ELECTRIC CHARGE ($\mathit Q$)

${{\mathit \gamma}}$ charge (mixed) $<1 \times 10^{-46}$ $\mathit e$
${{\mathit \gamma}}$ charge (single) $<1 \times 10^{-35}$ $\mathit e$
${{\mathit e}}$ $\rightarrow$ ${{\mathit \nu}_{{e}}}{{\mathit \gamma}}$ and astrophysical limits [1] $>6.6 \times 10^{28}$ yr CL=90.0%
${{\mathit \nu}}$ charge $<4 \times 10^{-35}$ $\mathit e$ CL=95.0%
$\vert {{\mathit q}_{{p}}}+{{\mathit q}_{{e}}}\vert /{{\mathit e}}$ [2] $<1 \times 10^{-21}$
${{\mathit n}}$ charge ($-2$ $\pm8$) $ \times 10^{-22}$ $\mathit e$
$\Gamma\mathrm {( {{\mathit n}} \rightarrow {{\mathit p}} {{\mathit \nu}_{{e}}} {{\overline{\mathit \nu}}_{{e}}} )}$ $/$ $\Gamma\mathrm {(total)}$ $<8\times 10^{-27}$ CL=68.0%
 
[1] This is the best limit for the mode ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \gamma}}$ . The best limit for Nuclear de-excitation experiments is $6.4 \times 10^{24}~$yr.
[2] The limit is from neutrality-of-matter experiments; it assumes $\mathit q_{{{\mathit n}}}$ = $\mathit q_{{{\mathit p}}}$ $+$ $\mathit q_{{{\mathit e}}}$. See also the charge of the neutron.