底夸克是带有电荷−1⁄3 e的 第三代夸克，又称为美夸克。
那些更精细的分析并没有发现这种假设的粒子，所以，也许它因为某些原因并不会衰变成底夸克。
Those more-refined analyses have not seen the hypothetical new particle, so for some reason it must not decay into bottom quarks.
在我们的宇宙中，底夸克的质量大约是顶夸克的两倍，造成中子比质子重大约0.1%。
In our universe, the down quark is about twice as heavy as the up quark, resulting in neutrons that are 0.1 percent heavier than protons.
Jaffe和他的同事建立了一个类型的宇宙，其中底夸克比顶夸克轻，而质子比中子重1%。
Jaffe and his colleagues modeled one family of universes in which the down quark was lighter than the up quark, and protons were up to a percent heavier than neutrons.
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