  We review some ideas on the relationship between massless superparticles and
the division algebras to provide a new perspective on ambitwsitor string
theories. The key concern is the critical theory. We show that this theory has
a reducible soft algebra, rather than a conventional Lie algebra. This algebra
only closes on-shell. The BV procedure is employed to deal with the on-shell
closure of the algebra and the classical Master Action is presented.

High Energy Physics - Theory