640 research outputs found
5D UED: Flat and Flavorless
5D UED is not automatically minimally flavor violating. This is due to flavor
asymmetric counter-terms required on the branes. Additionally, there are likely
to be higher dimensional operators which directly contribute to flavor
observables. We document a mostly unsuccessful attempt at utilizing
localization in a flat extra dimension to resolve these flavor constraints
while maintaining KK-parity as a good quantum number. It is unsuccessful
insofar as we seem to be forced to add brane operators in such a way as to
precisely mimic the effects of a double throat warped extra dimension. In the
course of our efforts, we encounter and present solutions to a problem common
to many extra dimensional models in which fields are "doubly localized:"
ultra-light modes. Under scrutiny, this issue seems tied to an intrinsic
tension between maintaining Kaluza-Klein parity and resolving mass hierarchies
via localization.Comment: 27 pages, 6 figure
Conformal Technicolor
We point out that the flavor problem in theories with dynamical electroweak
symmetry breaking can be effectively decoupled if the physics above the TeV
scale is strongly conformal, and the electroweak order parameter has a scaling
dimension d = 1 + epsilon with epsilon \simeq 1/few. There are many
restrictions on small values of epsilon: for epsilon << 1, electroweak symmetry
breaking requires a fine-tuning similar to that of the standard model; large-N
conformal field theories (including those obtained from the AdS/CFT
correspondence) require fine-tuning for d < 2; `walking technicolor' theories
cannot have d < 2, according to gap equation analyses. However, strong small-N
conformal field theories with epsilon \simeq 1/few avoid all these constraints,
and can give rise to natural dynamical electroweak symmetry breaking with a top
quark flavor scale of order 10^{1/epsilon} TeV, large enough to decouple
flavor. Small-N theories also have an acceptably small Peskin-Takeuchi S
parameter. This class of theories provides a new direction for dynamical
electroweak symmetry breaking without problems from flavor or electroweak
precision tests. A possible signal for these theories is a prominent scalar
resonance below the TeV scale with couplings similar to a heavy standard model
Higgs.Comment: 26 pages + References. Slight wording changes. Version appearing in
JHE
Radius-dependent gauge unification in AdS5
We examine the relation of the 4-dimensional low energy coupling of bulk
gauge boson in a slice of AdS5 to the 5-dimensional fundamental couplings as a
function of the orbifold radius R. This allows us to address the gauge coupling
unification in AdS5 by means of the radius running as well as the conventional
momentum running. We then compute the radius dependence of 1-loop low energy
couplings in generic AdS5 theory with 4-dimensional supersymmetry, and discuss
the low energy predictions when the 5-dimensional couplings are assumed to be
unified.Comment: 11 pages, 2 figures, revtex, v3: analysis was generalized to
S^1/Z_2*Z_2 orbifoldin
Signals of Supersymmetric Lepton Flavor Violation at the LHC
In a generic supersymmetric extension of the Standard Model, there will be
lepton flavor violation at a neutral gaugino vertex due to misalignment between
the lepton Yukawa couplings and the slepton soft masses. Sleptons produced at
the LHC through the cascade decays of squarks and gluinos can give a sizable
number of events with 4 leptons. This channel could give a clean signature of
supersymmetric lepton flavor violation under conditions which are identified.Comment: 21 page
QCD Corrections to Vector-Boson Fusion Processes in Warped Higgsless Models
We discuss the signatures of a representative Higgsless model with ideal
fermion delocalization in vector-boson fusion processes, focusing on the gold-
and silver-plated decay modes of the gauge bosons at the CERN-Large Hadron
Collider. For this purpose, we have developed a fully-flexible parton-level
Monte-Carlo program, which allows for the calculation of cross sections and
kinematic distributions within experimentally feasible selection cuts at
NLO-QCD accuracy. We find that Kaluza-Klein resonances give rise to very
distinctive distributions of the decay leptons. Similar to the Standard Model
case, within the Higgsless scenario the perturbative treatment of the
vector-boson scattering processes is under excellent control.Comment: 22 pages, 20 figure
Oblique Corrections from Higgsless Models in Warped Space
We calculate the tree-level oblique corrections to electroweak precision
observables generated in higgless models of electroweak symmetry breaking with
a 5D SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group on a warped background. In the
absence of brane induced kinetic terms (and equal left and right gauge
couplings) we find the S parameter to be ~1.15, while T,U~0, as in technicolor
theories. Planck brane induced kinetic terms and unequal left-right couplings
can lower S, however for sufficiently low values of S tree-level unitarity will
be lost. A kinetic term localized on the TeV brane for SU(2)_D will generically
increase S, however an induced kinetic term for U(1)_{B-L} on the TeV brane
will lower S. With an appropriate choice of the value of this induced kinetic
term S~0 can be achieved. In this case the mass of the lowest Z' mode will be
lowered to about ~300 GeV.Comment: 18 pages, LaTeX, 2 figures include
Discovering the composite Higgs through the decay of a heavy fermion
A possible composite nature of the Higgs could be revealed at the early stage
of the LHC, by analyzing the channels where the Higgs is produced from the
decay of a heavy fermion. The Higgs production from a singly-produced heavy
bottom, in particular, proves to be a promising channel. For a value \lambda=3
of the Higgs coupling to a heavy bottom, for example, we find that, considering
a 125 GeV Higgs which decays into a pair of b-quarks, a discovery is possible
at the 8 TeV LHC with 30 fb^{-1} if the heavy bottom is lighter than roughly
530 GeV (while an observation is possible for heavy bottom masses up to 650
GeV). Such a relatively light heavy bottom is realistic in composite Higgs
models of the type considered and, up to now, experimentally allowed. At
\sqrt{s}=14 TeV the LHC sensitivity on the channel increases significantly.
