Generic Tests of CP Violation in High-p_{T} Multilepton Signals at the LHC and Beyond.

We introduce a modification to the standard expression for tree-level CP violation in scattering processes at the LHC, which is important when the initial state is not self-conjugate. Based on that, we propose a generic and model-independent search strategy for probing tree-level CP violation in inclusive multilepton signals. We then use TeV-scale 4-fermion operators of the form tuℓℓ and tcℓℓ with complex Wilson coefficients as an illustrative example and show that it may generate O(10%) CP asymmetries that should be accessible at the LHC with an integrated luminosity of O(1000) fb^{-1}.

Pragmatic approach to the little hierarchy problem: the case for dark matter and neutrino physics.

We show that the addition of real scalars (gauge singlets) to the standard model can both ameliorate the little hierarchy problem and provide realistic dark matter candidates. To this end, the coupling of the new scalars to the standard Higgs boson must be relatively strong and their mass should be in the 1-3 TeV range, while the lowest cutoff of the (unspecified) UV completion must be > or ~ 5 TeV, depending on the Higgs boson mass and the number of singlets present. The existence of the singlets also leads to realistic, and surprisingly reach, neutrino physics. The resulting light neutrino mass spectrum and mixing angles are consistent with the constraints from the neutrino oscillations.

Difficulties for five-dimensional gauge-higgs unification.

We consider five-dimensional gauge theories where all fields propagate in the bulk and the fifth direction is compactified on the orbifold S1/Z2, and where the fifth components of the gauge bosons play the role of the standard model Higgs boson (gauge-Higgs unification). The gauge symmetry breaking is realized through the appropriate orbifold boundary conditions and through the Hosotani mechanism. We show that for any such theory (with neither brane gauge kinetic terms nor anomalous gauge-group factors) the assumption that the low-energy vector-boson spectrum consists of the W(+/-), Z, and gamma only, is inconsistent with the experimental requirements sin2thetaW approximately 1/4 and rho identical with mW2/(mZ2 cos2theta w) = 1.

CP violation from five-dimensional QED.

It is shown that QED in (1 + 4)-dimensional space-time, with the fifth dimension compactified on a circle, is, in general, a CP violating theory. Depending on the fermionic boundary conditions, CP violation may be either explicit (through the Scherk-Schwarz mechanism) or spontaneous (via the Hosotani mechanism). The fifth component of the gauge field acquires (at the one-loop level) a nonzero vacuum expectation value which, in the presence of two fermionic fields, leads to spontaneous CP violation when the boundary conditions are CP symmetric. Phenomenological consequences are illustrated by a calculation of the electric dipole moment for the fermionic zero modes.

Bounds on the Higgs-boson mass in the presence of nonstandard interactions.

The triviality and vacuum stability bounds on the Higgs-boson mass are derived in the presence of weakly coupled new interactions parametrized in a model-independent way by an effective Lagrangian. When the scale of new physics Lambda is below 50 TeV the triviality bound is unchanged but the stability lower bound is increased by 40-60 GeV if the effective Lagrangian parameters are O(1) at the scale Lambda. In this case a Higgs-boson mass close to its current lower experimental limit would indicate the presence of new physics at the scale of a few TeV.