97 research outputs found
A New Custodian for a Realistic Higgsless Model
We present an example of a realistic Higgsless model that makes use of
alternative assignments for the top and bottom quarks recently
proposed by Agashe et al. which results in an enhanced custodial symmetry.
Using these new representat ions reduces the deviations in the
coupling to for a wide range of parameters,
while this remaining correction can also be eliminated by varying the
localization parameter (bulk mass) for .Comment: 11 pages, 2 figure
Odd Decays from Even Anomalies: Gauge Mediation Signatures Without SUSY
We analyze the theory and phenomenology of anomalous global chiral symmetries
in the presence of an extra dimension. We propose a simple extension of the
Standard Model in 5D whose signatures closely resemble those of supersymmetry
with gauge mediation, and we suggest a novel scalar dark matter candidate.Comment: 26 pages, 1 figure; v2: references added; discussion of direct
collider constraints added; v3: corrected dark matter calculation in chapter
4.2 and replaced figure 1
Electroweak Symmetry Breaking From Monopole Condensation
We examine models where massless chiral fermions with both "electric" and
"magnetic" hypercharges could form condensates. When some of the fermions are
also electroweak doublets such condensates can break the electroweak gauge
symmetry down to electromagnetism in the correct way. Since ordinary
hypercharge is weakly coupled at the TeV scale, magnetic hypercharge is
strongly coupled and can potentially drive the condensation. Such models are
similar to technicolor, but with hypercharge playing the role of the
technicolor gauge group, so the standard model gauge group breaks itself. A
heavy top mass can be generated via the Rubakov-Callan effect and could thus
decouple the scale of flavor physics from the electroweak scale.Comment: Absence of pseudo-Goldstone bosons explain, discussion of the role of
flavor physics clarified, other minor changes. References adde
Flavor Alignment via Shining in RS
We present a class of warped extra dimensional models whose flavor violating
interactions are much suppressed compared to the usual anarchic case due to
flavor alignment. Such suppression can be achieved in models where part of the
global flavor symmetry is gauged in the bulk and broken in a controlled manner.
We show that the bulk masses can be aligned with the down type Yukawa couplings
by an appropriate choice of bulk flavon field representations and TeV brane
dynamics. This alignment could reduce the flavor violating effects to levels
which allow for a Kaluza-Klein scale as low as 2-3 TeV, making the model
observable at the LHC. However, the up-type Yukawa couplings on the IR brane,
which are bounded from below by recent bounds on CP violation in the D system,
induce flavor misalignment radiatively. Off-diagonal down-type Yukawa couplings
and kinetic mixings for the down quarks are both consequences of this effect.
These radiative Yukawa corrections can be reduced by raising the flavon VEV on
the IR brane (at the price of some moderate tuning), or by extending the Higgs
sector. The flavor changing effects from the radiatively induced Yukawa mixing
terms are at around the current upper experimental bounds. We also show the
generic bounds on UV-brane induced flavor violating effects, and comment on
possible additional flavor violations from bulk flavor gauge bosons and the
bulk Yukawa scalars.Comment: 28 page
New Confining N=1 Supersymmetric Gauge Theories
We examine N=1 supersymmetric gauge theories which confine in the presence of
a tree-level superpotential. We show the confining spectra which satisfy the 't
Hooft anomaly matching conditions and give a simple method to find the
confining superpotential. Using this method we fix the confining
superpotentials in the simplest cases, and show how these superpotentials are
generated by multi-instanton effects in the dual theory. These new type of
confining theories may be useful for model building, since the size of the
matter content is not restricted by an index constraint. Therefore, one expects
that a large variety of new confining spectra can be obtained using such
models.Comment: 26 pages, LaTe
Supersymmetry Breaking Triggered by Monopoles
We investigate N = 1 supersymmetric gauge theories where monopole
condensation triggers supersymmetry breaking in a metastable vacuum. The
low-energy effective theory is an O'Raifeartaigh-like model of the kind
investigated recently by Shih where the R-symmetry can be spontaneously broken.
