标题： 弥合代沟 显示英文标题

标题： Closing the Generation Gap

摘要： 我描述了四维M理论真空中的相变实例，在这些实例中净生成数发生了变化。存在一些简单的障碍阻止手征物质的跃迁，但存在漏洞使我们能够避开这些障碍。 我首先回顾了M理论的异质极限中手征性的出现、弦论中已知的拓扑变化形式以及六维的手征改变相变。 这引出了四维的例子，这些例子涉及包裹在$E_8$墙上的M理论五brane。 显示英文摘要

摘要： I describe recent examples of phase transitions in four-dimensional M theory vacua in which the net generation number changes. There are naive obstructions to transitions lifting chiral matter, but loopholes exist which enable us to avoid them. I first review how chirality arises in the heterotic limit of M theory, previously known forms of topology change in string theory, and chirality-changing phase transitions in six dimensions. This leads to the construction of the four-dimensional examples, which involve wrapped M-theory fivebranes at an $E_8$ wall.