2020ApJ...901..113F

SW Sex is a deeply eclipsing cataclysmic variable with an orbital period of 0.1349 days. Based on the new photometric observations together with the data collected in the literature, we find that the orbital period shows a period wiggle from 1980 to 2015, and then decreases severely until 2020, when our observations end. If the oscillation with an amplitude of 0.000973 days and a period of 36.57 yr is due to the presence of a third body, the mass of this component can be determined as M₃sini' = 0.014 M_☉. Supposing the companion and the central binary are coplanar, its mass would correspond to a giant planet. However, Applegate's mechanism can also provide enough energy to force such variation and more data will distinguish the reason. The rapid decline of the orbital period at a rate of -4.24 x 10^–10 s s^–1 in 2015-2020 cannot be attributed to magnetic braking. Also, Applegate's mechanism fails to produce such a fast decrease. It can be explained as the angular momentum loss caused by a strong disk wind, which declares its existence by synchronizing the period decrease with the brightness increase. In addition, the long-term brightness oscillation with an amplitude of 0.6 mag and a timescale of about 9.7 yr is discovered. This is the first it has been detected for nova-like cataclysmic variables (CVs). It will provide valuable information for understanding the disk activity and the evolution of the CVs.