Correlation between {R}_{D^{left(ast right)}} and top quark FCNC decays in leptoquark models

Tae Jeong Kim,Jiwon Park,Jinmian Li,Pyungwon Ko,Peiwen Wu

doi:10.1007/jhep07(2019)025

Tae Jeong Kim, Jiwon Park + Show 3 more

Open Access

https://doi.org/10.1007/jhep07(2019)025

Copy DOI

Abstract

Some interpretations of {R}_{D^{left(ast right)}} anomaly in B meson decay using leptoquark (LQ) models can also generate top quark decays through Flavor Changing Neutral Current (FCNC). In this work we focus on two LQs, i.e. scalar S1 and vector U1 which are both singlet under the SU(2)L gauge group in the Standard Model (SM). We investigate their implications on the 3-body top FCNC decays t → cℓiℓj at tree level and the 2-body t → cV at one-loop level, with ℓ being the SM leptons and V = γ, Z, g being the SM gauge bosons. We utilize the 2σ parameter fitting ranges of the LQ models and find that Br(t → cℓiℓj) at tree level can reach mathcal{O} (10−6) and Br(t → cV) at one-loop level can reach mathcal{O} (10−10). Some quick collider search prospects are also analyzed.

Highlights

In this work we are not going to be ambitious to explain both deviations, but limit ourselves to RD(∗) interpretations in the leptoquark (LQ) models [98–118] and its interesting correlations to the top quark Flavor Changing Neutral Current (FCNC) decays
In this work we studied the correlation between the interpretations of RD(∗) anomaly in B meson decay using LQ models and the top quark FCNC decays, i.e. 3-body processes t → c i j at tree level and 2-body processes t → cV at one-loop level, with being the Standard Model (SM)
We focus on the scalar LQ S1 and vector LQ U1 which are both singlet under the SM SU(2)L gauge group

Summary

LQ S1 and U1 for top quark FCNC

Square brackets indicate the chirality of couplings and replacement with particles in the round brackets generate processes involved in RD(∗). In figure 2 and figure 3 we show the one-loop contributions to top FCNC t → cγ from S1 and U1, respectively, in which replacing external photon γ with Z boson or gluon g with applicable vertices is straightforward. We utilize the parameter ranges in [110] for various LQ models which can fit the RD(∗) data at 2σ level (see table.II therein). We remind ourselves that moderate differences in the 2σ ranges of parameters presented in different papers do not affect the order of magnitude in top FCNC BRs we will discuss. The parameter ranges we take from [110] in the numerical studies are summarized in table 1. We assume all parameters are real in our analysis

Tree level

One-loop level

Collider search prospects

Cut-and-count analysis

Multi-variate analysis

Conclusion