Higher order terms in the inflaton potential and the lower bound on the
  tensor to scalar ratio r
  The MCMC analysis of the CMB+LSS data in the context of the Ginsburg-Landau
approach to inflation indicated that the fourth degree double--well inflaton
potential best fits the present CMB and LSS data. This provided a lower bound
for the ratio r of the tensor to scalar fluctuations and as most probable value
r = 0.05, within reach of the forthcoming CMB observations. We systematically
analyze here the effects of arbitrary higher order terms in the inflaton
potential on the CMB observables: spectral index ns and ratio r. Furthermore,
we compute in close form the inflaton potential dynamically generated when the
inflaton field is a fermion condensate in the inflationary universe. This
inflaton potential turns to belong to the Ginsburg-Landau class too. The
theoretical values in the (ns,r) plane for all double well inflaton potentials
in the Ginsburg-Landau approach (including the potential generated by fermions)
turn to be inside a universal banana-shaped region B. The upper border of the
banana-shaped region B is given by the fourth order double--well potential and
provides an upper bound for the ratio r.The lower border of B is defined by the
quadratic plus an infinite barrier inflaton potential and provides a lower
bound for the ratio r. For example, the current best value of the spectral
index ns = 0.964, implies r is in the interval: 0.021 < r < 0.053.
Interestingly enough, this range is within reach of forthcoming CMB
observations.
