"Big Bang'' as a result of first-order phase transition driven by changing scalar curvature in expanding early Universe: "hyperinflation'' scenario

Abstract

We suggest that the "Big Bang" may be a result of the first-order phase transition driven by changing scalar curvature of the 4D space-time in expanding cold Universe, filled with nonlinear scalar field $\phi $ and neutral matter with equation of state $p=\nu \varepsilon $ (where $p$ and $\varepsilon $ are pressure and energy density of matter). We consider a Lagrangian for scalar field in curved space-time with nonlinearity $\phi ^{4} $, which along with the quadratic term $-\xi R\left|\phi \right|^{2} $ (where $\xi $ is the interaction constant and $R$ is scalar curvature) contains a term $\sim \xi R\left(\phi +\phi ^{+} \right)$ linear in $\phi $. Due to this term the condition for the extrema of the potential energy of scalar field is given by a cubic equation. Provided $\nu > 1/3$ the scalar curvature $R=[\kappa (3\nu -1)\varepsilon -4\Lambda ]$ (where $\kappa $ and $\Lambda $ are Einstein's gravitational and cosmological constants) decreases along with decreasing $\varepsilon $ in the process of the Universe's expansion, and at some critical value $R_{c} < 0$ a first-order phase transition occurs, induced by an "external field" parameter proportional to $R$. Given certain conditions the critical radius of the early Universe at the point of the first-order phase transition may reach arbitrary large values, so this scenario of unrestricted "inflation" of the Universe may be called "hyperinflation". Beyond the point of phase transition the system is rolling down into the potential minimum with the release of the potential energy of scalar field, accompanied by oscillations of its amplitude $\phi $. The powerful heating of the Universe in the course of attenuation of these oscillations plays the role of "Big Bang".