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Register a new userSMEFT top-quark effects on $Delta F=2$ observables
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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.
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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.
In this work we study the flavor changing neutral current(FCNC) decays of the top quark, $tto cgamma$ and $tto c g$. The Standard Model, predictions for the branching ratios of these decays are about $sim 5times 10^{-14}$, and $sim 1times 10^{-12}$, respectively. The recent study presented by the ATLAS Collaboration gives a sensitivity on these branching ratios about $sim 10^{-5}$ at $%95$ C.L. The parameter space of $lambda$, $Lambda$, and $d$ where the branching ratios of $tto cgamma$ and $tto c g$ decays exceed these predictions is obtained.
We present a global interpretation of Higgs, diboson, and top quark production and decay measurements from the LHC in the framework of the Standard Model Effective Field Theory (SMEFT) at dimension six. We constrain simultaneously 36 independent directions in its parameter space, and compare the outcome of the global analysis with that from individual and two-parameter fits. Our results are obtained by means of state-of-the-art theoretical calculations for the SM and the EFT cross-sections, and account for both linear and quadratic corrections in the $1/Lambda^2$ expansion. We demonstrate how the inclusion of NLO QCD and $mathcal{O}left( Lambda^{-4}right)$ effects is instrumental to accurately map the posterior distributions associated to the fitted Wilson coefficients. We assess the interplay and complementarity between the top quark, Higgs, and diboson measurements, deploy a variety of statistical estimators to quantify the impact of each dataset in the parameter space, and carry out fits in BSM-inspired scenarios such as the top-philic model. Our results represent a stepping stone in the ongoing program of model-independent searches at the LHC from precision measurements, and pave the way towards yet more global SMEFT interpretations extended to other high-$p_T$ processes as well as to low-energy observables.
We investigated top quark effects on virtual photon structure functions by pQCD. We include the top quark mass effects on the virtual photon structure function with the quark parton model and with the operator product expansion up to the next-to-leading order in QCD. We also consider the threshold effect on the running coupling constant in the calculation to the effective photon structure function with a matching condition. The numerical calculations are investigated in the kinematical region expected at the future international linear collider.
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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