English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

This paper derives an upper limit on the density $\rho_{\scriptstyle\Lambda}$of dark energy based on the requirement that cosmological structure formsbefore being frozen out by the eventual acceleration of the universe. Byallowing for variations in both the cosmological parameters and the strength ofgravity, the resulting constraint is a generalization of previous limits. Thespecific parameters under consideration include the amplitude $Q$ of theprimordial density fluctuations, the Planck mass $M_{\rm pl}$, thebaryon-to-photon ratio $\eta$, and the density ratio $\Omega_M/\Omega_b$. Inaddition to structure formation, we use considerations from stellar structureand Big Bang Nucleosynthesis (BBN) to constrain these quantities. The resultingupper limit on the dimensionless density of dark energy becomes$\rho_{\scriptstyle\Lambda}/M_{\rm pl}^4<10^{-90}$, which is $\sim30$ orders ofmagnitude larger than the value in our universe$\rho_{\scriptstyle\Lambda}/M_{\rm pl}^4\sim10^{-120}$. This new limit is muchless restrictive than previous constraints because additional parameters areallowed to vary. With these generalizations, a much wider range of universescan develop cosmic structure and support observers. To constrain theconstituent parameters, new BBN calculations are carried out in the regimewhere $\eta$ and $G=M_{\rm pl}^{-2}$ are much larger than in our universe. Ifthe BBN epoch were to process all of the protons into heavier elements, nohydrogen would be left behind to make water, and the universe would not beviable. However, our results show that some hydrogen is always left over, evenunder conditions of extremely large $\eta$ and $G$, so that a wide range ofalternate universes are potentially habitable.

Constraints on Vacuum Energy from Structure Formation and Nucleosynthesis