影子费米子、信使标量和轻子生成
Shadow Fermions, Messenger Scalars and Leptogenesis
摘要：
在我们提出的暗能量和暗物质模型中，研究了弱电尺度下的一种稀薄成因机制。该模型包含一个渐近自由规范群SU（2）Z和一个具有SU（2）Z瞬子诱导势的类轴子粒子，这产生了一个暗能量的场景。此外，这个SU（2）Z模型的扩展粒子内容包含冷暗物质的一个可能候选者，即SU（2）Z“影子”费米子，它通过携带SU（2）Z和电弱量子数的标量“信使场”与标准模型轻子耦合。由于这些影子费米子是SU（2）Z的实表示，轻子数在汤川扇形中可以被破坏，轻子数的不对称性可以在SU（2）Z粒子的衰变中产生，这也是CP破坏和“失平衡”的。计算了信使标量衰变和影子费米子衰变的不对称性。事实证明，为了保持轻子不对称性和与幺正性条件一致，一些影子费米子必须衰变为更轻的信使标量，因此可能是轻子不对称性的候选“祖先”。
英文摘要：
A mechanism for leptogenesis at the electroweak scale was investigated in a model of dark energy and dark matter proposed by one of us (PQH). This model involves an asymptotically free gauge group SU(2)Z and an axion-like particle with an SU(2)Z-instanton-induced potential which yields a scenario for the dark energy. Furthermore, the extended particle content of this SU(2)Z model contains a possible candidate for the cold dark matter, namely, the SU(2)Z "shadow" fermion, which couples with the Standard Model lepton through a scalar "messenger field" carrying both SU(2)Z and electroweak quantum numbers. Since these shadow fermions are in a real representation of SU(2)Z, lepton number can be violated in the Yukawa sector and a lepton number asymmetry can be generated in the SU(2)Z particle's decay which is also CP-violating and "out-of-equilibrium". The asymmetry coming from the interference between the tree-level and one-loop amplitudes was calculated for both messenger scalar and shadow fermion decays. It turns out, in order to have a non-vanishing lepton asymmetry and to be consistent with the unitarity condition, some shadow fermions have to decay into lighter messenger scalars, hence could be a candidate "progenitor" for the lepton asymmetry.
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