Where new gravitational physics comes from: M-theory?

It is suggested [astro-ph/0306438] that current cosmic acceleration arises due to modification of general relativity by the terms with negative powers of curvature. We argue that time-dependent (hyperbolic) compactifications of (4 + n)-dimensional gravity (string/M-theory) lead to the effective 4d gravity which naturally contains such terms. The same may be achieved in the braneworld by the proper choice of the boundary action. Hence, such a model which seems to eliminate the need for dark energy may have the origin in M-theory. (C) 2003 Elsevier B.V. All rights reserved.