Aspects of bottom-up hidden sector models
(2020)
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- Abstract
- The standard model (SM) of particle physics is a hugely successful theory of nature, but it is incomplete. For instance, it cannot explain finite SM neutrino masses or the primordial baryon asymmetry (BAU). One way to address these and other problems is to postulate the existence of new but hidden particles. This thesis studies such “hidden sectors” via two complementary approaches: 1) an effective theory approach, where electroweak (EW) and GeV scale portal effective theories (PETs) are constructed that couple the SM to a generic light hidden mediator of spin 0, 1/2, or 1. The EW scale PETs contain all available portal operators of dimension d ≤ 5. The GeV scale PETs additionally contain all leading order (LO) portal operators of dimension d = 6,7. They are used to derive a LO PET chiral perturbation theory Lagrangian that describes generic hidden sector induced light meson transitions such as 𝐾^+ → 𝜋^+ 𝑆 in fixed target experiments such as NA62 or SHiP. 2) An investigation of the type-I seesaw model, which couples the SM to n ≥ 2 sterile neutrinos that can generate a BAU via the mechanism of “leptogenesis”. It is shown that thermal and spectator effects can result in a sign-flip and strong relative enhancement of the BAU in high-scale leptogenesis with two hierarchical sterile neutrinos of vanishing initial abundance. Much lighter sterile neutrinos may be detected via lepton number violating (LNV) decays at colliders, but LNV decays could be suppressed relative to lepton number conserving decays for ‘t Hooft natural parameter choices. It is shown that the corresponding parameter space consists of three regions: (a) with unsuppressed LNV decays, (b) with suppressed LNV decays, (c) with both suppressed and unsuppressed LNV decays.
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Citations
Klose, P. (2020). Aspects of bottom-up hidden sector models. https://hdl.handle.net/2078.5/128073