LHC-friendly freeze-in dark matter via the Higgs portal

It is known that single-field freeze-in dark matter barely leaves footprints in dark matter direct detection and collider experiments. This situation can be altered in the two-field context. In this work we propose a two-field freeze-in dark matter model through the Higgs portal. The observed dark matter relic abundance is obtained by a decay of scalar mediator thermalized in the early Universe. While there is a lack of direct dark matter signals, the scalar mediator is in the reach of High Luminosity LHC either through the vector boson fusion or mono-Z channels. Within the allowed scalar mass window of 10–50 GeV, we use improved cuts to derive both <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>2</a:mn><a:mi>σ</a:mi></a:math> exclusion and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>5</c:mn><c:mi>σ</c:mi></c:math> discovery limits, depending on the value of Higgs portal coupling. If verified, this scalar mediator signal allows us to infer the freeze-in dark matter.