arXiv subjects

Zhaohua Xiong

Publications and source records attributed to Zhaohua Xiong.

14 recordsLinked to original sources

arXiv2010

Can Non-unitary Effect be Prominent in Neutrino Oscillation Measurements?

Subject to the neutrino experiments, the mixing matrix of ordinary neutrinos can still have small violation from unitarity. We introduce a quasi-unitary matrix to interpret this violation and propose a natural scheme to parameterize it. A quasi-unitary factor $Δ_{\rm QF}$ is defined to be measured in neutrino oscillation experiments and our numerical results show that improvement of experimental precision may help us figure out the secret of neutrino mixing.

hep-ph↗

arXiv2009

Dark Matter in the Singlet Extension of MSSM: Explanation of Pamela and Implication on Higgs Phenomenology

As discussed recently by Hooper and Tait, the singlino-like dark matter in the Minimal Supersymmetric Standard Model (MSSM) extended by a singlet Higgs superfield can give a perfect explanation for both the relic density and the Pamela result through the Sommerfeld-enhanced annihilation into singlet Higgs bosons ($a$ or $h$ followed by $h->a a$) with $a$ being light enough to decay dominantly to muons or electrons. In this work we analyze the parameter space required by such a dark matter explanation and also consider the constraints from the LEP experiments. We find that although the light singlet Higgs bosons have small mixings with the Higgs doublets in the allowed parameter space, their couplings with the SM-like Higgs boson $h_{SM}$ (the lightest doublet-dominant Higgs boson) can be enhanced by the soft parameter $A_κ$ and, in order to meet the stringent LEP constraints, the $h_{SM}$ tends to decay into the singlet Higgs pairs $aa$ or $hh$ instead of $b\bar b$. So the $h_{SM}$ produced at the LHC will give a multi-muon signal, h_{SM} -> aa -> 4 muons or h_{SM} -> hh -> 4 a -> 8 muons.

hep-ph↗

arXiv2009

Residual effects of heavy sparticles in the bottom quark Yukawa coupling: a comparative study for the MSSM and NMSSM

If the sparticles are relatively heavy (a few TeV) while the Higgs sector is not so heavy ($m_A$ is not so large), the Higgs boson Yukawa couplings can harbor sizable quantum effects of sparticles and these large residual effects may play a special role in probing supersymmetry at foreseeable colliders. In this work, focusing on the supersymmetric QCD effects in the hbb coupling (h is the lightest CP-even Higgs boson), we give a comparative study for the two popular supersymmetric models: the MSSM and NMSSM. While for both models the supersymmetric QCD can leave over large residual quantum effects in hbb coupling, the NMSSM can allow for a much broader region of such effects. Since these residual effects can be over 20% for the hbb coupling (and thus over 40% for the ratio $Br(h->bb)/Br(h->ττ)), future measurements may unravel the effects of heavy sparticles or even distinguish the two models.

hep-ph↗

arXiv2008

B meson Dileptonic Decays in NMSSM with a Light CP-odd Higgs Boson

In the next-to-minimal supersymmetric model (NMSSM) a light CP-odd Higgs boson is so far allowed by current experiments, which, together with a large tan-beta, may greatly enhance the rare dileptonic decays B-> X_s l^+ l^- and B_s-> l^+ l^- gamma. We examine these decays paying special attention to the new operator allowed by the light CP-odd Higgs boson. We find that in the parameter space allowed by current experiments like LEP II and b-> s gamma, the branching ratios of these rare decays can be greatly enhanced and thus the existing experimental data on B-> X_s mu^+ mu^- can further stringently constrain the parameter space (especially the region with a super-light CP-odd Higgs boson and large tan-beta). In the surviving parameter space we give the predictions for other dileptonic decay branching ratios and also show the results for the forward-backward asymmetry.

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arXiv2003

Lepton flavor violating Z-decays in supersymmetric see-saw model

In supersymmetric see-saw model, the large flavor mixings of sleptons induce the lepton flavor violating (LFV) interactions $\ell_I \bar\ell_J V$ ($V=γ, Z$), which give rise to various LFV processes. In this work we examine the induced LFV decays $Z\to\ell_I \bar\ell_J$. Subject to the constraints from the existing neutrino oscillation data and the experimental bounds on the decays $\ell_J\to\ell_Iγ$, these LFV $Z$-decays are found to be sizable, among which the largest-rate channel $Z\to τ\barμ$ can ocuur with a branching ratio of $10^{-8}$ and may be accessible at the LHC or GiagZ experiment.

hep-ph↗

arXiv2003

Probing Topcolor-Assisted Technicolor from Top-Charm Associated Production at LHC

