Probing the Stau－Stau－Higgs Couplings in the MSSM at NLC

In the minimal supersymmetric standard model (MSSM) with CP violating phases, this paper discusses the production of the lJghtest neutral Higgs boson in association with tau sleptons at future high-energy e^ e^- linear colliders. In parameter space of the constrained MSSM, the production cross section of e^ e^→h^0T1 T1^- can be very substantial at high energies. This process would provide a production mechanism for probing couplings of neutral Higgs bosoas to tau sleptons as well as some soft supersymmetric breaking parameters at next linear colliders.     

Rare decays ^-Bs,d^0→e^＋e^- in a top quark two-Higgs-doublet model

In the framework of T2HDM, we calculated the new physics contributions involving neutral Higgs bosons to the branching ratios of ^-Bs,d^0→e^＋e^-（e= e,μ） decays. Comparing the theoretical predictions with the experimental upper-limits, we found that （a） The data of Br（^-Bs,d^0→e^＋e^-） give the upper bound on tanβ： tanβ≤22, while Br（^-Bs^0→e^＋e^-） give tanβ≤12 for fixed δ = 0^0, mH＋ = 350 CeV, mH^0 = 160 GeV, mh^0 = 115 GeV and mA^0 = 120 GeV; （b） A light neutral Higgs boson mass mho （mA^0） less than 50 GeV （120 GeV） is excluded by the data of branching ratios for ^-Bs,d^0→e^＋e^-（e = μ） decays with tanβ= 10; （c） The bounds on mh^0 and tanβ, or mA^0 and tanβ are strongly correlated： a smaller （larger） tanβ means a lighter （heavier） neutral Higgs boson.     

Production of Charged Higgs Bosons from Left-Right Twin Higgs Model at TeV Energy e-γ Colliders

The left-right twin Higgs （LRTH） model predicts the existence of three additional Higgs bosons： one neutral Higgs φo and a pair of charged Higgs bosons φ±. In this paper, we study two pair production processes of these new particles at the next generation eγ colliders, i.e., e-γ → e-φ＋φ- , and e-γ→vRφ-φ0. We find that the production cross section of the process e-γ → e-φ＋φ- are at the level of several tens fb, the production cross section of the process e-γ→vRφ-φ0 can reach 0.35 fb with the reasonable parameter values. As long as the charged Higgs bosons are not too heavy, we conclude that these processes might be used to test for the left-right twin Higgs model in future high-energy linear collider experiments.     

Charged Top-Pion Production at e^＋e^- and γγ Colliders

We study the charged top-pion in the topcolor assisted technicolor model（TC2）, and calculate the production of charged top-pion at e^＋ e^- and γγ colliders. At an e^＋ e^- collider, charged top-pion can be produced via the processes e^＋e^- → t^bπt^-（^tbπt^＋）. At a γγ collider, it can be produced via the processes γγ →t^bπt^-（t^-bπt^＋）. The cross section can reach to a few of fb depending on the mass of the charged top-pion.     

Precise measurement of the e^＋e^- →π^＋π^-（γ） cross section with the initial state radiation method at BABAR

We present a precise BABAR measurement on the cross section of the process e^＋e^- →π^＋π^-（γ） from threshold to an energy of 3 GeV with the initial state radiation （ISR） technique, using 232 fb^-1 of data collected with the BABAR detector at e^＋e^- center-of-mass energies near 10.58 GeV. The ISR luminosity is determined from a study of the leptonic process e^＋e^- →μ^＋μ^-γ（γ）. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the ππ cross section measured from threshold to 1.8 GeV is （514.1± 2.2（stat） ± 3.1（syst）） × 10^-10.     

Muon g-2 discrepancy： new physics or a relatively light Higgs？

After a brief review of the muon g-2 status, we discuss hypothetical errors in the Standard Model prediction that might explain the present discrepancy with the experimental value. None of them seems likely. In particular, a hypothetical increase of the hadroproduction cross section in low-energy e^＋e^- collisions could bridge the muon g-2 discrepancy, but it is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 135 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.     

Correction of the Littlest Higgs Model to Higgs Production Process e-γ→veW-H in e-γ Collisions

The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs （LH） model, we study the process e-γ → veW^-H and calculate the contributions of the LH model to the cross section of this process. The results show that in most of the parameter spaces preferred by the electroweak precision data, the value of the relative correction is larger than 10%. Such correction to the process e-γ →veW^-H is large enough to be detected via e-γ collisions in the future high energy linear e^＋ e^- collider （ILC） experiment with the c.m. energy √s = 500 GeV and a yearly integrated luminosity ￡ = 100fb^-1, which will give an idea/way to test the model.     

