We consider the universal extra dimensions scenario of Appelquist, Cheng, and Dobrescu, in which all of the SM fields propagate into one extra compact dimension, estimated therein to be as large as ∼ (350 GeV) −1 . Tree-level KK number conservation dictates that the associated KK excitations can not be singly produced. We calculate the cross sections for the direct production of KK excitations of the gluon, g n , and two distinct towers of quarks, q • n and q • n , in proton-antiproton collisions at the Tevatron Run I and II energies in addition to proton-proton collisions at the Large Hadron Collider energy. The experimental signatures for these processes depend on the stability of the lowest-lying KK excitations of the gluons and light quarks. We find that the Tevatron Run I mass bound for KK quark and gluon final states is about 350-400 GeV, while Run II can push this up to 450-500 GeV at its initial luminosity and 500-550 GeV if the projected final luminosity is reached. The LHC can probe much further: The LHC will either discover UED KK excitations of quarks and gluons or extend the mass limit to about 3 TeV. *

We propose a new mechanism for generating small neutrino masses which predicts the relation m ν ∼ v 4 /M 3 , where v is the electroweak scale, rather than the conventional seesaw formula m ν ∼ v 2 /M . Such a mass relation is obtained via effective dimension seven operators LLHH(H † H)/M 3 , which arise when an isospin 3/2 Higgs multiplet Φ is introduced along with iso-triplet leptons. The masses of these particles are naturally in the TeV scale. The neutral member of Φ acquires an induced vacuum expectation value and generates neutrino masses, while its triply charged partner provides the smoking gun signal of this scenario. These triply charged bosons can be pair produced at the LHC and the Tevatron, with Φ +++ decaying into W + ℓ + ℓ + or W + W + W + , possibly with displaced vertices. The leptonic decays of Φ +++ will help discriminate between normal and inverted hierarchies of neutrino masses. This scenario also allows for raising the standard Higgs boson mass to values in excess of 500 GeV.

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We suggest a novel approach towards resolving the fermion mass hierarchy problem within the framework of the Standard Model. It is shown that the observed masses and mixings can be explained with order one couplings using successive higher dimensional operators involving the SM Higgs doublet field. This scenario predicts flavor-dependent enhancement in the the Higgs boson coupling to the fermions (by a factor of 3 to the b-quark and τ and by a factor of 5 to µ relative to the SM). It also predicts flavor changing tch 0 interaction with a strength comparable to that of bbh 0 . This opens up a new discovery channel for the Higgs boson at the upgraded Tevatron and the LHC through t → ch 0 or h 0 → tc + ct. Additional tests of the framework include D 0 −D 0 mixing which is predicted to be near the current experimental limit and a host of new phenomena associated with flavor physics at the TeV scale.

We propose an extension of the Standard Model by extending the EW symmetry to SU (2) L ×U (1)×Z 2 and introducing three SU (2)×U (1) singlet right handed neutrinos, N R , and an additional Higgs doublet, φ. While the SM gauge bosons and the quarks and charged leptons acquire masses from the spontaneous breaking of SU (2) L × U (1) symmetry at the electroweak scale, the neutrinos acquire masses from the spontaneous breaking of the discrete Z 2 symmetry at a scale of 10 −2 eV. In addition to providing a new mechanism for generating tiny masses for the neutrinos, the model has interesting implications for neutrinoless double beta decay and the Higgs signals at high energy colliders, as well as in astrophysics and cosmology.