Heavy Particle Signatures in Cosmological Correlation Functions with Tensor Modes

TL;DR

This paper investigates how heavy particles during inflation, modeled as isocurvatons, leave signatures in cosmological correlation functions involving scalar and tensor modes, potentially measurable with future observations.

Contribution

It introduces a method to detect heavy particle effects in inflationary correlation functions using effective field theory and analyzes their signatures in scalar and tensor correlations.

Findings

Heavy particles can imprint detectable signals in cosmological correlations.

Future observations could measure the mass and couplings of these particles.

Higher-order graviton correlations can probe larger particle masses.

Abstract

We explore the possibility to make use of cosmological data to look for signatures of unknown heavy particles whose masses are on the order of the Hubble parameter during the time of inflation. To be more specific we take up the quasi-single field inflation model, in which the isocurvaton $\sigma $ is supposed to be the heavy particle. We study correlation functions involving both scalar ($\zeta $) and tensor ($\gamma $) perturbations and search for imprints of the $\sigma$-particle effects. We make use of the technique of the effective field theory for inflation to derive the $\zeta \sigma $ and $\gamma \zeta \sigma $ couplings. With these couplings we compute the effects due to $\sigma $ to the power spectrum $\langle \zeta \zeta \rangle $ and correlations $\langle \gamma^{s} \zeta \zeta \rangle$ and $\langle \gamma^{s_{1}} \gamma ^{s_{2}} \zeta \zeta \rangle $, where $s$, $s_{1}$ and $s_{2}$ are the polarization indices of gravitons. Numerical analyses of the $\sigma$-mass effects to these corrlations are presented. It is argued that future precise observations of these correlations could make it possible to measure the $\sigma$-mass and the strength of the $\zeta \sigma$ and $\gamma \zeta \sigma$ couplings. As an extension to the $N$-graviton case we also compute the correlations $\langle \gamma ^{s_{1}} \cdots \gamma ^{s_{N}} \zeta \zeta \rangle $ and $\langle \gamma ^{s_{1}} \cdots \cdots \gamma ^{s_{2N}} \zeta \zeta \rangle $ and their $\sigma$-mass effects. It is suggested that larger $N$ correlation functions are useful to probe larger $\sigma$-mass .