大爆炸核合成作为一级相变的探针
Big Bang Nucleosynthesis as a Probe of First-Order Phase Transitions
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中文总结 AI 辅助
本研究探讨过冷一级相变通过再加热产生温度不均匀性，进而影响重子-光子比，并利用大爆炸核合成中氘丰度测量约束相变参数，同时指出该约束与NANOGrav引力波信号解释存在张力，从而限制重子发生时机。
中文摘要 AI 辅助
过冷宇宙学一级相变（FOPTs）由于其随机再加热过程，会产生大的温度不均匀性。如果重子不对称性产生早于FOPT并在其中守恒，则温度对比会转移到重子-光子比η或重子-熵比Y_B上，产生可由大爆炸核合成（BBN）探测的不均匀性。我们通过纳入诱导Y_B涨落的再加热依赖性，扩展了最近关于该效应的形式体系，将有限气泡统计中的跃迁时间功率谱与BBN时期的质子和中子扩散相结合。当成核温度在10^{-2} GeV ≲ T_n ≲ 10^{2} GeV范围内时，氘丰度的精确测量在1σ水平上不利于具有可观潜热和长跃迁持续时间的参数区域。随着扩散变得更加高效，该约束向更高T_n方向减弱。我们进一步表明，该约束不利于与NANOGrav引力波信号兼容的FOPT参数区域。这一结论假设重子不对称性早于跃迁存在，且涨落谱在亚气泡尺度下仍然有效。因此，在NANOGrav信号的此类FOPT解释中，重子不对称性不能简单地早于跃迁存在。相反，如果局部重子产生追踪局部熵注入，它可以在再加热之后或跃迁期间产生。结果，重子发生的时机可能通过结合引力波观测和轻元素丰度测量而受到约束。
英文摘要
Supercooled cosmological first-order phase transitions (FOPTs) generate a large temperature inhomogeneity due to their stochastic reheating process. If a baryon asymmetry production predates the FOPT and is conserved during it, the temperature contrast is transferred onto the baryon-to-photon ratio $η$ or the baryon-to-entropy ratio $Y_{B}$, producing an inhomogeneity probed by big bang nucleosynthesis (BBN). We extend a recent formalism for this effect by including the reheating dependence of the induced $Y_{B}$ fluctuations, combining the transition-time power spectrum from finite-bubble statistics with proton and neutron diffusion at the BBN epoch. When the nucleation temperature is in the range $10^{-2}\,{\rm GeV} \lesssim T_{n} \lesssim 10^{2}\,{\rm GeV}$, the precise measurement of deuterium abundances disfavors parameter regions with a sizable latent heat and a long transition duration at the $1 σ$ level. The bound weakens towards higher $T_{n}$ as diffusion becomes more efficient. We further show that this bound disfavors FOPT parameter regions compatible with the NANOGrav gravitational wave signal. This conclusion assumes that the baryon asymmetry predates the transition and that the fluctuation spectrum remains valid down to sub-bubble scales. Therefore, in such FOPT explanations of the NANOGrav signal, the baryon asymmetry cannot simply predate the transition. It can instead be generated after reheating or during the transition if the local baryon production tracks the local entropy injection. As a result, the timing of baryogenesis may be constrained by combining gravitational wave observations with light element abundance measurements.
发表机构
- Center for High Energy Physics, Peking University（北京大学高能物理中心）
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