Centre for Modeling and Simulation
Savitribai Phule Pune University All Models Are False, Some Are Useful

Technical Report CMS-TR-20121226


Title From nonparametric power spectra to inference about cosmological parameters: A random walk in the cosmological parameter space
Author/s Amir Aghamousa
Centre for Modeling and Simulation, Savitribai Phule Pune University, Pune 411 007 India


Mihir Arjunwadkar
Centre for Modeling and Simulation, Savitribai Phule Pune University, Pune 411 007 India
and
National Centre for Radio Astrophysics, Savitribai Phule Pune University Campus, Pune 411 007, India


Tarun Souradeep
Inter-University Centre for Astronomy and Astrophysics, Savitribai Phule Pune University Campus, India
Abstract What do the data, as distinguished from cosmological models, tell us about cosmological parameters that determined the model of the universe? In this paper, we address this question in the context of the WMAP angular power spectra for the cosmic microwave background radiation. Nonparametric methods are ideally suited for this purpose because they are model-independent by construction, and therefore allow inferences that are as data-driven as possible. Our analysis is based on a nonparametric fit to the WMAP 7-year power spectrum data, with uncertainties characterized in the form of a high-dimensional confidence set centered at this fit. For the purpose of making inferences about cosmological parameters, we have devised a sampling method to explore the projection of this confidence set around the nonparametric fit, into the space of seven cosmological parameters Omega_b, Omega_c, Omega_Lambda, Omega_k, H_0, n_s, tau). Our sampling method is justified by its computational simplicity, and validated by the fact that well-known degeneracies in this cosmological parameter space are correctly reproduced in our results. Our results show that cosmological parameters are not as tightly constrained by these data alone. However, incorporating additional prior information in the analysis (e.g., constraining the values of H_0 or Omega_k) leads to tighter confidence intervals on parameters that are consistent with uncertainties estimated by the mainstream parametric methods.
Keywords cosmic background radiation; cosmological parameters; methods: data analysis; methods: statistical
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Citing This Document Amir Aghamousa, Mihir Arjunwadkar, and Tarun Souradeep , From nonparametric power spectra to inference about cosmological parameters: A random walk in the cosmological parameter space . Technical Report CMS-TR-20121226 of the Centre for Modeling and Simulation, Savitribai Phule Pune University, Pune 411007, India (2012); available at http://cms.unipune.ernet.in/reports/.
Notes, Published Reference, Etc.
Contact amir AT cms.unipune.ernet.in
mihir AT cms.unipune.ernet.in
Supplementary Material


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