Themes for Ph.D and Master theses

Please have a look at our research web page to see the research topics on which we are working. These are also the subjects in which we give some more specific and focused Ph.D. and Master thesis.

Effective Quantum Field Theories (EFTs) have become increasingly popular in particle physics during the last decades. They provide a realization of Wilson renormalization group ideas and fully exploit the properties of local Quantum Field Theories (QFT). An EFT is a QFT with the following properties: a) it contains the relevant degrees of freedom to describe phenomena that occur in certain limited range of energies and momenta and b) it contains an intrinsic energy scale Λ that sets the limit of applicability of the EFT. The Lagrangian of an EFT is organized in operators of increasing dimension, hence, an EFT is in general non-renormalizable in the usual sense. In spite of this, it can be made finite to any finite order in 1/Λ and maintains a predictive power that is often even reinforced by the reduction of the degrees of freedom, building QCD effective field theories is most relevant for the study of strong interactions, hadron and flavor physics, where it exists a rich interplay between the perturbative dynamical regime (small coupling constant) and the nonperturbative one. Our group has given relevant contributions to the construction of new QCD effective field theories for the study of systems made of heavy quarks. Our research interests include: the study and the development of QCD EFTs (HQET,NRQCD,pNRQCD,SCET) and their application to relevant processes taking place at accelerator experiments (B-factories, tau-charm factories, LHC-b); the development of new EFTs for the study of QCD at finite temperature and density for the processes taking place at heavy ion experiments (at BNL and CERN) in the search of quark gluon plasma formation; the precision determination of standard model parameters relevant for flavor physics and the search for physics beyond the standard model; the study of the nonperturbative QCD dynamics and the confinement mechanism in collaboration with lattice groups. In this framework we have several thesis work available, among those we list :

Precision determination of Standard Model parameters

Heavy quark bound states may be used to extract precise determinations of some of the Standard Model parameters like the heavy quark masses (charm, bottom,top) and the strong coupling constant. A precise knowledge of these quantities is relevant for the standard model and beyond the standard model physics. To this aim suitable observables have to calculated at high orders in perturbation theory within the EFT formalism, taking appropriate care and fixing the indetermination of the perturbative series (renormalons), resumming large logs and factorizing the non perturbative effects.

Heavy quarkonium decays and transitions

New data on bottomonium and charmonium decays and transition recently have appeared and others will soon come from running experiments. EFTs allow high and low energy factorizations, which in turn make possible model independent determinations of decays or decays ratios. In the framework of the EFT pNRQCD inclusive decay amplitudes and transition widths may be expressed in terms of a minimal number of nonperturbative low energy operators, eventually to be calculated on the lattice. The full potential of this approach has not been exploited yet on all observables and studies in particular for di-pion transitions are planned. The research work will be performed also in collaboration with lattice groups for the calculation of the low energy nonperturbative contributions.

Quarkonium production at Tevatron and the LHC

Up to 1995 inclusive quarkonium production at colliders has been studied inside the singlet color model or the color evaporation model. However only an EFT of QCD, Non Relativistic QCD (NRQCD) has allowed us to understand the quarkonium cross section production behaviour at Tevatron and the role of contributions of quark-antiquark pairs in the color octet state. Some recent measurements of the polarization of the cross section at high p_t challenge our present understanding of quarkonium production. The factorization inside the EFT should be reconsidered. This study is relevant also for bottomonium production at the Tevatron and in perspective at LHC. In particular it may be a relevant source of information for the parton shower Monte Carlo codes to predict differential rates for quarkonium production at the LHC.

Effective Field Theories for threshold states

Most of the charmonium resonances discovered in the last few years at the B factories (see, for instance, QWG-spectr/spectrnews.htm) are close or above threshold. In an EFT context, a systematic treatment of such states does not exist yet; note that at threshold many new degrees of freedom show up and some of them are exotic: tetraquarks, hybrids, molecules. However, at least in some cases (notably the X(3872), which is so close to threshold to induce a further hierarchy of scales), such a treatment should be possible and investigations are under way in collaboration with the theory group at Fermilab.

Effective Field Theories at finite T

Gauge theories at finite T are relevant to describe heavy ion collisions (studied at RHIC at BNL, NA60 at CERN and in perspective at LHC at CERN). In particular, heavy quarkonium formation and dissociation have been often advocated as a signature of the quark-gluon plasma formation. In recent years, the study of heavy quarkonium at finite T has been carried out by different groups by means of analytical tools and lattice calculations. A crucial ingredient is the definition and determination of the heavy quark potential. A satisfactory solution to the problem of what the potential for heavy quarkonium at finite T is has not been found yet and several puzzles remain open; an example is the dissociation temperature of the charmonium. It is natural to expect that a solution should be provided by the finite T version of pNRQCD at which we are working.

The above research will be performed inside the European Network Flavianet (Flavor Physics, Flavianet) and the international Quarkonium Working Group.
In particular we have running collaborations with members of the theory groups in Argonne National Laboratory, Brookhaven National Laboratory, Barcelona, Fermilab, Lisbon, Regensburg, Orsay and we work in relation with members of experimental groups at the B-factories (BaBar-SLAC and Belle-KEK), tau-charm machines (CLEO-Cornell; BES-IHEP), Hera (DESY), LHC (CERN). This research will allow the graduate (Ph. D) and undergraduate (Diploma) student to acquire a good and working knowledge of heavy quark phenomenology and accelerator experiments, field theory and in particular QCD, EFTs and renormalization group techniques. The student will be able to work inside international collaborations in direct contact both with the leading theorists and experimentalists in the field.