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Expected Lipschitz-Killing curvatures for spin random fields and other non-isotropic fields

Francesca Pistolato, Michele Stecconi

Abstract

Spherical spin random fields are used to model the Cosmic Microwave Background polarization, the study of which is at the heart of modern Cosmology and will be the subject of the LITEBIRD mission, in the 2030s. Its scope is to collect datas to test the theoretical predictions of the Cosmic Inflation model. In particular, the Minkowski functionals, or the Lipschitz-Killing curvatures, of excursion sets can be used to detect deviations from Gaussianity and anisotropies of random fields, being fine descriptors of their geometry and topology. In this paper we give an explicit, non-asymptotic, formula for the expectation of the Lipshitz-Killing curvatures of the excursion set of the real part of an arbitrary left-invariant Gaussian spin spherical random field, seen as a field on $SO(3)$. Our findings are coherent with the asymptotic ones presented in Carrón Duque, J. et al. "Minkowski Functionals in $SO(3)$ for the spin-2 CMB polarisation field", Journal of Cosmology and Astroparticle Physics (2024). We also give explicit expressions for the Adler-Taylor metric, and its curvature. We obtain such result as an application of a general formula that applies to any nondegenerate Gaussian random field defined on an arbitrary three dimensional compact Riemannian manifold. The novelty is that the Lipschitz-Killing curvatures are computed with respect to an arbitrary metric, possibly different than the Adler-Taylor metric of the field.

Expected Lipschitz-Killing curvatures for spin random fields and other non-isotropic fields

Abstract

Spherical spin random fields are used to model the Cosmic Microwave Background polarization, the study of which is at the heart of modern Cosmology and will be the subject of the LITEBIRD mission, in the 2030s. Its scope is to collect datas to test the theoretical predictions of the Cosmic Inflation model. In particular, the Minkowski functionals, or the Lipschitz-Killing curvatures, of excursion sets can be used to detect deviations from Gaussianity and anisotropies of random fields, being fine descriptors of their geometry and topology. In this paper we give an explicit, non-asymptotic, formula for the expectation of the Lipshitz-Killing curvatures of the excursion set of the real part of an arbitrary left-invariant Gaussian spin spherical random field, seen as a field on . Our findings are coherent with the asymptotic ones presented in Carrón Duque, J. et al. "Minkowski Functionals in for the spin-2 CMB polarisation field", Journal of Cosmology and Astroparticle Physics (2024). We also give explicit expressions for the Adler-Taylor metric, and its curvature. We obtain such result as an application of a general formula that applies to any nondegenerate Gaussian random field defined on an arbitrary three dimensional compact Riemannian manifold. The novelty is that the Lipschitz-Killing curvatures are computed with respect to an arbitrary metric, possibly different than the Adler-Taylor metric of the field.
Paper Structure (42 sections, 27 theorems, 152 equations)

This paper contains 42 sections, 27 theorems, 152 equations.

Table of Contents

  1. Introduction
  2. Overview
  3. Motivations
  4. Cosmology
  5. Lipschitz-Killing curvatures
  6. Setting and main results
  7. Structure of the paper
  8. Remarks
  9. Main novelties
  10. Comparison with articolo_dei_fisici_published
  11. Generalization of Adler and Taylor formulae
  12. Non-homothetic fields
  13. The case of spin fields on $SO(3)$
  14. Euclidean setting
  15. Further remarks
  16. ...and 27 more sections

Key Result

Theorem 1.1

Let $f:SO(3)\to \mathbb{R}$ be a random field defined as above, having spin $s\in \mathbb{Z}$ and with Then, for every $u\in \mathbb{R}$, and $j=0,1,2,3$, we can write where the functions $\Xi_i$, $i=0,1,2,3$ depends on the threshold $u$, are defined by and $\Phi(u)=\int_{-\infty}^u(2\pi)^{-\frac{1}{2}}\exp(-\frac{t^2}{2})dt$ denotes the cumulative distribution function of a normal Gaussian $\m

Theorems & Definitions (82)

  • Remark 1: On the regularity of $f$
  • Theorem 1.1
  • Remark 2
  • Remark 3
  • Theorem 1.2
  • Definition 1
  • Theorem 1.3
  • Proposition 1.3.1
  • Corollary 2.0.1
  • Remark 4
  • ...and 72 more