### Abstract

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 ζ 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 k_{min} 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 k_{min}≠ 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 k_{min} at a confidence level exceeding 8σ. Whereas purely slow-roll inflation would have stretched all fluctuations beyond the horizon, producing a P(k) with k_{min} = 0 - and therefore strong correlations at all angles - a k_{min} ≠ 0 would signal the presence of a maximum wavelength at the time (t_{dec}) 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 R_{h} = ct universe, the inferred k_{min} corresponds to the gravitational radius at t_{dec}.

Original language | English (US) |
---|---|

Article number | A87 |

Journal | Astronomy and Astrophysics |

Volume | 610 |

DOIs | |

State | Published - Feb 1 2018 |

### Fingerprint

### Keywords

- Cosmic background radiation
- Cosmology: Observations
- Cosmology: Theory
- Early Universe
- Inflation
- Large-scale structure of Universe

### ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science

### Cite this

*Astronomy and Astrophysics*,

*610*, [A87]. https://doi.org/10.1051/0004-6361/201732181

**Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background.** / Melia, Fulvio; López-Corredoira, M.

Research output: Contribution to journal › Article

*Astronomy and Astrophysics*, vol. 610, A87. https://doi.org/10.1051/0004-6361/201732181

}

TY - JOUR

T1 - Evidence of a truncated spectrum in the angular correlation function of the cosmic microwave background

AU - Melia, Fulvio

AU - López-Corredoira, M.

PY - 2018/2/1

Y1 - 2018/2/1

N2 - 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 ζ 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.

AB - 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 ζ 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.

KW - Cosmic background radiation

KW - Cosmology: Observations

KW - Cosmology: Theory

KW - Early Universe

KW - Inflation

KW - Large-scale structure of Universe

UR - http://www.scopus.com/inward/record.url?scp=85043576028&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85043576028&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201732181

DO - 10.1051/0004-6361/201732181

M3 - Article

AN - SCOPUS:85043576028

VL - 610

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A87

ER -