Cosmological Collider Physics and the Curvaton

TL;DR

This work analyzes a two-field curvaton framework in which inflationary expansion is driven by the inflaton while primordial fluctuations are sourced by a separate curvaton, allowing distinct EFT cutoffs $\Lambda_\phi$ and $\Lambda_\sigma$ and potentially large non-Gaussianity from heavy states at the inflationary scale $H$. It shows that coupling heavy charged scalars and fermions to the curvaton, rather than the inflaton, can produce order-unity or larger NG signals without fine-tuning, thanks to the lower curvaton EFT cutoff and possible mediator effects that reduce $\Lambda_\sigma$ further. Tree- and loop-level NG from Higgsed and symmetric-phase charged states are computed, with the curvaton scenario yielding NG magnitudes far above the standard inflationary expectations and potentially within observational reach. The results broaden cosmological collider prospects by highlighting how a two-field, EFT-tuned setup can probe heavy on-shell physics during inflation, with implications for collider-like signatures in future CMB, LSS, and 21-cm surveys.

Abstract

Primordial non-Gaussianity signatures of extremely heavy particles are re-examined within a simple alternative to the standard inflationary paradigm, in which the primordial fluctuations and the inflationary spacetime expansion are sourced by two different fields. The curvaton scenario provides an example of this in which the distinct roles are played by the curvaton and the inflaton fields, respectively. We study couplings of the curvaton to heavy particles with masses of order the inflationary Hubble scale, and show that they can lead to non-Gaussian signals orders of magnitude larger than those in standard inflation, consistent with explicit effective field theory control of inflationary dynamics. This brings various motivated particle physics signatures, such as loops of heavy gauge-charged scalars and fermions, within future observational reach.

Figures (7)

• Figure 1: Various energy scales discussed in this work. $H$ and $M_{\text{pl}}$ are respectively, the inflationary Hubble scale and the Planck scale. $V_{\text{inf}}^{1/4}$ and $\sqrt{\dot{\phi}_0}$ are respectively the potential and kinetic energy scales of the inflaton field. Similarly, $V_{\sigma}^{1/4}$ and $\sqrt{\dot{\sigma}_0}$ are respectively the potential and kinetic energy scales of the curvaton field. A sample set of values of the above scales can be obtained using the benchmark parameter point given in eq. \ref{['benchmark']}.
• Figure 2: Massive Higgs mediated (in red) tree level "in-in" contributions to the inflaton (in black) three point function. Depending on the number of massive scalar propagators, these diagrams are labelled from left to right: (a) single exchange diagram, (b) double exchange diagram, (c) triple exchange diagram. $\eta$ denotes conformal time which ends at the end of inflation.
• Figure 3: Massive charged particle mediated (in red) loop level "in-in" contributions to the inflaton (in black) three point function. Depending on the number of massive charged particle propagators, these diagrams are labelled from left to right: (a) double exchange diagram, (b) triple exchange diagram. $\eta$ denotes conformal time which ends at the end of inflation.
• Figure 4: The strength of NG for tree level Higgs exchange as a function of Higgs mass $m_\chi$ for $\rho_2=0.3H$ and $\dot{\sigma}_0=-H^2$. The function $|f_{\chi,\text{tree}}(\mu)|$ is defined in eq. \ref{['fscalartree']}.
• Figure 5: The strength of NG for loop level scalar exchange as a function of scalar mass $m_\chi$ for $\Lambda_{\sigma}=4H$ and $\dot{\sigma}_0=-H^2$. The function $|f_{\chi,\text{loop}}(\mu)|$ is defined in eq. \ref{['fscalarloop']}.