Form Factors for Semi-Leptonic and Radiative Decays of Heavy Mesons to Light Mesons

To know and understand form factors of hadronic currents is of decisive importance for analysing exclusive weak decays. The ratios of different form factors of a given process depend on the relativistic spin structure of initial and final particles. It is shown --- assuming simple properties of the spectator particle --- that these ratios can entirely be expresssed in terms of particle and quark mass parameters. For quark masses large compared to the spectator mass the Isgur-Wise relations follow. The corresponding amplitudes for heavy-to-light transitions show a very similar structure. In particular, the $F_0$ and $A_1$ form factors behave again differently from the $F_1, A_2, V$ and $T_1$ form factors.