Little Higgs and precision electroweak tests

I consider the low energy limit of Little Higgs models. The method consists in eliminating the heavy fields using their classical equations of motion in the infinite mass limit. After the elimination of the heavy degrees of freedom one can directly read off deviations from the precision electroweak data. I also examine the effects on the low energy precision experiments.Comment: Talk given at 39th Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 21-28 Mar 200

Charged Higgs in Models with Singlet Neutrino in Large Extra Dimensions

The charged Higgs decay in the channel H^- ->tau_L^- nu in models with a singlet neutrino can provide a test of large extra dimensions models with TeV scale quantum gravity since in the standard two Higgs doublet model type II, H^- -> tau_L^- nu is suppressed. In the present study, we focus on the decay H^- -> tau_L^- nu at the LHC for Higgs masses larger than the top-quark mass.Comment: 4 pages, LaTeX2e, 2 figures, 2 tables, Talk given at XXXVIIth Rencontres de Moriond, ElectroWeak Interactions and Unified Theories, March 9th - 16th 2002, Les Arcs, Franc

A quark loop model for heavy mesons

I consider a model based on a quark--meson interaction Lagrangian. The transition amplitudes are evaluated by computing diagrams in which heavy and light mesons are attached to quark loops. The light chiral symmetry relations and the heavy quark spin-flavour symmetry dictated by the heavy quark effective theory are implemented. The model allows to compute the decay form factors and therefore can give predictions for the decay rates, the invariant mass spectra and the asymmetries.Comment: 6 pages, 2 tables, LaTeX (aipproc style), Invited talk at QCD@Work, Martina Franca, Italy, June 16-20 200

Multi-tops at the LHC

The experiments at the LHC are searching for many different final states that can hint to the presence of new physics beyond the Standard Model. One of the most interesting and promising sectors for these searches is that of the top quark, for both theoretical and phenomenological reasons linked to its large mass and to its possible special role in the electroweak symmetry breaking sector. We suggest that multi-top events, beyond the standard $t$-$\bar t$ and four top searches, can bring further insight in constraining and discovering physics beyond the Standard Model, taking advantage of experimental techniques similar to those used in present top-quark analyses. This is relevant both for the next data taking runs at the LHC and even more at higher luminosity and higher energy collider options, which are discussed for future LHC upgrades and future accelerators. In particular we consider six top and eight top final states, discussing the generic colour representations for beyond the Standard Model particles giving rise to those final state. We also discuss the limits which can be extracted by using the present analyses sensitive to four top final states, as well as the potential bounds from new searches we propose to experimental collaborations as an alternative.Comment: 16 page

B0bar decays to D(*)0 eta and D(*)0 eta'

We consider the hadronic B decays B0bar -> D0 eta, B0bar -> D*0 eta, B0bar -> D0 eta', B0bar -> D*0 eta' in the framework of a quark-flavour basis and factorization. The formalism allows to compute the decays to the eta meson and to relate them to those of the eta'. Measuring the branching ratios of these processes may shed light on the nature of the eta-eta' mixing. On the experimental side, only upper limits on the branching ratios are known at present.Comment: 12 pages, 2 figures, 2 tables (LaTeX, revtex), minor revision: note added at the end concerning new data and few reference

Dark matter and localised fermions from spherical orbifolds?

We study a class of six-dimensional models based on positive curvature surfaces (spherical 2-orbifolds) as extra-spaces. Using the Newman-Penrose formalism, we discuss the particle spectrum in this class of models. The fermion spectrum problem, which has been addressed with flux compactifications in the past, can be avoided using localised fermions. In this framework, we find that there are four types of geometry compatible with the existence of a stable dark matter candidate and we study the simplest case in detail. Using the complementarity between collider resonance searches and relic density constraints, we show that this class of models is under tension, unless the model lies in a funnel region characterised by a resonant Higgs s-channel in the dark matter annihilation.Comment: 38 pages, 7 figure

A scalar hint from the diboson excess?

In view of the recent diboson resonant excesses reported by both ATLAS and CMS Collaborations, we suggest that a new weak singlet pseudo-scalar particle, $\eta_W$, may decay into two weak bosons while being produced in gluon fusion at the LHC. The couplings to the gauge bosons can arise from a Wess-Zumino-Witten anomaly term and thus we study an effective model based on the anomaly term as a well motivated phenomenological model. In models where the pseudo-scalar arises as a composite state, the coefficients of the anomalous couplings can be related to the fermion components of the underlying dynamics. We provide an example to test the feasibility of the idea.Comment: 6 pages, 2 figures, 2 tables, two column. Typos in (5)-(9) are corrected and several discussions are clarified. References added. Matches published version in PR