A stochastic gravitational wave background (GWB) can be generated by the superposition of countless astrophysical sources such as compact binaries, as well as by early-universe processes like inflation, phase transitions, or cosmic strings, each predicting different amplitudes and spectral shapes across frequency bands (Maggiore 2000; Romano & Cornish 2017). Within ΛCDM, fitting potential GWB signals consistently with constraints from the cosmic microwave background, nucleosynthesis, pulsar timing arrays, and ground-based detectors—without overproducing energy density or invoking finely tuned new physics—remains difficult, leaving significant uncertainty about whether any detected background is predominantly primordial, astrophysical, or some mixture of both (Caprini & Figueroa 2018; Christensen 2019).