Marco Guzzi | The University of Manchester (original) (raw)

Papers by Marco Guzzi

We illustrate the generalization of results concerning exclusive electromagnetic processes in the... more We illustrate the generalization of results concerning exclusive electromagnetic processes in the deeply virtual limit (DVCS) to the case of the weak interactions.We briefly describe the derivation of the differential cross section for neutrino-nucleon reactions mediated by the neutral current and the amplitude for similar reactions mediated by the charged currents.

This thesis work summarizes studies in QCD for applications both at hadron colliders and in exclu... more This thesis work summarizes studies in QCD for applications both at hadron colliders and in exclusive processes. In the first part we focus our attention on the study of the initial state scaling violations and the evolution of the unpolarized parton distributions through Next-to-Next to Leading Order (NNLO) in alphas\alpha_salphas, the strong coupling, suitable for precision studies of the parton model at the LHC. Specifically, we analize the methods available to solve the equations and develope the theory of the logarithmic expansions at the same perturbative order. A study of the Higgs total cross section is included. The theoretical analysis is accompanied by the developement of professional software partly documented in this thesis. We also include one study of the evolution of the transverse spin distributions (the Soffer inequality) and a parallel study of the asymmetries for the Drell-Yan process for the proposed Pax experiment at GSI at NLO. In the second part we introduce the extens...

EPJ Web of Conferences, 2014

A general overview on the parton distribution functions of the proton extracted by QCD global ana... more A general overview on the parton distribution functions of the proton extracted by QCD global analyses of experimental data is presented. In particular, their impact on physics observables of interest for the LHC and general results of QCD analyses at the next-to-next-to-leading order approximation are discussed. a

Nuclear Physics B - Proceedings Supplements, 2007

Journal of High Energy Physics, 2005

Nuclear Physics B, 2010

We present a study of a class of effective actions which show typical axion-like interactions, an... more We present a study of a class of effective actions which show typical axion-like interactions, and of their possible effects at the Large Hadron Collider. One important feature of these models is the presence of one pseudoscalar which is a generalization of the Peccei-Quinn axion. This can be very light and very weakly coupled, with a mass which is unrelated to its couplings to the gauge fields, described by Wess Zumino interactions. We discuss two independent realizations of these models, one derived from the theory of intersecting branes and the second one obtained by decoupling one chiral fermion per generation (one right-handed neutrino) from an anomaly-free mother theory. The key features of this second realization are illustrated using a simple example. Charge assignments of intersecting branes can be easily reproduced by the chiral decoupling approach, which remains more general at the level of the solution of its anomaly equations. Using considerations based on its lifetime, we show that in brane models the axion can be dark matter only if its mass is ultralight (∼ 10 −4 eV), while in the case of fermion decoupling it can reach the GeV region, due to the absence of fermion couplings between the heavy Higgs and the light fermion spectrum. For a GeV axion derived from brane models we present a detailed discussion of its production rates at the LHC.

Applied Physics Letters, 2011

We report on the observation of room temperature direct band gap photoluminescence in compressive... more We report on the observation of room temperature direct band gap photoluminescence in compressively strained-Ge multiple quantum wells with Ge-rich SiGe barriers. A detailed experimental study of the temperature dependence of the photoluminescence is carried out from 5 K up to room temperature. We find that the direct gap photoluminescence at room temperature is due to the thermal excitation of carriers from L-type to Gamma-type confined states. Room temperature photoluminescence shows that Ge/SiGe multiple quantum wells are promising candidates for efficient light emitting devices monolithically integrated on Si.

Computer Physics Communications, 2008

Physical Review D, 2012

We compute the dark matter relic densities of neutralinos and axions in a supersymmetric model wi... more We compute the dark matter relic densities of neutralinos and axions in a supersymmetric model with a gauged anomalous U (1) symmetry, kinetically mixed with U (1) Y of hypercharge. The model is a variant of the USSM (the U (1) extended NMSSM), containing an extra U (1) symmetry and an extra singlet in the superpotential respect to the MSSM, where gauge invariance is restored by Peccei-Quinn interactions using a Stückelberg multiplet. This approach introduces an axion (Im b) and a saxion (Re b) in the spectrum and generates an axino component for the neutralino. The Stückelberg axion (Im b) develops a physical component (the gauged axion) after electroweak symmetry breaking. We classify all the interactions of the Lagrangian and perform a complete simulation study of the spectrum, determining the neutralino relic densities using micrOMEGAs. We discuss the phenomenological implications of the model analyzing mass values for the axion from the milli-eV to the MeV region. The possible scenarios that we analyze are significantly constrained by a combination of WMAP data, the exclusion limits from direct axion searches and the veto on late entropy release at the time of nucleosynthesis.

