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K. Boguslavski, A. Pineiro Orioli:
"Unraveling the nature of universal dynamics in O(N) theories";
Physical Review D, 101 (2020), 091902.

Many-body quantum systems far from equilibrium can exhibit universal scaling dynamics which defy standard classification schemes.
Here, we disentangle the dominant excitations in the universal dynamics of highly-occupied N-component scalar systems using unequal-time correlators. While previous equal-time studies have conjectured the infrared properties to be universal for all N, we clearly identify for the first time two fundamentally different phenomena relevant at
different N. We find all N >= 3 to be indeed dominated by the same Lorentzian "large-N peak", whereas N=1 is characterized instead by a non-Lorentzian peak with different properties, and for N=2 we see a mixture of two contributions.
Our results represent a crucial step towards obtaining a classification scheme of universality classes far from equilibrium.

Bose gases, Quasiparticles & collective excitations, Nonequilibrium systems, Phase space methods

http://dx.doi.org/10.1103/PhysRevD.101.091902

https://publik.tuwien.ac.at/files/publik_292652.pdf