# Two-fluid solutions of particle-creation cosmologies

## TL;DR

This paper investigates cosmological models with two fluids, one with particle creation and one conserved, deriving a key differential equation for dynamics and exploring various particle creation rates.

## Contribution

It introduces a general framework for two-fluid cosmologies with particle creation, deriving a nonlinear differential equation governing their evolution.

## Key findings

- Derived a single nonlinear differential equation for two-fluid cosmologies with particle creation.
- Explored specific particle creation rates including constant, inverse Hubble, and exponential forms.
- Presented and analyzed singular algebraic solutions and their stability.

## Abstract

Cosmological evolution driven incorporating continuous particle creation by the time-varying gravitational field is investigated. We consider a spatially flat, homogeneous and isotropic universe with two matter fluids in the context of general relativity. One fluid is endowed with gravitationally induced `adiabatic' particle creation, while the second fluid simply satisfies the conservation of energy. We show that the dynamics of the two fluids is entirely controlled by a single nonlinear differential equation involving the particle creation rate, $\Gamma (t)$. We consider a very general particle creation rate, $\Gamma (t)$, that reduces to several special cases of cosmological interest, including $\Gamma =$ constant, $% \Gamma \propto 1/H^{n}$ ($n\in \mathbb{N}$), $\Gamma \propto \exp (1/H)$. Finally, we present singular algebraic solutions of the gravitational field equations for the two-fluid particle creation models and discuss their stability.