Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational waves from bubble collisions: analytic derivation   We consider gravitational wave production by bubble collisions during a
cosmological first-order phase transition. In the literature, such spectra have
been estimated by simulating the bubble dynamics, under so-called thin-wall and
envelope approximations in a flat background metric. However, we show that,
within these assumptions, the gravitational wave spectrum can be estimated in
an analytic way. Our estimation is based on the observation that the two-point
correlator of the energy-momentum tensor $\langle T(x)T(y)\rangle$ can be
expressed analytically under these assumptions. Though the final expressions
for the spectrum contain a few integrations that cannot be calculated
explicitly, we can easily estimate it numerically. As a result, it is found
that the most of the contributions to the spectrum come from single-bubble
contribution to the correlator, and in addition the fall-off of the spectrum at
high frequencies is found to be proportional to $f^{-1}$. We also provide
fitting formulae for the spectrum.

24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph