Inequalities for theKl3Form Factors

An inequality for the $K_{l3\mathrm{}}$ form factors is derived on the basis of current commutation relations and certain assumptions about the relative importance of the intermediate states. It includes the inequalities due to Quinn and Bjorken and to Suzuki. We find $\xi \le \frac{0.91}{f_{+}\mathrm{}\left(0\right)\mathrm{}}-1.35\mathrm{}$, where $\xi =\frac{f_{-}\mathrm{}\left(0\right)\mathrm{}}{f_{+}\mathrm{}\left(0\right)\mathrm{}}$ and $f_{+}\mathrm{}\left(0\right)\mathrm{}\le 1$.