Worldline einbein
= Worldline einbein
{title2=$e(t)$}
An einbein specifies a one-dimensional <metric tensor> along a <worldline>. In the <relativistic particle phase-space action> it is the <Lagrange multiplier> for the <mass-shell condition> and transforms as $\delta e=\dot\epsilon$ under the corresponding canonical <gauge transformation>. After eliminating the <momentum>, its geometric interpretation depends on the normalization of the particle <action>.