Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-dimensional Holstein-Hubbard model: Critical temperature, Ising
  universality, and bipolaron liquid   The two-dimensional Holstein-Hubbard model is studied by means of
continuous-time quantum Monte Carlo simulations. Using
renormalization-group-invariant correlation ratios and finite-size
extrapolation, the critical temperature of the charge-density-wave transition
is determined as a function of coupling strength, phonon frequency, and Hubbard
repulsion. The phase transition is demonstrated to be in the universality class
of the two-dimensional Ising model and detectable via the fidelity
susceptibility. The structure of the ground-state phase diagram and the
possibility of a bipolaronic metal with a single-particle gap above $T_c$ are
explored.

19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph