arXiv 0704.12562007-04hep-phhep-th

一种新的具有稳定质子、轻中微子和R宇称破坏的Z'弦

A Novel String Derived Z' With Stable Proton, Light-Neutrinos and R-parity violation

Claudio Coriano, Alon E. Faraggi, Marco Guzzi

备注：: 16 pages. Standard LaTex. minor changes
发表信息：: Eur.Phys.J.C53:421-428,2008
DOI：: 10.1140/epjc/s10052-007-0469-2

摘要：

标准模型表明了大统一结构在自然界中的实现，并且只能被视为在更高能量截止下的有效理论。虽然可重正化的标准模型由于偶然的全局对称性而禁止质子衰变介导算子，但标准模型的许多扩展引入了这样的四维、五维和六维算子。此外，预计量子引力效应会引起质子不稳定性，这表明更高的能量截止尺度必须高于10^{16}GeV。准现实杂化弦模型为微扰量子引力如何影响粒子物理现象学提供了舞台。阿贝尔规范对称性的存在抑制了质子衰变介导的运营商提供了一个有吸引力的解释质子寿命。此外，这种低尺度的U（1）对称性应该：允许通过跷跷板机制抑制左手中微子质量;允许费米子汤川耦合到电弱希格斯双重态;是无异常的;是族普适的。这些要求使得准现实杂化弦模型中存在这样的U（1）对称性是非常重要的。在自由费米子表述的一类左右对称杂化弦模型中，我们证明了满足上述所有要求的U（1）对称性的存在性。在未来实验可获得的能量范围内存在额外Z'的动机是需要充分抑制质子衰变介导。我们进一步证明了当额外U（1）不允许四维重子数破坏算符时，它允许四维轻子数破坏算符和R-宇称破坏.

英文摘要：

The Standard Model indicates the realization of grand unified structures in nature, and can only be viewed as an effective theory below a higher energy cutoff. While the renormalizable Standard Model forbids proton decay mediating operators due to accidental global symmetries, many extensions of the Standard Model introduce such dimension four, five and six operators. Furthermore, quantum gravity effects are expected to induce proton instability, indicating that the higher energy cutoff scale must be above 10^{16}GeV. Quasi-realistic heterotic string models provide the arena to explore how perturbative quantum gravity affects the particle physics phenomenology. An appealing explanation for the proton longevity is provided by the existence of an Abelian gauge symmetry that suppresses the proton decay mediating operators. Additionally, such a low-scale U(1) symmetry should: allow the suppression of the left-handed neutrino masses by a seesaw mechanism; allow fermion Yukawa couplings to the electroweak Higgs doublets; be anomaly free; be family universal. These requirements render the existence of such U(1) symmetries in quasi-realistic heterotic string models highly non-trivial. We demonstrate the existence of a U(1) symmetry that satisfies all of the above requirements in a class of left-right symmetric heterotic string models in the free fermionic formulation. The existence of the extra Z' in the energy range accessible to future experiments is motivated by the requirement of adequate suppression of proton decay mediation. We further show that while the extra U(1) forbids dimension four baryon number violating operators it allows dimension four lepton number violating operators and R-parity violation.

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英文摘要：

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