In fact it argues that there is no mystery behind having a cosmological constant as small as observations indicate.
It starts by recounting “Einstein’s biggest blunder” which, contrary to popular belief, was not introduction of [tex]\Lambda[/tex], but rather overlooking the instability of Einstein’s static universe. It then points out [tex]\Lambda[/tex] is a natural part of Einstein’s gravity, and is not to be afraid of!
The paper then goes on to the “coincidence problem”, i.e. why dark energy and matter densities are so close. They point out that the statement of the problem is vague, and eventually use the anthropic argument to dismiss it.
The most questionable part of the paper, however, is to dismiss the old cosmological constant problem. While they recount the argument for why QFT vacuum energy is 55 orders of magnitude bigger than observed \Lambda, they dismiss it as a problem of QFT, and unrelated to dark energy problem: “It is just one of the numerous open problems in high-energy physics.”
Now, there are several reasons to take issue with this conclusion. Here is one:
All the physical theories that we know of are non-linear. Therefore, high energy problems can and do directly affect low energy phenomena. In fact, particle cosmology is a vibrant field that emerged over the past thirty years, and include high energy effects such as BBN, inflation, baryogenesis, etc. that affect cosmology and low energy physics. The fact that we can now measure [tex]\Lambda[/tex] doesn’t dismiss the embarrassing predictions of high energy models for dark energy.
The paper says:
Neglecting the fact that this also rules out almost any application of GR. For example, all the CMB anisotropy calculations would be wrong because they use Thomson cross-sections derived from flat-space QFT.“To trust flat-space QFT telling us something about the origin or the nature of a term in Einstein equations which implies that spacetime cannot be flat, is a delicate and possibly misleading step.”
In the end, let me just quote the last paragraph of the paper, which in my opinion, is the most disturbing of them all:
“Why then all the hype about the mystery of the dark energy? Maybe because great mysteries help getting attention and funding. But offering a sober and scientifically sound account of what we understand and what we do not understand is preferable for science, on the long run.”