Distinguishing between MSSM and NMSSM through $\Delta F=2$ processes

Abstract

We study deviations between MSSM and $Z_3$-invariant NMSSM, with respect to their predictions in $\Delta F=2$ processes. We find that potentially significant effects arise either from the well known double-penguin diagrams, due to the extra scalar NMSSM states, or from neutralino-gluino box contributions, due to the extended neutralino sector. Both are discussed to be effective in the large $\tan \beta$ regime. Enhanced genuine-NMSSM contributions in double penguins are expected for a light singlet spectrum (CP-even,CP-odd), while the magnitude of box effects is primarily controlled through singlino mixing. The latter is found to be typically subleading (but non-negligible) for $\lambda \lesssim 0.5$, however it can become dominant for $\lambda \sim \mathcal{O}(1)$. We also study the low $\tan \beta$ regime, where a distinction between MSSM and NMSSM can come instead due to experimental constraints, acting differently on the allowed parameter space of each model. To this end, we incorporate the LHC Run-I limits from $H\to ZZ$, $A\to hZ$ and $H^{\pm }\to \tau \nu$ non-observation along with Higgs observables and set (different) upper bounds for new physics contributions in $\Delta F=2$ processes. We find that a $\sim 25\%$ contribution in $\Delta M_{s(d)}$ is still possible for MFV models, however such a large effect is nowadays severely constrained for the case of MSSM, due to stronger bounds on the charged Higgs masses.

30 pp. text, 13 pp. appendix. Phrase "Recent limits" replaced by the more appropriate "LHC Run-I limits" due to new data becoming available from ATLAS, CMS. Note added with a brief discussion on these preliminary results. Refs added

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