Signatures of anisotropic sources in the squeezed-limit bispectrum of the cosmic microwave background
- Department of Physics and Astrophysics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)
- Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Str. 1, 85741 Garching (Germany)
- School of Physics and Astronomy, University of Minnesota, Minneapolis 55455 (United States)
- Department of Applied Mathematics and Theoretical Physics, Center for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 0WA (United Kingdom)
The bispectrum of primordial curvature perturbations in the squeezed configuration, in which one wavenumber, k{sub 3}, is much smaller than the other two, k{sub 3} << k{sub 1} ≈ k{sub 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{sub 1} and k{sub 3} such that B{sub ζ}(k{sub 1},k{sub 2},k{sub 3}) → 2Σ{sub L}c{sub L}P{sub L}( k-circumflex {sub 1}· k-circumflex {sub 3})P{sub ζ}(k{sub 1})P{sub ζ}(k{sub 3}), where P{sub L} are the Legendre polynomials. While c{sub 0} is related to the usual local-form f{sub NL} parameter as c{sub 0} = 6f{sub NL}/5, the higher-multipole coefficients, c{sub 1}, c{sub 2}, etc., have not been constrained by the data. Primordial curvature perturbations sourced by large-scale magnetic fields generate non-vanishing c{sub 0}, c{sub 1}, and c{sub 2}. Inflation models whose action contains a term like I(φ){sup 2}F{sup 2} generate c{sub 2} = c{sub 0}/2. A recently proposed ''solid inflation'' model generates c{sub 2} >> c{sub 0}. A cosmic-variance-limited experiment measuring temperature anisotropy of the cosmic microwave background up to l{sub max} = 2000 is able to measure these coefficients down to δc{sub 0} = 4.4, δc{sub 1} = 61, and δc{sub 2} = 13 (68% CL). We also find that c{sub 0} and c{sub 1}, and c{sub 0} and c{sub 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.
- OSTI ID:
- 22282854
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2013, Issue 05; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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