218 research outputs found
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
Constraints on the Bulk Standard Model in the Randall-Sundrum Scenario
We derive constraints on the Randall-Sundrum scenario with the standard model
fields in the bulk. These result from tree level effects associated with the
deformation of the zero mode wave-functions of the W and the Z once electroweak
symmetry is broken. Recently Cs\'{a}ki, Erlich and Terning pointed out that
this implies large contributions to electroweak oblique parameters. Here we
find that when fermions are allowed in the bulk the couplings of the and
the to zero-mode fermions are also affected. We perform a fit to
electroweak observables assuming universal bulk fermion masses and including
all effects and find constraints that are considerably stronger than for the
case with fermions localized in the low energy boundary. These put the lowest
Kaluza-Klein excitation out of reach of the Large Hadron Collider. We then
relax the universality assumption and study the effects of flavor violation in
the bulk and its possible signatures.Comment: 18 pages, 2 ps figure
The Effective Lagrangian in the Randall-Sundrum Model and Electroweak Physics
We consider the two-brane Randall-Sundrum (RS) model with bulk gauge fields.
We carefully match the bulk theory to a 4D low-energy effective Lagrangian. In
addition to the four-fermion operators induced by KK exchange we find that
large negative S and T parameters are induced in the effective theory. This is
a tree-level effect and is a consequence of the shapes of the W and Z wave
functions in the bulk. Such effects are generic in extra dimensional theories
where the standard model (SM) gauge bosons have non-uniform wave functions
along the extra dimension. The corrections to precision electroweak observables
in the RS model are mostly dominated by S. We fit the parameters of the RS
model to the experimental data and find somewhat stronger bounds than
previously obtained; however, the standard model bound on the Higgs mass from
precision measurements can only be slightly relaxed in this theory.Comment: 16 pages, LaTeX, 1 figure included, uses JHEP.cls, extended
introduction, added reference
Precision Electroweak Data and Unification of Couplings in Warped Extra Dimensions
Warped extra dimensions allow a novel way of solving the hierarchy problem,
with all fundamental mass parameters of the theory naturally of the order of
the Planck scale. The observable value of the Higgs vacuum expectation value is
red-shifted, due to the localization of the Higgs field in the extra dimension.
It has been recently observed that, when the gauge fields propagate in the
bulk, unification of the gauge couplings may be achieved. Moreover, the
propagation of fermions in the bulk allows for a simple solution to potentially
dangerous proton decay problems. However, bulk gauge fields and fermions pose a
phenomenological challenge, since they tend to induce large corrections to the
precision electroweak observables. In this article, we study in detail the
effect of gauge and fermion fields propagating in the bulk in the presence of
gauge brane kinetic terms compatible with gauge coupling unification, and we
present ways of obtaining a consistent description of experimental data, while
allowing values of the first Kaluza Klein mode masses of the order of a few
TeV.Comment: 32 pages, 7 figures. References adde
Opaque Branes in Warped Backgrounds
We examine localized kinetic terms for gauge fields which can propagate into
compact, warped extra dimensions. We show that these terms can have a relevant
impact on the values of the Kaluza-Klein (KK) gauge field masses, wave
functions, and couplings to brane and bulk matter. The resulting
phenomenological implications are discussed. In particular, we show that the
presence of opaque branes, with non-vanishing brane-localized gauge kinetic
terms, allow much lower values of the lightest KK mode than in the case of
transparent branes. Moreover, we show that if the large discrepancies among the
different determinations of the weak mixing angle would be solved in favor of
the value obtained from the lepton asymmetries, bulk electroweak gauge fields
in warped-extra dimensions may lead to an improvement of the agreement of the
fit to the electroweak precision data for a Higgs mass of the order of the weak
scale and a mass of the first gauge boson KK excitation most likely within
reach of the LHC.Comment: 37 pages, 12 figures, improved analysis of the precision electroweak
constraint
Flavour Universal Dynamical Electroweak Symmetry Breaking
The top condensate see-saw mechanism of Dobrescu and Hill allows electroweak
symmetry to be broken while deferring the problem of flavour to an electroweak
singlet, massive sector. We provide an extended version of the singlet sector
that naturally accommodates realistic masses for all the standard model
fermions, which play an equal role in breaking electroweak symmetry. The models
result in a relatively light composite Higgs sector with masses typically in
the range of (400-700)~GeV. In more complete models the dynamics will
presumably be driven by a broken gauged family or flavour symmetry group. As an
example of the higher scale dynamics a fully dynamical model of the quark
sector with a GIM mechanism is presented, based on an earlier top condensation
model of King using broken family gauge symmetry interactions (that model was
itself based on a technicolour model of Georgi). The crucial extra ingredient
is a reinterpretation of the condensates that form when several gauge groups
become strong close to the same scale. A related technicolour model of Randall
which naturally includes the leptons too may also be adapted to this scenario.
