Field Theory and String Theory

**S. Penati, A. Tomasiello, A. Zaffaroni, S. Pasquetti, N. Mekareeya**

Our group focuses on the problem of finding a quantum theory of gravity, and of unifying it with the other elementary interactions. There are several reasons to think that the right candidate might be string theory, whose study is still in progress. Its basic assumption is that the fundamental constituents of the world are not pointlike, but rather extended one–dimensional objects: "strings". We also study more traditional quantum field theories, some of which are related to string theory via the so–called AdS/CFT correspondence.

Standard Model Quantum Field Theory

**P. Nason, C. Oleari, S. Alioli**

Our field of study is Quantum Chromo--Dynamics (QCD), the relativistic quantum theory of the strong interaction. Because of its complexity, this theory can only be approached with suitable approximation techniques. For some problems, such as scatterings at very high energies, various perturbation theory schemes are available. We are also interested in several aspects of the Standard Model of fundamental interactions, which provides a unified description of the electromagnetic and weak interactions of quarks and leptons. In spite of the successes of this model, there are many reasons to think it is actually incomplete, and that it will have to be extended to a complete unification of the fundamental forces. In particular, supersymmetry, a hypothetical new symmetry that would relate elementary forces and matter particles, is a candidate for such future developments.

Computational Physics and development of dedicated computers

**C. Destri, L. Giusti, M. Pepe, F. Rapuano, M. Dalla Brida**

Modeling spacetime with a discrete lattice is a useful approach to several problems in Field Theory, typically non--perturbative ones, such as the computation of quark masses in QCD. This approach has attracted much attention in recent years, in part thanks to its similarity with methods in the statistical mechanics of magnetic systems. Although exact solutions might exist in very special cases, in general the use of advanced computers is necessary: parallel clusters, or dedicated parallel supercomputers such as APEnext, to whose development our group has participated, in collaboration with INFN and other Universities, in Italy and abroad. Some of the results obtained also lead to applications in condensed matter, despite the seeming distance of that field from elementary particle physics.