# Exploring suppressed long-distance correlations as the cause of suppressed large-angle correlations

## TL;DR

This paper investigates the cause of suppressed large-angle correlations in the cosmic microwave background, testing whether primordial density perturbations lack large-scale correlations by using a wavelet basis, revealing the need for a mechanism affecting both real and harmonic space.

## Contribution

It introduces a wavelet basis approach to test the suppression of large-scale correlations and highlights that such suppression requires mechanisms influencing both real and harmonic space.

## Key findings

- Wavelet basis can suppress angular correlation functions
- Suppression of large-angle correlations alone is insufficient
- A mechanism affecting both real and harmonic space is necessary

## Abstract

The absence of large-angle correlations in the map of cosmic microwave background temperature fluctuations is among the well-established anomalies identified in full-sky and cut-sky maps over the past three decades. Suppressed large-angle correlations are rare statistical flukes in standard inflationary cosmological models. One natural explanation could be that the underlying primordial density perturbations lack correlations on large distance scales. To test this idea, we replace Fourier modes by a wavelet basis with compact spatial support. While the angular correlation function of perturbations can readily be suppressed, the observed monopole and dipole-subtracted correlation function is not generally suppressed. This suggests that suppression of large-angle temperature correlations requires a mechanism that has both real-space and harmonic-space effects.