Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1996-03-01
Phys.Rev. D54 (1996) 3296-3308
Physics
High Energy Physics
High Energy Physics - Phenomenology
35 pages, 5 Postscript figures, 10 Postscript files used in the tex file, uses epsf.sty
Scientific paper
10.1103/PhysRevD.54.3296
A study of $R_b$ and $R_c$ is presented in the context of a Two Higgs Doublet Model (2HDM) with flavor changing scalar currents (FCSC). Implications of the model for the $\rho$-parameter and for $b\to s\gamma$ are also considered. The experimental data on $R_b$ places stringent constraints on the model parameters. The configuration of the model needed to account for $R_b$ is found to be irreconcilable with constraints from $b\to s\gamma$ and $\rho$. In particular, if $R^{\rm exp}_b>R^{\sss{\rm SM}}_b$ persists then this version of 2HDM will be ruled out or require significant modifications. Noting that aspects of the experimental analysis for $R_b$ and $R_c$ may be of some concern, we also disregard $R^{\rm exp}_b$ and $R^{\rm exp}_c$ and give predictions for these using constraints from $b\to s\gamma$ and $\rho$ parameter only. We emphasize the theoretical and experimental advantages of the observable $R_{b+c}\equiv \Gamma(Z\to b\bar b\mbox{ or } c\bar c)/\Gamma(Z\to\mbox{hadrons})$. We also stress the role of $R_\ell\equiv \Gamma(Z\to\mbox{hadrons})/\Gamma(Z\to \ell^+\ell^-)$ in testing the Standard Model (SM) despite its dependence on QCD corrections. Noting that in models with FCNC the amplitude for $Z\to c\bar c$ receives a contribution which grows with $m^2_t$, the importance and uniqueness of precision $Z\to c\bar c$ measurements for constraining flavor changing $t\bar c$ currents is underscored.
Atwood David
Reina Laura
Soni Amarjit
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