Black Holes and Naked Singularities in Low Energy Limit of String   Gravity with Modulus Field
  We show that the black hole solutions of the effective string theory action, where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet term are taken into account, admit primary scalar hair. The requirement of absence of naked singularities imposes an upper bound on the scalar charges. 
S.Alexeyev, S.Mignemi