The scalar chemical potential in cosmological collider physics
Arushi Bodas, Kumar, Soubhik, Sundrum, Raman
Abstract
Abstract\n Non-analyticity in co-moving momenta within the non-Gaussian bispectrum is a distinctive sign of on-shell particle production during inflation, presenting a unique opportunity for the “direct detection” of particles with masses as large as the inflationary Hubble scale (H). However, the strength of such non-analyticity ordinarily drops exponentially by a Boltzmann-like factor as masses exceed H. In this paper, we study an exception provided by a dimension-5 derivative coupling of the inflaton to heavy-particle currents, applying it specifically to the case of two real scalars. The operator has a “chemical potential” form, which harnesses the large kinetic energy scale of the inflaton, $$ {\\overset{\\cdot }{\\phi}}_0^{1/2}\\approx 60H $$\n \n \n ϕ\n ⋅\n \n 0\n \n 1\n /\n 2\n \n \n ≈\n 60\n H\n , to act as an efficient source of scalar particle production. Derivative couplings of inflaton ensure radiative stability of the slow-roll potential, which in turn maintains (approximate) scale-invariance of the inflationary correlations. We show that a signal not suffering Boltzmann suppression can be obtained in the bispectrum with strength fNL ∼ $$ \\mathcal{O} $$\n O\n (0.01–10) for an extended range of scalar masses $$ \\lesssim {\\overset{\\cdot }{\\phi}}_0^{1/2} $$\n ≲\n \n \n ϕ\n ⋅\n \n 0\n \n 1\n /\n 2\n \n \n , potentially as high as 1015 GeV, within the sensitivity of upcoming LSS and more futuristic 21-cm experiments. The mechanism does not invoke any particular fine-tuning of parameters or breakdown of perturbation-theoretic control. The leading contribution appears at tree-level, which makes the calculation analytically tractable and removes the loop-suppression as compared to earlier chemical potential studies of non-zero spins. The steady particle production allows us to infer the effective mass of the heavy particles and the chemical potential from the variation in bispectrum oscillations as a function of co-moving momenta. Our analysis sets the stage for generalization to heavy bosons with non-zero spin.