Perspectives in string theory? L.Bonora SISSA,Trieste, Italy Belgrade, September 2012

Prologue We have good reasons to believe that there is ‘life’ beyond the standard model: dark energy dark matter inflation neutrino mass theoretical arguments….

What is beyond the SM? Grand unification Supersymmetry Supergravity / quantum gravity but certainly a renormalizable gauge field theory, which means UV completeness -and then..... superstring theory which offers quantum gravity and UV compleness

….but what string theory? At present there are superstring / M-theory in 10/11 D. These theories are formulated perturbatively These theories are connected by s- and t- dualities There is no unique formulation.

A complete string theory can only be a string field theory We have Open Bosonic String Field Theory (à la Witten). It works Closed Bosonic SFT (not a field theory) Superstring FT’s (incomplete)

Summary Review of SFT Exact solutions Dp-brane solutions Open-closed duality Prospects: fermions, supersymmetry (based on work done in collaboration with S.Giaccari, C.Maccaferri, D.D.Tolla)

z z

Prospects and Conjectures

Open-closed string duality D-branes can be expressed in terms of open strings (background independence) Perturbative closed string states are they limits of S-branes? Is there a unique string theory, rather than two? Closed ST does not seem to be a field theory. Is open SFT the fundamental theory?

Open SFT fundamental? It is unstable – is this important? It has a tachyon, perhaps two – so what? It does not contain gravity – gravity is effective It doesn’t contain fermions – this is worrying but not tragic, because….

D=26 or D=10 ? 26 = Fermions from bosons (old idea) Fermions exact solutions of bosonic SFT Susy as enhanced symmetry SSFT as effective theory of bosonic SFT Re-design the landscape….

THANKS