We discuss the low energy constraints on the massive gauge bosons and scalars
of these models as well as their phenomenology at the TeV scale.Comment: 22 pages, 3 fig
Constraints on Masses of Charged PGBs in Technicolor Model from Decay
In this paper we calculate the contributions to the branching ratio of from the charged Pseudo-Goldstone bosons appeared in one generation
Technicolor model. The current experimental results can eliminate large
part of the parameter space in the plane, and
specifically, one can put a strong lower bound on the masses of color octet
charged PGBs : at for free
.Comment: 9 pages, 3 figures(uuencoded), Minor changes(Type error), to appear
in Phys. Rev.
Higgsless Theory of Electroweak Symmetry Breaking from Warped Space
We study a theory of electroweak symmetry breaking without a Higgs boson,
recently suggested by Csaki et al. The theory is formulated in 5D warped space
with the gauge bosons and matter fields propagating in the bulk. In the 4D dual
picture, the theory appears as the standard model without a Higgs field, but
with an extra gauge group G which becomes strong at the TeV scale. The strong
dynamics of G breaks the electroweak symmetry, giving the masses for the W and
Z bosons and the quarks and leptons. We study corrections in 5D which are
logarithmically enhanced by the large mass ratio between the Planck and weak
scales, and show that they do not destroy the structure of the electroweak
gauge sector at the leading order. We introduce a new parameter, the ratio
between the two bulk gauge couplings, into the theory and find that it allows
us to control the scale of new physics. We also present a potentially realistic
theory accommodating quarks and leptons and discuss its implications, including
the violation of universality in the W and Z boson couplings to matter and the
spectrum of the Kaluza-Klein excitations of the gauge bosons. The theory
reproduces many successful features of the standard model, although some
cancellations may still be needed to satisfy constraints from the precision
electroweak data.Comment: 17 pages, Latex; important correction in discussions on effects from
brane terms, reference adde
RS1, Custodial Isospin and Precision Tests
We study precision electroweak constraints within a RS1 model with gauge
fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to
SU(2)_L \times SU(2)_R \times U(1)_{B-L}, thereby providing a custodial isospin
symmetry sufficient to suppress excessive contributions to the T parameter. We
then construct complete models, complying with all electroweak constraints, for
solving the hierarchy problem, without supersymmetry or large hierarchies in
the fundamental couplings. Using the AdS/CFT correspondence our models can be
interpreted as dual to a strongly coupled conformal Higgs sector with global
custodial symmetry, gauge and fermionic matter being fundamental fields
external to the CFT. This scenario has interesting collider signals, distinct
from other RS models in the literature.Comment: 32 pages, 6 figures, latex2e, minor changes, references adde
Fermions on an Interval: Quark and Lepton Masses without a Higgs
We consider fermions on an extra dimensional interval. We find the boundary
conditions at the ends of the interval that are consistent with the variational
principle, and explain which ones arise in various physical circumstances. We
apply these results to higgsless models of electroweak symmetry breaking, where
electroweak symmetry is not broken by a scalar vacuum expectation value, but
rather by the boundary conditions of the gauge fields. We show that it is
possible to find a set of boundary conditions for bulk fermions that would give
a realistic fermion mass spectrum without the presence of a Higgs scalar, and
present some sample fermion mass spectra for the standard model quarks and
leptons as well as their resonances.Comment: LaTeX, 36 pages, 5 figure
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