Fortschritte der Physik, 2010

We review recent work on the effective field theory description and the phenomenology of axion-li... more We review recent work on the effective field theory description and the phenomenology of axion-like and scalar particles in models characterized by gauge and/or conformal anomalies.

We present a brief overview of axion models associated to anomalous abelian (gauge) symmetries, d... more We present a brief overview of axion models associated to anomalous abelian (gauge) symmetries, discussing their main phenomenological features. Among these, the mechanism of vacuum misalignment introduced at the QCD and at the electroweak phase transitions, with the appearance of periodic potentials, responsible for the generation of a mass for these types of axions.

Physical Review D, 2009

We present a supersymmetric extension of the Standard Model (USSM-A) with an anomalous U (1) and ... more We present a supersymmetric extension of the Standard Model (USSM-A) with an anomalous U (1) and Stückelberg axions for anomaly cancellation, generalizing similar non-supersymmetric constructions. The model, built by a bottom-up approach, is expected to capture the low-energy supersymmetric description of axionic symmetries in theories with gauged anomalous abelian interactions, previously explored in the non-supersymmetric case for scenarios with intersecting branes. The choice of a USSM-like superpotential, with one extra singlet superfield and an extra abelian symmetry, allows a physical axion-like particle in the spectrum. We describe some general features of this construction and in particular the modification of the dark-matter sector which involves both the axion and several neutralinos with an axino component. The axion is expected to be very light in the absence of phases in the superpotential but could acquire a mass which can also be in the few GeV range or larger. In particular, the gauging of the anomalous symmetry allows independent mass/coupling interaction to the gauge fields of this particle, a feature which is absent in traditional (invisible) axion models. We comment on the general implications of our study for the signature of moduli from string theory due to the presence of these anomalous symmetries.

Nuclear Physics B - Proceedings Supplements, 2011

We illustrate the structure and the main phenomenological features of a supersymmetric model (the... more We illustrate the structure and the main phenomenological features of a supersymmetric model (the USSM-A) built following a bottom-up approach and containing an anomalous abelian gauge symmetry. This model supports a gauged axion in its spectrum and provides a generalization of the global (supersymmetric) Peccei-Quinn construction. Complete simulations of the neutralino relic density are performed. Bounds from CAST and WMAP, combined with dark matter simulations, provide significant constraints on the scale of the interactions between the axion and the gauge fields.

Physics Letters B, 2006

We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance r... more We perform a NLO numerical study of the double transverse-spin asymmetries in the J/ψ resonance region for proton-antiproton collisions. We analyze the large x kinematic region, relevant for the proposed PAX experiment at GSI, and discuss the implication of the results for the extraction of the transversity densities.

Axion-like particles are an important part of the spectrum of anomalous gauge theories involving ... more Axion-like particles are an important part of the spectrum of anomalous gauge theories involving modified mechanisms of cancellation of the gauge anomalies. Among these are intersecting brane models, which are characterized by the presence of one physical axion. We overview a recent study of their supersymmetric construction and some LHC studies of the productions rates for a gauged axion.

International Journal of Modern Physics: Conference Series, 2012

We summarize a new analysis of the distribution φ * η of charged leptons produced in decays of Z ... more We summarize a new analysis of the distribution φ * η of charged leptons produced in decays of Z and γ * bosons in the Collins-Soper-Sterman (CSS) formalism for transverse momentum resummation. By comparing the φ * η distribution measured at the Tevatron with the resummed CSS cross section with approximate O(α 2 s ) Wilson coefficients, we constrain the magnitude of the nonperturbative Gaussian smearing factor and analyze its uncertainty caused by variations in scale parameters. We find excellent agreement between the φ * η data and our theoretical prediction, provided by the ResBos resummation program. The nonperturbative factor that we obtained can be used to update resummed QCD predictions for precision measurements in inclusive W and Z production and for comparisons to various models of nonperturbative dynamics.

Nuclear Physics B - Proceedings Supplements, 2012

We discuss an NNLO realization of the general mass scheme S-ACOT-χ for treatment of heavy-flavor ... more We discuss an NNLO realization of the general mass scheme S-ACOT-χ for treatment of heavy-flavor production in neutral current deep-inelastic scattering. The connection of this scheme to the QCD factorization theorem with massive quarks is elucidated. As a new feature, kinematical constraints on collinear production of heavy quarks that are crucial near the heavy-quark threshold are included in the amended QCD factorization theorem. Practical implementation of the NNLO calculation is illustrated on the example of semi-inclusive structure functions F 2c (x, Q) and F Lc (x, Q).