| We study applied aspects of conformal field theories (CFTs) in two contexts.;Chapter 1 explores "unparticle physics," which is the situation in which a hidden conformal sector (or one that becomes conformal at an infrared fixed point) couples to ordinary particles. We ask how to describe and compute processes generated by the self-interactions of the unparticle sector, whose physics is encoded in higher correlation functions of the CFT. We argue that the production of unparticle stuff in standard model processes due to the unparticle self-interactions can be decomposed using the conformal partial wave expansion into a sum over contributions from the production of various kinds of unparticle stuff, corresponding to the various primary conformal operators in the CFT, often different from those to which the standard model couples directly. We discuss inclusive and exclusive techniques for computing these processes. We exemplify our methods by computing the effects of self-interactions in the 2D Thirring model which is exactly solvable.;We also study the Sommerfield model, that is a 2D theory of a massless fermion coupled to a massive vector boson which flows to the Thirring model at low energies. There we can see in detail how the production of the unparticle stuff from ordinary particles proceeds between the high-energy particle-like behavior of the unparticle sector and the low-energy unparticle behavior. In ordinary QCD, the short-distance perturbative physics of quarks and gluons turns into the physics of hadrons at large distances. We find that analogously to QCD there is a massive "hadron" in the spectrum of the Sommerfield model, but in sharp contrast with QCD there is also the unparticle stuff.;Chapter 2 addresses strongly-coupled large-N CFTs that are accessible via the AdS/CFT correspondence. We study how the shear viscosity (at finite temperature) is affected by R2 corrections to the AdS action. We present an example of a 4D theory in which the conjectured bound on the viscosity-to-entropy ratio, eta/s≥1/47pi, is violated by 1/N corrections. The existence of such examples may be relevant to the QCD quark-gluon plasma which has eta/s≈1/4pi. |
