Question

Do unoriented strings possess asymptotic states?

Answer 1

In QFT based particle theory, SU(N)-colored particles are not really present as asymptotic states, then raising some problems to build a S-matrix or other more axiomatic approaches to the theory.

Given that I have the imaginery of a oriented string as one terminated in a particle/antiparticle pair, and an unoriented string as one terminated in a pair of particles or antiparticles, I would expect that only oriented string theories have a S-matrix formulation.

Answer 2

Two-Dimensional Unoriented Strings And Matrix Models. projection of Type 0B string theory for which we show that the crosscap state vanishes.