A Planet Candidate Orbiting near the Hot Jupiter TOI-2818 b Inferred through Transit Timing

TOI-2818 b is a hot Jupiter orbiting a slightly evolved G-type star that shows transit timing variations (TTVs) suggestive of a decreasing orbital period. Over a 4-year TESS baseline, transits arrive ~8 minutes earlier than expected for a constant initial period. The implied orbital decay rate is too fast to be explained by tidal dissipation with a reasonable tidal quality factor. We use radial velocity measurements to rule out changes in light travel time from a distant companion as the cause. Apsidal precession due to tides requires impossible Love numbers to match the TTVs. The most likely possible cause of the TTVs is another short period planet. If the planet is in or near a mean motion resonance, it could produce large enough TTVs while remaining mostly hidden in the radial velocity and transit data. We conclude that a nearby planet is the most likely cause of the TTVs.