Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermalization/Relaxation in integrable and free field theories: an
  Operator Thermalization Hypothesis   Free or integrable theories are usually considered to be too constrained to
thermalize. For example, the retarded two-point function of a free field, even
in a thermal state, does not decay to zero at long times. On the other hand,
the magnetic susceptibility of the critical transverse field Ising is known to
thermalize, even though that theory can be mapped by a Jordan-Wigner
transformation to that of free fermions. We reconcile these two statements by
clarifying under which conditions conserved charges can prevent relaxation at
the level of linear response and how such obstruction can be overcome. In
particular, we give a necessary condition for the decay of retarded Green's
functions. We give explicit examples of composite operators in free theories
that nevertheless satisfy that condition and therefore do thermalize. We call
this phenomenon the Operator Thermalization Hypothesis as a converse to the
Eigenstate Thermalization Hypothesis.

34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg