Covariant generalization of the ISGW quark model

A fairly general Lorentz-covariant quark model of mesons is constructed. It has several versions whose nonrelativistic limit corresponds to the well-known Isgur, Scora, Grinstein, and Wise model. In the heavy-quark limit, the covariant model naturally and automatically produces the heavy-quark symmetry results for meson decay constants and semileptonic decay form factors. The meson decay constants and the Isgur-Wise functions are calculated for various versions of the covariant model and compared with other estimates. A general and adaptable structure of the covariant model ensures that it can be used to describe transitions involving light and/or heavy mesons.