Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effective picture of bubble expansion   Recently the thermal friction on an expanding bubble from the cosmic
first-order phase transition has been calculated to all orders of the
interactions between the bubble wall and thermal plasma, leading to a
$\gamma^2$-scaling instead of the previously estimated $\gamma^1$-scaling for
the thermal friction exerted on a fast-moving bubble wall with a Lorentz factor
$\gamma$. We propose for the first time the effective equation of motion (EOM)
for an expanding bubble wall in the presence of an arbitrary $\gamma$-scaling
friction to compute the efficiency factor from bubble collisions, which, in the
case of $\gamma^2$-scaling friction, is found to be larger than the recently
updated estimation when the bubble walls collide after starting to approach a
constant terminal velocity, leading to a slightly larger signal of the
gravitational waves background from bubble collisions due to its quadratic
dependence on the bubble collision efficiency factor, although the
$\gamma^2$-scaling friction itself has already suppressed the contribution from
bubble collisions compared to that with $\gamma^1$-scaling friction. We also
suggest a phenomenological parameterization for the out-of-equilibrium term in
the Boltzmann equation that could reproduce the recently found
$(\gamma^2-1)$-scaling of the friction term in the effective EOM of an
expanding bubble wall, which merits further study in future numerical
simulations of bubble expansion and collisions.

22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs