PHANTOM COSMOLOGY BASED ON PT SYMMETRY

We consider the PT-symmetric flat Friedmann model of two scalar fields with positive kinetic terms. While the potential of one "normal" field is taken real, that of the other field is complex. We study a complex classical solution of the system of the two Klein–Gordon equations together with the Friedmann equation. The solution for the normal field is real, while the solution for the second field is purely imaginary, realizing classically the "phantom" behavior. The energy density and pressure are real and the corresponding geometry is well defined. The Lagrangian for the linear perturbations has the correct potential signs for both the fields so that the problem of stability does not arise. The background dynamics is determined by an effective action including two real fields — one normal and one "phantom." Remarkably, the phantom phase in the cosmological evolution is transient and the Big Rip never occurs. Our model is contrasted with well known quintom models, which also include one normal and one phantom field.