Littlest Higgs Model and Spin Correlation of Top Quark Production at High Energy Linear e^＋e^- Colliders

Based on the littlest Higgs model, we investigate the spin correlation of the top quark pair production via the process e^＋e^- →tt at the high energy linear e^＋e^- collider （ILC） with a centre-of-mass energy √S = 800 GeV. Our numerical results show that the gauge boson ZH generates very small corrections to the spin correlation observable C in all the parameter space allowed by the electroweak data. However, with reasonable values of the free parameters, the value of the relative correction parameter RBH = （CBH-CSM）/CSM can reach 10%, which might be detected in future ILC experiments.     

具有T宇称的最小Higgs模型与LHC上Higgs波色子与弱规范波色子的联合产生

Considering the process pp→VH ＋X（V = W or Z） is a significant channel for searching for a light Higgs boson, we calculate the contributions of the littlest Higgs model with T-parity （called LHT model） to its production cross section. We find that, in most of the parameter space, the value of the relative correction parameter R is very small. However, with reasonable values of the free parameters, its value can be significantly larger.     

Probing the Stau-Stau-Higgs Couplings in the MSSM at NLC

In the minimal supersymmetric standard model (MSSM) with CP violating phases, this paper discussesthe production of the lightest neutral Higgs boson in association with tau sleptons at future high-energy e e- linearcolliders. In parameter space of the constrained MSSM, the production cross section of e e- → h0τ1 τ1- can be verysubstantial at high energies. This process would provide a production mechanism for probing couplings of neutral Higgsbosons to tau sleptons as well as some soft supersymmetric breaking parameters at next linear colliders.     

Study on the Effects of the Light CP-odd Higgs via the Leptonic Decays of Pseudoscalar Mesons

To explain the anomalously large decay rate of Σ⁺→p+μ⁺μ^-, it was proposed that a new mechanism where a light CP-odd pseudoscalar boson of m_A1⁰=214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π⁰→ e⁺e^- and r → γA₁⁰ in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of Σ⁺→ p+μ⁺μ^- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π⁰→ e⁺e^-;η(η')→ μ⁺μ^-; η_c→ μ⁺μ^-; η_b→τ⁺τ^- within the same framework. It is noted that for π⁰→ e⁺e^-, the standard model (SM) prediction is smaller than the data, whereas the experimental central value of η→μ⁺μ^- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A₁⁰ may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would check if we can obtain a universal mass for A₁⁰ which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible to have such a mass with the same coupling |gl|. Therefore we conclude that the phenomenology does not favor such a light A₁⁰, even though a small window is still open.     

Effects of a Family Non-universal Z' Boson in \bar{B}_d→μ+μ- and B- →π-μ+μ-,ρ-μ+μ- Decays

Motivated by the recently updated experimental measurement on \bar{B}_d→μ⁺μ^- and B^-→π^-μ⁺μ^- decays by CDF and Belle collaborations, we revisit these
decays, as well as B^-→ρ^-μ⁺μ^- decay, within the Standard Model, and evaluate the effects of a family non-universal Z' boson. Under the constraint from {\cal B}(B^-→π^-μ⁺μ^-), we find the ranges of the Z' couplings S^LR_μμ< -5.2×10^-2 or D^LR_μμ < -8.1× 10^-2 are excluded. Within the allowed Z' parameters spaces, comparing with the SM predictions, we find that {\cal B}(\bar{B}_d→ μ⁺μ^-, {\cal B}(B^-→ π^-μ⁺μ^-), and {\cal B}(B^-→ρ^-μ⁺μ^-) could be enhanced by a factor about
226%, 245%, and 254%, respectively, byZ' contributions. However, they are hardly to be reduced. Furthermore, the zero crossing in the normalized forward-backward asymmetry spectrum of B^- →ρ^-μ⁺μ^- decay at low dimuon mass always exists.     

Flavor Changing Top Quark Decay and Bottom-Strange Production in the Littlest Higgs Model with T-parity

Flavor changing effects on the processes t → ch, e+e- → bs, e+e-→ bsh and pp → bs in the LHT model are investigated in this paper. We calculate the one-loop level contributions from the T-parity odd mirror fermions and gauge bosons. The results show that the top quark rare decay t → ch in the LHT model can be significantly enhanced relative to that in the SM. The bs production at linear colliders in the LHT model can enhance the SM cross section a lot and reach 0.1 fb in some parameter space allowed in the experiment. But the heavy gauge boson and mirror fermion loops have small contribution to the processes pp → bs and e+e-→ bsh. So the LHT effect on e+e-→ bs might be detected at future linear colliders, while it is too small to be seen for the e+e-→ bsh and pp → bs processes at future linear colliders and LHC.     

