54 research outputs found
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
On the unfolding of the fundamental region in integrals of modular invariant amplitudes
We study generic one-loop (string) amplitudes where an integration over the
fundamental region F of the modular group is needed. We show how the known
lattice-reduction technique used to unfold F to a more suitable region S can be
modified to rearrange generic modular invariant amplitudes. The main aim is to
unfold F to the strip and, at the same time, to simplify the form of the
integrand when it is a sum over a finite number of terms, like in one-loop
amplitudes for closed strings compactified on orbifolds. We give a general
formula and a recipe to compute modular invariant amplitudes. As an application
of the technique we compute the one-loop vacuum energy \rho_n for a generic
\Z_n freely acting orbifold, generalizing the result that this energy is less
than zero and drives the system to a tachyonic divergence, and that
\rho_nm.Comment: 10 pages, 2 figure
D-type supersymmetry breaking and brane-to-brane gravity mediation
We revisit the issue of gravitational contributions to soft masses in
five-dimensional sequestered models. We point out that, unlike for the case of
F-type supersymmetry breaking, for D-type breaking these effects generically
give positive soft masses squared for the sfermions. This drastically improves
model building. We discuss the phenomenological implications of our result.Comment: 16 pages. Typos corrected, minor clarifications. To be published in
Phys. Lett.
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
Anomalies on orbifolds with gauge symmetry breaking
We embed two 4D chiral multiplets of opposite representations in the 5D N=2
gauge theory compactified on an orbifold .
There are two types of orbifold boundary conditions in the extra dimension to
obtain the 4D N=1 gauge theory from the bulk: in
Type I, one has the bulk gauge group at and the unbroken gauge group at
while in Type II, one has the unbroken gauge group at both fixed
points. In both types of orbifold boundary conditions, we consider the zero
mode(s) as coming from a bulk -plet and brane fields at the fixed
point(s) with the unbroken gauge group. We check the consistency of this
embedding of fields by the localized anomalies and the localized FI terms. We
show that the localized anomalies in Type I are cancelled exactly by the
introduction of a bulk Chern-Simons term. On the other hand, in some class of
Type II, the Chern-Simons term is not enough to cancel all localized anomalies
even if they are globally vanishing. We also find that for the consistent
embedding of brane fields, there appear only the localized log FI terms at the
fixed point(s) with a U(1) factor.Comment: LaTeX file of 19 pages with no figure, published versio
Effective theoretical approach of Gauge-Higgs unification model and its phenomenological applications
We derive the low energy effective theory of Gauge-Higgs unification (GHU)
models in the usual four dimensional framework. We find that the theories are
described by only the zero-modes with a particular renormalization condition in
which essential informations about GHU models are included. We call this
condition ``Gauge-Higgs condition'' in this letter. In other wards, we can
describe the low energy theory as the SM with this condition if GHU is a model
as the UV completion of the Standard Model. This approach will be a powerful
tool to construct realistic models for GHU and to investigate their low energy
phenomena.Comment: 18 pages, 2 figures; Two paragraphs discussing the applicable scope
of this approach are adde
Open string models with Scherk-Schwarz SUSY breaking and localized anomalies
We study examples of chiral four-dimensional IIB orientifolds with
Scherk--Schwarz supersymmetry breaking, based on freely acting orbifolds. We
construct a new Z3xZ3' model, containing only D9-branes, and rederive from a
more geometric perspective the known Z6'xZ2' model, containing D9, D5 and \bar
D 5 branes. The cancellation of anomalies in these models is then studied
locally in the internal space. These are found to cancel through an interesting
generalization of the Green--Schwarz mechanism involving twisted Ramond--Ramond
axions and 4-forms. The effect of the latter amounts to local counterterms from
a low-energy effective field theory point of view. We also point out that the
number of spontaneously broken U(1) gauge fields is in general greater than
what expected from a four-dimensional analysis of anomalies.Comment: v2: 28 pages, references added; v3: version to appear in Nucl.Phys.
Towards Z_2-protected gauge--Higgs unification
In theories with flux compactification in eight or higher dimensions, the
extra-dimensional components of the gauge field may be regarded as the Higgs
field candidates. We suggest a way to protect these components from getting
large tree-level masses by imposing a -symmetry acting on compact
manifolds and background fields on them. In our scheme the infinite series of
heavy KK modes naturally decouples from the light Higgs candidates, whose
number is generically larger than one. We also present toy models with three
families of leptons, illustrating that the Yukawa sector in our scheme is
fairly strongly constrained. In one of these models, one fermion gets a
tree-level mass after electroweak symmetry breaking, while two others remain
naturally massless at the tree level.Comment: A few points clarified. Journal versio
Minimal gauge-Higgs unification with a flavour symmetry
We show that a flavour symmetry a la Froggatt-Nielsen can be naturally
incorporated in models with gauge-Higgs unification, by exploiting the heavy
fermions that are anyhow needed to realize realistic Yukawa couplings. The case
of the minimal five-dimensional model, in which the SU(2)_L x U(1)_Y
electroweak group is enlarged to an SU(3)_W group, and then broken to U(1)_em
by the combination of an orbifold projection and a Scherk-Schwarz twist, is
studied in detail. We show that the minimal way of incorporating a U(1)_F
flavour symmetry is to enlarge it to an SU(2)_F group, which is then completely
broken by the same orbifold projection and Scherk-Schwarz twist. The general
features of this construction, where ordinary fermions live on the branes
defined by the orbifold fixed-points and messenger fermions live in the bulk,
are compared to those of ordinary four-dimensional flavour models, and some
explicit examples are constructed.Comment: LaTex, 37 pages, 2 figures; some clarifying comments and a few
references adde
Symmetry breaking from Scherk-Schwarz compactification
We analyze the classical stable configurations of an extra-dimensional gauge
theory, in which the extra dimensions are compactified on a torus. Depending on
the particular choice of gauge group and the number of extra dimensions, the
classical vacua compatible with four-dimensional Poincar\'e invariance and zero
instanton number may have zero energy. For SU(N) on a two-dimensional torus, we
find and catalogue all possible degenerate zero-energy stable configurations in
terms of continuous or discrete parameters, for the case of trivial or
non-trivial 't Hooft non-abelian flux, respectively. We then describe the
residual symmetries of each vacua.Comment: 24 pages, 1 figure, Section 4 modifie
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