The term 'pomeron' was apparently important in the early stages of QCD. I can't find any reference to it in modern QFT books, but older resources sometimes refer to it offhand, and I've yet to find any explanation of what it actually is.
Old theoretical sources such as this throw up a wall of math and seem to say that a pomeron is a purely mathematical object, whose meaning is not clear to me:
The formal definition of Reggeon is the pole in the partial wave in t-channel of the scattering process. [...] Pomeron is a Reggeon with the intercept close to 1. [...] “Hard” Pomeron is a substitute for the following sentence: the asymptotic for the cross section at high energy for the “hard” processes which occur at small distances of the order of $1/Q$ where $Q$ is the largest transverse momentum scale in the process.
But old experimental sources say that the pomeron is a particle, and that its exchange explains some features of hadron scattering cross sections. That mismatch confuses me, but Wikipedia goes even further and says the pomeron has been found:
By the 1990s, the existence of the pomeron as well as some of its properties were experimentally well established, notably at Fermilab and DESY. The pomeron carries no charges. The absence of electric charge implies that pomeron exchange does not lead to the usual shower of Cherenkov radiation, while the absence of color charge implies that such events do not radiate pions.
This makes me really confused. If the pomeron has been found, how come no modern sources ever talk about it? Is it some other particle, a glueball or a meson, maybe, under a different name? Or have pomerons been ruled out? Are the cross sections they were invented to explain now well-understood? If not, why does nobody talk about pomerons anymore?
Edit: after searching around some more, I'm getting the impression that the pomeron is an 'effective' particle, the result of the exchange of one of a whole infinite family of particles that lie on a particular Regge trajectory. But what really mystifies me is that every source steadfastly refuses to say what those particles are, i.e. their quark and gluon content. This is apparently part of the spirit of the bootstrap program, where such questions are just not allowed to be asked, but shouldn't we be able to understand this in conventional QCD?