ON SPHERICALLY SYMMETRICAL STRING SOLUTIONS IN 4 DIMENSIONS

We reconsider here the problem of finding the general 4D spherically s ymmetric, asymptotically nat and time-independent solutions to the low est-order string equations in the alpha' expansion. Our construction i ncludes earlier work, but differs from it in three ways: (1) We work w ith general background metric, dilaton, axion, and U(1) gauge fields. (2) Much of the original solutions were required to be nonsingular at the apparent horizon, motivated by an interest in finding string corre ctions to black hole spacetimes. We relax this condition throughout, m otivated by the realization that string theory has a less restrictive notion of what constitutes a singular field configuration than do poin t-particle theories. (3) We can construct the general solution from a particularly simple one, by generating it from successive applications of the noncommuting SL(2, R) and O(1, 1) symmetries of the low-energy string equations containing S and target space dualities respectively . This allows its construction using relatively simple, purely algebra ic, techniques. The general solution is determined by the asymptotic b ehaviour of the various fields: i.e. by the mass, dilaton charge, axio n charge, electric charge, magnetic charge, and Taub-NUT parameter.