If a sector other than inflaton survives in the late universe, its quantum fluctuation generically brings isocurvature modes. The typical case is the complex scalar with spontaneous symmetry breaking, with the remaining U(1) global symmetry and the associated massless goldstone boson. The goldstone mode can be recognized as the QCD axion or axion-like particle (ALP) and form cold dark matter via the misalignment mechanism. We found a whole new suite of cosmological observables for cold dark matter isocurvature, which could help test the presence of axions, as well as its coupling to the inflaton and other heavy spectator fields during inflation such as the radial mode of the Peccei-Quinn field. They include correlated clock signals in the curvature and isocurvature spectra, and mixed cosmological-collider non-Gaussianities involving both curvature and isocurvature fluctuations with shapes and running unconstrained by the current data analyses. We will also briefly mention further developments in progress.

Biography

Lingfeng Li graduated from Peking University in 2013 and received his PhD in Theoretical High Energy Physics from the University of California, Davis in 2018 under the supervision of Prof. Hsin-Chia Cheng. Then he worked at HKUST and Brown University as a Postdoctoral Researcher. He is interested in precision tests of the Standard Model and probing new physics with new models, methods, and mindsets.