Searching for Fossil Fields in the Gravity Sector

Evidence for the presence of extra fields during inflation may be found in the anisotropies of the scalar and tensor spectra across a vast range of scales. Indeed, beyond the single-field slow-roll paradigm, a long tensor mode modulating the power spectrum can induce a sizable quadrupolar anisotropy. We investigate how these dynamics play out for the tensor two-point correlator. The resulting quadrupole stores information on squeezed tensor non-Gaussianities, including those sourced by extra field content and responsible for the breaking of so-called consistency relations. We underscore the potential of anisotropies as a probe of new physics: testable at cosmic microwave background scales through the detection of B modes, they are accessible at smaller scales via pulsar timing arrays and interferometers. Our findings are particularly relevant in that recent studies show a considerable suppression for tensor non-Gaussianities if all modes are well inside the horizon. Quadrupolar anisotropies instead probe an unsuppressed ultrasqueezed bispectrum where the long mode can be horizon size.