Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational waves from first order phase transitions as a probe of an
  early matter domination era and its inverse problem   We investigate the gravitational wave background from a first order phase
transition in a matter-dominated universe, and show that it has a unique
feature from which important information about the properties of the phase
transition and thermal history of the universe can be easily extracted. Also,
we discuss the inverse problem of such a gravitational wave background in view
of the degeneracy among macroscopic parameters governing the signal.

3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas