= Gauge transformation in cosmological perturbation theory
{title2=$\widetilde x^\mu=x^\mu+\xi^\mu$}
= Cosmological gauge transformation
{synonym}
A cosmological gauge transformation changes the identification of a perturbed spacetime with its homogeneous background. Individual field perturbations can change without changing physical observables. At first order the metric change is the <linear metric gauge-transformation law>; matter scalars obey the corresponding background-shift rule.
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