## Abstract

The bispectrum of primordial curvature perturbations in the squeezed configuration, in which one wavenumber, k_{3}, is much smaller than the other two, k_{3} << k_{1} k_{2}, plays a special role in constraining the physics of inflation. In this paper we study a new phenomenological signature in the squeezed-limit bispectrum: namely, the amplitude of the squeezed-limit bispectrum depends on an angle between k _{1} and k_{3} such that B_{ζ}(k_{1},k _{2},k_{3}) 2∑_{LcLPL}( _{1·3})P_{ζ}(k_{1})P _{ζ}(k_{3}), where P_{L} are the Legendre polynomials. While c_{0} is related to the usual local-form f _{NL} parameter as c_{0} = 6f_{NL}/5, the higher-multipole coefficients, c_{1}, c_{2}, etc., have not been constrained by the data. Primordial curvature perturbations sourced by large-scale magnetic fields generate non-vanishing c_{0}, c_{1}, and c_{2}. Inflation models whose action contains a term like I(φ)^{2}F^{2} generate c_{2} = c_{0/2}. A recently proposed ''solid inflation'' model generates c_{2} >> c_{0}. A cosmic-variance-limited experiment measuring temperature anisotropy of the cosmic microwave background up to ℓ_{max} = 2000 is able to measure these coefficients down to δc_{0} = 4.4, δc_{1} = 61, and δc_{2} = 13 (68% CL). We also find that c_{0} and c_{1}, and c_{0} and c_{2}, are nearly uncorrelated. Measurements of these coefficients will open up a new window into the physics of inflation such as the existence of vector fields during inflation or non-trivial symmetry structure of inflaton fields. Finally, we show that the original form of the Suyama-Yamaguchi inequality does not apply to the case involving higher-spin fields, but a generalized form does.

Original language | English (US) |
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Article number | 002 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2013 |

Issue number | 5 |

DOIs | |

State | Published - May 2013 |

## Keywords

- cosmological perturbation theory
- inflation
- non-gaussianity
- primordial magnetic fields