1,169 research outputs found
Associated production of a Kaluza-Klein excitation of a gluon with a t t(bar) pair at the LHC
In Randall-Sundrum models, the Kaluza-Klein (KK) excitations of the gluon,
g_{KK} have enhanced couplings to the right-handed quarks. In the absence of a
gg g_{KK} coupling in these models, the single production of a g_{KK} from an
initial gg state is not possible. The search for other production mechanisms at
the LHC, therefore, becomes important. We suggest that the associated
production of a g_{KK} with a t t(bar) pair is such a mechanism. Our study
shows that through this process the LHC can probe KK gluon masses in the range
of 2.8 -- 2.9 TeV.Comment: 11 pages, 3 figure
Warped Unification, Proton Stability and Dark Matter
Many extensions of the Standard Model have to face the problem of new
unsuppressed baryon-number violating interactions. In supersymmetry, the
simplest way to solve this problem is to assume R-parity conservation. As a
result, the lightest supersymmetric particle becomes stable and a
well-motivated dark matter candidate. In this paper, we show that solving the
problem of baryon number violation in non supersymmetric grand unified theories
(GUT's) in warped higher-dimensional spacetime can lead to a stable
Kaluza-Klein particle. This exotic particle has gauge quantum numbers of a
right-handed neutrino, but carries fractional baryon-number and is related to
the top quark within the higher-dimensional GUT. A combination of baryon-number
and SU(3) color ensures its stability. Its relic density can easily be of the
right value for masses in the 10 GeV--few TeV range. An exciting aspect of
these models is that the entire parameter space will be tested at near future
dark matter direct detection experiments. Other exotic GUT partners of the top
quark are also light and can be produced at high energy colliders with
distinctive signatures.Comment: 4 pages, 4 figures; v2: some comments added, figures updated; v3:
Final version to appear in Phys. Rev. Let
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
Theoretical Predictions for Collider Searches
I review recent developments in extensions of the Standard Model that address
the question of electroweak symmetry breaking and discuss how these theories
can be tested at future colliders.Comment: 13 pages, 2 figures, invited talk at the 21st International Symposium
on Lepton and Photon Interactions at High Energies (Lepton Photon 2003),
11-16 Aug 2003, Batavia, Illinois, US
B-factory Signals for a Warped Extra Dimension
We study predictions for B-physics in a class of models, recently introduced,
with a non-supersymmetric warped extra dimension. In these models few () TeV Kaluza-Klein masses are consistent with electroweak data due to bulk
custodial symmetry. Furthermore, there is an analog of GIM mechanism which is
violated by the heavy top quark (just as in SM) leading to striking signals at
-factories:(i) New Physics (NP) contributions to transitions
are comparable to SM. This implies that, within this NP framework, the success
of SM unitarity triangle fit is a ``coincidence'' Thus, clean extractions of
unitarity angles via e.g. are likely to
be affected, in addition to O(1) deviation from SM prediction in mixing.
(ii) O(1) deviation from SM predictions for in rate as well
as in forward-backward and direct CP asymmetry. (iii) Large mixing-induced CP
asymmetry in radiative B decays, wherein the SM unamibgously predicts very
small asymmetries. Also with KK masses 3 TeV or less, and with anarchic Yukawa
masses, contributions to electric dipole moments of the neutron are roughly 20
times larger than the current experimental bound so that this framework has a
"CP problem".Comment: On further consideration, we found that our framework does have a "CP
problem" in that though contributions to neutron's electric dipole moment
from CKM-like phases vanish at the one-loop level, sizeable contributions are
induced by Majorana-like phases. Last sentence of abstract is changed along
with para #3 and 4 on page
Probing RS scenarios of flavour at LHC via leptonic channels
We study a purely leptonic signature of the Randall-Sundrum scenario with
Standard Model fields in the bulk at LHC: the contribution from the exchange of
Kaluza-Klein (KK) excitations of gauge bosons to the clear Drell-Yan reaction.
We show that this contribution is detectable (even with the low luminosities of
the LHC initial regime) for KK masses around the TeV scale and for sufficiently
large lepton couplings to KK gauge bosons. Such large couplings can be
compatible with ElectroWeak precision data on the Zff coupling in the framework
of the custodial O(3) symmetry recently proposed, for specific configurations
of lepton localizations (along the extra dimension). These configurations can
simultaneously reproduce the correct lepton masses, while generating acceptably
small Flavour Changing Neutral Current (FCNC) effects. This LHC
phenomenological analysis is realistic in the sense that it is based on fermion
localizations which reproduce all the quark/lepton masses plus mixing angles
and respect FCNC constraints in both the hadron and lepton sectors.Comment: 15 pages, 6 Figures, Latex fil
An Improved Model of Direct Gauge Mediation
We present a new, improved model of gauge mediation of dynamical SUSY Breaking: the model does not have gauge messengers or TeV scalars charged under the Standard Model (SM), thus avoiding the problem of negative (mass) for supersymmetric SM (SSM) scalars faced by some earlier models. The gauge mediation is direct, i.e., the messengers which communicate SUSY breaking to the SSM fields carry quantum numbers of the gauge group which breaks SUSY. These messenger fields couple to a modulus field. The model has a very simple particle content: the modulus and the messengers are the only chiral superfields (other than the SSM fields) in the model. The inverted hierarchy mechanism is used to generate a local SUSY breaking minimum for the modulus field in a perturbative regime thus making the model calculable
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