 P(X, phi) scalar field theory

A $P(X,\varphi )$ scalar theory has Lagrangian density $P$ depending on the field and $X=-g^{\mu \nu }{\partial }_{\mu }\varphi {\partial }_{\nu }\varphi /2$. It includes canonical scalar theory and models with noncanonical kinetic interactions.

A k-essence model uses noncanonical kinetic terms for cosmological acceleration; a general P(X, phi) scalar field theory need not have that application.