= Canonical scalar stress as a perfect fluid
{title2=$\rho=K+V,\quad p=K-V$}
For a canonical scalar with timelike gradient, its <stress-energy tensor> has perfect-fluid form. In a homogeneous background, $\rho=\dot\phi^2/2+V$ and $p=\dot\phi^2/2-V$. Potential domination gives negative pressure, while the scalar's physical rest-frame <sound speed> is one. A constant negative background $w$ therefore does not force its perturbations to obey the adiabatic barotropic closure $\delta p=w\delta\rho$.
// Target: cosmology.bigb
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