Understanding UV/IR Terminology in Physics

[ramparts]

UV/IR - what do they mean??

Alright, I'm posting here in sheer frustration. I've read a bunch of papers lately which mention the ultraviolet and infrared in pretty strange ways - talking about a theory's UV-completeness or if it's UV-finite, IR modification, and so on.

So - what does this mean? I've scoured the web and papers looking for a definition but I have yet to find a single paper bothering to define the terminology. Thanks!

 

[Avodyne]

These refer to concepts of the renormalization group in quantum field theory, and can't be explained adequately in a brief reply. A theory is said to be "UV complete" if the ultraviolet cutoff can be consistently taken to infinity. For example QCD is UV complete, but QED is not.

 

[ramparts]

No, I wouldn't expect that to be explainable in a brief reply, but thanks :) I suppose I'll wait for a QFT class then.

 

[DrFaustus]

Ramparts -> QFT, as you might already know, is literally plagued with infinities. That's why you frequently hear people talking about "renormalization" of a theory - "removing" those infinities. The two most frequently encountered ones are ultraviolet divergencies (so called as they are associated with large values of momenta, i.e. short wavelengths - hence "ultraviolet") and infrared divergences (theories with massless particles have problems also with small momenta/large wavelengths - hence "infrared"). And those terms you came across refer to ways to handle/modify a theory, if possible, so as to "solve" the problem of divergences in a physically and mathematically meaningful way.

 

[ramparts]

Thanks, DrFaustus :) I've done some wiki-ing (now that I know where to even look) and I've got a better idea, but obviously I'll have to wait to really learn some QFT to get an understanding. Oh well, I was just wondering what these papers were saying.