Slepton mass splittings and cLFV in the SUSY seesaw in the light of recent experimental results

Abstract

Following recent experimental developments, in this study we re-evaluate if the interplay of high-and low-energy lepton flavour violating observables remains a viable probe to test the high-scale type-I supersymmetric seesaw. Our analysis shows that fully constrained supersymmetric scenarios no longer allow to explore this interplay, since recent LHC data precludes the possibility of having sizeable slepton mass differences for a slepton spectrum sufficiently light to be produced, and in association to BR(µ → eγ) within experimental reach. However, relaxing the strict universality of supersymmetric soft-breaking terms and fully exploring heavy neutrino dynamics, still allows to have slepton mass splittings O(few %), for slepton masses accessible at the LHC, with associated µ → eγ rates within future sensitivity. For these scenarios, we illustrate how the correlation between high-and low-energy lepton flavour violating observables allows to probe the high-scale supersymmetric seesaw.

Lepton flavour violation and neutrino masses

“…One ; light (dark) surfaces denote currently allowed (excluded) regimes due to the violation of the associated experimental bound (from [42]). On the right panel, 1 st and 2 nd generation charged slepton mass splittings vs. BR(µ → eγ), with CR(µ − e, Ti) on the secondary y-axis in a type I SUSY seesaw, for different values of the heaviest right-handed neutrino mass M R 3 = 10 13,14,15 GeV (M R 1 ,R 2 = 10 10,11 GeV) and for a flavour conserving modified mSUGRA benchmark (from [43]).…”

“…such example is shown on the right panel of Fig. 5, in which the vertical axes correspond to low-energy cLFV observables (µ → eγ and µ − e conversion), displayed as a function of the relative mass splittings between left-handed smuons and selectrons -a high-energy cLFV observable [43]. The strong synergy of these observables can be explored to falsify the model, or then allow to infer hints in the scale of the seesaw mediators -which would be otherwise unreachable.…”

Report on scipost_201811_00022v1

“…; light (dark) surfaces denote currently allowed (excluded) regimes due to the violation of the associated experimental bound (from [42]). On the right panel, 1 st and 2 nd generation charged slepton mass splittings vs. BR(µ → eγ), with CR(µ − e, Ti) on the secondary y-axis in a type I SUSY seesaw, for different values of the heaviest right-handed neutrino mass M R 3 = 10 13,14,15 GeV (M R 1 ,R 2 = 10 10,11 GeV) and for a flavour conserving modified mSUGRA benchmark (from [43]).…”

“…One such example is shown on the right panel of Fig. 5, in which the vertical axes correspond to low-energy cLFV observables (µ → eγ and µ − e conversion), displayed as a function of the relative mass splittings between left-handed smuons and selectrons -a high-energy cLFV observable [43]. The strong synergy of these observables can be explored to falsify the model, or then allow to infer hints in the scale of the seesaw mediators -which would be otherwise unreachable.…”

Lepton Flavor Violation beyond the MSSM

“…The LFV phenomenology of SUSY seesaw models has been studied by many authors. For the type-I seesaw, low-energy LFV decays such as i → j γ and i → 3 j have been calculated in [56,57,[63][64][65][66][67][68][69][70][71][72][73]. Similarly, µ−e conversion in nuclei has been studied in [74,75].…”