We examine several implementations with varying degrees of phenomenological
interest.Comment: 20 pages, 4 figures (v2: minor clarifications and typos fixed
N=1 Supersymmetric Product Group Theories in the Coulomb Phase
We study the low-energy behavior of N=1 supersymmetric gauge theories with
product gauge groups SU(N)^M and M chiral superfields transforming in the
fundamental representation of two of the SU(N) factors. These theories are in
the Coulomb phase with an unbroken U(1)^(N-1) gauge group. For N >= 3, M >= 3
the theories are chiral. The low-energy gauge kinetic functions can be obtained
from hyperelliptic curves which we derive by considering various limits of the
theories. We present several consistency checks of the curves including
confinement through the addition of mass perturbations and other limits.Comment: 22 pages, LaTeX, minor changes. Eqs. (20) and (42) correcte
Black Diamonds at Brane Junctions
We discuss the properties of black holes in brane-world scenarios where our
universe is viewed as a four-dimensional sub-manifold of some
higher-dimensional spacetime. We consider in detail such a model where
four-dimensional spacetime lies at the junction of several domain walls in a
higher dimensional anti-de Sitter spacetime. In this model there may be any
number p of infinitely large extra dimensions transverse to the brane-world. We
present an exact solution describing a black p-brane which will induce on the
brane-world the Schwarzschild solution. This exact solution is unstable to the
Gregory-Laflamme instability, whereby long-wavelength perturbations cause the
extended horizon to fragment. We therefore argue that at late times a
non-rotating uncharged black hole in the brane-world is described by a deformed
event horizon in p+4 dimensions which will induce, to good approximation, the
Schwarzschild solution in the four-dimensional brane world. When p=2, this
deformed horizon resembles a black diamond and more generally for p>2, a
polyhedron.Comment: 13 pages, 1 figure, latex, JHEP.cl
Supergravity Models for 3+1 Dimensional QCD
The most general black M5-brane solution of eleven-dimensional supergravity
(with a flat R^4 spacetime in the brane and a regular horizon) is characterized
by charge, mass and two angular momenta. We use this metric to construct
general dual models of large-N QCD (at strong coupling) that depend on two free
parameters. The mass spectrum of scalar particles is determined analytically
(in the WKB approximation) and numerically in the whole two-dimensional
parameter space. We compare the mass spectrum with analogous results from
lattice calculations, and find that the supergravity predictions are close to
the lattice results everywhere on the two dimensional parameter space except
along a special line. We also examine the mass spectrum of the supergravity
Kaluza-Klein (KK) modes and find that the KK modes along the compact D-brane
coordinate decouple from the spectrum for large angular momenta. There are
however KK modes charged under a U(1)xU(1) global symmetry which do not
decouple anywhere on the parameter space. General formulas for the string
tension and action are also given.Comment: 27 pages, LaTeX, 11 figures include
Curing the Ills of Higgsless Models: the S Parameter and Unitarity
We consider various constraints on Higgsless models of electroweak symmetry
breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped
space. First we show that the S parameter which is positive if fermions are
localized on the Planck brane can be lowered (or made vanishing) by changing
the localization of the light fermions. If the wave function of the light
fermions is almost flat their coupling to the gauge boson KK modes will be
close to vanishing, and therefore contributions to the S parameter will be
suppressed. At the same time the experimental bounds on such Z' and W' gauge
bosons become very weak, and their masses can be lowered to make sure that
perturbative unitarity is not violated in this theory before reaching energies
of several TeV. The biggest difficulty of these models is to incorporate a
heavy top quark mass without violating any of the experimental bounds on bottom
quark gauge couplings. In the simplest models of fermion masses a sufficiently
heavy top quark also implies an unacceptably large correction to the Zb\bar{b}
vertex and a large splitting between the KK modes of the top and bottom quarks,
yielding large loop corrections to the T-parameter. We present possible
directions for model building where perhaps these constraints could be obeyed
as well.Comment: 21 pages, LaTeX, 5 figures. References and acknowledgements adde
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