Friedmann cosmology with particle creation in modified $f(R,T)$ gravity
  The theoretical and observational consequences of thermodynamics of open systems, which allow particle creation are investigated in modified $f(R,T)$ ($R$ is the Ricci scalar and $T$ is the trace of energy-momentum tensor) theory of gravity within the framework of a flat Friedmann-Robertson-Walker line element. A simplest particular model $f(R,T)=R+2f(T)$ and "gamma-law" equation of state $p=(\gamma-1)\rho$ are assumed to explore the role of particle creation in the early and late time evolution of the universe. A power-law expansion model is proposed for $0\leq \gamma \leq 2$ by considering the natural phenomenological particle creation rate $\psi=3\beta nH$, where $\beta$ is a pure number of the order of unity. A Big Rip singularity is observed for $\gamma<0$, which describes the phantom cosmology. We observe that the accelerated expansion of the universe is driven by the particle creation without any exotic "quintessence" component or a cosmological constant. It is also found by density parameter that the model becomes of negative curvature due to particle creation and the entropy increases with the evolution of the universe. Some kinematics tests such as lookback time, luminosity distance, proper distance, angular diameter versus redshift are discussed in detail to observe the role of particle creation in early and late time evolution of the universe. 
C.P.Singh and Vijay Singh
gr-qc