corrections to charged matter couplings forbidden by the global
symmetries and may play an important role in moduli stabilization. Finally, for
the purpose of studying the landscape, we discuss certain advantages of
studying quiver gauge theories which arise from type II orientifold
compactifications rather than globally defined models. We utilize the type IIa
geometric picture and CFT techniques to illustrate the main physical points,
though sometimes we supplement the discussion from the type IIb perspective
using complex algebraic geometry.Comment: 35 pages. Based on lectures given by M.C. at TASI 2010. v2: added
references, fixed typo
Singlet Extensions of the MSSM in the Quiver Landscape
We map out possible extensions of the MSSM in the context of type II string
theory. We systematically investigate three-stack and four-stack quivers which
realize the MSSM spectrum with the addition of a single MSSM singlet S with an
allowed S H_u H_d term, which can lead to a dynamical electroweak-scale
mu-term. We present the three quivers which satisfy stringent string-theoretic
and phenomenological constraints, including the presence of non-zero masses for
all three families of quarks and leptons, the perturbative and non-perturbative
absence of R-parity violating couplings and rapid dimension-five proton decay,
and a mechanism for small neutrino masses. We find that these quivers can
realize many models in the class of singlet-extended (supersymmetric) standard
models, as D-instanton effects can in principle generate a superpotential of
the form f(S), where f is a polynomial. Finally, we address the issue of the
stabilization and decoupling of charged moduli which generically appear in
D-instanton corrections to the superpotential.Comment: 15 pages, plus references. Version 2: accepted to JHE
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