Kaluza-Klein andHdyons in string theory

Kaluza-Klein monopole and H-monopole solutions, which are T dual to each other, are the well-known solutions of string theory compactified on $T^6.$ Since string theory in this case has an S-duality symmetry, we explicitly construct the corresponding dyonic solutions by expressing the $D=4\mathrm{}$ string effective action in a manifestly $\mathrm{SL}(2,R)\mathrm{}$ invariant form with an $\mathrm{SL}(2,R)\mathrm{}$ invariant constraint. The Schwarz-Sen charge spectrum, the Bogomol’nyi-Prasad-Sommerfield saturated mass formula as well as the stability of these states are discussed briefly.