From the sources I have mentioned, the last one, authored by jao maguiejo, is perhaps the easiest to understand. He says:
6.3 Threshold and gamma-ray anomalies and other experimental
tests
Besides its motivation as a phenomenological description of quantum gravity, non-linear relativity
has gained respectability as a possible solution to the puzzle of threshold anomalies[59,
60] (see also [69, 56, 57, 58, 157, 158, 159, 64] for other experimental implications).
Ultra high energy cosmic rays (UHECRs) are rare showers derived from a primary cosmic
ray, probably a proton, with energy above 1011 Gev. At these energies there are no known
cosmic ray sources within our own galaxy, so it’s expected that in their travels, the extragalactic
UHECRs interact with the cosmic microwave background (CMB). These interactions
should impose a hard cut-off above Eth0 ≈ 1011 Gev, the energy at which it becomes kinematically
possible to produce a pion. This is the so-called Greisen-Zatsepin-Kuzmin (GZK)
cut-off; however UHECRs have been observed beyond the threshold [161, 162] (see Fig. 6.3).
A similar threshold anomaly results from the observation of high energy gamma rays above
10 Tev [163], but in this case it’s far less obvious that there is indeed an observational crisis....
8 The observational status of VSL
In the middle of the current observational revolution in cosmology, it’s easy to forget that
some nasty surprises have also fallen from the sky. Examples include claims for cosmic
acceleration [1, 2, 3, 4], or the mounting evidence [19, 18] for a redshift dependence in the
fine structure constant α. Cosmologists can no longer, as in Dirac’s quote opening this paper,
make “any assumptions that they fancy”; instead it appears that they must grapple with the
issue of selecting which observations to take seriously. Most of what passes for observation
in cosmology is plagued by systematic errors. Some of these “facts” could evaporate like fog
should a new technological revolution come on line unexpectedly.
It is nonetheless interesting that several observational puzzles can be solved by VSL.With
appropriate supplementary observations, the redshift dependence in α could be seen as the
result of a varying c. Another puzzle, already studied in Section 6.3, was the observation
of rare very high energy cosmic rays, in conflict with standard kinematic calculations based
on special relativity, which predict a cut-off well below the observed energies. This could
represent the first experimental mishap of special relativity, and evidence for some VSL
theories. Finally, even the accelerating universe may be part of a varying c picture of the
world.
How can this meager evidence be extended? Unfortunately there are two obstacles to
the observation of a varying speed of light. The first relates to the discussion in Section 2
and affects those aspects of VSL which are not dimensionless. It is easy to place oneself
in a no-win situation (e.g. by defining units in which c is a constant), but as explained in
Section 2 the impasse may be solved by testing the dynamics of the theory. The issue of
testability is more direct regarding the dimensionless aspects of a varying c.
More seriously, however, all tests of a varying c face a second hurdle: the effects predicted
are invariably either well beyond the reach of current technology, or at best on the threshold.
In what follows we describe a number of observations which would either provide positive
detection of VSL effects, or imply constraints upon the parameters of the theory. We also
stick the neck out, venturing a number of predictions of the theory.
Tell me, does the above paper indicate whether the author is conservative or liberal????
