We evaluate the top-quark FCNC productions induced by the topcolor-assisted technicolor (TC2) model at the LHC. These productions proceed, respectively, through the parton-level processes gg -> t (c) over bar, cg -> t, cg -> tg, cg -> tZ, and cg -> t gamma. We show the dependence of the production rates on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that for each channel the TC2 model allows for a much larger production rate than the supersymmetric model. All these rare productions in the TC2 model can be enhanced above the 3 sigma sensitivity of the LHC. Since in the minimal supersymmetric model only cg -> t is slightly larger than the corresponding LHC sensitivity, the observation of these processes will favor the TC2 model over the supersymmetric model. In case of unobservation, the LHC can set meaningful constraints on the TC2 parameters.

Top-quark FCNC Productions at CERN LHC in Topcolor-assisted Technicolor Model

We present a systematic light-cone QCD sum rule study of the exclusive rare radiative decay Λb → Λγ and rare semileptonic decay Λb → Λl+l− within the framework of the standard model. Although some light-cone sum rule (LCSR) studies on these rare processes can be found in different literatures, it is necessary to reanalyze them systematically for the reason that either the baryonic distribution amplitudes are improved or different interpolating currents for the Λb baryon may lead to quite different results. In addition, the rare process Λb → Λγ has not yet been analyzed by LCSR with the Ioffe-type current. Taking all these reasons into account, we perform LCSR calculations of both the processes with two types of interpolating currents. Our calculations show that the choice of the interpolating current for the Λb baryon can affect the predictions significantly, especially for the rare radiative decay process.

Improved Light-Cone QCD Sum Rule Analysis of Rare Decays Λb → Λγ and Λb → Λl+l−

New physics upper bound on the branching ratio of Bs→l+l−

Based on the low-energy effective Hamiltonian, we calculate new physics corrections to the branching ratio and the differential distributions of the rare decay $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}\ensuremath{\gamma}$ induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs-doublet model with the restriction ${\ensuremath{\lambda}}_{\mathrm{ij}}^{U,D}=0$ for $i\ensuremath{\ne}j.$ Within the considered parameter space, we see the following: (a) the standard model predictions of $\mathcal{B}(\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}\ensuremath{\gamma})$ and ${A}_{\mathrm{FB}}$ have a moderate ${m}_{s}$ dependence; (b) in model III, the prediction of the branching ratio $\mathcal{B}(\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}\ensuremath{\gamma})$ ranges from one-third to three times the standard model prediction, but is highly correlated with that of $\mathcal{B}(\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma});$ (c) the new physics enhancement to the branching ratio $\mathcal{B}(\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}\ensuremath{\gamma})$ in model II can be as large as $(30\char21{}50)%;$ (d) the contribution from one-particle reducible diagrams is dominant and hence four normalized differential distributions are insensitive to the variation of scale \ensuremath{\mu} and possible new physics corrections; (e) because of the smallness of its decay rate and the long-distance background, the $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}\ensuremath{\gamma}$ decay is not a better process in detecting new physics than the $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}$ decay.

B→Xsγγdecay in the standard model and the general two-Higgs-doublet model

In the framework of general two-Higgs-doublet models, we calculate the branching ratios of various inclusive charmless b decays by using the low energy effective Hamiltonian including next-to-leading order QCD corrections, and examine the current status and the new physics effects on the determination of the charm multiplicity $n_c$ and semileptonic branching ratio $B_{SL}$. Within the considered parameter space, the enhancement to the ratio $BR(b \to s g)$ due to the charged-Higgs penguins can be as large as a factor of 8 (3) in the model III (II), while the ratio $BR(b \to no charm)$ can be increased from the standard model prediction of 2.49% to 4.91% (2.99%) in the model III (II). Consequently, the value of $B_{SL}$ and $n_c$ can be decreased simultaneously in the model III. The central value of $B_{SL}$ will be lowered slightly by about 0.003, but the ratio $n_c$ can be reduced significantly from the theoretical prediction of $n_c= 1.28 \pm 0.05$ in the SM to $n_c= 1.23 \pm 0.05$, $1.18 \pm 0.05$ for $m_{H^+}=200, 100$ GeV, respectively. We find that the predicted $n_c$ and the measured $n_c$ now agree within roughly one standard deviation after taking into account the effects of gluonic charged Higgs penguins in the model III with a relatively light charged Higgs boson.

