  Orbital dynamics provide valuable insights into the evolution and diversity
of exoplanetary systems. Currently, only one hot Jupiter, WASP-12b, is
confirmed to have a decaying orbit. Another, WASP-4b, exhibits hints of a
changing orbital period that could be caused by orbital decay, apsidal
precession, or the acceleration of the system towards the Earth. We have
analyzed all data sectors from NASA's Transiting Exoplanet Survey Satellite
together with all radial velocity (RV) and transit data in the literature to
characterize WASP-4b's orbit. Our analysis shows that the full RV data set is
consistent with no acceleration towards the Earth. Instead, we find evidence of
a possible additional planet in the WASP-4 system, with an orbital period of
~7000 days and $M_{c}sin(i)$ of $5.47^{+0.44}_{-0.43} M_{Jup}$. Additionally,
we find that the transit timing variations of all of the WASP-4b transits
cannot be explained by the second planet but can be explained with either a
decaying orbit or apsidal precession, with a slight preference for orbital
decay. Assuming the decay model is correct, we find an updated period of
1.338231587$\pm$0.000000022 days, a decay rate of -7.33$\pm$0.71 msec/year, and
an orbital decay timescale of 15.77$\pm$1.57 Myr. If the observed decay results
from tidal dissipation, we derive a modified tidal quality factor of
$Q^{'}_{*}$ = 5.1$\pm$0.9$\times10^4$, which is an order of magnitude lower
than values derived for other hot Jupiter systems. However, more observations
are needed to determine conclusively the cause of WASP-4b's changing orbit and
confirm the existence of an outer companion.
