EXTRA DIMENSIONS IN SUPERSTRING THEORY

It was earlier shown that an SO(9,1) theta(alpha) spinor variable can be constructed from RNS matter and ghost fields. theta(alpha) has a bo sonic world-sheet super-partner lambda(alpha) which plays the role of a twister variable, satisfying lambda Gamma(mu)lambda = partial deriva tive x(mu) + i theta Gamma(mu)partial derivative theta. For Type IIA s uperstrings, the left-moving [theta(L)(alpha), lambda(L)(alpha)] and r ight-moving [theta(R alpha), lambda(R alpha)] can be combined into 32- component SO(10,1) spinors [theta(A), lambda(A)]. This suggests that l ambda(A) Gamma(AB)(11)lambda(B) = 2 lambda(L)(alpha)lambda(R alpha) ca n be interpreted as momentum in the eleventh direction. Evidence for t his interpretation comes from the zero-momentum vertex operators of th e Type IIA superstring and from consideration of D-0-branes. As in the work of Bars, one finds an SO(10,2) structure for the Type IIA supers tring and an SO(9,1) x SO(2,1) structure for the Type IIB superstring. (C) 1997 Elsevier Science B.V.