A geometrical ghost field and its cosmological implications

This paper studies the cosmic evolution in an extended theory of gravity obtained geometrically by transforming the normal-gauge Lyra displacement vector field Φ_μ as a vectorial function depending on a dynamical scalar field with negative kinetic energy. By using the latest observational data, it is revealed that for ω⁰ = -0.98 the geometric fluid starts behaving as dark energy at the critical scale factor a_de = 0.196844 corresponding to a redshift z_de = 4.080165 while the universe starts accelerating at the critical scale factor a_ac = 0.625436 corresponding to a redshift of z_ac = 0.598885, and the age of the universe is t₀ = 13.6423 Gyr. (author)