再论CP守恒过程在宇宙学粒子-反粒子不对称性中的作用
Revisiting the role of CP-conserving processes in cosmological particle-antiparticle asymmetries
摘要：
我们指出定性不同的可能性CP守恒过程中产生的宇宙学粒子反粒子不对称性的作用，从leptogenesis和不对称的暗物质生产模型的说明性例子。特别是，我们考虑的情况下，CP-违反和CP-保存过程要么都衰变或散射，从而自然是可比的速率。这是在不同的跷跷板机制，其中的CP守恒散射通常具有较低的速率相比，CP违反衰变，由于玻尔兹曼抑制模型中的leptogenesis先前考虑的CP守恒过程。我们进一步指出，CP守恒过程可以发挥双重作用，如果在母亲部门本身产生的不对称性，在传统的情况下，它是在女儿部门。这是因为，CP守恒过程最初通过控制浴粒子的非平衡数密度来抑制不对称性的产生，但随后通过对湮灭消除浴粒子的对称分量来修改当前时期的粒子反粒子产率的比率，从而导致不同时期的相同过程产生的竞争效应。我们发现，相关的粒子-反粒子系统的不对称产额可以根据CP守恒和违反反应速率的相对大小而变化几个数量级。
英文摘要：
We point out qualitatively different possibilities on the role of CP-conserving processes in generating cosmological particle-antiparticle asymmetries, with illustrative examples from models in leptogenesis and asymmetric dark matter production. In particular, we consider scenarios in which the CP-violating and CP-conserving processes are either both decays or both scatterings, thereby being naturally of comparable rates. This is in contrast to the previously considered CP-conserving processes in models of leptogenesis in different see-saw mechanisms, in which the CP-conserving scatterings typically have lower rates compared to the CP-violating decays, due to a Boltzmann suppression. We further point out that the CP-conserving processes can play a dual role if the asymmetry is generated in the mother sector itself, in contrast to the conventional scenarios in which it is generated in the daughter sector. This is because, the CP-conserving processes initially suppress the asymmetry generation by controlling the out-of-equilibrium number densities of the bath particles, but subsequently modify the ratio of particle anti-particle yields at the present epoch by eliminating the symmetric component of the bath particles through pair-annihilations, leading to a competing effect stemming from the same process at different epochs. We find that the asymmetric yields for relevant particle-antiparticle systems can vary by orders of magnitude depending upon the relative size of the CP-conserving and violating reaction rates.
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