With \lambda=3 a discovery can occur, with 100 fb^{-1}, for heavy bottom masses
up to 1040 GeV. In the case the heavy bottom was as light as 500 GeV, the 14
TeV LHC would be sensitive to the measure of the \lambda\ coupling in basically
the full range \lambda>1 predicted by the theory.Comment: 25 pp. v2: Minor changes. v3: Version accepted for publication in
JHEP. v4: typos fixe
Low-scale warped extra dimension and its predilection for multiple top quarks
Within warped extra dimension models that explain flavor through geometry,
flavor changing neutral current constraints generally force the Kaluza-Klein
scale to be above many TeV. This creates tension with a natural electroweak
scale. On the other hand, a much lower scale compatible with precision
electroweak and flavor changing neutral current constraints is allowed if we
decouple the Kaluza-Klein states of Standard Model gauge bosons from light
fermions bulk mass parameters). The main
signature for this approach is four top quark production via the Kaluza-Klein
excitations' strong coupling to top quarks. We study single lepton, like-sign
dilepton, and trilepton observables of four-top events at the Large Hadron
Collider. The like-sign dilepton signature typically has the largest discovery
potential for a strongly coupled right-handed top case (M_{KK} \sim 2-2.5
\TeV), while single lepton is the better when the left-handed top couples most
strongly (M_{KK} \sim 2 \TeV). We also describe challenging lepton-jet
collimation issues in the like-sign dilepton and trilepton channels. An
alternative single lepton observable is considered which takes advantage of the
many bottom quarks in the final state. Although searches of other particles may
compete, we find that four top production via Kaluza-Klein gluons is most
promising in a large region of this parameter space.Comment: 35 pages, 8 figures. discussions improved, references adde
Heavy-light decay topologies as a new strategy to discover a heavy gluon
We study the collider phenomenology of the lightest Kaluza-Klein excitation
of the gluon, G*, in theories with a warped extra dimension. We do so by means
of a two-site effective lagrangian which includes only the lowest-lying spin-1
and spin-1/2 resonances. We point out the importance of the decays of G* to one
SM plus one heavy fermion, that were overlooked in the previous literature. It
turns out that, when kinematically allowed, such heavy-light decays are
powerful channels for discovering the G*. In particular, we present a
parton-level Montecarlo analysis of the final state Wtb that follows from the
decay of G* to one SM top or bottom quark plus its heavy partner. We find that
at \sqrt{s} = 7 TeV and with 10 fb^{-1} of integrated luminosity, the LHC can
discover a KK gluon with mass in the range M_{G*} = (1.8 - 2.2) TeV if its
coupling to a pair of light quarks is g_{G*qqbar} = (0.2-0.5) g_3. The same
process is also competitive for the discovery of the top and bottom partners as
well. We find, for example, that the LHC at \sqrt{s} = 7 TeV can discover a 1
TeV KK bottom quark with an integrated luminosity of (5.3 - 0.61) fb^{-1} for
g_{G*qqbar} = (0.2-0.5) g_3.Comment: 36 pages, 13 figures. v2: a few typos corrected, comments added,
version published in JHE
SUSY Splits, But Then Returns
We study the phenomenon of accidental or "emergent" supersymmetry within
gauge theory and connect it to the scenarios of Split Supersymmetry and Higgs
compositeness. Combining these elements leads to a significant refinement and
extension of the proposal of Partial Supersymmetry, in which supersymmetry is
broken at very high energies but with a remnant surviving to the weak scale.
The Hierarchy Problem is then solved by a non-trivial partnership between
supersymmetry and compositeness, giving a promising approach for reconciling
Higgs naturalness with the wealth of precision experimental data. We discuss
aspects of this scenario from the AdS/CFT dual viewpoint of higher-dimensional
warped compactification. It is argued that string theory constructions with
high scale supersymmetry breaking which realize warped/composite solutions to
the Hierarchy Problem may well be accompanied by some or all of the features
described. The central phenomenological considerations and expectations are
discussed, with more detailed modelling within warped effective field theory
reserved for future work.Comment: 29 pages. Flavor and CP constraints on left-right symmetric structure
briefly discussed. References adde
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