[chaotic_clanger]

having you here i'd like to take the opportunity and to ask about tetraquarks. if i recall correctly there have been several identified tetraquark particles over past years (many of detections coming from LHC) with hint of possibility of pentaquark.

i always wondered how does standard model includes/describes these?

[cshimmin]

Good question! That kind of stuff is a bit out of my area of expertise, but I have asked around my colleagues at CERN and various Unis with more or less the same question.

As far as I know, there's nothing too exotic (from a theoretical perspective), about tetra/pentaquarks. They are just QCD bound states of more than 3 quarks. The problem with QCD is that it's a non-perturbative theory, so we generally can't even do a good job computing the hadronic bound states that we already know exist!

So, I get the impression that these observations are mostly of interest to people doing QCD on the lattice (or other calculational methods), as inputs to their modeling. I.e. perhaps having an "answer key" for some tetraquark masses will allow them to better determine whether they should be modeling these states as bound states of two mesons (which each have 2 quarks), or as a totally different 4-quark structure.