We use gravitational Lagrangians RakRJ-s and linear combinations of them motivated from trials how to overcome the non-renormalizability of Einstein's theory. We ask under which circumstances the de Sitter space-time represents an attractor solution in the set of spatially flat Friedman models. This property ensures the inflationary model to be a typical solution; nowadays, this property is called cosmic no hair theorem because it is analogous to the no hair theorem for black holes.Results are: for arbitrary k, i.e., for arbitrarily large order 2k + 4 of the field equation, one can always find examples where the attractor property takes place. Such examples necessarily need a non-vanishing R2-term. T h e main formulas do not depend on the dimension, so one gets similar results also for l+l-dimensional gravity and for Kaluza-Klein cosmology.K e y words: cosmology -unified field theories and other theories of gravitation AAA subject ctasszfication: 161
IntroductionOver the years, the notion "no hair conjecture" drifted to "no hair theorem" without possessing a generally accepted formulation or even a complete proof. Several trials have been made to formulate and prove it at least for certain special cases. They all have the overall structure: "For a geometrically defined class of space-times and physically motivated properties of the energy-momentum tensor, all the solutions of the gravitational field equation asymptotically converge to a space of constant curvature." The paper of Weyl (1927) is cited in Barrow and Gotz (1989) with the phrase "The behaviour of every world satisfying certain natural homogeneity conditions in the large follows the de Sitter solution asymptotically" to be the first published version of the no hair conjecture. Barrow and Gotz (1989) apply the formulation "All ever-expanding universes with A > 0 approach the de Sitter space-time locally." The first proof of the stability of the de Sitter solution (here: within the steady-state theory), is due to Hoyle and Narlikar (1963).In the papers of Price (1972a,b) perturbations of scalar fields have been considered for the no hair theorem. The probability of inflation is large, if the no hair theorem is valid, cf. Altshuler (1990). Peter et al. (1994) and Kofman et al. (1996) compared the double-inflationary models with cosmological observations. Barrow and Gotz (1989) and Brauer et al. (1994) discussed the no hair conjecture within Newtonian cosmological models. Hiibner and Ehlers (1991) and Burd (1993) considered inflation in an open Friedman universe and have noted that inflationary models need not to be spatially flat. Gibbons and Hawking (1977) have found two of the earliest strict results on the no hair conjecture for Einstein's theory, cf. also Hawking and Moss (1982) and Demianski (1984). Barrow (1986) gave examples that the no hair conjecture fails if the energy condition is relaxed and points out, that this is necessary to solve the graceful exit problem. He uses the formulation of the no hair conjecture "in the presence of an effect...