用轻轴胶子解释t-tbar不对称性
Explaining the t-tbar asymmetry with a light axigluon
摘要：
我们提出了一个轴胶子与质量之间的400和450 GeV和风味普遍耦合夸克来解释Tevatron的t-tbar的前后不对称性。该模型预测了一个小的负不对称性不变的质量低于450 GeV和一个大的正不对称性高于450 GeV的t-tbar对。这种不对称性是由s-通道胶子和轴胶子图之间的干涉引起的，需要一个相对弱耦合的轴胶子（$g_{a} = g_{qcd}/3$）。轴胶子-胶子干涉对t-tbar截面没有贡献。新的贡献的截面只出现在第四阶的轴胶子耦合和一个足够宽的轴胶子是非常小的。Dijet测量不显着约束轴胶子耦合。我们提出了几种可能的UV完成的唯象轴胶子解释所需的小耦合和大的宽度。这样的紫外线完成必然包含新的有色费米子或标量低于轴胶子质量和预测多喷流事件与大截面在Tevatron和大型强子对撞机。
英文摘要：
We propose an axigluon with mass between 400 and 450 GeV and flavor universal couplings to quarks to explain the Tevatron t-tbar forward-backward asymmetry. The model predicts a small negative asymmetry for t-tbar pairs with invariant mass below 450 GeV and a large positive asymmetry above 450 GeV. The asymmetry arises from interference between s-channel gluon and axigluon diagrams and requires a relatively weakly coupled axigluon ($g_{a} = g_{qcd}/3$). Axigluon-gluon interference does not contribute to the t-tbar cross section. New contributions to the cross section arise only at fourth order in the axigluon coupling and are very small for a sufficiently broad axigluon. Dijet measurements do not significantly constrain the axigluon couplings. We propose several possible UV completions of the phenomenological axigluon which explain the required small couplings and large width. Such UV completions necessarily contain new colored fermions or scalars below the axigluon mass and predict multi-jet events with large cross sections at the Tevatron and LHC.
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