Grand unified theories and proton decay
Grand unified theories and proton decay
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DOI：
10.1360/n972018-00002
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发表时间：
2018-08
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通讯作者：
Tianjun Li
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文献类型：
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作者：
Tianjun Li
自然界中存在四种基本相互作用：强相互作用、弱相互作用、超荷相互作用和引力相互作用。基于所有基本相互作用具有相同起源的猜想，物理学家探索了描述宇宙中最基本定律的大统一理论。从历史的角度来看，第一次统一是由牛顿完成的，他统一了天体和地球的引力;第二次统一是由麦克斯韦完成的，他将电和磁的相互作用统一为电磁相互作用; Nordstrom、卡鲁扎和克莱因第一次提出了额外维度，并试图将已知的引力和电磁相互作用统一为一个五维引力。这个想法确实很伟大，但不幸的是并不能描述自然。第三次统一是由Alfrehow完成的，Salam和温伯格通过电弱理论描述了电磁和弱相互作用。因此，如何构造描述所有基本相互作用的大统一理论是一个非常重要和基本的问题。我们知道，强、弱和超荷相互作用都是规范相互作用，它们的规范群是SU（3）_C\times~SU（2）_L\times~U（1）_Y$，因此我们认为它们有着相同的起源：一个具有规范群SU（5）$或SO（10）$等的高尺度大统一理论。（2）费米子统一。本文只考虑第一种定义，不考虑统一三代标准模型费米子的大统一理论。然而，大统一理论并不包括引力，特别是引力量子化是物理学中的另一个重要问题。现在，最有希望的量子引力理论是弦理论。因此，能够统一自然界中所有四种基本相互作用的模型很可能是弦模型，特别是弦模型能够自然地解决四维大统一理论中的主要问题，因此，大统一理论和弦模型将给我们一个万物理论。从理论上讲，它可以解释宇宙中的一切现象，是物理学的最终目标。历史上，爱因斯坦等许多伟大的物理学家都对大统一理论进行了研究。目前，我们已经建立了各种各样的大统一理论和弦模型，因此还需要进一步的实验来检验它们.本文首先简要介绍了标准模型及其存在的问题.在正则规范化U（1）_Y$和大沙漠假设的基础上，我们可以通过引入TeV尺度附近的新粒子来实现规范耦合统一.特别是对超对称标准模型进行了详细的解释，讨论了四维Pati-Salam $SU（4）_C\times~ SU（2）_L\times~ SU（2）_R$模型、Georgi-Schmidhow $SU（5）$模型、Flipped $SU（5）\times~U（1）_X$模型和SO（10）$模型，对非超对称和超对称$SU（5）$模型进行了详细的解释，包括其正确的预言，主要问题和解决方法，以及质子衰变等，并简要讨论了高维轨道大统一理论和弦模型。最后，我们研究了如何探测这些模型：在对撞机上寻找具有预测性质的新粒子，以及当前和未来的质子衰变实验和可能的新建议。
There exists four fundamental interactions in Nature: strong, weak, hypercharge, and gravity interactions.Based on the conjecture that all the fundamental interactions have the same origin,physicists have explored the Grand Unified Theories,which describes the most fundamental laws in the Universe. From the historical point of view,the first unification was done by Newton, who unified the celestial and terrestrial gravity.The second unification was done by Maxwell, who unified the electric and magnetic interactions into an electromagnetic interaction.Nordstrom, Kaluza, and Klein for the first time proposed the extra dimension(s),and tried to unify the known gravity and electromagnetic interaction into a five-dimensional gravity.This idea is indeed great, but unfortunately does not describe Nature.The third unification was done by Glashow, Salam, and Weinberg, who describedthe electromagnetic and weak interactions via an electroweak theory. Therefore,how to construct the Grand Unified Theories to describe all the fundamental interactions is a very importantand fundamental problem. As we know, strong, weak, and hypercharge interactionsare gauge interactions, whose gauge groups are $SU(3)_C\times~SU(2)_L\times~U(1)_Y$.Thus, we believe they have the same origin: a high scale Grand Unified Theory with gauge group $SU(5)$ or $SO(10)$, etc.Exactly speaking, there are two kinds of definitions for the Grand Unified Theories: (1) Gauge interaction unification;(2) Fermion unification. In this paper, we only consider the first definition, and do not consider the Grand Unified Theorieswhich unify three generations of the Standard Model fermions. However, the Grand Unified Theories do not include gravity.Especially, gravity quantization is another important problem in physics. Right now, the most promising theory for quantum gravityis string theory. Therefore, the models, which can unify all the four fundamental interactions in Nature, are probably the string models.In particular, string models can solve the major problems in the four-dimensional Grand Unified Theories naturally.Thus, the Grand Unified Theories and string models will give us a Theory of Everthing. In principle,it can explain all the phenomena in the Universe, and thus it is the final goal of the physics.Historically, many great physicists such as Einstein et al have studied the Grand Unified Theories. Right now.we have constructed various Grand Unified Theories and string models, and thus need further experiments to test them.In this paper, we first briefly explain the Standard Model and its problems.With the canonical normalized $U(1)_Y$ and Grand Desert Hypothesis, we can achieve the gauge coupling unificationby introducing new particles around TeV scale. Especially, we explain the supersymmetric Standard Models in details.We discuss the four-dimensional Pati-Salam $SU(4)_C\times~SU(2)_L\times~SU(2)_R$ models,Georgi-Glashow $SU(5)$ models, Flipped $SU(5)\times~U(1)_X$ models, and $SO(10)$ models.We explain the non-supersymmetric and supersymmetric $SU(5)$ models in details, including its correct predictions,the main problems and solutions, as well as proton decays, etc. We also briefly discuss the high dimensionalorbifold Grand Unified Theories and string models. Finally, we study how to probe these models: searches for the new particles withpredicted properties at the colliders, as well as the current and future proton decay experiments and possible new proposals.