434 research outputs found
Naturalness from a Composite Top?
We consider a theory with composite top quarks but an elementary Higgs boson.
The hierarchy problem can be solved by supplementing TeV scale top
compositeness with either supersymmetry or Higgs compositeness appearing at the
multi-TeV scale. The Higgs boson couples to uncolored partons within the top
quark. We study how this approach can give rise to a novel screening effect
that suppresses production of the colored top partners at the LHC. Strong
constraints arise from Z to bb, as well potentially from flavor physics.
Independent of flavor considerations, current constraints imply a compositeness
scale near a TeV; this implies that the model is likely tuned at the percent
level. Four top quark production at the LHC is a smoking-gun probe of this
scenario. New CP violation in D meson mixing is also possible.Comment: Improved discussion of precision electroweak constraints. Expanded
discussion of potential mixing between composite and elementary fields.
Version to appear in JHE
Testing a U(1) Solution to the Mu Problem
We discuss the collider phenomenology of TeV Z' gauge bosons related to the
absence of a bare mu-term in the superpotential. Decays of the type Z' -->
Higgsinos can directly test whether a gauge symmetry is responsible for
forbidding the Higgsino mass. Decays to multi-lepton final states may allow
these signatures to be observed at the Large Hadron Collider. We comment on
whether it will be possible to state definitively that the mu-term is forbidden
via a gauge symmetry.Comment: 16+1 pages, 4 figure
Neutrinos from Off-Shell Final States and the Indirect Detection of Dark Matter
We revisit the annihilation of dark matter to neutrinos in the Sun near the
WW and tt kinematic thresholds. We investigate the potential importance of
annihilation to WW* in a minimal dark matter model in which a Majorana singlet
is mixed with a vector-like electroweak doublet, but many results generalize to
other models of weakly-interacting dark matter. We re-evaluate the indirect
detection constraints on this model and find that, once all annihilation
channels are properly taken into account, the most stringent constraints on
spin-dependent scattering for dark matter mass 60 GeV < mX < mt are derived
from the results of the Super-Kamiokande experiment. Moreover, we establish the
model-independent statement that Majorana dark matter whose thermal relic
abundance and neutrino signals are both controlled by annihilation via an
s-channel Z boson is excluded for 70 GeV < mX < mW. In some models,
annihilation to tt* can affect indirect detection, notably by competing with
annihilation to gauge boson final states and thereby weakening neutrino
signals. However, in the minimal model, this final state is largely negligible,
only allowing dark matter with mass a few GeV below the top quark mass to evade
exclusion.Comment: 22 pages, 5 figure
Sfermion Interference in Neutralino Decays at the LHC
If the two lightest neutralinos of the Minimal Supersymmetric Standard Model
have a mass splitting less than the Z boson mass, interference effects in the
three-body decay chi_2^0 --> chi_1^0 f f can be important. We formulate an
observable that contains information on the nature of the interference: the
ratio BR(chi_2^0 --> chi_1^0 b b) / BR(chi_2^0 --> chi_1^0 l+ l-). This will
give a constraint on the supersymmetry breaking parameters that is
complementary to many techniques already existing in the literature. We present
some ideas on how to perform a simple counting experiment to determine this
ratio.Comment: 14 pages, 6 figure
Exotic Top Partners and Little Higgs
Little Higgs models often give rise to top partners beyond the minimal ones
necessary for the cancellation of quadratic divergences. We review how this
occurs and discuss the phenomenology of these exotic states. We emphasize the
possible importance of new pseudo-Nambu-Goldstone bosons in top partner decays.
Indeed, cascade decays of exotic top partners may be the best way to discover
these new bosons. We illustrate these points with a new Little Higgs
construction based on an SO(10)/SO(5)^2 coset structure, which fills a gap in
the model building literature. These observations motivate new search
strategies for top partners at the LHC, including for final states with b-jets
and a large multiplicity of electroweak bosons.Comment: 27 pages, 2 figures, 4 tables; v3: JHEP revision -- updated to
include discussion of naturalness and section 2.1 expande
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