New Thermal-Relic Targets for sub-GeV Dark Matter Direct Detection
University of Chicago（芝加哥大学）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）
Dark matter direct detection experiments involving electron recoils are beginning to test highly-predictive, thermal-relic milestones for sub-GeV dark matter models. Due to the Lee-Weinberg bound, thermal dark matter candidates in this mass range necessarily require comparably-light mediator particles to achieve a suitably large annihilation cross section. Here we present new thermal-relic milestones for sub-GeV dark matter candidates that couple to vector mediators. In these models, the mediators are massive gauge bosons of anomaly-free abelian extensions to the Standard Model, including the dark photon, gauged $L_i - L_j, B-L$, and $B-3L_i$ models, where $B$ is the baryon number, $L$ is the lepton number, and $i,j$ index the lepton families. Since the same interactions that govern cosmological production also govern electron scattering, the targets we present are firmly predictive and allow for these models to be robustly discovered or falsified. Furthermore, since the mediators we study exhaust the minimal anomaly-free U(1) extensions to the Standard Model, our results offer a complete list of predictive milestones for sub-GeV dark matter coupled to vector mediators.
Sub-GeV thermal relic dark matter typically requires the existence of a light mediator particle. We introduce the light two-Higgs-doublet portal, illustrated by a minimal UV-complete model for sub-GeV dark matter with kinematically forbidden annihilations into leptons. All new physics states in this scenario lie at or below the electroweak scale, affecting Higgs physics, the muon anomalous magnetic moment and potentially neutrino masses. Observation of radiative dark matter annihilation by future MeV gamma-ray telescopes would be key to unambiguously identify the scenario.
We study the effective field theory (including operators up to dimension five) of models in which dark matter is composite, consisting of either an electroweak doublet Dirac fermion (`higgsino-like dark matter') or an electroweak triplet Majorana fermion (`wino-like dark matter'). Some of the dimension-five operators in the former case cause mass splittings between the neutralino and chargino states, leading to a depleted rate of coannihilations and viable thermal relic dark matter with masses of the order of tens to hundreds of GeV rather than the usual pure higgsino thermal relic mass of 1 T…
We demonstrate the existence of a generic, efficient and purely gravitational channel producing a significant abundance of dark relics during reheating after the end of inflation. The mechanism is present for any inert scalar with the non-minimal curvature coupling $ξRχ^2$ and the relic production is efficient for natural values $ξ= {\cal O}(1)$. The observed dark matter abundance can be reached for a broad range of relic masses extending from $m \sim 1 {\rm k eV}$ to $m \sim 10^{8} {\rm GeV}$, depending on the scale of inflation and the dark sector couplings. Frustratingly, such relics escape…
Precise Relic WIMP Abundance and its Impact on Searches for Dark Matter Annihilation
如果暗物质（DM）是一种弱相互作用大质量粒子（WIMP），是早期宇宙的热遗迹，那么它的总自湮灭截面可以通过它现在的质量密度来揭示。一般的WIMP的正则热平均截面通常表示为3*10^-26 cm ^3 s ^-1，不确定性没有具体说明，并且被认为与WIMP的质量无关。最近对DM湮没产物的搜索已经达到了排除100%分支比的正则截面的灵敏度，以确定最终状态和小WIMP质量。最终目标是探测所有运动学上允许的最终状态作为质量的函数，如果所有状态都被充分排除，则为WIMP质量设置下限。由于最近在直接和间接搜索中对轻WIMP的暗示，探测低质量区域的动机进一步增强。我们重新审视了一个通用的WIMP的热遗迹丰度计算，并表明所需的截面可以精确计算。当质量低于10 GeV时，它随质量变化很大，在质量约为0.3 GeV时达到最大值5.2*10^-26 cm ^3 s ^-1，当质量高于10 GeV时，它为2.2*10^-26 cm ^3 s ^-1，质量依赖性很弱。这些结果，显着不同的典型值，并没有考虑到在搜索湮灭产品从通用WIMPs，有一个显着的影响，从费米-LAT和WMAP+ACT目前的限制的解释。
Producing an acceptable thermal relic abundance of dark matter with masses $\gg 10^2$ TeV is a challenge. We propose a novel mechanism where GeV-scale states establish a tiny thermal relic abundance for dark matter, which is later promoted to ultra massive status by a very light scalar. We refer to this dark matter as a THermal Ultra Massive Particle (THUMP). Direct detection of THUMPs can be naturally expected due to large scattering cross sections mediated by low mass states that couple THUMPs to the Standard Model. Our model generically leads to signals for the associated GeV-scale states a…
We consider the long-range effect of the Higgs on the density of thermal-relic dark matter. While the electroweak gauge boson and gluon exchange have been previously studied, the Higgs is typically thought to mediate only contact interactions. We show that the Sommerfeld enhancement due to a 125 GeV Higgs can deplete TeV-scale dark matter significantly, and describe how the interplay between the Higgs and other mediators influences this effect. We discuss the importance of the Higgs enhancement in the Minimal Supersymmetric Standard Model, and its implications for experiments.
The 130 GeV gamma-ray line and Sommerfeld enhancements
最近，可能的迹象表明，在费米-LAT光子光谱朝向银河系中心的线光谱特征已被报道。如果明显的线特征来自暗物质（DM）湮灭到$γX (X=γ, Z^{0} or h^{0})$中，则对于典型的环诱导辐射过程，相应的湮灭截面不自然地大。另一方面，它仍然太小，无法对观测到的DM遗迹密度负责。我们表明，索末菲增强标量力载体的机制可以提供一个简单的解决方案，这些难题。可能的大索末菲增强的横截面的s波DM湮灭可以显着减少所需的有效耦合DM和带电粒子之间的典型的回路图。DM粒子必然会通过三能级p波过程湮灭为标量力载流子，在冻结时，p波过程可以主导DM湮灭截面，得到正确的热遗迹密度，但由于速度抑制，对今天的DM湮灭贡献较小。本文详细分析了p波索末菲增强对冻结的影响。结果表明，在热遗迹密度的约束下，所需的有效耦合可以减少一个数量级。
We fully explore the thermal freezeout histories of a vector-portal dark matter model, in the region of parameter space in which the ratio of masses of the dark photon $A^{\prime}$ and dark matter $χ$ is in the range $1 \lesssim m_{A^{\prime}}/m_χ \lesssim 2$. In this region $2 \rightarrow 2$ and $3 \rightarrow 2$ annihilation processes within the dark sector, as well as processes that transfer energy between the dark sector and the Standard Model, play important roles in controlling the thermal freezeout of the dark matter. We carefully track the temperatures of all species, relaxing the assu…
The dark matter annihilation channels sometimes involve sharp resonances. In such cases the usual momentum averaged approximations for computing the DM abundance may not be accurate. We develop an easily accessible momentum dependent framework for computing the DM abundance accurately and efficiently near such features. We apply the method to the case of a singlet scalar dark matter $s$ interacting with SM through higgs portal $λ_{\rm hs}s^2 h^2$ and compare the results with different momentum averaged methods. The accuracy of the latter depend strongly on the strength of the elastic interacti…
