Missing large-angle correlations versus even-odd point-parity imbalance in the cosmic microwave background

¹ Instituto de Física Corpuscular (IFIC) and Departamento de Física Teórica, Centro Mixto Universitat de València-CSIC, Dr. Moliner 50, 46100 Burjassot, Spain
e-mail: Miguel.Angel.Sanchis@ific.uv.es
² Department of Physics, The Applied Math Program, and Department of Astronomy, The University of Arizona, Tucson, AZ 85721, USA
e-mail: fmelia@email.arizona.edu
³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
e-mail: fuego.templado@gmail.com
⁴ Departamento de Astrofisica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁵ Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA), Campus de Santiago, 3810-183 Aveiro, Portugal

Received: 24 September 2021
Accepted: 13 February 2022

Abstract

Context. The existence of a maximum correlation angle (θ_max ≳ 60°) in the two-point angular temperature correlations of cosmic microwave background (CMB) radiation, measured by WMAP and Planck, stands in sharp contrast to the prediction of standard inflationary cosmology, in which the correlations should extend across the full sky (i.e., 180°). The introduction of a hard lower cutoff (k_min) in the primordial power spectrum, however, leads naturally to the existence of θ_max. Among other cosmological anomalies detected in these data, an apparent dominance of odd-over-even parity multipoles has been seen in the angular power spectrum of the CMB. This feature, however, may simply be due to observational contamination in certain regions of the sky.

Aims. In attempting to provide a more detailed assessment of whether this odd-over-even asymmetry is intrinsic to the CMB, we therefore proceed in this paper, first, to examine whether this odd-even parity imbalance also manifests itself in the angular correlation function and, second, to examine in detail the interplay between the presence of θ_max and this observed anomaly.

Methods. We employed several parity statistics and recalculated the angular correlation function for different values of the cutoff k_min in order to optimize the fit to the different Planck 2018 data.

Results. We find a phenomenological connection between these features in the data, concluding that both must be considered together in order to optimize the theoretical fit to the Planck 2018 data.

Conclusions. This outcome is independent of whether the parity imbalance is intrinsic to the CMB, but if it is, the odd-over-even asymmetry would clearly point to the emergence of new physics.