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Cosmological constraints from $μE$ cross-correlations

We derive general expressions of the $C^{μX}_l$, the cross correlation function between the cosmic microwave background spectral $μ$ distortion and the linear perturbations in the cosmic microwave background such as the temperature perturbations and the polarizations. The cross correlations are known as new tests for the extremely squeezed shape of primordial non-Gaussianity, which is inaccessible through the direct observations of the temperature 3-point functions. Our formulae are applicable to the arbitrary combinations of the scalar and the tensor perturbations, and we discuss the potential for detecting these quantities. We provide signal-to-noise ratio of the $μE$ as well as $μT$, based on an experiment like the Primordial Inflation Explorer. We also find the signal-to-noise ratio from the scale dependent nonlinearity. For instance, we show that $f^{\rm loc}_{\rm NL}(k_1,k_2,k_3)=\left(k_1k_2k_3\right)^{1/3}k_0^{-1}F_0$ with $k_0=0.05{\rm Mpc}^{-1}$ can be detectable at 1$σ$ level even for $F_0 \sim \mathcal O(1)$.