Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time-crystal ground state and production of gravitational waves from QCD
  phase transition   We propose a novel mechanism for the production of gravitational waves in the
early Universe that originates from the relaxation processes induced by the QCD
phase transition. While the energy density of the quark-gluon mean-field is
monotonously decaying in real time, its pressure undergoes a series of violent
oscillations at the characteristic QCD time scales that generates a primordial
multi-peaked gravitational waves' signal in the radio frequencies' domain. The
signal as an echo of the QCD phase transition, and is accessible by the FAST
and SKA telescopes.

3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