Hidden dark matter sector, dark radiation, and the CMB
Hidden dark matter sector, dark radiation, and the CMB
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隐藏的暗物质扇区、暗辐射和宇宙微波背景
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发表时间：
2015
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通讯作者：
Takemichi Okui
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作者：
Z. Chacko;Yanou Cui;Sungwoo Hong;Takemichi Okui
我们考虑的理论认为，暗物质是由弱尺度质量的热遗迹组成的，然而，它与标准模型（SM）的耦合太小，无法产生观测到的丰度。相反，丰度是由湮灭到在SM规范相互作用下不带电荷的隐藏扇区状态而确定的。在这种情况下，直接和间接探测以及对撞机搜索暗物质的限制很容易得到满足。如果它们是南布-戈德斯通玻色子、费米子或规范玻色子，那么这种光隐藏态的质量可以通过对称性得到保护。然后，这些状态可以作为暗辐射贡献给宇宙能量密度，从而在宇宙微波背景（CMB）中产生可观测信号。此外，根据光隐藏扇区状态是否自相互作用，自由流占总能量密度的比例或减少或增加，导致对CMB各向异性的标量和张量分量的特征影响，从而使这两种情况得以区分。这些信号的大小取决于隐藏扇区中光自由度的数量，以及它与SM动力学解耦的温度。我们考虑了一个简单的模型来实现这一场景，该模型基于一个框架，在这个框架中，SM和隐藏扇区最初通过希格斯门户处于热平衡状态，并表明所得到的信号与最近的普朗克结果兼容，同时足够大，可以在即将进行的实验中检测到，如CMBPol和CMB Stage-IV。在对撞机中，希格斯粒子进入隐藏扇区状态的不可见衰变可以提供对该模型的补充探测。
We consider theories where dark matter is composed of a thermal relic of weak scale mass, whose couplings to the Standard Model (SM) are however too small to give rise to the observed abundance. Instead, the abundance is set by annihilation to light hidden sector states that carry no charges under the SM gauge interactions. In such a scenario the constraints from direct and indirect detection, and from collider searches for dark matter, can easily be satisfied. The masses of such light hidden states can be protected by symmetry if they are Nambu-Goldstone bosons, fermions, or gauge bosons. These states can then contribute to the cosmic energy density as dark radiation, leading to observable signals in the cosmic microwave background (CMB). Furthermore, depending on whether or not the light hidden sector states self-interact, the fraction of the total energy density that free-streams is either decreased or increased, leading to characteristic effects on both the scalar and tensor components of the CMB anisotropy that allows these two cases to be distinguished. The magnitude of these signals depends on the number of light degrees of freedom in the hidden sector, and on the temperature at which it kinetically decouples from the SM. We consider a simple model that realizes this scenario, based on a framework in which the SM and hidden sector are initially in thermal equilibrium through the Higgs portal, and show that the resulting signals are compatible with recent Planck results, while large enough to be detected in upcoming experiments such as CMBPol and CMB Stage-IV. Invisible decays of the Higgs into hidden sector states at colliders can offer a complementary probe of this model.