8 research outputs found
Constraining the string scale: from Planck to Weak and back again
String and field theory ideas have greatly influenced each other since the so
called second string revolution. We review this interrelation paying particular
attention to its phenomenological implications. Our guiding principle is the
radical shift in the way that we think about the fundamental scale, in
particular the way in which string models have been able to accommodate values
from the Planck GeV down to the electroweak scale
TeV.Comment: Invited review aimed at an experimental audienc
M-theory Compactifications on Manifolds with G2 Structure
In this paper we study M-theory compactifications on manifolds of G2
structure. By computing the gravitino mass term in four dimensions we derive
the general form for the superpotential which appears in such compactifications
and show that beside the normal flux term there is a term which appears only
for non-minimal G2 structure. We further apply these results to
compactifications on manifolds with weak G2 holonomy and make a couple of
statements regarding the deformation space of such manifolds. Finally we show
that the superpotential derived from fermionic terms leads to the potential
that can be derived from the explicit compactification, thus strengthening the
conjectures we make about the space of deformations of manifolds with weak G2
holonomy.Comment: 34 pages. Minor changes: typos corrected, references added. Version
to appear in Class. Quantum Gra
Intersecting Brane Worlds -- A Path to the Standard Model ?
In this review we describe the general geometrical framework of brane world
constructions in orientifolds of type IIA string theory with D6-branes wrapping
3-cycles in a Calabi-Yau 3-fold. These branes generically intersect in points
on the internal space, and the patterns of intersections govern the chiral
fermion spectra. We discuss how the open string spectra in intersecting brane
models are constructed, how the Standard Model can be embedded, and also how
supersymmetry can be realized in this class of string vacua. After the general
considerations we specialize the discussion to the case of orbifold backgrounds
with intersecting D6-branes and to the quintic Calabi-Yau manifold. Then, we
discuss parts of the effective action of intersecting brane world models.
Specifically we compute from the Born-Infeld action of the wrapped D-branes the
tree-level, D-term scalar potential, which is important for the stability of
the considered backgrounds as well as for questions related to supersymmetry
breaking. Second, we review the recent computation concerning of gauge coupling
unification and also of one-loop gauge threshold corrections in intersecting
brane world models. Finally we also discuss some aspects of proton decay in
intersecting brane world models.Comment: 31 pages, To appear in the proceedings of the RTN-workshop ``The
quantum structure of spacetime and the geometric nature of fundamental
interactions'', September 2003 in Copenhagen, revised version contains new
refs and one corrected equatio
Building MSSM Flux Vacua
We construct N=1 and N=0 chiral four-dimensional vacua of flux
compactification in Type IIB string theory. These vacua have the common
features that they are free of tadpole instabilities (both NSNS and RR) even
for models with N=0 supersymmetry. In addition, the dilaton/complex structure
moduli are stabilised and the supergravity background metric is warped. We
present an example in which the low energy spectrum contains the MSSM spectrum
with three generations of chiral matter. In the N=0 models, the background
fluxes which stabilise the moduli also induce soft supersymmetry breaking terms
in the gauge and chiral sectors of the theory, while satisfying the equation of
motion. We also discuss some phenomenological features of these three
generation MSSM flux vacua. Our techniques apply to other closed string
backgrounds as well and, in fact, also allow to find new N=1 D-brane models
which were believed not to exist. Finally, we discuss in detail the consistency
conditions of these flux compactifications. Cancellation of K-theory charges
puts additional constraints on the consistency of the models, which render some
chiral D-brane models in the literature inconsistent.Comment: 33 pages, 1 figure. Minor correction
D = 4 chiral string compactifications from intersecting branes
Intersecting Dp -branes often give rise to chiral fermions living on their intersections. We study the construction of four-dimensional chiralgauge theories by considering configurations of type II D(3+n) -branes wrapped on nontrivial n -cycles on T 2n Ă(R 2(3ân) /Z N ), for n=1,â2,â3. The gauge theories on the four noncompact dimensions of the brane world-volume are generically chiral and nonsupersymmetric. We analyze consistency conditions (RR tadpole cancellation) for these models, and their relation to four-dimensional anomaly cancellation. Cancellation of U(1) gauge anomalies involves a GreenâSchwarz mechanism mediated by RR partners of untwisted and/or twisted moduli. This class of models is of potential phenomenological interest, and we construct explicit examples of SU(3)ĂSU(2)ĂU(1) three-generation models. The models are nonsupersymmetric, but the string scale may be lowered close to the weak scale so that the standard hierarchy problem is avoided. We also comment on the presence of scalar tachyons and possible ways to avoid the associated instabilities. We discuss the existence of (meta)stable configurations of D-branes on 3-cycles in (T 2 ) 3 , free of tachyons for certain ranges of the six-torus moduli
The Supermembrane with Central Charges on a G2 Manifold
We construct the 11D supermembrane with topological central charges induced
through an irreducible winding on a G2 manifold realized from the T7/Z2xZ2xZ2
orbifold construction. The hamiltonian H of the theory on a T7 target has a
discrete spectrum. Within the discrete symmetries of H associated to large
diffeomorphisms, the Z2xZ2xZ2 group of automorphisms of the quaternionic
subspaces preserving the octonionic structure is relevant. By performing the
corresponding identification on the target space, the supermembrane may be
formulated on a G2 manifold, preserving the discretness of its supersymmetric
spectrum. The corresponding 4D low energy effective field theory has N=1
supersymmetry.Comment: Reviewed version. spectral propertis discussed, two more sections
added, 27 pages,Late
On N=1 gauge models from geometric engineering in M-theory
We study geometric engineering of four-dimensional N=1 gauge models from M-theory on a seven-dimensional manifold with G_2 holonomy. The manifold is constructed as a K3 fibration over a three-dimensional base space with ADE geometry. The resulting gauge theory is discussed in the realm of (p,q) webs. We discuss how the anomaly cancellation condition translates into a condition on the associated affine ADE Lie algebras