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Cosmological Parameters from Pre-Planck CMB Measurements

Erminia Calabrese, Renée A. Hlozek, Nick Battaglia, Elia S. Battistelli, J. Richard Bond, Jens Chluba, Devin Crichton, Sudeep Das, Mark J. Devlin, Joanna Dunkley, Rolando Dünner, Marzieh Farhang, Megan B. Gralla, Amir Hajian, Mark Halpern, Matthew Hasselfield, Adam D. Hincks, Kent D. Irwin, Arthur Kosowsky, Thibaut Louis, Tobias A. Marriage, Kavilan Moodley, Laura Newburgh, Michael D. Niemack, Michael R. Nolta, Lyman A. Page, Neelima Sehgal, Blake D. Sherwin, Jonathan L. Sievers, Cristóbal Sifón, David N. Spergel, Suzanne T. Staggs, Eric R. Switzer, Edward J. Wollack

TL;DR

The paper combines ACT, SPT, and WMAP9 CMB temperature power spectra to estimate cosmological parameters from CMB data alone. The analysis fits a spatially flat $\Lambda$CDM model with six parameters and explores $N_{\rm eff}$ as an extension, using a Gibbs-sampling pipeline to marginalize over secondary foregrounds and construct a joint likelihood. They find a significant tilt in the primordial spectrum with $n_s = 0.9690 \pm 0.0089$ and constrain $N_{\rm eff}$ around the standard value, with joint data including lensing yielding $N_{\rm eff} = 3.28 \pm 0.40$, while ACT and SPT damping-tail measurements show only mild tension. Overall, the results support the standard cosmology and demonstrate improved precision on key parameters, with Planck data anticipated for independent cross-checks.

Abstract

Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat LCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n_s = 0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of light neutrinos.

Cosmological Parameters from Pre-Planck CMB Measurements

TL;DR

The paper combines ACT, SPT, and WMAP9 CMB temperature power spectra to estimate cosmological parameters from CMB data alone. The analysis fits a spatially flat CDM model with six parameters and explores as an extension, using a Gibbs-sampling pipeline to marginalize over secondary foregrounds and construct a joint likelihood. They find a significant tilt in the primordial spectrum with and constrain around the standard value, with joint data including lensing yielding , while ACT and SPT damping-tail measurements show only mild tension. Overall, the results support the standard cosmology and demonstrate improved precision on key parameters, with Planck data anticipated for independent cross-checks.

Abstract

Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat LCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n_s = 0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of light neutrinos.

Paper Structure

This paper contains 4 sections, 2 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data and Analysis Method
  3. Results and discussion
  4. Conclusions

Figures (4)

  • Figure 1: WMAP9 temperature data and ACT and SPT CMB lensed bandpowers marginalized over secondary emissions. The ACT bandpowers are estimated separately for ACT-S and ACT-E and coadded here with an inverse variance weighting. The SPT bins are highly correlated, ($50-65\%$) at small scales, $\ell \gtrsim 2000$, due to foreground uncertainty. The correlation is about $5\%$ between neighbouring ACT bins. The solid line shows the lensed CMB best fit obtained combining the three datasets. The ACT and SPT bandpowers are available on LAMBDA (http://lambda.gsfc.nasa.gov/).
  • Figure 2: Marginalized one-dimensional distributions for the six basic $\Lambda$CDM parameters, for combinations of WMAP9 (W9), ACT (A) and SPT (S) data.
  • Figure 3: Residual power after subtracting the same best-fitting lensed CMB model. The reduced $\chi^2$/dof for ACT is $40.1/42$ (PTE=0.55) and for SPT $55.7/47$ (PTE=0.18). We show ACT-E and ACT-S coadded residuals. The grey band in the bottom panel shows the $2\sigma$ uncertainty in the Poisson source component. Overall calibration errors are not included.
  • Figure 4: Left: Marginalized distribution of $N_{\rm{eff}}$ for different data combinations, showing consistency with three neutrino species. Middle and Right panels: Marginalized $68\%$ and $95\%$ contours in the $N_{\rm{eff}}$- $n_s$ and $N_{\rm{eff}}$- $H_0$ planes; Neff is correlated with both parameters. The standard model expectation of $N_{\rm{eff}} = 3.046$ is indicated with dashed lines.