CMB, CRB, CIB, CXB and CGB Share a Universal Harmonic Signature: Inter-Domain Evidence

Cosmological background radiation fields are traditionally analyzed as independent observational domains. In this work, we show that the CMB, CRB, CIB, CXB and CGB exhibit a common harmonic organization when projected into a dimensionless spectral space. Using a locked harmonic pipeline based on FFT amplitude ratios and cosine similarity, we report a near-saturated coherence among cosmological backgrounds (T_obs = 0.9931). This result is obtained directly from measured cosmological spectra and establishes the empirical core of the study. Robustness tests and independent validation procedures confirm that this harmonic structure is not explained by random spectral ordering or scale-dependent effects. The analysis is fully dimensionless, parameter-locked and statistically validated, without cosmological model fitting. These results reveal a previously unexplored large-scale harmonic coherence within cosmological background radiation and open new perspectives for comparative spectral studies across cosmic observations.