TE/EE Low-Ell Anomaly

The temperature-polarization (TE) and E-mode polarization (EE) power spectra of the CMB at low multipoles (ℓ < 30) show deviations from ΛCDM predictions that, while individually below 2-sigma, combine to suggest that the reionization and recombination history assumed in the standard model may not fully capture the physics at these scales. The EE spectrum at ℓ ~ 3–5 in particular is anomalously low, and the TE spectrum shows phase shifts relative to expectation. In SCT, low-ℓ polarization anomalies have the same root cause as the low-ℓ temperature deficit: the finite collision size suppresses power in the largest modes, and the rotational component of the collision dynamics generates mixing between temperature and polarization at low multipoles through the mode-coupling mechanism described above.

Furthermore, the pre-existing matter in the colliding pockets would have included ionized gas and early stellar populations that created a non-standard early reionization environment. If some fraction of the collision energy went into ionizing pre-existing neutral gas at high redshift, the effective optical depth τ to the last scattering surface would be modified relative to the clean τ from standard ΛCDM reionization alone. A modified τ shifts both the amplitude and phase of the low-ℓ EE reionization bump. The SCT prediction is that τ carries a component from pre-existing ionized matter that shifts the effective reionization redshift slightly, producing the observed phase shifts in TE and amplitude anomaly in EE at the lowest multipoles in a physically motivated and internally consistent way.