Impact of a midband gravitational wave experiment on detectability of cosmological stochastic gravitational wave backgrounds

We make forecasts for the impact a future "midband" space-based gravitational wave experiment, most sensitive to $10^{-2}- 10$ Hz, could have on potential detections of cosmological stochastic backgrounds (SGWBs). Specific proposed midband experiments considered are TianGo, B-DECIGO and AEDGE. propose combined power-law integrated sensitivity (CPLS) curve combining GW over different frequency bands, which shows improves SGWBs by up two orders magnitude at $10^{-2} - Hz. consider emission from cosmic strings phase transitions as benchmark examples SGWBs. explicitly model various astrophysical SGWB sources, importantly unresolved black hole mergers. Using Markov Chain Monte Carlo, we demonstrated that can, when with LIGO A+ LISA, significantly improve sensitivities better separate them In particular, forecast experiment string tension $G\mu$ factor $10$, driven improved component separation sources. For transitions, can detect signals peaking $0.1 1$ our fiducial corresponds early Universe temperatures $T_*\sim 10^4 10^6$ GeV, generally beyond reach LISA. The closes an energy gap captures characteristic spectral shape information. It thus substantially measurement properties lower energies $T_* \sim O(10^3)$ potentially relevant new physics electroweak scale, whereas in this range LISA alone will excess but not effectively measure transition parameters. Our modelling code chains publicly available.