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Through the Looking Glass
另外，文章的二/三段里，说到proton和neutron和neutrino时（忘记具体是说这三者中的哪一个）用到了“lightweight”这个词。
WHAT KIND OF particle could dark matter be made of? Astronomical observation and theory provide some general clues. It cannot be protons, neutrons, or anything that was once made of protons or neutrons, such as massive stars that became black holes. According to calculations of particle synthesis during the big bang, such particles are simply too few in number to make up the dark matter. Those calculations have been corroborated by measurements of primordial hydrogen, helium and lithium in the universe.
第二段:提问,暗物质是由什么组成的?P和N不是,接下来是"Nor can more than a few of Neutrino怎么怎么的,意思是Neutrino也不是暗物质. 接下来高亮"一个关于neutrino的实验,说它很轻啦,速度很快啦,因此很 ”hot"总之也不是dark matter.
Nor can more than a small fraction of the dark matter be neutrinos, a lightweight breed of particle that zips through space and is unattached to any atom. Neutrinos were once a prominent possibility for dark matter, and their role remains a matter of discussion, but experiments have found that they are probably too lightweight [see “Detecting Massive Neutrinos,” by Edward Kearns, Takaaki Kajita and Yoji Totsuka; , August 1999]. Moreover, they are “hot”—that is, in the early universe they were moving at a velocity comparable to the velocity of light. Hot particles were too fleet-footed to settle into observed cosmic structures.
第三段: 记得个fit的词(我理解是根据以上neutrino特征的反面推出的dark matter的特征), 能fit dark matter的物质具有的特点是cold, sluggish等等. 貌似在现在的cosmatic中不存在,但是在standard的假说中有一种neutranilo的物质符合
The best fit to the astronomical observations involves “cold” dark matter, a term that refers to some undiscovered particle that, when it formed, moved sluggishly. Although cold dark matter has its own problems in explaining cosmic structures [see “The Life Cycle of Galaxies,” by Guinevere Kauffmann and Frank van den Bosch; , June 2002], most cosmologists consider these problems minor compared with the difficulties faced by alternative hypotheses. The current Standard Model of elementary particles contains no examples of particles that could serve as cold dark matter, but extensions of the Standard Model—developed for reasons quite separate from the needs of astronomy—offer many plausible candidates.
By far the most studied extension of this kind is supersymmetry, so I will concentrate on this theory. Supersymmetry is an attractive explanation for dark matter because it postulates a whole new family of particles—one “superpartner” for every known elementary particle. These new particles are all heavier (hence more sluggish) than known particles. Several are natural candidates for cold dark matter. The one that gets the most attention is the neutralino, which is an amalgam of the superpartners of the photon (which transmits the electromagnetic force), the boson (which transmits the so-called weak nuclear force) and perhaps other particle types. The name is somewhat unfortunate: “neutralino” sounds much like “neutrino,” and the two particles indeed share various properties, but they are otherwise quite distinct.
当时看这里时，有点不理解，为什么是“轻”而stable，而不是“重”而stable。当时以为是狗主笔误。不过原题的英文的确是“轻”，用的是“lightest”这个词。
第三段开始说一种extension of standard model开始suggest了supersymmetry，里面提到了superparticle，可能是组成dark matter的。superparticle中的neutrolina最有可能是dark matter的组成单位，因为它比较轻。如果一个superparticle不够轻，就可能被再分成两个更轻的superparticle，就不稳定。而且它电中性，所以不受电磁场影响。这里专门说了neutrolina不是neutron中子的反物质，虽然它们有些properties是一样的。然后说因为neutrolina满足了组成dark matter的三个条件：mass, stabilility and neutral，所以它很有可能就是dark matter的单位。
第四段: 主要讲neutronilo的,这里提到它不被electromagnetic怎么着(在比较俩个N不同的选项里出现),同时它又是最轻的,它又很stable, 因为如果不够轻的话就会不stable从而被分成俩个更轻的(很绕的逻辑),
Although the neutralino is heavy by normal standards, it is generally thought to be the lightest supersymmetric particle. If so, it has to be stable: if a superparticle is unstable, it must decay into two lighter superparticles, and the neutralino is already the lightest. As the name implies, the neutralino has zero charge, so it is unaffected by electromagnetic forces (such as those involving light). The hypothesized mass, stability and neutrality of the neutralino satisfy all the requirements of cold dark matter.
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发表于 2019-10-12 15:04:56
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