分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, which demonstrated that were our universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as `intelligently designed,' with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. More generally, this mechanism appears to be important for data science analysis on constrained sets. Finally, we consider wider applications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We revisit the possibility that Dark Matter is composed of stable scalar glueballs of a confining dark ${\rm SU}(3)$ gauge theory coupled only to gravity. The relic abundance of dark glueballs is studied for the first time in a thermal effective theory accounting for strong-coupling dynamics. An important ingredient of our analysis is the use of an effective potential for glueballs that is fitted by lattice simulations. We predict the relic abundance to be in the range $0.12\zeta_{T}^{-3}\Lambda/(137.9 {\rm eV}) \lesssim \Omega h^{2}\lesssim 0.12\zeta_{T}^{-3}\Lambda/(82.7 {\rm eV})$, with $\Lambda$ being the confinement scale, $\zeta_{T}$ the visible-to-dark sector temperature ratio and the uncertainty is coming from the fit to lattice data. This prediction is an order of magnitude smaller than the existing glueball abundance results in the literature. Our framework can be easily generalised to different gauge groups and modified cosmological histories paving the way towards consistent exploration of strongly-coupled dark sectors and their cosmological implications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, which demonstrated that were our universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as `intelligently designed,' with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. More generally, this mechanism appears to be important for data science analysis on constrained sets. Finally, we consider wider applications.
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