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Register a new userHiggs Decay To bar{b}b: Different Approaches To Resummation Of QCD Effects
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The comparison between parameterisations of the perturbation results for the decay width of the Standard Model Higgs boson to bar{b}b-quarks pairs, based on application of bar{MS}-scheme running quark mass and pole b-quark mass, are presented. In the case of the latter parameterisation taking into account of order O(alpha_s^3) term is rather important. It is minimising deviations of the results obtained at the O(alpha_s^2) level from the results, which follow from the running quark mass approach
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We study effects of charged Higgs boson exchange in $bar B to D tau bar u_{tau}$. The Yukawa couplings of Model II of two-Higgs-doublet model, which has the same Yukawa couplings as MSSM, is considered. We evaluate the decay rate including next-to-leading QCD corrections and estimate uncertainties in the theoretical calculation. Our analysis will contribute to probe an extended Higgs sector at B factory experiments.
We have evaluated the decay modes of the $Upsilon(4s), Upsilon(3d), Upsilon(5s), Upsilon(6s)$ states into $Bbar B, Bbar B^*+c.c., B^* bar B^*, B_s bar B_s, B_s bar B^*_s +c.c., B^*_s bar B_s^* $ using the $^3P_0$ model to hadronize the $bbar b$ vector seed, fitting some parameters to the data. We observe that the $Upsilon(4s)$ state has an abnormally large amount of meson-meson components in the wave function, while the other states are largely $bbar b$. We predict branching ratios for the different decay channels which can be contrasted with experiment for the case of the $Upsilon(5s)$ state. While globally the agreement is fair, we call the attention to some disagreement that could be a warning for the existence of more elaborate components in the state.
We evaluate long-distance electromagnetic (QED) contributions to $bar{B}{}^0 to D^+ tau^{-} bar{ u}_{tau}$ and $B^- to D^0 tau^{-} bar{ u}_{tau}$ relative to $bar{B}{}^0 to D^+ mu^{-} bar{ u}_{mu}$ and $B^- to D^0 mu^{-} bar{ u}_{mu}$, respectively, in the standard model. We point out that the QED corrections to the ratios $R(D^{+})$ and $R(D^{0})$ are not negligible, contrary to the expectation that radiative corrections are almost canceled out in the ratio of the two branching fractions. The reason is that long-distance QED corrections depend on the masses and relative velocities of the daughter particles. We find that theoretical predictions for $R(D^{+})^{tau/mu}$ and $R(D^{0})^{tau/mu}$ can be amplified by $sim4%$ and $sim3%$, respectively, for the soft-photon energy cut in range $20$-$40$ MeV.
We study the decay modes $bar{B}_sto phi pi^0$ and $bar{B}_sto phi rho^0$ within the frameworks of two-Higgs doublet models type-II and typ-III. We adopt in our study Soft Collinear Effective Theory as a framework for the calculation of the amplitudes. We derive the contributions of the charged Higgs mediation to the weak effective Hamiltonian governing the decay processes in both models. Moreover we analyze the effect of the charged Higgs mediation on the Wilson coefficients of the electrowek penguins and on the branching ratios of $bar{B}_sto phi pi^0$ and $bar{B}_sto phi rho^0$ decays. We show that wthin two-Higgs doublet models type-II and type-III the Wilson coefficients corresponding to the electroweak penguins can be enhanced due to the contributions from the charged Higgs mediation leading into enhancement in the branching ratios of $ bar{B}_sto phi pi^0$ and $bar{B}_sto phi rho^0 $ decays. We find that, within two-Higgs doublet models type-II, the enhancement in the branching ratio of $bar{B}_sto phi pi^0$ can not exceed $18%$ with respect to the SM predictions. For the branching ratio of $bar{B}_sto phi rho^0$, we find that the charged Higgs contribution in this case is small where the branching ratio of $bar{B}_sto phi rho^0$ can be enhanced or reduced by about $4% $ with respect to the SM predictions. For the case of the two-Higgs doublet models type-III we show that the branching ratio of $bar{B}_sto phi pi^0$ can be enhanced by about a factor $2$ of its value within two-Higgs doublet models type-II. However no sizable enhancement with respect to the SM predictions can be obtained for both $bar{B}_sto phi pi^0$ and $bar{B}_sto phi rho^0$ decays.
We study the one loop electroweak radiative corrections to $h^0to bbar{b}$ and $h^0to tau^+tau^-$ in the framework of two Higgs doublet Model (2HDM). We evaluate the deviation of these couplings from their Standard Model (SM) values. $h^0to bbar{b}$ and $h^0to tau^+tau^-$ may receives large contribution from triple couplings $h^0H^0H^0$, $H^0h^0h^0$, $h^0A^0A^0$ and $h^0H^+H^-$ which are absent in the Standard Model. It is found that in 2HDM, these corrections could be significant and may reach more than 20% for not tow heavy $H^0$ or $A^0$ or $H^pm$. We also study the ratio of branching ratios $R=BR(h^0to bbar{b})/BR(h^0to tau^+tau^-)$ of Higgs boson decays which could be used to disentangle SM from other models such as 2HDM.
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