分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The characteristic axion couplings could be generated via effective couplings between the Standard Model (SM) fermions to a pseudo-Goldstone from a high-scale $U(1)$ Peccei-Quinn (PQ) symmetry breaking. Assuming that the UV-induced effective operators generate necessary couplings before the PQ symmetry breaking, and any low-scale couplings to the SM are restricted to the Yukawa sector, three minimal natural scenarios can be formulated, which provides a connection between the QCD-axions and mediators at the GUT/string scales. We find that the PQ symmetry breaking scale could be about $10^{15}$ GeV, higher than the classical QCD dark matter axion window but possible if the anthropic window is considered. We also propose an experiment to probe such scenarios. If the dark matter axion is discovered, they might suggest that we live in an atypical Hubble volume.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) have been studied in the generic no-scale supergravity inflationary models. By adding an exponential term to the K\"ahler potential, the inflaton experiences a period of ultraslow-roll and the amplitude of primordial power spectrum at small scales is enhanced to $\mathcal{O}(10^{-2})$. The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. A wide mass range of PBHs can be produced in our model, and the frequencies of the accompanied SIGWs are ranged form nanohertz to kilohertz. We show four benchmark points where the generated PBH masses are around $\mathcal{O}(10^{-16}M_{\odot})$, $\mathcal{O}(10^{-12}M_{\odot})$, $\mathcal{O}(10^{-2}M_{\odot})$ and $\mathcal{O}(10^{2}M_{\odot})$. The PBHs with masses around $\mathcal{O}(10^{-16}M_{\odot})$ and $ \mathcal{O}(10^{-12}M_{\odot})$ can make up almost all the dark matter, and the accompanied SIGWs can be probed by the upcoming space-based gravitational wave observatory. Also, the SIGWs accompanied with the formation of stellar mass PBHs can be used to interpret the stochastic GW background in the nanohertz band, detected by the North American Nanohertz Observatory for gravitational waves, and can be tested by future interferometric gravitational wave observatory.
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