http://arxiv.org/abs/1902.08075
We present an improved version of our original cosmological model to explain the current phase of cosmological acceleration without resorting to a cosmological constant or any other mass scale. Like the original, this phenomenological approach is based on an effective quantum gravitational action, but now depends on the original nonlocal dimensionless scalar $X = \square^{-1} R$ only through $Y = \square^{-1} g^{\mu\nu} X_{,\mu} X_{,\nu}$. Both $X$ and $Y$ are quiescent during the radiation-dominated ($R=0$) era, both only grow logarithmically during matter dominance, and neither affects the propagation of gravitational radiation. However, while $X$ has the same sign for gravitationally bound systems as for cosmology, we show that the sign of $Y$ differs for the two cases: it is positive for cosmology and negative for gravitationally bound systems. We can therefore enforce the $\Lambda$CDM expansion history by making a suitable choice of the nonlocal distortion function $f(Y)$ for $Y > 0$, while ensuring that there is no change in the heavily constrained phenomenology of gravitationally bound systems simply by making $f$ vanish for $Y < 0$. We numerically determine the required function $f(Y>0)$: it has a surprisingly simple exponential form.
S. Deser and R. Woodard
Fri, 22 Feb 19
8/52
Comments: 18 pages, 4 figures, uses LaTeX2e
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