The modification of Einstein gravity at high energies is mandatory from a quantum approach. In this work, we point out that this modification necessarily introduces new degrees of freedom. We analyze the possibility that these new gravitational states can provide the main contribution to the nonbaryonic dark matter of the Universe. By following an effective field theory approach, we illustrate this idea with the first and simplest high energy modification of the Einstein-Hilbert action: $R^2$ gravity.

We show that, in the context of brane-world scenarios with low tension $\tau =f^4$, massive brane fluctuations (branons) are natural dark matter candidates. We calculate the present abundances for both hot (warm) and cold branons in terms of the branon mass $M$ and the tension scale $f$. The results are compared with the current experimental bounds on these parameters. We also study the prospects for their detection in direct search experiments and comment on their characteristic signals in the indirect ones.

Collisionless, cold dark matter in the form of weakly interacting massive particles (WIMPs) is well motivated in particle physics, naturally yields the observed relic density, and successfully explains structure formation on large scales. On small scales, however, it predicts too much power, leading to cuspy halos, dense cores, and large numbers of subhalos, in apparent conflict with observations. We consider super-WIMP dark matter, produced with large velocity in late decays at times ${10}^5–{10}^8\mathrm{s}$. As analyzed by Kaplinghat in a more general setting, we find that super-WIMPs have sufficiently large free-streaming lengths and low phase space densities to help resolve small scale structure problems while preserving all of the above-mentioned WIMP virtues.

We study the metric solutions for the gravitational equations in Modified Gravity Models (MGMs). In models with negative powers of the scalar curvature, we show that the Newtonian Limit (NL) is well defined as a limit at intermediate energies, in contrast with the usual low energy interpretation. Indeed, we show that the gravitational interaction is modified at low densities or low curvatures.