For definitions of the axial-vector $\mathit F_{\mathit A}$ and vector $\mathit F_{\mathit V}$ form factor, see the “Note on ${{\mathit \pi}^{\pm}}$ $\rightarrow$ ${{\mathit \ell}^{\pm}}{{\mathit \nu}}{{\mathit \gamma}}$ and ${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \ell}^{\pm}}{{\mathit \nu}}{{\mathit \gamma}}$ Form Factors” in the ${{\mathit \pi}^{\pm}}$ section. In the kaon literature, often different definitions $\mathit a_{\mathit K}$ = $\mathit F_{\mathit A}/\mathit m_{\mathit K}$ and $\mathit v_{\mathit K}$ = $\mathit F_{\mathit V}/{\mathit m}_{{{\mathit K}}}$ are used.