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Superimposed Oscillations in the WMAP Data?

Jerome Martin, Christophe Ringeval

TL;DR

The paper tackles whether WMAP cosmic variance outliers can be explained by oscillations in the primordial power spectrum arising from trans-Planckian physics during inflation. It develops trans-Planckian corrections to the scalar and tensor spectra under α-vacuum–like initial conditions, yielding oscillatory modulations with amplitude proportional to $|x| σ_0$ and wavelength $Δk/k ∝ σ_0/ε$, and implements these in CAMB/COSMOMC to fit WMAP data in a 9-parameter space. The best-fit model reduces the overall χ² by about $Δχ² ≈ 15$ with a significance $p < 0.06%$, but the required oscillation amplitude strays from backreaction constraints, casting doubt on the physical viability of the trans-Planckian interpretation. The results suggest a potential oscillatory imprint in the data, contingent on future Planck measurements to confirm the outliers and the persistence of the signal, and they acknowledge alternative theoretical origins for such oscillations.

Abstract

The possibility that the cosmic variance outliers present in the recently released WMAP multipole moments are due to oscillations in the primordial power spectrum is investigated. Since the most important contribution to the WMAP likelihood originates from the outliers at relatively small angular scale (around the first Doppler peak), special attention is paid to these in contrast with previous studies on the subject which have concentrated on the large scales outliers only (i.e. the quadrupole and octupole). As a physically motivated example, the case where the oscillations are of trans-Planckian origin is considered. It is shown that the presence of the oscillations causes an important drop in the WMAP chi square of about fifteen. The F-test reveals that such a drop has a probability less than 0.06% to occur by chance and can therefore be considered as statistically significant.

Superimposed Oscillations in the WMAP Data?

TL;DR

The paper tackles whether WMAP cosmic variance outliers can be explained by oscillations in the primordial power spectrum arising from trans-Planckian physics during inflation. It develops trans-Planckian corrections to the scalar and tensor spectra under α-vacuum–like initial conditions, yielding oscillatory modulations with amplitude proportional to and wavelength , and implements these in CAMB/COSMOMC to fit WMAP data in a 9-parameter space. The best-fit model reduces the overall χ² by about with a significance , but the required oscillation amplitude strays from backreaction constraints, casting doubt on the physical viability of the trans-Planckian interpretation. The results suggest a potential oscillatory imprint in the data, contingent on future Planck measurements to confirm the outliers and the persistence of the signal, and they acknowledge alternative theoretical origins for such oscillations.

Abstract

The possibility that the cosmic variance outliers present in the recently released WMAP multipole moments are due to oscillations in the primordial power spectrum is investigated. Since the most important contribution to the WMAP likelihood originates from the outliers at relatively small angular scale (around the first Doppler peak), special attention is paid to these in contrast with previous studies on the subject which have concentrated on the large scales outliers only (i.e. the quadrupole and octupole). As a physically motivated example, the case where the oscillations are of trans-Planckian origin is considered. It is shown that the presence of the oscillations causes an important drop in the WMAP chi square of about fifteen. The F-test reveals that such a drop has a probability less than 0.06% to occur by chance and can therefore be considered as statistically significant.

Paper Structure

This paper contains 4 sections, 11 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. The trans-Planckian power spectra
  3. Comparison with the CMB data
  4. Discussion and conclusion

Figures (3)

  • Figure 1:
  • Figure 2: Top left and right panels: the best fit obtained for trans-Planckian angular TT and TE power spectra compared to the best fit standard inflationary power spectra. Bottom left and right panels: the same best fit trans-Planckian TT and TE power spectra but this time compared to the binned WMAP data wmap.
  • Figure 3: Cumulative residual $\Delta \chi^2(\ell)$ between the trans-Planckian fit and the WMAP best fit. The contributions stemming from the temperature and the polarization angular power spectra are also plotted. The final $\Delta\chi^2$ improvement is of order $15$.