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Friday, November 1st 2019

12:30 pm:

The cosmological collider allows one to measure, through non-analytic correlations of inflationary density perturbations, three parameters of a heavy particle during inflation: spin, coupling, and mass. To date though, the cosmological collider literature focuses solely on models which have these three parameters as independent variables, and there is thus essentially no differentiating power between the different models. We propose the first models where relations can be established between different measurable parameters, and therefore the first that can be conclusively distinguished from other models. These models provide the most minimal signatures of the Standard Model at the cosmological collider depending on a single coupling between Standard Model fermions and the inflaton, making the cosmological collider a new tool to look for physics beyond the Standard Model.

In this talk, I will mainly discuss how these new measurements could suggest the existence of a high-energy second minimum in the Higgs potential. If the Higgs field resided in this new minimum during inflation and was brought back to the electroweak vacuum by thermal corrections during reheating, the Standard Model particles would leave their imprints on the bispectrum. I will focus on the SM fermions, whose dispersion relation can be modified by the coupling to the inflaton, leading to an enhanced particle production during inflation even if their mass during inflation is larger than the Hubble scale. This results in a large non-analytic contribution to non-Gaussianities. Measuring the contributions from two fermions would allow us to compute the ratio of their masses, and to ascribe the origin of the signal to a new Higgs minimum.

I will also touch upon the observable signature in the case of a stable low energy Higgs minimum, where fermion production induces electroweak symmetry breaking dynamically. The production of fermions stops when the Higgs expectation value and hence the fermion masses become too large, suppressing fermion production. The dynamical equilibrium between these processes gives the SM fermions masses that are uniquely determined by their coupling to the inflation, leaving a distinct cosmological collider physics signal.

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