New physics at the TeV scale is highly anticipated at the LHC. New particles with color, if within the LHC energy reach, will be copiously produced. One such particle is a diquark, having the quantum numbers of two quarks, and can be a scalar or a ve
ctor. It will decay to two light quarks, or two top quarks, or a top and a light quark, (up or down type depending on the quantum number of the produced diquark). If singly produced, it can be looked for as a dijet resonance, or as giving extra contribution to the single top production or tt production. In this work, we consider a color sextet vector diquark having the quantum number of (ud) type, its resonance production, and the subsequent decay to tb, giving rise to excess contribution to the single top production. Even though the diquark mass is large, its strong resonance production dominate the weak production of tb for a wide range of the diquark mass. Also its subsequent decay to tb produce a very hard b-jet compared to the usual electroweak production. In addition, the missing energy in the final state event is much larger from the massive diquark decays. Thus, with suitable cuts, the final state with b, bar{b} and a charged lepton together with large missing energy stands out compared to the Standard Model background. We make a detailed study of both the signal and the background. We find that such a diquark is accessible at the 7 TeV LHC upto a mass of about 3.3 TeV with the luminosity 1 fb^{-1}, while the reach goes up to about 4.3 TeV with a luminosity of 10 fb^{-1}.
In this talk, I present a new mechanism for the generation of neutrino masses via dimension 7 operators: llHH(H*H)/M^3. This leads to new formula for the light neutrino masses, m_ u~v^4/M^3. This is distinct from the usual see-saw formulae: m_ u~v^2/
M. The scale of new physics can naturally be at the TeV scale. Microscopic theory that generated d=7 operator has an isospin 3/2 Higgs multiplet Phi, which contains a triply charged Higgs boson with mass around ~TeV or less. These particles can be produced at the LHC (and possibly at the Tevatron) with distinctive multi-W and multi-lepton final states. For some choice of the parameter space, these particles can also be long-lived with the possibility of displaced vertices, or even escaping the detector. Their leptonic decay modes carry information about the nature of the neutrino mass hierarchy.
We explore a scenario in the Standard Model in which dimension four Yukawa couplings are either forbidden by a symmetry, or happen to be very tiny, and the Yukawa interactions are dominated by effective dimension six interactions. In this case, the H
iggs interactions to the fermions are enhanced in a large way, whereas its interaction with the gauge bosons remains the same as in the Standard Model. In hadron colliders, Higgs boson production via gluon gluon fusion increases by a factor of nine. Higgs decay widths to fermion anti-fermion pairs also increase by the same factor, whereas the decay widths to photon photon and gamma Z are reduced. Current Tevatron exclusion range for the Higgs mass increases to ~ 142-200 GeV in our scenario, and new physics must appear at a scale below a TeV.
We propose a simple extension of the Standard Model (SM) by adding an extra U(1) symmetry which is hidden from the SM sector. Such a hidden U(1) has not been considered before, and its existence at the TeV scale can be explored at the LHC. This hidde
n U(1) does not couple directly to the SM particles, and couples only to new SU(2)_L singlet exotic quarks and singlet Higgs bosons, and is broken at the TeV scale. The dominant signals at the high energy hadron colliders are multi lepton and multi b-jet final states with or without missing energy. We calculate the signal rates as well as the corresponding Standard Model background for these final states. A very distinctive signal is 6 high p_T b-jets in the final state with no missing energy. For a wide range of the exotic quarks masses the signals are observable above the background at the LHC.
We present a new approach for generating tiny neutrino masses. The Dirac neutrino mass matrix gets contributions from two new Higgs doublets with their vevs at the electroweak (EW) scale. Neutrino masses are tiny not because of tiny Yukawa couplings,
or very heavy ($sim 10^{14}textrm{GeV}$) right handed neutrinos. They are tiny because of a cancelation in the Dirac neutrino mass matrix (fine tuning). After fine tuning to make the Dirac neutrino mass matrix at the $10^{-4}$ GeV scale, light neutrino masses are obtained in the correct scale via the see-saw mechanism with the right handed neutrino at the EW scale. The proposal links neutrino physics to collider physics. The Higgs search strategy is completely altered. For a wide range of Higgs masses, the Standard Model Higgs decays dominantly to $ u_L N_R$ mode giving rise to the final state $bar{ u} u bar{b} b$, or $bar{ u} u tau^+tau^-$. This can be tested at the LHC, and possibly at the Tevatron.
In this talk, I present a new framework to understand the long-standing fermion mass hierarchy puzzle. We extend the Standard Model gauge symmetry by an extra local U(1)_S symmetry, broken spontaneously at the electroweak scale. All the SM particles
are singlet with respect to this U(1)_S. We also introduce additional flavor symmetries, U(1)_Fs, with flavon scalars F_i, as well as vectorlike quarks and leptons at the TeV scale. The flavon scalars have VEV in the TeV scale. Only the top quark has the usual dimension four Yukawa coupling. EW symmetry breaking to all other quarks and leptons are propagated through the messenger field, S through their interactions involving the heavy vector-like fermions and S, as well as through their interactions involving the vector-like fermions and F_i. In addition the explaining the hierarchy of the charged fermion masses and mixings, the model has several interesting predictions for Higgs decays, flavor changing neutral current processes in the top and the b quark decays, decays of the new singlet scalars to the new Z boson, as well as productions of the new vectorlike quarks. These predictions can be tested at the LHC.
We propose a new mechanism for generating small neutrino masses which predicts the relation m_ u ~ v^4/M^3, where v is the electroweak scale, rather than the conventional seesaw formula m_ u ~ v^2/M. Such a mass relation is obtained via effective dim
ension seven operators LLHH(H*H)/M^3, which arise when an isospin 3/2 Higgs multiplet Phi is introduced along with iso-triplet leptons. The masses of these particles are naturally in the TeV scale. The neutral member of Phi 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 Phi^{+++} decaying into W^+l^+l^+ or W^+W^+W^+, possibly with displaced vertices. The leptonic decays of Phi^{+++} 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.
