Partial breaking of N=1, D=10 supersymmetry

We describe the spontaneous partial breaking of N = 1, D = 10 supersymmetry to N = (1,0), d = 6 and its dimensionally-reduced versions in the framewor k of nonlinear realizations. The basic Goldstone superfield is N = (1,0), d =6 hypermultiplet superfield satisfying a nonlinear generalization of the s tandard hypermultiplet constraint. We interpret the generalized constraint as the manifestly worldvolume supersymmetric form of equations of motion of the type I super 5-brane in D = 10. The related issues we address are a po ssible existence of brane extension of off-shell hypermultiplet actions, th e possibility to utilize vector N = (1,0), d=6 supermultiplet as the Goldst one one, and the description of 1/4 breaking of N = 1, D = 11 supersymmetry . (C) 1999 Published by Elsevier Science B.V. All rights reserved.