Supergravite `no-scale': une solution geometrique au probleme de la constante cosmologique

par M. Michel Rausch de Traubenberg (IPHC Starsbourg)

mardi 18 déc. 2012, 12:30 → 13:30 Europe/Paris

Bat. 24, bibliotheque (IPHC)

Supersymmetry or supergravity cannot be an exact symmetry and has to be spontaneously broken. There exists several mechanisms to break supergravity but all share a common feature, that is supergravity is broken in a hidden sector. The interactions (gravitational, gauge, etc) of the hidden sector with the observable sector induce supergravity breaking. Differently than in supersymmetry, in supergravity the potential is no longer positive. This means that a positivity of the potential is no more a signature of supergravity breaking. In particular, since supergravity is a theory of gravitation, the value of the potential at the minimum is the cosmological constant. Thus, it desirable to have a theory where supergravity is broken and the potential vanishes at the minimum. It is possible to obtain such a solution, for instance within the framework of gravity mediated supersymmetry breaking, but this requires an unnatural fine-tuning. In this talk we present a geometrical solution to the vanishing of the cosmological constant. More precisely we show that it is possible to have a Kahler potential such that the scalar potential vanishes identically. Since there is no mass scale but the Planck mass these models are called no-scale supergravity. We then study the mass matrix and show how interactions can be incorporated.