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

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, e.g., 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 the galaxy bispectrum.

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 $A_{{\mu }_1\cdots {\mu }_s}^{\mathrm{IR}}$ act as nontrivial 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

$1\text{−}\sigma$ confidence ellipses for the coefficients $C_n$ from EUCLID survey as a function of $k_{\max }(z=0)$. The fiducial values of biases and cosmological parameters are given in the text.

Figure 3

1- and $2\text{−}\sigma$ 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 $2\text{−}\sigma$ 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 $2\text{−}\sigma$ 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.