Tevatron Wjj异常的弦状起源
Stringy origin of Tevatron Wjj anomaly
摘要：
CDF合作组最近在Tevatron上观测到的与W玻色子有关的双喷注的不变质量分布，揭示了双喷注质量在120-160 GeV/c^2，3σ范围内超出了标准模型的预期。我们指出，这种过剩是低质量弦论的一个普遍特征，这是由于疏轻子Z '的产生和衰变造成的，疏轻子Z'是SU（3）胶子的一个主要与U（1）重子数耦合的单重态伙伴。在这个框架中，U（1）和SU（3）表现为U（3）的子群，与结束于一堆3D膜的开弦相关联。此外，极小模型包含另外两个堆栈，以容纳电弱SU（2）\in U（2）和超荷U（1）。在三个U（1）规范玻色子中，两个重的Z'和Z”通过格林-施瓦茨机制获得质量。对于给定的Z'质量，模型是相当受约束的。微调它的三个自由参数刚好足以同时确保：一个小的Z-Z'混合符合严格的LEP数据的$Z$质量;非常小的（小于1%）分支比轻子;和一个大的层次之间的Z”和Z'的质量。更重的中性规范玻色子Z”在LHC的范围内。
英文摘要：
The invariant mass distribution of dijets produced in association with W bosons, recently observed by the CDF Collaboration at Tevatron, reveals an excess in the dijet mass range 120-160 GeV/c^2, 3σbeyond Standard Model expectations. We show that such an excess is a generic feature of low mass string theory, due to the production and decay of a leptophobic Z', a singlet partner of SU(3) gluons coupled primarily to the U(1) baryon number. In this framework, U(1) and SU(3) appear as subgroups of U(3) associated with open strings ending on a stack of 3 D-branes. In addition, a minimal model contains two other stacks to accommodate the electro-weak SU(2) \in U(2) and the hypercharge U(1). Of the three U(1) gauge bosons, the two heavy Z' and Z" receive masses through the Green-Schwarz mechanism. For a given Z' mass, the model is quite constrained. Fine tuning three of its free parameters is just sufficient to simultaneously ensure: a small Z-Z' mixing in accord with the stringent LEP data on the $Z$ mass; very small (less than 1%) branching ratio into leptons; and a large hierarchy between Z" and Z' masses. The heavier neutral gauge boson Z" is within the reach of LHC.
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