The time evolution of the quark gluon plasma in the early Universe

Abstract

Abstract.Our knowledge of the equation of state of the quark gluon plasma has been continuously growing due to the experimental results from heavy ion collisions and also due to the advances in lattice QCD calculations. The new findings about this state may have consequences on the time evolution of the early Universe, which can estimated by solving the Friedmann equations. The solutions of these equations give the time evolution of the energy density and also of the temperature in the beginning of the Universe. In this work we compute the time evolution of the QGP in the early Universe, comparing several equations of state, some of them based on the MIT bag model (and on its variants) and some of them based on lattice QCD calculations. Among other things, we investigate the effects of a finite baryon chemical potential in the evolution of the early Universe. IntroductionIn the last ten years relativistic heavy-ion collision experiments have provided us with information about the properties of matter in the early Universe (at the time when its age was about 10 microseconds and its temperature was higher than 150 MeV). It is believed that, during this period, the Universe was formed by a hot phase of deconfined quarks and gluons, i.e., a quark gluon plasma (QGP). In parallel with these experimental developments there has been a significant progress on the theoretical side, coming from the numerical simulation of finite temperature QCD on a lattice. The new findings about the nature of the QGP motivate us to investigate their consequences in the primordial Universe. This can be done by solving the Friedmann equations, which allow us to determine the precise time evolution of the thermodynamic quantities in the early Universe.Previous works along this line and with the same motivation already exist in the literature. For a review see, e.g., [1] and for recent papers on the subject see [2,3] and references therein. Most of these works focused on the nature of the phase transiton from the QGP to the hadron gas. There are exotic phenomena associated with the order of the phase transition. In [3] a realistic EOS was used in cosmological calculations. In this EOS the transition was actually a crossover and not a first order transition as commonly believed until recent years. The results showed a very smooth time dependence of various thermodynamic quantities and suggested indirectly that there are small chances for the observation of various exotic phenomena such as quark nuggets, strangelets, cold dark matter clumps, etc. Such phenomena are associated typically with first order phase transitions. Apart from these exotic phenomena, changing the

Quark gluon plasma in the early universe expansion with quasi-particle approach

“…So, this information may provide us more about the order of the phase transition between these two phases of QCD. Also, our results closely match wi t h the results of Sanches et al [28,50]. Various approaches predict that the phase transition which occurred at the time of the big bang is an order one phase shift, but the Lattice QCD computations indicate that the cosmic phase shift for hadronization process is always a crossover phase transition even in the appearance of magnetic fields [52].…”

“…( 9), we solve time evolution of temperature T(t). One should note that since the EoS are different, keeping a fixed starting point of energy density suggests that, the early universe evolution begins at different starting temperatures for separate models [28,50]. Finally, we obtained the results of time evolution of temperature and energy density which help us to understand the evolution of early universe.…”

“…The time evolution equation (eqn. ( 1)) assumes that the universe's expansion is isentropic and it aids us in finding the time variation of energy density once we ascertain the pressure quantity which depends on energy density, p(ε) [28]. In this study, a quasi-particle approach is adopted, in which, a finite (thermal dependent) quark mass is considered instead of the earlier assumed dynamic quark mass.…”

Quantum Gravity Effect on The Time History of The Universe

“…Also, the bag model has showed a reasonable description of the phase transition, but there are other factors of the QGP should be theorized, e.g. the number of leptons and the strong magnetic field [38,39]. Since the universe started to expand from the moment of the big bang till the present time, and this expansion is accelerating through observations of distant supernovae [40][41][42].…”