There isn’t a link in your post, but it looks like you’re referring to this preprint. The article has been published in a peer reviewed journal paywall warning.
This is a review article, so it isn’t proposing anything new and is instead giving a summary of the current state of the field. These sorts of articles are typically written by someone who is deeply familiar with the subject. They’re also super useful if you’re learning about a new area - think of them as a short, relatively up-to-date textbook.
I’m not sure how you’re interpreting this review as an alternative to the standard model of cosmology and the Big Bang. Everything is pretty standard quantum field theory. The only mention of the CMB is in regards to the possibility that gravitons in the early universe would leave detectable signatures (anisotropies and polarization). They aren’t proposing an alternative production mechanism for the CMB.
Haha it’s in the title: “Cosmological Particle Production: A Review”. Also the journal it was published in is for review articles: Reports on Progress in Physics. Mostly though the abstract promises to give a review of the subject.
Another indication is its lengthy (28 pages) with tons of citations throughout. If someone is doing new work, citations will mostly be in the introduction and discussion sections.
i cannot understand everything (far from it) but here is the part where I believe is an alternative explanation for the CMB :
Equations (2.38), (2.39), (2.40), and (2.53) all illustrate that the creation rate of particles with energies larger than the
inverse expansion time, ρ, is exponentially suppressed. Parker [11] has noted that these exponential factor are similar
to those which appear in thermal spectrum at finite temperature.
So unfortunately the article they reference by Parker is paywalled. I have access but can’t share it easily. The article is essentially the foundation of quantum field theory in curved space time - in other words the genesis of the standard cosmological model. Cosmological particle production in an expanding universe isn’t an alternative to the Big Bang, it’s an essential part of it.
May I take another route and ask you what you know about the history of science ... about paradigm shifts ... and about how people very knowledgeable on the current paradigm cannot see (most of times historicaly) that a paradigm shift is about to happen ?