%0 Generic %1 park2019lambdacdm %A Park, Minsu %A Kreisch, Christina D. %A Dunkley, Jo %A Hadzhiyska, Boryana %A Cyr-Racine, Francis-Yan %D 2019 %K tifr %T $Łambda$CDM or self-interacting neutrinos? - how CMB data can tell the two models apart %U http://arxiv.org/abs/1904.02625 %X Of the many proposed extensions to the $Łambda$CDM paradigm, a model in which neutrinos self-interact until close to the epoch of matter-radiation equality has been shown to provide a good fit to current cosmic microwave background (CMB) data, while at the same time alleviating tensions with late-time measurements of the expansion rate and matter fluctuation amplitude. Interestingly, CMB fits to this model either pick out a specific large value of the neutrino interaction strength, or are consistent with the extremely weak neutrino interaction found in $Łambda$CDM, resulting in a bimodal posterior distribution for the neutrino self-interaction cross section. In this paper, we explore why current cosmological data select this particular large neutrino self-interaction strength, and by consequence, disfavor intermediate values of the self-interaction cross section. We show how it is the $1000$ CMB temperature anisotropies, most recently measured by the Planck satellite, that produce this bimodality. We also establish that smaller scale temperature data, and improved polarization data measuring the temperature-polarization cross-correlation, will best constrain the neutrino self-interaction strength. We forecast that the upcoming Simons Observatory should be capable of distinguishing between the models.

@misc{park2019lambdacdm, abstract = {Of the many proposed extensions to the $\Lambda$CDM paradigm, a model in which neutrinos self-interact until close to the epoch of matter-radiation equality has been shown to provide a good fit to current cosmic microwave background (CMB) data, while at the same time alleviating tensions with late-time measurements of the expansion rate and matter fluctuation amplitude. Interestingly, CMB fits to this model either pick out a specific large value of the neutrino interaction strength, or are consistent with the extremely weak neutrino interaction found in $\Lambda$CDM, resulting in a bimodal posterior distribution for the neutrino self-interaction cross section. In this paper, we explore why current cosmological data select this particular large neutrino self-interaction strength, and by consequence, disfavor intermediate values of the self-interaction cross section. We show how it is the $\ell \gtrsim 1000$ CMB temperature anisotropies, most recently measured by the Planck satellite, that produce this bimodality. We also establish that smaller scale temperature data, and improved polarization data measuring the temperature-polarization cross-correlation, will best constrain the neutrino self-interaction strength. We forecast that the upcoming Simons Observatory should be capable of distinguishing between the models.}, added-at = {2019-04-05T10:30:07.000+0200}, author = {Park, Minsu and Kreisch, Christina D. and Dunkley, Jo and Hadzhiyska, Boryana and Cyr-Racine, Francis-Yan}, biburl = {https://www.bibsonomy.org/bibtex/2e77c633b6cb2ede7a774eba9685cce7d/citekhatri}, description = {$\Lambda$CDM or self-interacting neutrinos? - how CMB data can tell the two models apart}, interhash = {9cbe9e25ddc004e3bdeaaa1c121a7300}, intrahash = {e77c633b6cb2ede7a774eba9685cce7d}, keywords = {tifr}, note = {cite arxiv:1904.02625Comment: 6 pages, 7 figures, comments welcome}, timestamp = {2019-04-05T10:30:07.000+0200}, title = {$\Lambda$CDM or self-interacting neutrinos? - how CMB data can tell the two models apart}, url = {http://arxiv.org/abs/1904.02625}, year = 2019 }