${{\mathit K}^{\pm}}$ $\rightarrow$ ${{\mathit \ell}^{\pm}}{{\mathit \nu}}{{\mathit \gamma}}$ FORM FACTORS

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.

$\mathit F_{\mathit A}$ $−$ $\mathit F_{\mathit V}$, DIFFERENCE OF AXIAL-VECTOR AND VECTOR FORM FACTOR FOR ${{\mathit K}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \nu}_{{e}}}{{\mathit \gamma}}$

INSPIRE   PDGID:
S010F-E
VALUE CL% DOCUMENT ID TECN
$\bf{<0.49}$ 90 1
HEINTZE
1979
SPEC
1  HEINTZE 1979 quotes $\vert \mathit F_{\mathit A}$ $−$ $\mathit F_{\mathit V}\vert $ $<~\sqrt {11 }$ $\vert \mathit F_{\mathit A}$ $+$ $\mathit F_{\mathit V}\vert $.
References:
HEINTZE 1979
NP B149 365 A Measurement of the ${{\mathit K}^{+}}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit \nu}}{{\mathit \gamma}}$ Structure Decay