Polarization predictions for inflationary CMB power spectrum features

Temporal features during single-field inflation that break the time-translation invariance of the de Sitter expansion lead to the breaking of scale invariance in the curvature and cosmic microwave background temperature power spectra. The large-angle temperature power spectrum is known to contain low to moderate significance features whose inflationary interpretation also allows for substantial tensor contributions. We conduct a model-independent analysis of large-angle features using 20 principal components for the temporal history including the possibility of non-negligible tensor contributions. The suppression of power at low multipoles beginning with a glitch at multipoles l similar to 20-40 implies deviations in two to three of them with 2-3 sigma deviations in each, with larger values reflecting cases where tensors are allowed. If tensors are absent, the corresponding E-mode polarization features follow a similar pattern but are predicted to be up to twice as large. They offer the opportunity to soon double the significance of inflationary features or eliminate them as an explanation of temperature features. The tensor degeneracy with features in the temperature power spectrum is broken not only by B but also by E polarization. A precision measurement of E-mode polarization at multipoles from l similar to 20-60 can potentially provide an independent constraint on tensors that is less subject to dust foreground uncertainties.