论文标题
Nanograv结果的含义和快速扩张的宇宙中的紫外线冻结
Implications of NANOGrav results and UV freeze-in in a fast-expanding Universe
论文作者
论文摘要
Nanograv协作报告的最新PULSAR计时数据表明，在频率$ f \ sim 10^{ - 8}〜\ rm Hz $的频率$ f \ sim 10^{ - 8}〜\ rm Hz $上存在随机引力波（GW）背景。我们表明，一个由标准模型（SM）量程单元费用$χ$和一个单身标量$ ϕ $组成的黑暗部门都可以通过$ Z_4 $对称的对称性收费，能够通过强大的一级相位过渡（SFOPT）通过修改标准的宇宙学历史上的新频率扩展，并通过较低的一阶相变（Sfopt）来产生如此低的频率GW，我们可以在其中逐步建立了较高的宇宙学家。 $φ$，其能量密度红移，比例因子为$ρ_φ\ propto a^{ - \ left（4+n \ right）} $。根据快速扩展参数的选择，理论的再加热温度和有效尺度，还可以通过冻结来解决正确的暗物质（DM）遗物丰度。我们表明，成功的一阶相变解释了Nanograv结果，而普朗克观察到的DM丰度则限制了快速扩展参数，需要$ n \ lyssim 4 $来解释这两者。
Recent pulsar timing data reported by the NANOGrav collaboration indicates the existence of a stochastic gravitational wave (GW) background at a frequency $f\sim 10^{-8}~\rm Hz$. We show that a dark sector consisting of a Standard Model (SM) gauge singlet fermion $χ$ and a singlet scalar $ϕ$, both charged under a $Z_4$ symmetry, is capable of generating such a low frequency GW via strong first order phase transition (SFOPT) through the modification of the standard cosmological history, where we assume faster-than-usual expansion at pre-BBN times driven by a new cosmological species $φ$ whose energy density red-shifts with the scale factor as $ρ_φ\propto a^{-\left(4+n\right)}$. Depending on the choice of the fast expansion parameters, reheat temperature and effective scale of the theory, it is also possible to address correct dark matter (DM) relic abundance via freeze-in. We show that a successful first order phase transition explaining NANOGrav results together with PLANCK observed DM abundance put bound on the fast expansion parameters requiring $n\lesssim 4$ to explain both.
