Narrow Results

A simple extension of the Standard Model (SM), based on the gauge group $\mathrm{\text{SU}}{(3)}_C\otimes \mathrm{\text{SU}}{(3)}_L\otimes \mathrm{\text{U}}{(1)}_Y$ with $Y$ being the hypercharge, is considered. We show that, by imposing an approximate global $\mathrm{\text{SU}}{(2)}_L\times \mathrm{\text{SU}}{(2)}_R$ custodial symmetry at the SM energy scale, the $Z-Z^{\prime }$ mixing is absent at tree level and the value of the $\rho$ parameter can be kept close to one. Tree-level flavor-changing neutral currents (FCNCs) are also reduced to three particles, namely $Z^{\prime }$, a CP-odd Higgs and a CP-even Higgs. The model predicts new leptons with electric charges of ±1/2e and new quarks with ±1/6e charges as well as new gauge and scalar bosons with ±1/2e charges. Electric charge conservation requires that one of them must be stable. Their masses are unfortunately free parameters.

We present the results of a search for new particles decaying to tau pairs. Hypothetical particles, such as Z′ and MSSM Higgs boson A can potentially produce such pairs. The low-mass region, dominated by Z → ττ, is used as a control. No significant excess events over the estimated backgrounds is observed in the high-mass region, and we set upper limits on the cross section times branching ratio as a function of the Z′ and A mass.

D-brane realizations of the Standard Model predict extra abelian gauge fields which are superficially anomalous. The anomalies are cancelled via appropriate couplings to axions and Chern-Simons-like couplings. The presence of such couplings has dramatic experimental consequences: a) they provide masses to the anomalous abelian gauge fields (which masses can be of order of a few TeV), b) they provide new contributions to couplings like Z'-¿gammaZ, that may be considerable at LHC. This proceeding is mainely based on hep-th/0605225.

The question if the Bose statistics is broken at the TeV scale is discussed. The decay of a new heavy spin-1 gauge boson Z′ into two photons, Z′ → γγ, is forbidden by the Bose statistics among other general principles of quantum field theory (Landau–Yang theorem). We point out that the search for this decay can be effectively used to probe the Bose symmetry violation at the CERN LHC.

An anomaly-free U(1)′ effective Lagrangian as a benchmark of new physics beyond the standard model is proposed to survey the maximal parameter space constrained by the precise electroweak measurements at the Large Electron-Positron Collider (LEP) and direct detection of the dilepton decay channel at at the Large Hadron Collider (LHC). By the global fit of the effective couplings of the Z boson to the Standard Model fermions, parameters Δ₁₁, Δ₂₁ and g^′′Δ₃₁ related to mixings and r related to the U(1)′ charge assignment are bounded. The allowed areas are plotted not only in the r–g^′′ plane, but also in the m_Z′–g^′′ plane. They show that a sub-TeV Z′ is still permissible as long as the coupling g^′′ is of order ~0.01. The results hint at possible new physics beyond the standard model. A prediction of the possible signal for the dilepton decay channel at at LHC is also provided.