Equation of State in Quantum Chromodynamics

where T is temperature; V , volume; and H is the Hamiltonian defining the considered system. In recent years there has been much attention paid to understanding the equation of state in quantum chromodynamics. The state of matter, called quark–gluon plasma, almost certainly existed in the early Universe up to 10s after the Big Bang and is likely to be found in the interior of neutron stars. One hopes that this state can be formed in the collisions of relativistic heavy nuclei where it can be studied in a controlled and systematic way [1–6]. The formation of quark droplets in colliding nuclei can occur at already existing accelerator energies, leading to the cumulative effect [7]. There are two ways of obtaining the equation of state in quantum chromodynamics. One is a numerical way based on lattice simulation, and another way is by employing statistical models. A discussion of these ways can be found in the recent review [6]. In this report we advance the third possibility of deriving the equation of state in quantum chromodynamics. This novel way is based on the summation of perturbative series in powers of the coupling parameter. The method of summation we use here is a variant of the self–similar approximation theory [8–15] employing self–similar exponential approximants [16]. This method has been successfully used for constructing accurate equations of state for several physical systems [15,16].