0 < v<2/3
A substance having such an equation of state has been called the "quintessence". It is
supposed, that the quintessence is a real scalar field. No wonder, that modeling of the perfect fluid
with negative preassure is provided with a rather strange scalar field Lagrangian.
Let us designate the scalar field of quintessence as Φ(\(x\)a )and postulate, that its Lagrangian
density is given as follows