Crossing of phantom divide in F(R) gravity

[[abstract]]An explicit model of F(R) gravity with realizing a crossing of the phantom divide is reconstructed. In particular, it is shown that the Big Rip singularity may appear in the reconstructed model of F(R) gravity. Such a Big Rip singularity could be avoided by adding R2 term or non-singular viable F(R) theory1 to the model because phantom behavior becomes transient.[[fileno]]2010129010112[[department]]物理