String Theory

The idea that the elementary constituents of matter be one-dimensional string-like objects rather than point-like particles has brought about remarkable progress in the understanding of fundamental interactions in the past 40 years or so. String Theory provides a consistent framework in which gravity can be incorporated within quantum physics. Issues related to Black Holes thermodynamics or cosmological singularities can be quantitatively addressed within String Theory. While massive higher spin states are a hallmark of the perturbative formulation, the presence of branes in the non-perturbative spectrum has been discovered and appreciated more recently. As a result several surprising duality relations between theories in different dimensions and with rather distinct perturbative descriptions have been conjectured and partly established. Most notably, the holographic principle finds a concrete realization in String Theory through the AdS/CFT correspondence relating gravity or strings in negatively curved anti De Sitter spaces to conformal field theories on their boundaries. Unexpected generalizations of the holographic correspondence have been proposed that seem to capture the dynamics of strongly coupled systems in a variety of contexts, including exotic condensed matter systems.   Within this framework, the activity of the Tor Vergata Section has been devoted to further the study of string theory and explore its modern ramifications. In particular, the following aspects are currently under investigation:

- Study of soft theorems in scattering amplitudes, in particular for supergravity theories. By studying double soft-scalar limits of scattering amplitudes, we work out the realization of all duality symmetries for supergravity theories in 4D and 3D. Along this line, we also discovered new soft theorems for supergravity scattering amplitudes by considering fermions to be soft, which is tightly related to spontaneously supersymmetry breaking.

- Study of the 4-point correlation function of the stress-energy tensor in a general conformal invariant quantum field theory in four dimensional space-time.

- Study of non-perturbative corrections to N=2 gauge theories, mass deformations of quiver gauge theories and flux vacua of type II string theories.

- Investigation of the limit for large number of colors of supersymmetric gauge theories with eight supersymmetries and a mass for the scalar fields in the hypermultiplet. Using a modular anomaly it is possible to exactly evaluate the prepotential in the above mentioned limit and prove that instanton contributions vanish.

- Study of the "wrapping rules" that allow to derive the number of single-brane half-BPS states in a given dimension once the branes in one (or more) dimension higher are known. They can be extended to theories with less than maximal supergravity using string-string dualities. In particular, the duality has been extended to the case with eight supercharges, giving an interpretation for geometric vs non-geometric orbit of the T-duality group.

The group at Tor Vergata is currently made of 5 Staff members, 1 Post-doc and 4 PhD Students.