Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational waves and the polarizations in Ho\v{r}ava gravity after
  GW170817   The gravitational waves of Ho\v{r}ava gravity, their polarization states and
their possible observational signatures are discussed. Using the
gauge-invariant variable formalism, we found the three polarization modes in
Ho\v{r}ava gravity excited by the three physical degrees of freedom contained
in this theory. In particular, the scalar degree of freedom excites a mix of
the transverse breathing and the longitudinal polarizations. The constraints
from the previous experimental observations are taken into account, especially
including the speed bound from the observations of GW170817 and GRB 170817A. It
was found that Ho\v{r}ava theory is highly constrained. Within the
experimentally allowed parametric space, we studied whether the pulsar timing
arrays and the Gaia mission can be used to distinguish the different
polarizations. After calculating the cross-correlation functions between the
redshifts of photons and the astrometric positions of stars, one concludes that
it is possible to tell whether there exits the scalar polarization using pulsar
timing arrays and the Gaia mission.

1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess