The impact of the cosmological constant on past and future star formation
| Autor: | Sorini, Daniele, Peacock, John A., Lombriser, Lucas |
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| Rok vydání: | 2024 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.1093/mnras/stae2236 |
| Popis: | We present an extended analytic model for cosmic star formation, with the aim of investigating the impact of cosmological parameters on the star formation history within the $\Lambda$CDM paradigm. Constructing an ensemble of flat $\Lambda$CDM models where the cosmological constant varies between $\Lambda = 0$ and $10^5$ times the observed value, $\Lambda_{\rm obs}$, we find that the fraction of cosmic baryons that are converted into stars over the entire history of the universe peaks at $\sim$27% for $0.01 \lesssim \Lambda/\Lambda_{\rm obs} \lesssim 1$. We explain, from first principles, that the decline of this asymptotic star-formation efficiency for lower and higher values of $\Lambda$ is driven respectively by the astrophysics of star formation, and by the suppression of cosmic structure formation. However, the asymptotic efficiency declines slowly as $\Lambda$ increases, falling below 5% only for $\Lambda>100 \, \Lambda_{\rm obs}$. Making the minimal assumption that the probability of generating observers is proportional to this efficiency, and following Weinberg in adopting a flat prior on $\Lambda$, the median posterior value of $\Lambda$ is $539 \, \Lambda_{\rm obs}$. Furthermore, the probability of observing $\Lambda\leq \Lambda_{\rm obs}$ is only $0.5\%$. Although this work has not considered recollapsing models with $\Lambda<0$, the indication is thus that $\Lambda_{\rm obs}$ appears to be unreasonably small compared to the predictions of the simplest multiverse ensemble. This poses a challenge for anthropic reasoning as a viable explanation for cosmic coincidences and the apparent fine-tuning of the universe: either the approach is invalid, or more parameters than $\Lambda$ alone must vary within the ensemble. Comment: Published in the Monthly Notices of the Royal Astronomical Society (MNRAS). This is a pre-copyedited, author-produced version of the article accepted for publication in MNRAS following peer review. The version of record is available online at the DOI: 10.1093/mnras/stae2236 |
| Databáze: | arXiv |
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