报告题目：Big Bang Nucleosynthesis as a Precision Probe of New Physics: Heavy Neutral Leptons, Primordial Black Holes, and Others

报告人：吴泉锋 博士后（Institute of High Energy Physics, Chinese Academy of Sciences (IHEP), and Kaiping Neutrino Research Center (KNRC)）

报告摘要：Big Bang Nucleosynthesis (BBN) provides a precision laboratory for the MeV-era Universe, turning light-element abundances and the radiation content into stringent tests of new physics. I will review the key ingredients of BBN and emphasize how departures from the standard expansion history and neutron–proton conversion processes translate into constraints on exotic energy injection. In particular, hadronic decay products injected at the relevant epoch — such as mesons and (anti)nucleons — can drive efficient nonstandard neutron–proton conversion and distort the freeze-out proton–neutron ratio, thereby shifting the primordial helium abundance. Firstly, I discuss MeV–GeV heavy neutral leptons (HNLs). Using recent cosmological analyses that consistently track both the background evolution and meson-driven neutron–proton conversion, I show that introducing sizable “dark” decay channels does not generically weaken BBN bounds. Instead, dark decays typically increase the dark-sector energy density around the BBN epoch, enhancing deviations in the primordial helium abundance and the effective number of relativistic species, and can even strengthen exclusions in regions targeted by laboratory experiments. Secondly, I present updated BBN constraints on primordial black holes (PBHs) evaporating before nucleosynthesis. A careful treatment of hadronization and meson/nucleon effects implies that observable BBN sensitivity requires PBH masses above about 10⁹ grams, with limits on the initial PBH fraction at the level of 10⁻¹⁷ to 10⁻¹⁹ for PBH masses between 10⁹ and 10¹⁰ grams. In future work, we will continue to leverage BBN as a precision probe to explore a broader range of dark-matter scenarios and other manifestations of new physics.

报告时间：2026年3月5日（周四）10:00

报告地点：仙林园区3-302室

欢迎大家参加！