Abstract

The dream of unifying the Fundamental Interactions has nurtured Physics for centuries. In the 1970’s it finally materialized in the Standard Model of Strong, Weak and Electromagnetic Interactions, an unchallenged setting that combines the Poincaré symmetries of flat spacetime with Quantum Mechanics, the gauge principle and spontaneous symmetry breaking. This last key option results from ground states that respect only part of an underlying symmetry, accounts naturally for the short range of Weak interactions and allows precise computations of their effects. However, the Standard Model remains primarily a compendium of experimental facts on the Fundamental Interactions below the TeV energy scale, and indeed most particle attributes have long resisted attempts to frame them into similarly compelling terms.

Although gravity does not enter the Standard Model proper, it rests intriguingly on similar if more sophisticated manifestations of the gauge principle, which reflect diffeomorphisms in general spacetimes. General Relativity, however, does not afford a global minimum energy principle, so that key aspects of our Universe seem mere accidents of its early stages. Unifying gravity with the other interactions leads naturally to extensions of the gauge principle. String Theory replaces elementary particles with extended objects (strings and extended solitons, usually termed p-branes), albeit in a Universe where six or seven additional dimensions are curled up and are likely to remain secluded even to our most sophisticated instruments. The resulting four-dimensional scenarios are thus manifold but, strikingly and enticingly, they all rest on a unique, if elusive, gauge principle. This makes it imperative to qualify it, although the special properties of General Relativity that we have alluded to seem to make our world only one of its possible manifestations.

String Theory in ten dimensions involves supersymmetry, which links Bose and Fermi particles and ought to be spontaneously broken, if present at all, in Nature. This project aims to explore further the breaking of Supersymmetry in String Theory and some of its implications for Cosmology and Particle Physics, with an eye to its very lessons for the underlying principles. Supersymmetry breaking in String Theory brings along vacuum instabilities and deep puzzles, and yet it might even underlie some features of the low-l CMB. Some authors are even starting to formulate low-energy constraints on gravity, consistently with the widespread feeling that these problems touch somehow the foundations of the whole picture. In the recent past, some useful progress was made in characterizing low-energy manifestations of broken supersymmetry in a non-linear phase, but its full potential has yet to be exploited.

We are proposing a combination of closely related activities aimed at widening the catalogue of available non-supersymmetric string vacua and at clarifying their stability properties, with an eye to some general constraints on gravitational interactions that have been proposed lately. We plan to rely on Supergravity, Holography and integrability techniques, which have already played a role in the AdS/CFT setting, also in order to investigate the nature of black-hole microstates in more general settings. The novelty here is that we would like to investigate whether and how supersymmetric methods, which are in some respects a counterpart, in Quantum Field Theory, of the complex variables of Analysis, can help to address the puzzles (of at least special string-inspired scenarios) of broken Supersymmetry. Concretely, the methods of “Fake Supergravity” have a real potential of leading to new solutions and more powerful stability arguments, while the very issue of stability impinges on the notion of energy in gravity, which is at the root of many apparent shortcomings of the whole picture centered on String Theory.

In order to pursue the proposed research lines, we have devised a combination of four research Units, which include leading experts who have often interacted in the past, although so far they have effectively collaborated only to a limited extent. We have thus a common language, but we possess independent skills to deal with string constructions, Supergravity, flux compactifications, integrable systems, black holes and branes and various aspects of Quantum Field Theory. All of these, in our view, will be instrumental to grant this project the best chances of success.