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arXiv 2006.05064hep-ph
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KOTO过剩的宇宙学意义

Cosmological implications of the KOTO excess

Wolfgang Altmannshofer, Benjamin V. Lehmann, Stefano Profumo

摘要:

KOTO实验报告了超过标准模型预测的过量的$K_L\toπ^0ν\barν$事件,与Grossman-Nir(GN)界限紧张。GN界严重限制了对这个通道中过剩的新物理解释,但另一种可能性是,观察到的事件起源于一个完全不同的过程:$K_L\toπ^0X$形式的衰变,其中$X$表示一个或多个新的不可见物质。我们引入了一类模型来研究这种情况下,两个轻标量发挥作用的$X$,我们研究的可能性,较轻的两个新的国家也可能占宇宙学暗物质(DM)。我们表明,这个物种可以产生热的存在下,除了那些需要考虑的KOTO过剩的额外的相互作用。相反,在模型的最小版本中,DM必须非热产生。在这种情况下,避免生产过剩对低能理论的结构施加了限制。此外,这一要求对早期宇宙的再加热规模有着重要的影响,一般来说,最好是一个低的但观测允许的再加热温度O(10 MeV)。我们讨论天体物理和地球的签名,将允许在未来几年进一步测试这个范例。

英文摘要:

The KOTO experiment has reported an excess of $K_L\toπ^0ν\barν$ events above the Standard Model prediction, in tension with the Grossman-Nir (GN) bound. The GN bound heavily constrains new physics interpretations of an excess in this channel, but another possibility is that the observed events originate from a different process entirely: a decay of the form $K_L\toπ^0X$, where $X$ denotes one or more new invisible species. We introduce a class of models to study this scenario with two light scalars playing the role of $X$, and we examine the possibility that the lighter of the two new states may also account for cosmological dark matter (DM). We show that this species can be produced thermally in the presence of additional interactions apart from those needed to account for the KOTO excess. Conversely, in the minimal version of the model, DM must be produced nonthermally. In this case, avoiding overproduction imposes constraints on the structure of the low-energy theory. Moreover, this requirement carries significant implications for the scale of reheating in the early Universe, generically preferring a low but observationally permitted reheating temperature of O(10 MeV). We discuss astrophysical and terrestrial signatures that will allow further tests of this paradigm in the coming years.

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