# Research activity

The Standard Model (SM) of the electroweak and strong interactions has been very successful in describing many different elementary particle processes at various energy scales, but suffers, on the other hand, from various severe problems.

For instance, if one considers the interplay between particle physics and cosmology, it is immediately clear that the observed matter/antimatter asymmetry in the universe can not be explained only in terms of the fundamental interactions described by the Standard Model, but requires in general an extension that includes a larger particle spectrum. The latter is also needed to explain the observed dark matter content of the universe. Moreover the SM does not include neutrino masses and mixing and, on the more theoretical side, it suffers from the "hierarchy problem" (i.e. the fact that quantum corrections to the Higgs boson mass have a quadratic dependence on the UV cutoff used in the computation) and from the fact that the gauge and Yukawa structure is not explained but assumed.

Aside from these issues, now that the Higgs boson has been discovered a quest has started to understand if its properties are compatible with the predictions of the Standard Model.

The Large Hadron Collider (LHC) has been designed to explore all these different questions, providing the necessary tools to search and understand the Higgs boson and allowing the production of new particles in the TeV mass range, if they exist. The very successful first run of the accelerator has been accompanied by an already large amount of high-quality data. From the first analysis of these data, it seems that there are no apparent important deviations from the Standard Model. This in turn makes the use of this huge amount of data to perform precision physics the next logic step. Such a class of studies requires not only a very high accuracy in experimental measures but also a control over the uncertainties in theoretical computations.

Up to now I have been involved in a series of projects whose aim was to improve either the accuracy of predictions, accounting for new effects, or the control over the uncertainties of theoretical calculations.

Among the theoretical uncertainties, a prominent role is occupied by the always-present problem, in precise calculations in quantum field theory, of how to estimate the contributions from missing higher orders in the perturbative expansion, the so-called Missing Higher Order Uncertainty (MHOU). Traditionally, these uncertainties have been estimated by varying the unphysical scales present in the result around their central values. Various prescriptions for this procedure are conventionally used by the community, however all are based on arbitrary choices and fail in giving a statistical meaning to the interval they produce. With M. Cacciari (LPTHE) and A. Guffanti and L. Jenniches, both at the N. Bohr Institute in Copenhagen, we studied the extension of the CH Bayesian model to hadronic observables, with the specific aim of giving a more consistent estimate of the MHOU for LHC observables in general, and Higgs-boson production in particular. The CH model tries to address the shortcomings of the standard prescription used to evaluate MHOU, the scale variation procedure. It is based on a totally different approach, where the behavior of the perturbative series is understood in the context of Bayesian probability. The advantage of this framework is its coherent theoretical formulation and the fact that it produces an uncertainty interval with an intrinsic statistical interpretation in terms of DoB, which can be then consistently plugged in the machinery that experimental physicists use to analyze LHC data. As a byproduct of this study, we also revisited the application of the model to observables without initial state hadrons, its original field of definition and applicability, and we also studied statistically the performances of the scale variation procedure.

Due to the importance of Higgs boson physics in the context of the LHC research program, it is of primary importance to have precise predictions of Higgs observables that are measured at the LHC and to have a deep understanding of the uncertainties that characterize them. My studies have been focused along two main lines.

The first one is the study of the theoretical uncertainties of the total inclusive cross section for Higgs production in gluon fusion and bottom annihilation in the MSSM. These include not only MHOU but also PDF+$\alpha_s$ uncertainty, renormalization scheme choices for the bottom Yukawa and the range of validity of the approximations used in the computation of supersymmetric corrections. This work was done in collaboration with R. Harlander (U. Wuppertal), S. Liebler (U. Hamburg), H. Mantler (CERN), P. Slavich (LPTHE) and A.Vicini (U. Milano) and it recently led to a publication in the Journal of High Energy Physics.

For a few years, with G. Degrassi (U. Roma 3), P. Slavich and A. Vicini I have been studying Higgs-boson production in gluon fusion process in the POWHEG-BOX framework, with specific attention to the problem of including the complete top and bottom amplitudes and of studying their effects on the calculation of the Higgs transverse-momentum distribution. The POWHEG method provides a systematic recipe to obtain the matching of a NLO calculation with a Parton Shower. These matched computations are extremely important to correctly and realistically simulate physical processes in a collider, with the possibility of imposing in a flexible way experimental acceptance cuts and to have, at the end, a sensible comparison between data and theoretical predictions. Our contribution was well appreciated by the experimental collaborations of ATLAS and CMS, which are now using our program and results in their analyses. Furthermore, it has created a rich debate in the community and it has led to several meetings between experimentalists and theorists on the issue. The work was originally done for the Standard Model and for the light Higgs of the MSSM. It was then extended to the heavy and the pseudoscalar Higgs of the MSSM. All code is freely available in the POWHEG-BOX SVN tree. More recently I have studied with Alessandro Vicini the issue of the uncertainties related to the matching procedure in the computation of this observable.

During my graduate studies I have also participated in the computation of threshold corrections in split-SUSY and high-scale SUSY models. The idea at the base of split-SUSY is that the mass scale $\tilde{m}$ of the scalar superpartners of the SM is much higher than the EW scale. The only remaining superpartners at the EW scale are higgsinos and gauginos. In high-scale SUSY also the latter are supposed to be at the high scale $\tilde{m}$. To properly study these theories and their predictions at the weak scale, it is necessary to define an effective theory where the heavy particles are integrated out. This and the use of RG methods, allow to properly resum the large logarithms of the ratio of the $\tilde{m}$ over the weak scale that otherwise spoil the accuracy of the prediction. This technical computation is part of an ongoing study of the prediction of the Higgs mass in these models. The Higgs mass can indeed be used as a proxy to derive an estimate of the mass scale $\tilde{m}$ and hence to perform a phenomenological study of the two models. The work was performed in collaboration with G. Giudice (CERN), P.Slavich (LPTHE) and A. Strumia (U. Pisa).

All my work was supported by the Research Executive Agency (REA) of the European Commission under the Grant Agreements PITN-GA-2010-264564 (LHCPhenoNet).