59 research outputs found
Symmetry Breaking Bulk Effects in Local D-brane Models
We study symmetry breaking effects in local D-brane models that arise as a
result of compactification, taking models constructed on C^3/Z_3 as prototype.
Zero-modes of the Lichnerowicz operator in cone-like geometries have a power
law behaviour; thus the leading symmetry breaking effects are captured by the
modes with the lowest scaling dimension which transform non-trivially under the
isometry group. Combining this with the fact that global symmetries in local
models are gauged upon compactification we determine the strength and form of
the leading operators responsible for the symmetry breaking. We find a
hierarchical separation in the size of symmetry breaking parameters.Comment: 13 pages, 1 figure; v2 typos removed; v3 JHEP versio
Models of Particle Physics from Type IIB String Theory and F-theory: A Review
We review particle physics model building in type IIB string theory and
F-theory. This is a region in the landscape where in principle many of the key
ingredients required for a realistic model of particle physics can be combined
successfully. We begin by reviewing moduli stabilisation within this framework
and its implications for supersymmetry breaking. We then review model building
tools and developments in the weakly coupled type IIB limit, for both local
D3-branes at singularities and global models of intersecting D7-branes. Much of
recent model building work has been in the strongly coupled regime of F-theory
due to the presence of exceptional symmetries which allow for the construction
of phenomenologically appealing Grand Unified Theories. We review both local
and global F-theory model building starting from the fundamental concepts and
tools regarding how the gauge group, matter sector and operators arise, and
ranging to detailed phenomenological properties explored in the literature.Comment: 79 pages, Invited review article for the International Journal of
Modern Physics
Generalized Gross-Neveu Models and Chiral Symmetry Breaking from String Theory
We consider intersecting D-brane models which have two dimensional chiral
fermions localized at the intersections. At weak coupling, the interactions of
these fermions are described by generalized Gross-Neveu models. At strong
coupling, these configurations are described by the dynamics of probe D-branes
in a curved background spacetime. We study patterns of dynamical chiral
symmetry breaking in these models at weak and strong coupling, and also discuss
relationships between these two descriptions.Comment: 23 pages, LaTeX; 16 figure
N-flation with Hierarchically Light Axions in String Compactifications
We present an explicit embedding of axionic N-flation in type IIB string
compactifications where most of the Kahler moduli are stabilised by
perturbative effects, and so are hierarchically heavier than the corresponding
N >> 1 axions whose collective dynamics drives inflation. This is achieved in
the framework of the LARGE Volume Scenario for moduli stabilisation. Our set-up
can be used to realise a model of either inflation or quintessence, just by
varying the volume of the internal space which controls the scale of the
axionic potential. Both cases predict a very high scale of supersymmetry
breaking. A viable reheating of the Standard Model degrees of freedom can be
achieved after the end of inflation due to the perturbative decay of the N
light axions which drive inflation.Comment: 28 pages, no figures, Journal versio
Inflationary Predictions and Moduli Masses
A generic feature of inflationary models in supergravity/string constructions
is vacuum misalignment for the moduli fields. The associated production of
moduli particles leads to an epoch in the post-inflationary history in which
the energy density is dominated by cold moduli particles. This modification of
the post-inflationary history implies that the preferred range for the number
of e-foldings between horizon exit of the modes relevant for CMB observations
and the end of inflation depends on moduli masses. This in turn implies
that the precision CMB observables and are sensitive to moduli
masses. We analyse this sensitivity for some representative models of inflation
and find the effect to be highly relevant for confronting inflationary models
with observations.Comment: 17 pages, 3 figures; v2 minor additions in tex
Wave Functions and Yukawa Couplings in Local String Compactifications
We consider local models of magnetised D7 branes in IIB string
compactifications, focussing on cases where an explicit metric can be written
for the local 4-cycle. The presence of an explicit metric allows analytic
expressions for the gauge bundle and for the chiral matter wavefunctions
through solving the Dirac and Laplace equations. The triple overlap of the
normalised matter wavefunctions generates the physical Yukawa couplings. Our
main examples are the cases of D7 branes on P1xP1 and P2. We consider both
supersymmetric and non-supersymmetric gauge backgrounds and both Abelian and
non-Abelian gauge bundles. We briefly outline potential phenomenological
applications of our results.Comment: 50 pages, 1 figur
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