It is established that in the tensionless limit chiral superstring integrand reduced to of ambitwistor string.

We study superstring theories on the Penrose limit of the enhançon geometry realized by the D(p + 4)-branes wrapped on a K3 surface. We first examine the null geodesics with fixed radius in general brane backgrounds, which give solvable superstring theories with constant masses. In most cases, the superstring theories contain negative mass-squared. We clarify a condition that the world-sheet fr...

We propose a Batalin-Vilkovisky (BV) formulation of boundary superstring field theory. The superstring field action is defined in terms of a closed one-form in the space of couplings, and we compute it explicitly for exactly solvable tachyon perturbations. We also argue that the superstring field action defined in this way is the partition function on the disc, in accord with a previous proposal.

Superstring amplitudes of an arbitrary genus are calculated through super-Schottky parameters by a summation over the fermion strings. For a calculation of divergent multiloop fermion string amplitudes a supermodular invariant regularization procedure is used. A cancellation of divergences in the superstring amplitudes is established. Grassmann variables are integrated, the superstring amplitud...

I review the construction of an action for open superstring field theory which does not suffer from the contact term problems of other approaches. This action resembles a Wess-Zumino-Witten action and can be constructed in a manifestly D=4 super-Poincaré covariant manner. This review is based on lectures given at the ICTP LatinAmerican String School in Mexico City and the Komaba 2000 Workshop i...

Synopsis: (i) how superstring theories are unified by M-theory; (ii) how superstring and supermembrane properties follow from the D=10 and D=11 supersymmetry algebras; (iii) how D=10 and D=11 supergravity theories determine the strong coupling limit of superstring theories; (iv) how properties of Type II p-branes follow from those of M-branes. Over the decade from 1984-94 superstring theory cam...

We show that the supersymmetric Wilson loops in IIB matrix model give a transition from supersymmetric Yang-Mills theory to supersymmetric space-time theory. In comparison with Green-Schwarz superstring we identify the supersymmetric Wilson loops with the asymptotic states of IIB superstring. It is pointed out that the supersymmetry transformation law of the Wilson loops is the inverse of that ...

A bstract Superstring/M-theory compactified on compact Ricci flat manifolds have recently been conjectured to exhibit instabilities whenever the metrics do not special holonomy. We use worldsheet conformal field theory investigate of Type II superstring theories compact, flat, spin 3-manifolds including a description their structures. The are signalled by appearance stringy tachyons at small ra...