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arXiv 0901.2459hep-thhep-ph
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简单Yukawa系统的渐近安全性

Asymptotic safety of simple Yukawa systems

Holger Gies, Michael M. Scherer

摘要:

研究了具有无质量费米子和实标量场的Z_2不变Yukawa系统的平凡性和层次问题,该系统作为标准模型Higgs扇区的玩具模型。使用功能RG,我们寻找UV稳定的不动点,可以使系统渐近安全。RG流中的费米子和玻色子贡献的平衡是否引起这样的不动点取决于系统的代数结构和自由度。在有效作用量的非微扰次导阶导数展开所能控制的参数空间区域内,我们发现在一个或多个费米子味的情况下没有非高斯不动点.费米子玻色子平衡仍然可以证明在一个模型系统中的一个小的分数味数的破缺制度。这个小N_f系统的紫外行为受共形Higgs期望值的控制。这个系统只有两个物理参数,这意味着希格斯粒子的质量是可以预测的。它也自然地解释了顶夸克的重质量,因为没有RG轨迹连接UV固定点和轻顶质量。

英文摘要:

We study the triviality and hierarchy problem of a Z_2-invariant Yukawa system with massless fermions and a real scalar field, serving as a toy model for the standard-model Higgs sector. Using the functional RG, we look for UV stable fixed points which could render the system asymptotically safe. Whether a balancing of fermionic and bosonic contributions in the RG flow induces such a fixed point depends on the algebraic structure and the degrees of freedom of the system. Within the region of parameter space which can be controlled by a nonperturbative next-to-leading order derivative expansion of the effective action, we find no non-Gaussian fixed point in the case of one or more fermion flavors. The fermion-boson balancing can still be demonstrated within a model system with a small fractional flavor number in the symmetry-broken regime. The UV behavior of this small-N_f system is controlled by a conformal Higgs expectation value. The system has only two physical parameters, implying that the Higgs mass can be predicted. It also naturally explains the heavy mass of the top quark, since there are no RG trajectories connecting the UV fixed point with light top masses.

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