Strings in an arbitrary constant magnetic field with arbitrary constant   metric and stringy form factors
  We quantize the open string in an arbitrary constant magnetic field with a non factorized metric on a torus. We then discuss carefully the vertexes which describe the emission of dipole open strings and closed strings in the non compact limit. Finally we compute various stringy form factors which in the compact case induces a Kaehler and complex structure dependence and suppression of some amplitudes with KK states. 
Igor Pesando
hep-th