sage
发表文章数: 1125
武功等级: 天山六阳掌
(第六重)
内力值: 535/535
Physics Benchmarks of String theory 3, Unitarity
4) unitarity
A sensible physics theory must be unitary. One of the basic requirement for
a unitary theory is that there is no state in the spectrum with a
negative mass square. (it is neither sufficient nor
necessary. however, it is usually a valid requirement to have)
However, if we simply have bosonic fields in string theory, the
spectrum has a tachyon (negative mass squared mode). There seems to be
no consistent way to get rid of it in a flat background.
Neveu, Schwarz, as well as Ramond, independently realized that by
introducing fermionic degrees of freedom, it is possible to
consistently get rid of the tachyon mode.
Incidentally, this is one of the ways that supersymmetry is
discovered because there is space-time supersymmetry in their
formulation.
This is the official formulation of the so-called superstring
theories. After this, string theory seems to be one step closer to the
reality since one has at one way to write down a fully consistent
theory.
| 发表时间：2005-09-23, 08:56:02 |
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萍踪浪迹
发表文章数: 1983
武功等级: 深不可测
内力值: 645/645
Re: Physics Benchmarks of String theory 3, Unitarity
sage出场，不同凡响
严重支持一下
以后有时间再慢慢谈Superstring
漫漫长夜不知晓 日落云寒苦终宵
痴心未悟拈花笑 梦魂飞度同心桥|
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红叶晚萧萧，长亭酒一瓢
残云归太华，疏雨过中条
树色随山迥，河声入海遥
帝乡明日到，犹自梦渔樵
| 发表时间：2005-09-23, 09:05:51 |
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