Prospects for Detecting Exoplanets around Double White Dwarfs with LISA and Taiji

Recently, Tamanini & Danielski (2019) discussed the possibility to detect circumbinary exoplanets (CBPs) orbiting double white dwarfs (DWDs) with Laser Interferometer Space Antenna (LISA). Extending their methods and criteria, we discuss prospects for detecting around DWDs not only by LISA, but also Taiji, a Chinese space-borne gravitational-wave (GW) mission which has slightly better sensitivity at low frequencies. We first explore how different binary masses mass ratios affect abilities of LISA Taiji CBPs. Second, certain known detached high signal-to-noise ratios, quantify CBP detections them. Third, based on DWD population obtained from Mock Data Challenge, present basic assessments in our Galaxy during 4-year time Taiji. constraints detectable zone each system, as well distributions inner/outer edge zone. Based population, further inject two planet an occurrence rate $50\%$ constrain total detection rates. finally briefly habitable CBPs simplified model. These results can provide helpful inputs upcoming exoplanetary projects help analyze planetary systems after common envelope phase.