# Are there any serious alternatives to QCD nowadays?

I've read several posts here where people talk about the history of the developement of the theory of strong interactions. And they mention Regge theory, pomerons, S-matrix and so on.

I'm confused because I see the S-matrix in my QFT books, while wikipedia says: " it was a proposal for replacing QFT..."? What?

Also in the article on Pomeron wikipedia says that it is still used and that pomeron carries no charge etc...?

Are pomerons real?

My question is whether there are any serious competitors to QCD today?

Perhaps I should split this into several question, but I don't know.

I would like to get an overview of the history of the development of the theory of strong interactions from someone neutral, but that's too much to ask for I guess.

See for instance @Ron Maimon's reply to this question.

• I don't know much about pomerons, but from my understanding they are not as much an alternative to QCD but a convenient model that works in a the high energy regime. – JeffDror Mar 13 '14 at 15:01

Those whom I know that work to unite Electroweak force with Strong force are actually very hopeful in reconciling them pretty soon. Strong interactions are there and we need them to see the big picture. The problem is that in low energies (large scales) the strong coupling constant becomes truly close to unity and hence there is no hope for the survival of Perturbation theory in such scales (~ the nucleon's rest mass/energy). However, there is Lattice QCD which comes to play an important and crucial role in reconciling two seemingly different extremes of QCD. So, what we need is to push the frontier to unite QCD with EW so that at least three fundamental forces of Nature are united. I don't think there is any need of having an alternative to QCD when we know it successfully solves lots of problems in the field. I am hopeful someday we will see the unification of QCD and EW.

QCD developed into the standard model as SU(3) in the SU(3)xSU(2)XU(1) from fitting an enormous number of experimental data.

The S matrix means the Scattering crossection, which depends on the feynman diagrams to formulate for calculation the interactions under study. Before the 1960's and 1970's we worked with Regge pole theory for the strong interactions. My doctorate in experimental physics was in identifying Regge trajectories in K- p scattering. Regge pole theory started from the simple feynman exchange diagrams which worked so well for QED. It was found that one could mathematically exchange Regge poles and a whole clutch of data fell into a consistent pattern.

Pomerons were the zero quantum number exchange of Regge trajectories, and they are as real as all virtual particles, i.e. a mathematical construct fitting data, as they enter into a propagator in a feynman type diagram.

The eye hitting symmetries of the eightfold way led to the quark model and SU(3) for strong interactions, a very successful model as the standard model fits the grand majority of data and predicts future behaviors.

Now string theories include a string version of QCD, and once we have a definitive model one might talk of an expanded QCD theory. It is interesting that string theories and Regge poles have the same roots.

You can find many answers in this book. It contains 11 chapters and the first five are:

1. Introduction
2. Preliminary
3. Kinematics
4. Relativistic $S$-Matrix
5. Regge theory

Also I recommend to read 7th chapter ("Soft diffraction: phenomenological survey"). Subsequent chapters describe relation between Pomeron (or Pomerons) and QCD. Actually introduction covers most of your questions (there is a historical overview in it).

Nowadays there are bunch of models that can simultaneously describe data (differential cross sections, total cross-sections ...) in a wide range of energies. If you wish you can search for "Pomeron phenomenology" on arxiv.