In this Letter, we present results of a relativistic calculation of decay constants in the framework of full Salpeter equation. The full Salpeter equation is a relativistic equation describing a bound state. Since this method has a very solid basis in quantum field theory, it is very good in describing a bound state which is a relativistic system. In a previous paper [16], we solved the instantaneous Bethe–Salpeter equation [17], which is also called full Salpeter equation [18]. After we solved the full Salpeter equation, we obtained the relativistic wave function of the bound state. We used this wave function to calculate the average kinetic energy of the heavy quark inside a heavy meson in 0− state, and obtained values which agree very well with recent experiments. We also found there that the relativistic corrections are quite large and cannot be ignored [16]. In this Letter we use this method to predict the values of decay constants of heavy mesons in 0− state.
