Dyonic BIon black hole in string inspired model - art. no. 024027

We construct static and spherically symmetric particlelike and black hole s olutions with magnetic and/or electric charge in the Einstein-Born-Infeld-d ilaton-axion system, which is a generalization of the Einstein-Maxwell-dila ton-axion (EMDA) system and of the Einstein-Born-Infeld (EBI) system. They have remarkable properties which are not seen for the corresponding solutio ns in the EMDA and EBI systems. If solutions do not have both magnetic and electric charge, the axion field becomes trivial. In the electrically charg ed case, neither extreme nor the BPS saturated solutions exist. Although we can take the zero horizon radius limit for any Born-Infeld (BI) parameter b, there is no particlelike solution. In the magnetically charged case, an extreme solution does exist for the critical BI parameter (or charge) root bQ(m) = 1/2. The critical BI parameter divides the solutions qualitatively. For root bQ(m)>1/2, there exists a particlelike solution for which the dil aton field is finite everywhere, while a no particlelike solution exists an d the solution in the r(h)-->0 limit becomes naked for root bQ(m)>1/2. Thou gh there is an extreme solution, the BPS saturated solution does not exist in this case. When the solutions have both magnetic and electric charge, we obtain the nontrivial axion field which plays an important role particular ly for small black holes. The thermodynamical properties and the configurat ion of the dilaton field approach those in the magnetically charged case in the zero horizon limit, although the gravitational mass does not. This is related to the nontrivial behavior of the axion field. We can prove that th ere is no inner horizon and that the global structure is the same as the Sc hwarzschild black hole in any charged case.