我们考虑了一个希格斯门模型，其中125 GeV的希格斯玻色子与光单重态介质$h_2$耦合到暗区的粒子，并研究潜在的$b\to s h_2$衰变的Belle II实验。将规范依赖的离壳标准模型$b$ - $s$ -Higgs顶点乘以Higgs混合角的正弦并不能得到正确的$b$ - $s$ - $h_2$顶点。我们澄清这个问题，通过计算$b$ - $s$ - $h_2$顶点在任意的$R_ξ$规范，并演示了如何$ξ$的依赖性取消从物理衰变率涉及壳或壳外$h_2$。然后，我们重新审视$b\to s h_2$现象学，并指出，同时研究$B\to K^* h_2$和$B\to K h_2$有助于区分希格斯门和黑暗部门的替代模型。我们进一步提倡使用置换顶点数据中包含的$h_2$寿命信息，其中$h_2$衰减回标准模型粒子，以更好地约束$h_2$质量或揭示额外的$h_2$衰减模式为长寿命粒子。
英文摘要：
We consider a Higgs portal model in which the 125-GeV Higgs boson mixes with a light singlet mediator $h_2$ coupling to particles of a Dark Sector and study potential $b\to s h_2$ decays in the Belle II experiment. Multiplying the gauge-dependent off-shell Standard-Model $b$-$s$-Higgs vertex with the sine of the Higgs mixing angle does not give the correct $b$-$s$-$h_2$ vertex. We clarify this issue by calculating the $b$-$s$-$h_2$ vertex in an arbitrary $R_ξ$ gauge and demonstrate how the $ξ$ dependence cancels from physical decay rates involving an on-shell or off-shell $h_2$. Then we revisit the $b\to s h_2$ phenomenology and point out that a simultaneous study of $B\to K^* h_2$ and $B\to K h_2$ helps to discriminate between the Higgs portal and alternative models of the Dark Sector. We further advocate for the use of the $h_2$ lifetime information contained in displaced-vertex data with $h_2$ decaying back to Standard-Model particles to better constrain the $h_2$ mass or to reveal additional $h_2$ decay modes into long-lived particles.
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Higgs-portal effective field theories are widely used as benchmarks in order to interpret collider and astroparticle searches for dark matter (DM) particles. To assess the validity of these effective models, it is important to confront them to concrete realizations that are complete in the ultraviolet regime. In this paper, we compare effective Higgs-portal models with scalar, fermionic and vector DM with a series of increasingly complex realistic models, taking into account all existing constraints from collider and astroparticle physics. These complete realizations include the inert doublet …
