= Gauge singlet
{title2=$R(g)=1$}
A field is a <gauge singlet> if it transforms in the <trivial representation> of the entire <gauge group>: every gauge transformation leaves it unchanged. A singlet of only one factor need not be a gauge singlet of the product group. For example a <right-handed neutrino> with representation $(\mathbf1,\mathbf1)_0$ is a <Standard Model> gauge singlet, whereas a color-singlet charged <lepton> is still acted on by the electroweak group. A singlet can have ordinary derivatives in its <kinetic term> and gauge-invariant masses, subject to <Lorentz invariance> and any additional global symmetries.
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