Vector-like quarks in a composite Higgs model

Vector-like quarks are a common feature of "composite" Higgs models, where they intervene in cutting off the top-loop contribution to the Higgs boson mass and may, at the same time, affect the Electroweak Precision Tests (EWPT). A model based on SO(5)/SO(4) is here analyzed. In a specific non minimal version, vector-like quarks of mass as low as 300-500 GeV are allowed in a thin region of its parameter space. Other models fail to be consistent with the EWPT.Comment: 17 pages with 8 figures Small modifications according to JHEP requirement

LHC bounds on large extra dimensions

We derive new dominant bounds on the coefficient of the effective operator generated by tree-level graviton exchange in large extra dimensions from pp \rightarrow jj data at LHC: M_T > 2.1TeV (ATLAS after 3.1/pb of integrated luminosity), M_T > 3.4 TeV (CMS after 36/pb), MT > 3.2 TeV (ATLAS after 36/pb). We clarify the role of on-shell graviton exchange and compare the full graviton amplitude to ATLAS data, setting bounds on the fundamental quantum-gravity scale.Comment: 16 pages, 6 figures. v2: updated with CMS data. v3: updated with ATLAS data at 36/pb; final published versio

A naturally light dilaton

Goldstone's theorem does not apply straightforwardly to the case of spontaneously broken scale invariance. We elucidate under what conditions a light scalar degree of freedom, identifiable with the dilaton, can naturally arise. Our construction can be considered an explicit dynamical solution to the cosmological constant problem in the scalar version of gravity.Comment: v2: published versio

Supersymmetry without a light Higgs boson but with a light pseudoscalar

We consider the lambda-SUSY model, a version of the NMSSM with large lambda H_1 H_2 S coupling, relaxing the approximation of large singlet mass and negligible mixing of the scalar singlet with the scalar doublets. We show that there are regions of the parameter space in which the lightest pseudoscalar can be relatively light, with unusual consequences on the decay pattern of the CP-even Higgs bosons and thus on the LHC phenomenology.Comment: 11 pages, 3 figures. v3: Conforms to published versio

Trasformata di Fourier e problemi di ambiguita`

In questa tesi si richiama la nozione di trasformata di Fourier, insieme ad alcuni importanti fatti ad essa collegati, come le relazioni di indeterminazione e il teorema di Paley e Wiener. Successivamente si applicano tali risultati allo studio di alcuni famosi ''problemi di ambiguità'': l'unicità di Pauli, il Phase Retrieval, e il Radar Ambiguity problem. Il primo problema è strettamente correlato con la Meccanica Quantistica, e corrisponde al domandarsi se una funzione di L^2(R) sia univocamente determinata (a meno di una fase) conoscendo il suo modulo ed il modulo della sua trasformata di Fourier. Nel caso del Phase Retrieval si vuole invece cercare di ricostruire una funzione f in L^2(R) conoscendo solo il modulo della sua trasformata di Fourier. Chiaramente f avra` sempre dei ''partner'' banali, ossia funzioni che differiscono da f per costanti moltiplicative unitarie o per traslazioni nella variabile indipendente, ma è interessante andare a studiare quali funzioni possono avere partner non banali. Il Radar Ambiguity problem sorge nella teoria dei segnali e consiste nel chiedersi quali funzioni di L^2(R) hanno lo stesso modulo della ''funzione di ambiguità'', che è ciò che in realtà viene misurato dal radar. I risultati riportati si trovano in gran parte in letteratura; il contributo originale di questa tesi consiste prevalentemente nel lavoro di sintesi, in alcune precisazioni, e nella costruzione di alcuni esempi

Radiation Problem in Transplanckian Scattering

We investigate hard radiation emission in small-angle transplanckian scattering. We show how to reduce this problem to a quantum field theory computation in a classical background (gravitational shock wave). In momentum space, the formalism is similar to the flat-space light cone perturbation theory, with shock wave crossing vertices added. In the impact parameter representation, the radiating particle splits into a multi-particle virtual state, whose wavefunction is then multiplied by individual eikonal factors. As a phenomenological application, we study QCD radiation in transplanckian collisions of TeV-scale gravity models. We derive the distribution of initial state radiation gluons, and find a suppression at large transverse momenta with respect to the standard QCD result. This is due to rescattering events, in which the quark and the emitted gluon scatter coherently. Interestingly, the suppression factor depends on the number of extra dimensions and provides a new experimental handle to measure this number. We evaluate the leading-log corrections to partonic cross-sections due to the initial state radiation, and prove that they can be absorbed into the hadronic PDF. The factorization scale should then be chosen in agreement with an earlier proposal of Emparan, Masip, and Rattazzi. In the future, our methods can be applied to the gravitational radiation in transplanckian scattering, where they can go beyond the existing approaches limited to the soft radiation case.Comment: 41 pp, v2: minor changes and added refs, conforms with published versio

Supersymmetry phenomenology beyond the MSSM after 5/fb of LHC data

We briefly review the status of motivated beyond-the-MSSM phenomenology in the light of the LHC searches to date. In particular, we discuss the conceptual consequences of the exclusion bounds, of the hint for a Higgs boson at about 125 GeV, and of interpreting the excess of direct CP violation in the charm sector as a signal of New Physics. We try to go into the various topics in a compact way while providing a relatively rich list of references, with particular attention to the most recent developments.Comment: 20 pages + refs. v2: minor modifications, published versio