Aldo Deandrea

Higgs couplings: disentangling New Physics with off-shell measurements

After the discovery of a scalar resonance, resembling the Higgs boson, its couplings have been extensively studied via the measurement of various production and decay channels on the invariant mass peak. Recently, the possibility of using off-shell measurements has been suggested: in particular, the CMS Collaboration has published results based on the high-invariant mass cross section of the process gg→ZZ, which contains a contribution from the Higgs boson. While this measurement has been interpreted as a constraint on the Higgs width after very specific assumptions are taken on the Higgs couplings, in this Letter, we show that a much more model-independent interpretation is possible.

Search for the lepton flavor violating decay A0 / H0 ---> tau+- mu-+ at hadron colliders

In the two Higgs doublet model type III and in several other extensions of the Standard Model, there are no discrete symmetries that suppress flavor changing couplings at tree level. The experimental observation of the nu_mu -- nu_tau flavor oscillation may suggest the non-conservation of lepton number. This would lead to the decay of the type A^0/H^0 --> tau^{+/-} mu^{+/-}. We determine the present low energy limit on lepton flavor violating (LFV) couplings from the muon g-2 measurement and discuss the prospects for detecting lepton flavor violating decays at the TeVatron and at the Large Hadron Collider. The achievable bounds on the LFV coupling parameter lambda_{tau mu} are presented.

Semileptonic B → ρ and B → a 1 transitions in a quark-meson model

We evaluate the form factors governing the exclusive decays

Fully hadronic decays of a singly produced vectorlike top partner at the LHC

stackrel{ensuremath{rightarrow}}{B}ensuremath{rho}lensuremath{nu}, stackrel{ensuremath{rightarrow}}{B}{a}_{1}lensuremath{nu},

Analysis of narrow s channel resonances at lepton colliders

by using an effective quark-meson Lagrangian. The model is based on meson-quark interactions, and the computation of the mesonic transition amplitudes is performed by considering diagrams with heavy mesons attached to loops containing heavy and light constituent quarks. This approach was successfully employed to compute the Isgur-Wise form factors and other hadronic observables for negative and positive parity heavy mesons and is presently used for exclusive heavy-to-light weak transitions. We also evaluate a few strong coupling constants appearing in chiral effective Lagrangians for heavy and light mesons.

Anomaly mediated supersymmetric models and Higgs data from the LHC

Single production of vector-like top partners is becoming a major focus of new searches, as the increasing mass limits on vector-like quarks obtained by the ATLAS and CMS collaborations are such that single production is becoming competitive with respect to pair production. Typically searches focus on decays containing leptons in the final state in order to have less background from the Standard Model processes. However the current centre of mass energies available in the latest LHC runs limit the searches to low masses. Fully hadronic final states may be an alternative option for discovery, as they allow a larger number of signal events if backgrounds can be kept under control. We study the fully hadronic decay of a singly produced vector-like top partner and we show a strategy to extract the signal over the background, considering as a benchmark the 20 fb^-1 of data collected at 8 TeV with the latest run of the LHC.

Evolution of Yukawa couplings and quark flavor mixings in two universal extra dimension models

The procedures for studying a single narrow s-channel resonance or nearly degenerate resonances at a lepton collider, especially a muon collider, are discussed. In particular, we examine four methods for determining the parameters of a narrow s-channel resonance: scanning the resonance, measuring the convoluted cross section, measuring the Breit-Wigner area, and sitting on the resonance while varying the beam energy resolution. This latter procedure is new and appears to be potentially very powerful. Our focus is on computing the errors in resonance parameters resulting from uncertainty in the beam energy spread. Means for minimizing these errors are discussed. The discussion is applied to the examples of a light SM-Higgs, of the lightest pseudogoldstone boson of strong electroweak breaking, and of the two spin-1 resonances of the Degenerate BESS model (assuming that the beam energy spread is less than their mass splitting). We also examine the most effective procedures for nearly degenerate resonances, and apply these to the case of Degenerate BESS resonances with mass splitting of order the beam energy spread.

K→πνbar nu from standard to new physics

decay channels. The minimal Anomaly Mediated Supersymmetry Breaking (AMSB) scenario can satisfy in part of its parameter space the dark matter requirement but is only marginally consistent with the current Higgs boson mass value. The HyperCharge-AMSB and Mixed Moduli-AMSB scenarios can better describe present data from dark matter, avour, low energy physics and are consistent with the measured mass of the Higgs boson. The inclusion of the preferred signal strengths for the Higgs boson decay channels shows that for tan & 5 the HyperCharge-AMSB and Mixed Moduli-AMSB models can be consistent with the present Higgs boson data. In contrast the minimal AMSB has a narrower allowed range in tan . These dierent AMSB scenarios, while consistent with present Higgs boson measurements, can be further tested by future more precise data in the Higgs sector.

K ---> pi nu anti-nu from standard to new physics

The evolution equations of the Yukawa couplings and quark mixings are derived for the one-loop renormalization group equations in the two Universal Extra Dimension Models (UED), that is six-dimensional models, compactified in different possible ways to yield standard four space-time dimension. Different possibilities for the matter fields are discussed, such as the case of bulk propagating or localised brane fields. We discuss in both cases the evolution of the Yukawa couplings, the Jarlskog parameter and the CKM matrix elements, and we find that, for both scenarios, as we run up to the unification scale, significant renormalization group corrections are present. We also discuss the results of different observables of the five-dimensional UED model in comparison with these six-dimensional models and the model dependence of the results.

The Exclusive

Flavour changing neutral current decays are a very sensitive test of the standard model and its extensions. In particular the decay K -> pi nu nubar constitutes a clean way to provide constraints, independent of long distance effects. Motivated by the recent experimental data of the E787 and E865 collaborations and by the difference between the standard model prediction and data, we consider in detail new physics scenarios such as the minimal supersymmetric standard model and R-parity violating supersymmetry. We begin with analysing the impact of new measurements on the standard model result obtaining B(K^+ -> pi^+ nu nubar)=(8.18 +/- 1.22) x 10^(-11). Predictions for other rare kaon decays are discussed, too. Our results allow to improve the limits on R-parity violating couplings with respect to previous analyses.