Problems with time-varying extra dimensions or “Cardassian expansion” as alternatives to dark energy

Abstract

It has recently been proposed that the Universe might be accelerating as a consequence of extra dimensions with time-varying size. We show that, although these scenarios can lead to acceleration, they run into serious difficulty when taking into account the limits on the time variation of the four-dimensional Newton constant. On the other hand, models of ''Cardassian'' expansion based on extra dimensions which have been constructed so far violate the weak energy condition for the bulk stress energy, for parameters that give an accelerating Universe.

Large-scale structure in non-standard cosmologies

“…As an example, consider the following (original Cardassian) form of g (ρ) (Freese & Lewis 2002) (we omit the subscript M from now on): At early times the Universe is dominated by the κ 2 ρ term (provided that B is small enough at the time of interest), and at late times the ρ n term becomes significant, providing acceleration compared to the standard case. The term of the form ρ n in the Friedmann equation, and hence the Cardassian model(s), is motivated by considering our Universe as a brane embedded in extra dimensions (Chung & Freese 2000) [this idea was, however, critically reviewed in Cline & Vinet (2003)]. In terms of the scale ρ C , can be written as hence B =κ 2 ρ 1− n C .…”

Kaluza–klein Cosmological Models With Anisotropic Dark Energy

“…Astronomical observations indicate that our universe is flat and currently consists of approximately 2/3 dark energy and 1/3 dark matter. The nature of dark energy as well as dark matter is unknown, and many radically different models have been proposed, such as, a tiny positive cosmological constant, quintessence, 12,37,69 DGP branes, 24,22 the nonlinear F (R) models, 13,14,44 and dark energy in braneworlds, among many others 26,73,71,[45][46][47]75,63,18,15,8,27,42,40,43,28,51,11 ; see also the review articles, 20,49 and references therein. As mentioned before, the existence of dark energy fluids comes from the observations of the accelerated expansion of the universe and the isotropic pressure cosmological models give the best fitting of the observations.…”

Star models with dark energy

“…Astronomical observations indicate that our universe is flat and currently consists of approximately 2/3 dark energy and 1/3 dark matter. The nature of dark energy as well as dark matter is unknown, and many radically different models have been proposed, such as, a tiny positive cosmological constant, quintessence [16][17][18], DGP branes [19,20], the nonlinear F(R) models [21][22][23], and dark energy in brane worlds, among many others [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]; see also the review articles [44,45], and references therein.…”