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

Autori
Doršner, Ilja ; Fajfer, Svjetlana ; Košnik, Nejc ; Nišandžić, Ivan

Izvornik
Journal of High Energy Physics (1029-8479) (2013); 84-1

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
colored scalars; SU(5) unification; B decays

Sažetak
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.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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