engleski

Minimally flavored colored scalar in $\bar B \to D^{; ; ; ; (*)}; ; ; ; \tau \bar \nu$ and the mass matrices constraints

The presence of a colored scalar that is a weak doublet with fractional electric charges of $|Q|=2/3$ and $|Q|=5/3$ with mass below $1$\, TeV can provide an explanation of the observed branching ratios in $B \to D^{; ; ; ; (*)}; ; ; ; \tau \bar \nu$ decays. The required combination of scalar and tensor operators in the effective Hamiltonian for $b \to c \tau \bar \nu$ is generated through the $t$-channel exchange. We focus on a scenario with a minimal set of Yukawa couplings that addresses a semitauonic puzzle and show that its resolution puts a nontrivial bound on the product of the scalar couplings to $\bar \tau b$ and $\bar c \nu$. We also derive additional constraints posed by $Z \to b\bar b$, muon magnetic moment, $\tau \to \mu \gamma$, $\tau \to e \gamma$ and $\tau$ electric dipole moment. The minimal set of Yukawa couplings is not only compatible with the mass generation in an $SU(5)$ unification framework, a natural environment for colored scalars, but specifies all matter mixing parameters except for one angle in the up-type quark sector. We accordingly spell out predictions for the proton decay signatures through gauge boson exchange and show that $p \rightarrow \pi^0 e^+$ is suppressed with respect to $p \rightarrow K^+ \bar{; ; ; ; \nu}; ; ; ; $ and even $p \rightarrow K^0 e^+$ in some parts of available parameter space. Impact of the colored scalar embedding in $45$-dimensional representation of $SU(5)$ on low-energy phenomenology is also presented. Finally, we make predictions for rare top and charm decays where presence of this scalar leptoquark can be tested independently.

colored scalars; SU(5) unification; B decays

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