标题： 中子-胶子喷注在强耦合状态下吗？ 大$N_f$极限下的结果 显示英文标题

标题： Are in-medium quark-gluon showers strongly coupled? Results in the large-$N_f$ limit

摘要： 在介质内部，由极高能量粒子引发的阵雨通过介质诱导的分裂过程（如韧致辐射和电子对产生）发展。 在阵雨的发展过程中，两次连续的分裂有时会在量子力学上重叠，因此不能被独立处理。 其中一些效应可以被吸收进一个被称为$\hat q$的介质参数的有效值中。 先前的计算（在某些简化假设下）发现，在调整了$\hat q$的值后，对于纯胶子的大$N_c$阵雨，重叠分裂的剩余效应非常小，但在相同$N\alpha$值下的大$N_f$QED 阵雨中却大得多。 在这里，通过研究带有夸克的大$N_f$夸克味限制下的 QCD 中相同问题，我们首次探讨了纯胶子阵雨中小效应是否仅仅是偶然现象（i），或者更广泛地反映了 QCD 中这类重叠效应的特性（ii）。 我们还对 QED 和 QCD 中效应大小差异提供了定性解释。 显示英文摘要

摘要： Inside a medium, showers originating from a very high energy particle develop via medium-induced splitting processes such as bremsstrahlung and pair production. During shower development, two consecutive splittings sometimes overlap quantum mechanically, so that they cannot be treated independently. Some of these effects can be absorbed into an effective value of a medium parameter known as $\hat q$. Previous calculations (with certain simplifying assumptions) have found that, after adjusting the value of $\hat q$, the leftover effect of overlapping splittings is quite small for purely gluonic large-$N_c$ showers but is very much larger for large-$N_f$ QED showers, at comparable values of $N\alpha$. Here, by investigating the same problem for QCD with *quarks* in the large-$N_f$ limit of many quark flavors, we make a first study of whether the small effect in purely gluonic showers (i) was merely an accident or (ii) is more broadly characteristic of such overlap effects in QCD. We also offer a qualitative explanation for the large size of the effect in QED vs. QCD.