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| Main Authors: | , , , |
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| Format: | Preprint |
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2024
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| Online Access: | https://arxiv.org/abs/2407.18102 |
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| _version_ | 1866911980075352064 |
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| author | Barenboim, Gabriela Sanchis, Héctor Kinney, William H. Rios, Diego |
| author_facet | Barenboim, Gabriela Sanchis, Héctor Kinney, William H. Rios, Diego |
| contents | We consider the possibility that the cosmic neutrino background might have a nonthermal spectrum, and investigate its effect on cosmological parameters relative to standard $Λ$-Cold Dark Matter ($Λ$CDM) cosmology. As a specific model, we consider a thermal $y$-distortion, which alters the distribution function of the neutrino background by depleting the population of low-energy neutrinos and enhancing the high-energy tail. We constrain the thermal $y$-parameter of the cosmic neutrino background using Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) measurements, and place a $95\%$-confidence upper bound of $y \leq 0.043$. The $y$-parameter increases the number of effective relativistic degrees of freedom, reducing the sound horizon radius and increasing the best-fit value for the Hubble constant $H_0$. We obtain an upper bound on the Hubble constant of $H_0 = 71.12\ \mathrm{km/s/Mpc}$ at $95\%$ confidence, substantially reducing the tension between CMB/BAO constraints and direct measurement of the expansion rate from Type-Ia supernovae. Including a spectral distortion also allows for a higher value of the spectral index of scalar fluctuations, with a best-fit of $n_{\mathrm{S}} = 0.9720 \pm 0.0063$, and a $95\%$-confidence upper bound of $n_{\mathrm{S}} \leq 0.9842$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2407_18102 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A bound on thermal y-distortion of the cosmic neutrino background Barenboim, Gabriela Sanchis, Héctor Kinney, William H. Rios, Diego Cosmology and Nongalactic Astrophysics We consider the possibility that the cosmic neutrino background might have a nonthermal spectrum, and investigate its effect on cosmological parameters relative to standard $Λ$-Cold Dark Matter ($Λ$CDM) cosmology. As a specific model, we consider a thermal $y$-distortion, which alters the distribution function of the neutrino background by depleting the population of low-energy neutrinos and enhancing the high-energy tail. We constrain the thermal $y$-parameter of the cosmic neutrino background using Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) measurements, and place a $95\%$-confidence upper bound of $y \leq 0.043$. The $y$-parameter increases the number of effective relativistic degrees of freedom, reducing the sound horizon radius and increasing the best-fit value for the Hubble constant $H_0$. We obtain an upper bound on the Hubble constant of $H_0 = 71.12\ \mathrm{km/s/Mpc}$ at $95\%$ confidence, substantially reducing the tension between CMB/BAO constraints and direct measurement of the expansion rate from Type-Ia supernovae. Including a spectral distortion also allows for a higher value of the spectral index of scalar fluctuations, with a best-fit of $n_{\mathrm{S}} = 0.9720 \pm 0.0063$, and a $95\%$-confidence upper bound of $n_{\mathrm{S}} \leq 0.9842$. |
| title | A bound on thermal y-distortion of the cosmic neutrino background |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2407.18102 |