(NS5-brane, D5-brane, D3-brane) bound state, open D3-brane, open D5-brane limits, andSL(2,Z)duality

We generalize the non-threshold bound state in type IIB supergravity of the form (NS5, D5, D3) constructed by the present authors (in hep-th/0011236) to non-zero asymptotic value of the axion $(\chi_0$). We identify the decoupling limits corresponding to both the open D3-brane theory and open D5-brane theory for this supergravity solution as expected. However, we do not find any non-commutative Yang-Mills theory (NCYM) limit for this solution in the presence of NS5 branes. We then study the $SL(2, Z)$ duality symmetry of type IIB theory for both OD3-limit and OD5-limit. We find that for OD3 theory, a generic $SL(2, Z)$ duality always gives another OD3-theory irrespective of the value of $\chi_0$ being rational or not. This indicates that OD3-theory is self-dual. But, under a special set of $SL(2, Z)$ transformations for which $\chi_0$ is rational OD3-theory goes over to a 5+1 dimensional NCYM theory and these two theories in this case are related to each other by strong-weak duality symmetry. On the other hand, for OD5-theory, a generic $SL(2, Z)$ duality gives another OD5-theory if $\chi_0$ is irrational, but when $\chi_0$ is rational it gives the little string theory limit indicating that OD5-theory is S-dual to the type IIB little string theory.Comment: 21 pages, Revtex, v3: minor corrections and physical meaning of the parameters $l$ and $\tilde{l}$ is given, version to appear in PR