In article , "Richard D.
Saam" writes:

No WIMPS have been found in reference to the dark matter problem.
What are the dark matter alternatives?

Primordial black holes are still viable.

but there are arguments against black holes as dark matter
https://arxiv.org/abs/1808.05910

First, note that the title contains "clustered". So it is addressing
only the question of clustered primordial black holes. Second,
apparently this hasn't been accepted by any journal, perhaps not even
submitted, so there might have been no external check. Note also that
they write "Throughout this letter we have assumed a monochromatic
initial PBH mass distribution." They do cite Carr, Kühnel, and
Sandstad. Read that paper. It has almost 300 references. Read them as
well. Those folks have done their homework.

As luck would have it, just a few days ago I heard a talk on this topic
by Florian Kühnel. He pointed out that many constraints are too strong
because they are derived based on wrong or flawed assumptions. At

https://indico.cern.ch/event/736594/...ew=nicecompact

you can download his presentation (first talk after lunch on Tuesday 23
October).

[[Mod. note -- The presentation in question seems to be in Apple
"keynote" format. At least on my computer, Libreoffice (v6.0.2.2.1)
was unable to read it.
-- jt]]

Collective Effects in Nuclear Collisions: Experimental Overview
https://arxiv.org/abs/1810.06978
Viscosity plays an important role in measured LHC RHIC nuclear dynamics
Does this viscosity experimental result
influence BBN gas phased mechanisms?

Do you have reason to think so? BBN seems reasonably successful.

Yes, observed BBN expressions are reasonably successful
(except for the Lithium problem),
but the realm of fluid viscosity is different the gas kinematics.
It implies that we are looking at gas phase BBN
and there also exists a viscous BBN,
something like looking at the steam
but knowing the presence of water somewhere.

If you can show that some sort of viscous BBN solves the lithium
problem, fine, but merely juxtaposing various words with another might
not even indicate a problem, much less a solution.

MILKY WAY CEPHEID STANDARDS FOR MEASURING COSMIC DISTANCES AND
APPLICATION TO Gaia DR2:
IMPLICATIONS FOR THE HUBBLE CONSTANT
https://arxiv.org/abs/1804.10655
The Planck H0 = 67.4 km/s/Mpc is based on CMB.
The reported H0 = 73.24 km/s/Mpc is based on photometric parallaxes.
What mechanism explains the difference?

Add the error bars and you have a three-sigma difference. Most would
consider it irresponsible to base a detection on three sigma, so why
base a tension on it.

The paper reports a 96.5% confidence level
for the difference in the HOs 67.4 and 73.24 km/s/Mpc:
'The best-fit distance scale is 1.006 ± 0.033 , relative to the scale
from Riess et al. (2016) with H0 = 73.24 km/s/Mpc used to predict
the parallaxes photometrically, and is inconsistent with the scale
needed to match the Planck 2016 CMB data combined with LambdaCDM at the
2.9\sigma confidence level (99.6%). At 96.5% confidence we find that the
formal DR2 errors may be underestimated as indicated.'

So only 2.9 sigma. Again, a claimed detection at 2.9 sigma would be
deemed over-confident, so the same rules should apply for a claimed
tension. In both cases, there might be something interesting, but one
is far from being able to claim that something is seriously wrong. Note
that not long ago there were claims that the Hubble constant was as low
as 30 or as high as 100, with about 20% errors. Did any "new physics"
come of that? No. Probably something similar will happen here.

The universe increased expanding rate
is an expression of dark energy measured by supernovae type II events.
What is dark energy?

Observationally, it is indistinguishable from a cosmological constant.
Theoretically, there is no reason it is not the cosmological constant.
There is no problem.

Here are some Weinberg's thoughts on the problem:
http://supernova.lbl.gov/~evlinder/weinberg.pdf

'The problem of the dark energy is also central to today's physics.
Our best attempts at a fundamental theory
suggest the presence of a cosmological constant
that is many (perhaps as many as 120) orders of magnitude greater
than the upper bound set by astronomical observations.Until it is
solved, the problem of the dark energy
will be a roadblock on our path
to a comprehensive fundamental physical theory.'

Weinberg presented an anthropic argument for the observed value of the
cosmological constant, and many believe that there is no better
explanation. It is not a FUNDAMENTAL explanation, but then there might
not be one. There is no FUNDAMENTAL explanation for the distance of the
Earth from the Sun, but there is an easily understood anthropic effect.

The cosmological constant problem or the vacuum catastrophe
indicates a vacuum energy theory differing from experiment
by 120 orders of magnitude.
What is the vacuum energy?

It is clear from quantum field theory what it is. Why the observed
cosmological constant is much smaller is not completely clear, but
years ago Weinberg came up with an anthropic explanation, which no-one
has refuted. Also, look for the paper by Bianchi and Rovelli. This is
probably another non-problem.

ditto Weinberg's thoughts from above

The point is that Bianchi and Rovelli explicitly address the concerns of
Weinberg but not vice versa. No progress can be made by just quoting
someone who supports one's own point of view and ignoring others,
especially if the latter explicitly address issues raised by the former.

Is there a common theoretical mechanistic thread
connecting these experimental dots?

Probably not. To prove that there is, one would have to construct such
a theory.

Maybe the mechanism as simple as recognizing an entirely different phase
analogous to liquid and gas relationships.
Then observational cosmology and associated theories
are not eliminated but complemented.

Without some quantitative results, this is just a collection of
buzzwords. If you think that this idea can somehow solve some problems,
then present some quantitative results.