Resilience and implications of adiabatic CMB cooling
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866908570256146432 |
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| author | Ruchika Giarè, William Teixeira, Elsa M. Melchiorri, Alessandro |
| author_facet | Ruchika Giarè, William Teixeira, Elsa M. Melchiorri, Alessandro |
| contents | We investigate potential deviations from the standard adiabatic evolution of the cosmic microwave background (CMB) temperature, $T_{\rm CMB}(z)$, using the latest Sunyaev-Zeldovich (SZ) effect measurements and molecular line excitation data, covering a combined redshift range of $0 < z \lesssim 6$. We follow different approaches. First, we reconstruct the redshift evolution of $T_{\rm CMB}(z)$ in a model-independent way using Gaussian Process regression. The tightest constraints come from SZ measurements at $z < 1$, while molecular line data at $z > 3$ yield broader uncertainties. By combining both datasets, we find good consistency with the standard evolution across the full analysed redshift range, inferring a present-day CMB monopole temperature of $T_0 = 2.744 \pm 0.019$ K. Next, we test for deviations from the standard scaling by adopting the parameterisation $T_{\rm CMB}(z) = T_0(1+z)^{1-β}$, where $β$ quantifies departures from adiabaticity, with $β= 0$ corresponding to the standard scenario. In this framework, we use Gaussian Process reconstruction to test the consistency of $β= 0$ across the full redshift range and perform $χ^2$ minimisation techniques to determine the best-fit values of $T_0$ and $β$. In both cases, we find good consistency with the standard temperature-redshift relation. The $χ^2$-minimisation analysis yields best-fit values of $β= -0.0106 \pm 0.0124$ and $T_0 = 2.7276 \pm 0.0095$ K, in excellent agreement with both $β= 0$ and independent direct measurements of $T_0$ from FIRAS and ARCADE. We discuss the implications of our findings, which offer strong empirical support for the standard cosmological prediction and place tight constraints on a wide range of alternative scenarios of interest in the context of cosmological tensions and fundamental physics. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_02909 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Resilience and implications of adiabatic CMB cooling Ruchika Giarè, William Teixeira, Elsa M. Melchiorri, Alessandro Cosmology and Nongalactic Astrophysics We investigate potential deviations from the standard adiabatic evolution of the cosmic microwave background (CMB) temperature, $T_{\rm CMB}(z)$, using the latest Sunyaev-Zeldovich (SZ) effect measurements and molecular line excitation data, covering a combined redshift range of $0 < z \lesssim 6$. We follow different approaches. First, we reconstruct the redshift evolution of $T_{\rm CMB}(z)$ in a model-independent way using Gaussian Process regression. The tightest constraints come from SZ measurements at $z < 1$, while molecular line data at $z > 3$ yield broader uncertainties. By combining both datasets, we find good consistency with the standard evolution across the full analysed redshift range, inferring a present-day CMB monopole temperature of $T_0 = 2.744 \pm 0.019$ K. Next, we test for deviations from the standard scaling by adopting the parameterisation $T_{\rm CMB}(z) = T_0(1+z)^{1-β}$, where $β$ quantifies departures from adiabaticity, with $β= 0$ corresponding to the standard scenario. In this framework, we use Gaussian Process reconstruction to test the consistency of $β= 0$ across the full redshift range and perform $χ^2$ minimisation techniques to determine the best-fit values of $T_0$ and $β$. In both cases, we find good consistency with the standard temperature-redshift relation. The $χ^2$-minimisation analysis yields best-fit values of $β= -0.0106 \pm 0.0124$ and $T_0 = 2.7276 \pm 0.0095$ K, in excellent agreement with both $β= 0$ and independent direct measurements of $T_0$ from FIRAS and ARCADE. We discuss the implications of our findings, which offer strong empirical support for the standard cosmological prediction and place tight constraints on a wide range of alternative scenarios of interest in the context of cosmological tensions and fundamental physics. |
| title | Resilience and implications of adiabatic CMB cooling |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2505.02909 |