Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background
Department of Physics, The Applied Math Program, and Department of Astronomy, The University of Arizona,
2 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
3 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
Accepted: 21 December 2017
Aim. The lack of large-angle correlations in the fluctuations of the cosmic microwave background (CMB) conflicts with predictions of slow-roll inflation. But while probabilities (≲0.24%) for the missing correlations disfavour the conventional picture at ≳3σ, factors not associated with the model itself may be contributing to the tension. Here we aim to show that the absence of large-angle correlations is best explained with the introduction of a non-zero minimum wave number kmin for the fluctuation power spectrum P(k).
Methods. We assumed that quantum fluctuations were generated in the early Universe with a well-defined power spectrum P(k), although with a cut-off kmin ≠ 0. We then re-calculated the angular correlation function of the CMB and compared it with Planck observations.
Results. The Planck 2013 data rule out a zero kmin at a confidence level exceeding 8σ. Whereas purely slow-roll inflation would have stretched all fluctuations beyond the horizon, producing a P(k) with kmin = 0 – and therefore strong correlations at all angles – a kmin ≠ 0 would signal the presence of a maximum wavelength at the time (tdec) of decoupling. This argues against the basic inflationary paradigm, and perhaps even suggests non-inflationary alternatives, for the origin and growth of perturbations in the early Universe. In at least one competing cosmology, the Rh = ct universe, the inferred kmin corresponds to the gravitational radius at tdec.
Key words: cosmic background radiation / cosmology: observations / cosmology: theory / early Universe / inflation / large-scale structure of Universe
© ESO, 2018