Laurence G. Yaffe
How well can we compute transport coefficients in weakly coupled theories?
In equilibrium (at non-zero temperature) topological defects like monopoles will diffuse due to Brownian motion. What is the diffusion rate?
Domain (or bubble) walls (such as those separating hot and cold domains in a first order electroweak phase transion) experience ``frictional'' damping related by fluctuation-dissipation to their diffusion in equilibrium. For electroweak domain walls, the damping involves non-perturbative physics. What is the diffusion (or damping) rate?
In a (weakly coupled) theory with a second-order phase transition, cool from the hot to the cold phase by uniformly expanding the system at a fixed expansion rate .
small non-perturbative critical phenomena.
big complete perturbative control?
Can one reliably compute, for weak coupling and sufficiently large cooling rate, the complete time dependence of the effective temperature, the spatial correlation length, or the full probability distribution of long-wavelength fluctuations?
Euclidean QFT cutoff Euclidean QFT
Integrate out hard d.o.f. Sum of local operators in effective theory
High energy excitations can propagate for long times.
Suitable effective theories may have completely different forms:
Fundamental weak coupling
long lived elementary excitations,
(appripriate) kinetic theory is leading order effective theory.
Can one systematically improve the leading order description?
N.B. Off-shell corrections are only suppressed by a power of g.
Must multiparticle correlations be included explicitly?
UV regularization of (most) real-time effective theories is highly non-trivial;
when are resulting theories well-defined & simulatable?