arXiv subjects

Pieter Braat

Publications and source records attributed to Pieter Braat.

4 recordsLinked to original sources

arXiv2026

Big Bang Nucleosynthesis and the Neutrino-Extended Standard Model Effective Field Theory

We study the impact of light GeV-scale heavy neutral leptons (HNLs) on Big Bang nucleosynthesis (BBN) in the neutrino-extended Standard Model Effective Field Theory ($ν$SMEFT). We show that, based on very general considerations, BBN constraints complement laboratory searches at colliders, beam dumps, and neutrinoless double beta decay, by providing an upper bound on the cut-off scale of the effective field theory for HNL masses above $\sim$100 MeV. We identify target regions for future laboratory probes of the $ν$SMEFT parameter space that is bounded from above and below.

hep-ph↗

arXiv2025

Big Bang Nucleosynthesis constraints on resonant DM annihilations

We perform a systematic study of BBN constraints from photodisintegration for scenarios in which dark-matter annihilations are resonantly-enhanced. To this end, we implement and make available a new class ResonanceModel within an updated version v1.3.0 of ACROPOLIS. While the corresponding implementation is done in a rather model-independent way, we also make available three benchmark models that can be used to calculate constraints for more concrete scenarios. Using this new version of ACROPOLIS, we present for the first time the corresponding constraints on resonantly-enhanced $s$-wave and $p$-wave annihilations. We show that for $s$-wave annihilations the bounds are usually very similar to the ones without a resonance, while for $p$-wave annihilations the bounds can be significantly stronger. The updated version v1.3.0 of ACROPOLIS can be found at https://github.com/hep-mh/acropolis .

hep-ph↗

arXiv2025

Scattering meets absorption in dark matter detection

Direct detection experiments have started to explore dark matter scattering off electrons and nucleons through light mediators. Mediators with sub-keV masses are efficiently produced in the Sun and can be absorbed in the same detectors that probe dark matter scattering. We investigate the interplay of dark matter scattering and mediator absorption for two models with a dark photon as mediator. For Dirac dark matter, we find that scattering and absorption can be simultaneously observed at direct detection experiments in the near future. For atomic dark matter, we predict additional signals due to scattering of both dark atoms and constituents from ionized dark atoms. In both models, we determine the parameter space that respects bounds from cosmology and astrophysics, where the strongest constraints come from dark matter self-interactions. In this way, we identify viable targets for dark matter with light mediators at upcoming direct detection experiments. Distinguishing between the various signals, for instance by measuring energy distributions, will be crucial to reveal the underlying model in case of a discovery.

hep-ph↗

arXiv2023

SIMPly add a dark photon

Pions of a dark sector gauge group can be strongly interacting massive particle (SIMP) dark matter, produced by the freeze-out of $3 \to 2$ interactions, with naturally large self-interactions. We study if adding a dark photon to the set-up can do it all: i) maintain thermalization with the visible sector, ii) resonantly enhance the $3\to2$ interactions, thus allowing for a perturbative pion description, and iii) provide a velocity dependent self-interaction that can affect small scale structure formation. For $N_f=3$ this minimal setup is marginally excluded, as the required kinetic mixing is too small to maintain thermal equilibrium with the SM. Adding an extra dark quark opens up parameter space, and -- perhaps somewhat surprisingly -- we find that all bounds can be satisfied for dark pion masses $m_π\sim 250-600\,$MeV. Dropping the small scale structure requirement iii), a viable setup is reproduced for dark charges of $α_d = 0.01-1$ and a dark pion mass $m_π\geq 30$ MeV. Late time annihilations are non-negligible making the SIMP dark pion a bit WIMPy.

hep-ph↗