Charm multiplicity and the branching ratios of inclusive charmless b quark decays in the general two Higgs doublet models

We calculate the contributions to the rare decays and from one-loop -penguin diagrams in the framework of topcolor-assisted technicolor model. Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental data.

https://iopscience.iop.org/article/10.1088/0253-6102/33/2/269/pdf

Rare Decays and in the ,Topcolor-Assisted Technicolor Model*

We calculate the contributions to the rare B-decays, $B \to X_{s,d} \nu \bar \nu$, $B_{s,d} \to l^+l^- $ from the unit-charged technipions. Within the considered parameter space we find that: (a) the enhancements to the branching ratios in question can be as large as three orders of magnitude; (b) the ALEPH data of $B \to X_s \nu \bar \nu$ lead to strong mass bounds on $m_{p1}$ and $m_{p8}$: $m_{p8} \geq 620, 475 GeV$ for $F_Q=40GeV$ and $m_{p1}=100, 400 GeV$ respectively. (c) the CDF data of $B_s \to \mu \bar \mu$ lead to a relatively weak limit: $m_{p8} \geq 320 GeV$ for $F_Q=40GeV$ and $m_{p1}=200 GeV$.

The rare decays $B \to X_{s,d} \nu \bar \nu$ and $B_{s,d} \to l^+l^- $ in the Multiscale Walking Technicolor Model

Employing improved calculations of the decay form factors from light-cone sum rules, we evaluate the invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes B → K(*)l+l− in the SM and T2HDM From the recent measurements of their branching ratios, we find that these processes do provide additional bounds on the new parameters in the model considered here After the inclusion of the new physics contributions, the large enhancement of FBA, which is unobservably small within the SM and of the lepton polarization at large tanβ, may precisely test the SM or reveal new physics in forthcoming accurate experiments

Exclusive Semileptonic Rare Decays B → K(*)l+l− in a Top Quark Two-Higgs-Doublet Model

Using the form factors calculated in the three-point QCD sum rules, we calculate the new physics contributions to the physical observables of Bc → D*sμ+μ− decay in a family non-universal Z' model. Under the consideration of three cases of the new physics parameters, we find that: (a) the Z' boson can provide large contributions to the differential decay rates; (b) the forward-backward asymmetry (FBA) can be increased by about 47%, 38%, and 110% at most in S1, S2, and extreme limit values (ELV), respectively. In addition, the zero crossing can be shifted in all the cases; (c) when > 0.08, the value of PL can be changed from −1 in the Standard Model (SM) to −0.5 in S1, −0.6 in S2, and 0 in extreme limit values, respectively; (d) the new physics corrections to PT will decrease the SM prediction about 25% for the cases of S1 and S2, 100% for the case of ELV.

Rare Decay B c → D s *μ + μ − in a Family Non-Universal Z ′ Model

We calculate the contributions to the rare decays $B \to X_{s,d} \nu \bar \nu$ and $B_{s,d} \to l^+l^-$ from one-loop $Z^0$-penguin diagrams in the framework of Topcolor-assisted Technicolor Model Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental data

Lü Lin-Xia

Papers

Rare Decays and in the ,Topcolor-Assisted Technicolor Model*

The rare decays $B \to X_{s,d} \nu \bar \nu$ and $B_{s,d} \to l^+l^- $ in the Multiscale Walking Technicolor Model

Exclusive Semileptonic Rare Decays B → K(*)l+l− in a Top Quark Two-Higgs-Doublet Model

Rare Decay B c → D s *μ + μ − in a Family Non-Universal Z ′ Model

Rare decays $B \to X_{s,d} \nu \bar \nu$ and $B_{s,d} \to l^+ l^-$ in the Topcolor-assisted Technicolor Model