Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The H0 tension: did a QCD meV axion emerge?   I discuss the possibility that the difference in the measured Hubble constant
Ho between the current, Late, and the z ~1100, Early, epochs is due to the
emergence in between of a new particle. I connect that difference with a change
in the effective cosmological constant observed by LambdaCDM, which is induced
by the energy density of the vacuum of the field of the new particle. Then I
try to provide the main characteristics of the particle, boson vs fermion and
mass, using the measured change in Ho and a Lorentz invariant regularization of
the energy density of vacuum, which relates it to such characteristics. The
result indicates that a boson of mass in the range of few meV emerged. A QCD
post-inflation cosmological axion in this mass range is allowed by recent
analysis and its detection may be attempted according to recent experimental
proposals.

19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
2
The categories of this paper are: math