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 in new inflation gives an excellent fit of 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 \simeq 0.05 , within reach of the forthcoming CMB observations . In this paper we systematically analyze the effects of arbitrarily higher order terms in the inflaton potential on the CMB observables : spectral index n _ { s } 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 out to belong to the Ginsburg-Landau class too . The theoretical values in the ( n _ { s } ,r ) plane for all double well inflaton potentials in the Ginsburg-Landau approach ( including the potential generated by fermions ) fall inside a universal banana-shaped region \cal B . The upper border of the banana-shaped region \cal B is given by the fourth order double–well potential and provides an upper bound for the ratio r . The lower border of \cal 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 n _ { s } = 0.964 , implies r is in the interval : 0.021 < r < 0.053 . Interestingly enough , this range is within reach of forthcoming CMB observations .