Detection of Charged Higgs Bosons in e+e-(γγ)→tbφ- Production at the ILC

In the context of the left-right twin Higgs (LRTH) model, we have studied the charged Higgs bosons production processes e⁺e^-(γγ)→tbφ^- at the International Linear Collider (ILC). It is found that the cross sections of these two processes could reach a few fb with reasonable parameter values. With the yearly integrated luminosity of L=500 fb^-1 expected at the ILC, one could collect hundreds up to thousands of charged Higgs events via these two processes. Therefore, our researches in this paper can help us search for charged Higgs bosons, and furthermore, to test the LRTH model.     

Two Higgs Doublet Model III and Double-Lepton Polarization Asymmetries in ∧b→∧μ+μ- Decays

Using the form factors calculated both in lattice QCD and HQET, we analyze the branching ratio, double- lepton polarization asymmetries and averaged double-lepton polarization asymmetries of ∧_b→∧μ⁺μ^- decay in the 2HDM III, respectively. Combining the experimental constrains on the 2HDM III parameters, we take two set of representative parameter spaces in our calculations. For the branching ratio of ∧_b→∧μ⁺μ^- decay, considering the uncertainties of the form factors and input parameters, we find the results of both SM and 2HDM III can satisfy the current experimental data in the framework of lattice QCD, but not in HQET. Then we calculate the double-lepton polarization asymmetries P_ij and their averaged values ij>, we find the double-lepton polarization asymmetries P_LT, P_NN, and P_TT are sensitive to the 2HDM III. However, P_LN, P_NL, P_NT, and P_TN show the opposite results. The contribution of the 2HDM III to their averaged values have similar results.     

Constraints on the R-Parity Violating Couplings Using the Newest Measurement of the Decay B_s~0→μ~+μ~-

Recently, the LHCb collaboration reported the first evidence for the decay B0s→μ+μ-. A branching ratio of B(B0s→μ+μ-)=(3.2+1.51.2)×10 9is given. Using the newest data, and together with the most precise predictions of the Standard Model contributions to the decay, we derive the constraints on the combinations of the R-parity violating parameters. Our results are several orders of magnitudes stronger than the constraints in the previous literature. We also update the constraints on the relevant parameters using the upper limit ofB(B0d→μ+μ-).     

Single Production of Doubly Charged Higgs Boson via eγ Collision in Higgs Triplet Model

The Higgs triplet model (HTM) predicts the existence of a pair of doubly charged Higgs bosons H^±± . Single production of H^±± via eγcollision at the next generation e⁺e^- International Linear Collider (ILC) and the Large Hadron electron Collider (LHeC) is considered. The numerical results show that the production cross sections are very sensitive to the neutrino oscillation parameters. Their values for the inverted hierarchy mass spectrum are larger than those for the normal hierarchy mass spectrum at these two kinds of collider experiments. With reasonable values of the relevant free parameters, the possible signals of the doubly charged Higgs bosons predicted by the HTM might be detected in future ILC experiments.     

Littlest Higgs Model and Higgs Boson Associated Production with Top Quark Pair at High Energy Linear e+e- Collider

In the parameter space allowed by the electroweak precision measurement data, we consider the contributions of the new particles predicted by the littlest Higgs model to the Higgs boson associated production with top quark pair in the future high energy linear e⁺e^- collider (ILC). We find that the contributions mainly come from the new gauge bosons Z_H and B_H. For reasonable values of the free parameters, the absolute value of the relative correction parameter δσ/σ^SM can be significanly large, which might be observed in the future ILC experiment with √{S}=800 GeV.     

Production of Charged Scalars from the Littlest Higgs Model Associated with Top Quark at LHC

The littlest Higgs （LH） model is the most economical one among various little Higgs models, which predicts the existence of the charged scalars Φ^±. In this paper, we study the production of the charged Higgs boson Φ^- with single top quark via the process gb →tΦ^- at the CERN Large Hadron Collider （LHC）. The numerical results show that the production cross section is sma/ler than 0.2 pb in most of the parameters space, it is very difficult to observe the signatures of the charged scalars via the process pp → gb ＋ X → tΦ^- ＋ X at the LHC experiments. However, it can open a window to distinguish the top-pions in the TC2 model or charged Higgs in the MSSM from Φ^±.