The trivial representation sends every group element to the identity operator. A one-dimensional constant-coordinate line in a permutation representation is an example: relabelling positions leaves a uniform assignment unchanged. A trivial action on a higher-dimensional vector space has many invariant subspaces and is therefore not an irreducible representation.
The trivial representation of a molecular point group: every symmetry operation is represented by . Labels such as or depend on the group and its labelling convention.
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 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.
A scalar representation is the one-dimensional trivial representation: every group element acts as the identity. Scalar polarization labels are unchanged by the relevant rotation group.
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In the context of representation theory, which studies how groups can be represented through matrices and linear transformations, the trivial representation is a fundamental concept. The **trivial representation** of a group \( G \) is the simplest way of mapping elements of \( G \) to linear transformations. In this representation, every element of the group is represented by the identity transformation.