Perspectives in string theory ?

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

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

4. 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

5. ….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.

6. 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)

7. 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)

18. z z

35. Prospects and Conjectures

36. 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?

37. 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….

38. D=26 or D=10 ? • 26 = 10 + 16 • 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….

39. THANKS