论文标题
QCD常数的$ \barθ$参数吗？
Is the $\bar θ$ parameter of QCD constant?
论文作者
论文摘要
测试自然基本常数的宇宙学变化可以为新物理场景提供宝贵的见解。尽管已经针对标准模型耦合常数和质量得出了许多此类约束，但QCD的$ \barθ$参数尚未得到广泛的检查。这封信讨论了研究$ \barθ$参数的时间依赖性的潜在有希望的路径。虽然实验室搜索$ \barθ$的CP侵略信号的范围是当今价值$ \barθ$的最强大界限，但我们表明，CP支持效应对$ \barθ$的变化提供了限制。我们没有发现$ \barθ$变化的证据，这可能暗示着较高的红移处的“缺陷型”宇宙。通过将最新的原子钟约束转换在常数的变化上，我们推断$ d（{\barθ}^2）/dt \ leq 6 \ times 10^{ - 15} \ text {yr}^{ - 1} $，在1- $σ$上。最后，我们还绘制一个轴支型模型，该模型会导致$ \barθ$变化，并且可能导致过量的弥漫性伽玛射线背景，这是由于在高红移超新星爆炸中产生的轴腐烂而产生的。
Testing the cosmological variation of fundamental constants of Nature can provide valuable insights into new physics scenarios. While many such constraints have been derived for Standard Model coupling constants and masses, the $\barθ$ parameter of QCD has not been as extensively examined. This letter discusses potentially promising paths to investigate the time dependence of the $\barθ$ parameter. While laboratory searches for CP-violating signals of $\barθ$ yield the most robust bounds on today's value of $\barθ$, we show that CP-conserving effects provide constraints on the variation of $\barθ$ over cosmological timescales. We find no evidence for a variation of $\barθ$ that could have implied an "iron-deficient" Universe at higher redshifts. By converting recent atomic clock constraints on a variation of constants, we infer $ d({\barθ}^2)/dt \leq 6\times 10^{-15}\text{yr}^{-1}$, at 1-$σ$. Finally, we also sketch an axion model that results in a varying $\barθ$ and could lead to excess diffuse gamma ray background, from decays of axions produced in high redshift supernova explosions.
