Baryogenesis from combined Higgs - scalar field inflation

Abstract

We study a modification of the Higgs inflation scenario where we introduce an extra scalar $\varphi$, with mass $m$, coupled to the Ricci scalar as $g{\varphi }^{2}R$, and mixed with the Higgs field $h$ via the Lagrangian term $\mu \varphi h^2$. Both fields participate in the inflation process in a unitary theory that predicts values of the cosmological observables in agreement with the results from the Planck/BICEP/Keck collaborations. In addition, by means of a $\mathcal{C}\mathcal{P}$-odd effective operator that couples $\varphi$ to the Chern-Simons term of the hypercharge gauge group as $f_{\varphi }^{-1}\varphi Y_{\mu \nu }{\tilde{Y}}^{\mu \nu }$, maximally helical magnetic fields are produced during the last $e$-folds of inflation. We found a window in the coupling $f_{\varphi }$ where these fields survive all constraints until the electroweak phase transition, and source the baryon asymmetry of the Universe through the Standard Model chiral anomaly. From a phenomenological perspective, the model can solve the Standard Model instability problem at the scale ${\mathcal{Q}}_I\simeq 10^{11}$ GeV, provided that $\mu \lesssim m\lesssim {\mathcal{Q}}_I$, and for $m\lesssim \mathcal{O}$(few)~TeV, the $\varphi$-$h$ mixing becomes sizable while the theory turns natural. The latter thus predicts modifications of the trilinear and quartic couplings that could be explored at the HE-LHC, as well as at future colliders, and allows for direct $\varphi$ production at the LHC followed by decay into $hh$. Present results from ATLAS and CMS already put (mild) bounds on the mass of the heavy scalar as $m\gtrsim 0.55$~TeV at 95\% C.L.

Comments: Version to appear in Physical Review D, 56 pages, 11 figures