Search

We study thermal corrections to a model of real scalar dark matter interacting feebly with a SM fermion and a gauge-charged vector-like fermion. We employ the Closed-Time-Path (CTP) formalism for our calculation and go beyond previous works by including the full dependence on the relevant mass scales as opposed to using (non)relativistic approximations. In particular, we use 1PI-resummed propagators without relying on the Hard-Thermal-Loop approximation. We conduct our analysis at leading order in the loop expansion of the 2PI effective action and compare our findings to commonly used approximation schemes, including the aforementioned Hard-Thermal-Loop approximation and results obtained from solving Boltzmann equations using thermal masses as a regulator for $t$-channel divergences. We find that the Boltzmann approach deviates between $-10\%$ and $+30\%$ from our calculation, where the size and sign strongly depends on the mass splitting between the DM candidate and the gauge-charged parent. The HTL-approximated result is more precise for small gauge couplings and is percent level accurate for large mass splittings, whereas it overestimates the relic density up to $25 \%$ for small mass splittings. Tree-level propagators lead to underabundant DM as they do not account for scattering contributions and can deviate up to $-100\%$ from the 1PI-resummed result., Comment: 67 pages, 15 figures, 4 appendices

We investigate the production of particle Dark Matter (DM) in a minimal freeze-in model considering a non-instantaneous reheating phase after inflation. We demonstrate that for low reheating temperatures, bosonic or fermionic reheating from monomial potentials can lead to a different evolution in the DM production and hence to distinct predictions for the parent particle lifetime and mass, constrained by long-lived particle (LLP) searches. We highlight that such scenario predicts parent particle decay lengths larger compared to using the instantaneous reheating approximation. Moreover, we demonstrate the importance of an accurate definition of the reheating temperature and emphasize its relevance for the correct interpretation of experimental constraints. We explore different models of inflation, which can lead to the considered reheating potential. We find that the extent to which the standard DM freeze-in production can be modified crucially depends on the underlying inflationary model. Based on the latest CMB constraints, we derive lower limits on the decay length of the parent particle and confront these results with the corresponding reach of LLP searches. Our findings underscore the impact of the specific dynamics of inflation on DM freeze-in production and highlight their importance for the interpretation of collider signatures. At the same time, our results indicate the potential for LLP searches to shed light on the underlying dynamics of reheating., Comment: Adjusted to JCAP version. 15 pages + appendices, 10 figures

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential., Comment: 429 pages, contribution to Snowmass 2021

The existence of a dark matter model with a rich dark sector could be the reason why WIMP dark matter has evaded its detection so far. For instance, colored co-annihilation naturally leads to the prediction of heavier dark matter masses. Importantly, in such a scenario the Sommerfeld effect and bound state formation must be considered in order to accurately predict the relic abundance. Based on the example of the currently widely studied $t$-channel simplified model with a colored mediator, we demonstrate the importance of considering these non-perturbative effects for correctly inferring the viable model parameters. We emphasize that a flat correction factor on the relic abundance is not sufficient in this context. Moreover, we find that parameter space thought to be excluded by direct detection experiments and LHC searches remains still viable. Additionally, we illustrate that long-lived particle searches and bound-state searches at the LHC can play a crucial role in probing such a model. We demonstrate how future direct detection experiments will be able to close almost all of the remaining windows for freeze-out production, making it a highly testable scenario., Comment: 47 pages + appendices, 14 Figures