THERMODYNAMIC PROPERTIES OF GAMMA-FLUIDS AND THE QUANTUM VACUUM

The thermodynamic behavior of a relativistic perfect simple fluid obey ing the equation of state p = (gamma - 1)rho, where 0 less than or equ al to gamma less than or equal to 2 is a constant, is investigated. Pa rticular cases include a vacuum (p = -rho, gamma = 0), a randomly orie nted distribution of cosmic strings (p = -1/3 rho, gamma = 2/3), black body radiation (p = -1/3 rho, gamma = 4/3), and stiff matter (p = rho, gamma = 2). Fluids with gamma < 1 become hotter when they expand adia batically (T proportional to V1-gamma). By assuming that such fluids m ay be regarded as a kind of generalized radiation, the general Planck- type form of the spectrum is deduced. As a Limiting case, a new Lorent z-invariant spectrum of the vacuum which is compatible with the equati on of state and other thermodynamic constraints is proposed. Some poss ible consequences to early universe physics are also discussed.