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Register a new userMSSM vs. NMSSM in $Delta F=2$ transitions
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Jacky Kumar
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We study deviations between MSSM and NMSSM in the predictions of $Delta F=2$ processes. We found that there can be two sources which can cause such deviations, emph{i.e}, due to certain neutralino-gluino cross box diagrams and due to well known double penguin diagrams. Both are effective at large $tan beta$. In addition to this, taking into account 8 TeV direct search constraints from the heavy Higgs searches, we study the maximum allowed MFV like new physics (NP) effects on $Delta M_s$ in the two models. In NMSSM such NP effects can be as large as $25 %$, on the other hand in MSSM such large contributions are severely constrained.
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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 $tanbeta$ 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 $lambdasim mathcal{O}(1)$. We also study the low $tanbeta$ 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 $Hrightarrow Z Z$, $A rightarrow hZ$ and $H^pm rightarrow tau u $ 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.
We present a model-independent anatomy of the $Delta F=2$ transitions $K^0-bar K^0$, $B_{s,d}-bar B_{s,d}$ and $D^0-bar D^0$ in the context of the Standard Model Effective Field Theory (SMEFT). We present two master formulae for the mixing amplitude $big[M_{12} big]_text{BSM}$. One in terms of the Wilson coefficients (WCs) of the Low-Energy Effective Theory (LEFT) operators evaluated at the electroweak scale $mu_text{ew}$ and one in terms of the WCs of the SMEFT operators evaluated at the BSM scale $Lambda$. The coefficients $P_a^{ij}$ entering these formulae contain all the information below the scales $mu_text{ew}$ and $Lambda$, respectively. Renormalization group effects from the top-quark Yukawa coupling play the most important role. The collection of the individual contributions of the SMEFT operators to $big[M_{12}big]_text{BSM}$ can be considered as the SMEFT ATLAS of $Delta F=2$ transitions and constitutes a travel guide to such transitions far beyond the scales explored by the LHC. We emphasize that this ATLAS depends on whether the down-basis or the up-basis for SMEFT operators is considered. We illustrate this technology with tree-level exchanges of heavy gauge bosons ($Z^prime$, $G^prime$) and corresponding heavy scalars.
We investigate model independent top-quark corrections to $Delta F = 2$ processes for the down-type quarks within the framework of the Standard Model Effective Field Theory. Dimension-six $Delta F = 1$ operators contribute to them through renormalization group evolutions and matching conditions. We provide a complete one-loop matching formula from the top quarks for $Delta F=2$ transitions. We also demonstrate these corrections on $Delta M_{B_s}$ in the left-right symmetric model, which are compared with the conventional calculation.
In this work we analyze a new piece present in the $Delta F = 2$ effective Lagrangian in models with extra vector-like quarks. This piece, which was not taken into account previously, is required in order to preserve gauge invariance once the unitarity of the CKM matrix is lost. We illustrate the effects of this new piece in both, CP conserving and CP violating processes.
We show that the interplay between the LHC and the e^+ e^- International Linear Collider (ILC) with sqrt{s}=500 GeV might be crucial for the discrimination between the minimal and next-to-minimal supersymmetric standard model. We present an NMSSM scenario that cannot be distinguished from the MSSM by cross sections and mass measurements if only the light neutralinos and the lightest chargino are kinematically accessible, even if one of the neutralinos has a significant singlino component. Mass predictions for the heavier neutralinos from the ILC analysis and their observation at the LHC lead to an identification of the neutralino mixing character and the underlying supersymmetric model in a combined LHC/ILC analysis. In our numerical example we include errors in the mass measurements and use standard methods of supersymmetric parameter determination.
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