On spherically symmetric string solutions in four dimensions
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We reconsider here the problem of finding the general 4D spherically
symmetric, asymptotically flat and time-independent solutions to the
lowest-order string equations in the $\ap$ expansion. Our construction includes
earlier work, but differs from it in three ways. (1) We work with 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 corrections to black hole
spacetimes. We relax this condition throughout, motivated by the realization
that string theory has a less restrictive notion of what constitutes a singular
field configuration than do point particle theories. (3) We can construct the
general solution from a particularly simple one, by generating it from
successive applications of the {\it noncommuting} \sltwor\ and \ooneone\
symmetries of the low-energy string equations containing $S$ and target--space
dualities respectively. This allows its construction using relatively simple,
purely algebraic, techniques. The general solution is determined by the
asymptotic behaviour of the various fields: \ie\ by the mass, dilaton charge,
axion charge, electric charge, magnetic charge, and Taub-NUT parameter.