Anomaly Cancellation in Supergravity with Fayet-Iliopoulos Couplings

We review and clarify the cancellation conditions for gauge anomalies which occur when N=1, D=4 supergravity is coupled to a Kahler non-linear sigma-model with gauged isometries and Fayet-Iliopoulos couplings. For a flat sigma-model target space and vanishing Fayet-Iliopoulos couplings, consistency requires just the conventional anomaly cancellation conditions. A consistent model with non-vanishing Fayet-Iliopoulos couplings is unlikely unless the Green-Schwarz mechanism is used. In this case the U(1) gauge boson becomes massive and the D-term potential receives corrections. A Green-Schwarz mechanism can remove both the abelian and certain non-abelian anomalies in models with a gauge non-invariant Kahler potential.Comment: 27 page

Kahler Anomalies in Supergravity and Flux Vacua

We review the subject of Kahler anomalies in gauged supergravity, emphasizing that field equations are inconsistent when the Kahler potential is non-invariant under gauge transformations or when there are elementary Fayet-Iliopoulos couplings. Flux vacua solutions of string theory with gauged U(1) shift symmetries appear to avoid this problem. The covariant Kahler anomalies involve tensors which are composite functions of the scalars as well as the gauge field strength and space-time curvature tensors. Anomaly cancellation conditions will be discussed in a sequel to this paper.Comment: 29 pages; v2: revised presentation, section on Fayet-Iliopoulos couplings cut, effects of gauginos on anomalies included, references adde

Hierarchically Split Supersymmetry with Fayet-Iliopoulos D-terms in String Theory

We show that in string theory or supergravity with supersymmetry breaking through combined F-terms and Fayet-Iliopoulos D-terms, the masses for charged scalars and fermions can be hierarchically split. The mass scale for the gauginos and higgsinos of the MSSM is controlled by the gravitino mass m_{3/2}, as usual, while the scalars get extra contributions from the D-terms of extra abelian U(1) factors, which can make them much heavier. The vanishing of the vacuum energy requires that their masses lie below {m_{3/2} M_{Pl}}^{1/2}, which for m_{3/2}=O(TeV) sets a bound of 10^{10-13} GeV. Thus, scalars with non-vanishing U(1) charges typically become heavy, while others remain light, producing a spectrum of scalars with masses proportional to their charges, and therefore non-universal. This is a modification of the split supersymmetry scenario, but with a light gravitino. We discuss how Fayet-Iliopoulos terms of this size can arise in orientifold string compactifications with D-branes. Furthermore, within the frame work of D-term inflation, the same vacuum energy that generates the heavy scalar masses can be responsible for driving cosmological inflation.Comment: 25 pages, 1 figure; v2: references adde

A Supersymmetric Stueckelberg U(1) Extension of the MSSM

A Stueckelberg extension of the MSSM with only one abelian vector and one chiral superfield as an alternative to an abelian extension with Higgs scalars is presented. The bosonic sector contains a new gauge boson Z' which is a sharp resonance, and a new CP-even scalar, which combines with the MSSM Higgs bosons to produce three neutral CP-even massive states. The neutral fermionic sector has two additional fermions which mix with the four MSSM neutralinos to produce an extended 6x6 neutralino mass matrix. For the case when the LSP is composed mostly of the Stueckelberg fermions, the LSP of the MSSM will be unstable, which leads to exotic decays of sparticles with many leptons in final states. Prospects for supersymmetry searches and for dark matter are discussed.Comment: 10 page

String Loop Corrections to Kahler Potentials in Orientifolds

We determine one-loop string corrections to Kahler potentials in type IIB orientifold compactifications with either N=1 or N=2 supersymmetry, including D-brane moduli, by evaluating string scattering amplitudes.Comment: 80 pages, 4 figure

A Stueckelberg Extension of the Standard Model

An extension of the standard model of electro-weak interactions by an extra abelian gauge boson is given, in which the extra gauge boson and the hypercharge gauge boson both couple to an axionic scalar in a form that leads to a Stueckelberg mass term. The theory leads to a massive Z$'$ whose couplings to fermions are uniquely determined and suppressed by small mixing angles. Such a Z$'$ could have low mass and appear in $e^+e^-$ collisions as a sharp resonance. The branching ratios into $f\bar f$ species, and the forward-backward asymmetry are found to have distinctive features. The model also predicts a new unit of electric charge $e'=Q'e$, where $Q'$ is in general irrational, in the coupling of the photon with hidden matter that is neutral under $SU(2)_L\times U(1)_Y$.Comment: 8 pages, no figures. To appear in Physics Letters

Asymmetric Orbifolds, Noncommutative Geometry and Type I String Vacua

We investigate the D-brane contents of asymmetric orbifolds. Using T-duality we find that the consistent description of open strings in asymmetric orbifolds requires to turn on background gauge fields on the D-branes. We derive the corresponding noncommutative geometry arising on such D-branes with mixed Neumann-Dirichlet boundary conditions directly by applying an asymmetric rotation to open strings with pure Dirichlet or Neumann boundary conditions. As a concrete application of our results we construct asymmetric type I vacua requiring open strings with mixed boundary conditions for tadpole cancellation.Comment: TeX, harvmac, 24 pages, 2 figures, v2: Clarifying remarks concerning the identification of commutative and non-commutative theories on asymmetric orbifolds; additional reference

Fluxes and Branes in Type II Vacua and M-theory Geometry with G(2) and Spin(7) Holonomy

We discuss fluxes of RR and NSNS background fields in type II string compactifications on non-compact Calabi-Yau threefolds together with their dual brane description which involves bound states of branes. Simultaneously turning on RR and NSNS 2-form fluxes in an 1/2 supersymmetric way can be geometrically described in M-theory by a SL(2,Z) family of metrics of G(2) holonomy. On the other hand, if the flux configuration only preserves 1/4 of supersymmetries, we postulate the existence of a new eight-dimensional manifold with spin(7) holonomy, which does not seem to fit into the classes of known examples. The latter situation is dual to a 1/4 supersymmetric web of branes on the deformed conifold. In addition to the 2-form fluxes, we also present some considerations on type IIA NSNS 4-form and 6-form fluxes.Comment: 34 pages, latex, no figures, changed appendix on Spin(7) metrics, more references adde

Moduli Stabilization for Intersecting Brane Worlds in Type 0' String Theory

Starting from the non-supersymmetric, tachyon-free orientifold of type 0 string theory, we construct four-dimensional brane world models with D6-branes intersecting at angles on internal tori. They support phenomenologically interesting gauge theories with chiral fermions. Despite the theory being non-supersymmetric the perturbative scalar potential induced at leading order is shown to stabilize geometric moduli, leaving only the dilaton tadpole uncanceled. As an example we present a three generation model with gauge group and fermion spectrum close to a left-right symmetric extension of the Standard Model.Comment: 20 pages, 2 figures, LaTe