Constraints on long-lived, higher-spin particles from galaxy bispectrum

TL;DR

This paper investigates how long-lived higher-spin particles during inflation imprint an anisotropic, Legendre-expanded bispectrum on primordial curvature fluctuations, and how upcoming EUCLID galaxy surveys can constrain the associated coefficients. Using a dS/CFT-inspired framework, it models the primordial bispectrum from spinning fields and derives an angle-averaged template with even Legendre terms up to n = 2s, plus a partially massless alternative with helicity-mixing parameters. The observed galaxy bispectrum is modeled at tree level with redshift-space and Alcock-Paczynski effects, incorporating bias terms and FoG, and its Fisher forecast is computed under EUCLID specifications, with Planck priors and three C_n-parameter scenarios. Results show EUCLID can constrain C_n to order unity when varied independently, and tighter C0 constraints arise when C_n are linked by a theoretical model (e.g., HS-inflaton coupling), though non-Gaussian variance significantly degrades constraints. The work emphasizes that detecting higher multipoles would be crucial to confirming a higher-spin inflationary signature and demonstrates the power of LSS bispectrum analyses to probe spin and couplings of fields present during inflation.

Abstract

The presence of massive particles with spin during inflation induces distinct signatures on correlation functions of primordial curvature fluctuations. In particular, the bispectrum of primordial perturbations obtains an angular dependence determined by the spin of the particle, which can be used to set constraints on the presence of such particles. If these particles are long-lived on super-Hubble scales, as is the case for example for partially massless particles, their imprint on correlation functions of curvature perturbations would be unsuppressed. In this paper, we make a forecast for how well such angular dependence can be constrained by the upcoming EUCLID spectroscopic survey via the measurement of galaxy bispectrum.

Figures (5)

• Figure 1: A schematic representation of various realizations of the first $N-N_k$ e-folds of inflation in which the long-lived IR (i.e. super-Hubble) higher-spin modes $A_{\mu_1 \cdots \mu_s }^{IR}$ act as non-trivial background. The cosmological perturbations depend on the particular value the IR modes assume in a single realization of the ensemble of possible universes.
• Figure 2: 1-$\sigma$ confidence ellipses for the coefficients $C_n$ from EUCLID survey as a function of $k_{\rm max}(z=0)$. The fiducial values of biases and cosmological parameters are given in the text.
• Figure 3: 1- and 2-$\sigma$ confidence ellipses for the coefficients $C_n$ from EUCLID survey, marginalizing over all the other parameters. We chose $C_n =1$ as our fiducial values. The fiducial values of biases and cosmological parameters are given in the text.
• Figure 4: 1- and 2-$\sigma$ confidence ellipses for the biases and the coefficients $C_n$ from EUCLID survey, marginalizing over all the other parameters. The fiducial values of biases and cosmological parameters are given in the text.
• Figure 5: 1- and 2-$\sigma$ confidence ellipses for $C_0$ from HS massive particles with $s=5$, and cosmological parameters and the biases from EUCLID survey, marginalizing over all the other parameters. The fiducial values of biases and cosmological parameters are given in the text.