Tensor to scalar ratio of phantom dark energy models

We investigate the anisotropies in the cosmic microwave background in a class of models which possesses a positive cosmic energy density but negative pressure, with a constant equation of state $w=(p/\ensuremath{\rho})l\ensuremath{-}1.$ We calculate the temperature and polarization anisotropy spectra for both scalar and tensor perturbations by modifying the publicly available code CMBFAST. For a constant initial curvature perturbation or tensor normalization, we have calculated the final anisotropy spectra as a function of the dark energy density and equation of state w and of the scalar and tensor spectral indices. This allows us to calculate the dependence of the tensor-to-scalar ratio on w in a model with phantom dark energy, which may be important for interpreting any future detection of long-wavelength gravitational waves.