Interacting Tachyon: generic cosmological evolution for a tachyon and a scalar field

Understand

We study the cosmological evolution of a tachyon scalar field T with a Dirac-Born-Infeld type lagrangian and potential V(T) coupled to a canonically normalized scalar field \phi with an arbitrary interaction term B(T,\phi) in the presence of a barotropic fluid $\rb$, which can be matter or radiation.

• The force between the barotropic fluid and the scalar fields is only gravitational.
• We show that the dynamics is completely determine by only three parameters L1 = - V_T/ V^{3/2}, L2= - B_T /B^{3/2} and L3 =-B_{\phi}/B.
• We determine analytically theconditions for $\lm_i$ under which the energy density of T, \phi and $\rb$ have the same redshift.