Flavor changing neutral current decays $t\to c X$ ($X=\gamma,\,g,\, Z,\,  H$) and $t\to c\bar \ell\ell $ ($\ell=\mu,\,\tau$) via scalar leptoquarks

Bolaños, A.; Sánchez-Vélez, R.; Tavares-Velasco, G.

doi:10.1140/epjc/s10052-019-7211-8

Flavor changing neutral current decays $t\to c X$ ( $X=\gamma,\,g,\, Z,\, H$ ) and $t\to c\bar \ell\ell$ ( $\ell=\mu,\,\tau$ ) via scalar leptoquarks

A. Bolaños
(
- Iberoamericana U. and
- ITESM, Monterrey
)
,
R. Sánchez-Vélez
(
- Puebla U., Mexico
)
,
G. Tavares-Velasco
(
- Puebla U., Mexico
)

Jul 12, 2019

24 pages

Published in:

Eur.Phys.J.C 79 (2019) 8, 700

Published: Aug 21, 2019

e-Print:

1907.05877 [hep-ph]

DOI:

10.1140/epjc/s10052-019-7211-8

View in:

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Abstract: (Springer)

The flavor changing neutral current decays

t\rightarrow c X

(

X=\gamma ,\,g,\, Z,\, H

) and

t\rightarrow c{{\bar{\ell }}}\ell

(

\ell =\mu ,\,\tau

) are studied in a renormalizable scalar leptoquark (LQ) model with no proton decay, where a scalar SU(2) doublet with hypercharge

Y=7/6

is added to the standard model, yielding a non-chiral LQ

\varOmega _{5/3}

. Analytical results for the one-loop (tree-level) contributions of a scalar LQ to the

f_i\rightarrow f_j X

(

f_i\rightarrow f_j {\bar{f}}_m f_l

) decays, with

f_a=q_a, \ell _a

, are presented. We consider the scenario where

\varOmega _{5/3}

couples to the fermions of the second and third families, with its right- and left-handed couplings obeying

\lambda _R^{\ell u_i}/\lambda _L^{\ell u_i}=O(\epsilon )

, where

\epsilon

parametrizes the relative size between these couplings. The allowed parameter space is then found via the current constraints on the muon

(g-2)

, the

\tau \rightarrow \mu \gamma

decay, the LHC Higgs boson data, and the direct LQ searches at the LHC. For

m_{\varOmega _{5/3}}=1

TeV and

\epsilon =10^{-3}

, we find that the

t\rightarrow c X

branching ratios are of similar size and can be as large as

10^{-8}

in a tiny area of the parameter space, whereas

{\mathrm{Br}}(t\rightarrow c{{\bar{\tau }}}\tau )

[

{\mathrm{Br}}(t\rightarrow c{{\bar{\mu }}}\mu )

] can be up to

10^{-6}

(

10^{-7}

).

Note:

24 pags, 10 figures, 1 table

leptoquark: scalar
leptoquark: mass
charge: 5/3
neutral current: flavor changing
top: decay
top: branching ratio
decay: flavor changing
tau: radiative decay
p: decay
coupling: left-handed

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