We propose to probe the topcolor-assisted technicolor (TC2) model from the top-charm associated productions at the LHC, which are highly suppressed in the Standard Model. Due to the flavor-changing couplings of the top quark with the scalars (top-pions and top-Higgs) in TC2 model, the top-charm associated productions can occur via both the s-channel and t-channel parton processes by exchanging a scalar field at the LHC. We examined these processes through Monte Carlo simulation and found that they can reach the observable level at the LHC in quite a large part of the parameter space of the TC2 model.

hep-ph↗

arXiv2002

SUSY-Induced Top Quark FCNC Processes at Linear Colliders

In the Minimal Supersymmetric Model (MSSM) the hitherto unconstrained flavor mixing between top-squark and charm-squark will induce the flavor-changing neutral-current (FCNC) interaction between top quark and charm quark, which then give rise to various processes at the next generation linear collider (NLC), i.e., the top-charm associated productions via $e^+ e^-$, $e^- γ$ and $γγ$ collisions as well as the top quark rare decays $t \to c V$ ($V=g$, $γ$ or $Z$). All these processes involve the same part of the parameter space of the MSSM. Through a comparative analysis for all these processes at the NLC, we found the best channel to probe such SUSY-induced top quark FCNC is the top-charm associated production in $γγ$ collision, which occurs at a much higher rate than $e^+ e^-$ or $e^- γ$ collision and may reach the detectable level for some part of the parameter space. Since the rates predicted by the Standard Model are far below the detectable level, the observation of such FCNC events would be a robust indirect evidence of SUSY.

hep-ph↗

arXiv2002

B_{s,d}--> mu^+ mu^- in technicolor model with scalars

Rare decays B_{s,d}-->mu^+ mu^- are evaluated in technicolor model with scalars. R_b is revisited to constrain the model parameter space. It is found that restriction on f/f' arising from R_b which was not considered in previous studies requires f/f' no larger than 1.9 at 95% confidence level, implying no significantly enhancement for Br(B_{s,d}-->mu^+μ^-) from neutral scalars in the model. However, the branching ratio of B_s--> mu^+ mu^- can still be enhanced by a factor of 5 relative to the standard model prediction. With the value of f/f' about 1.9, an upgraded Tevatron with an integrated luminosity 20fb^-1 will be sensitive to enhancement of B_s-->mu^+ mu^- in this model provided that neutral scalar mass m_sigma is below 580 GeV.

hep-ph↗

arXiv2002

Can MSSM with light sbottom and light gluino survive Z-peak constraints ?

In the framework of minimal supersymmetric model we examine the Z-peak constraints on the scenario of one light sbottom (2--5.5 GeV) and light gluino (12--16 GeV), which has been successfully used to explain the excess of bottom quark production in hadron collision. Such a scenario is found to be severely constrained by LEP Z-peak observables, especially by R_b, due to the large effect of gluino-sbottom loops. To account for the R_b data in this scenario, the other mass eigenstate of sbottom, i.e., the heavier one, must be lighter than 125 (195) GeV at 2-sigma (3-sigma) level, which should have been produced in association with the lighter one at LEP II and will probobaly be within the reach of Tevatron Run 2.

hep-ph↗

arXiv2001

B-meson dileptonic decays enhanced by supersymmetry with large $\tanβ$

We examined the rare decays $B\to X_s\ell^+\ell^-$ and $B_s\to\ell^+\ell^-γ$ in the minimal supersymmetric model with large $\tanβ$. Taking into account the gluino-loop and neutralino-loop effects, we found that for a large $\tanβ$ the neutral Higgs exchanging diagrams could enhance $Br(B\to X_sτ^+τ^-)$ by a factor of 5 and $Br(B_s\toτ^+τ^-γ)$ by a couple of orders in some part of supersymmetric parameter space allowed by current experiments such as $b\to sγ, B\to K^{(*)}\ell^+\ell^-$ and $B_s\to\ell^+\ell^-$. The forward-backward asymmetry and the distributions of differential branching ratios are also found to differ significantly from the standard model results. Such enhanced branching ratios reach the level of $10^{-5}$ and thus might be observable in the new generation of B experiments.

hep-ph↗

arXiv2001

Prospect of a very long baseline neutrino oscillation experiment: HIPA to Beijing

We discuss the prospects of a very long baseline neutrino oscillation experiment from HIPA to Beijing. The current understanding of neutrino oscillations, both theoretically and experimentally, are summarized. The figure of merits for interested physics measurements are defined and compared at different distances: 300 km, 700 km, 2100 km and 3000 km. We conclude that a baseline more than 2100 km is optimal. A large water cerenkov calorimeter was proposed and its performance is satisfactory from a Monte Carlo simulation study. Such a large detector can do many other measurements on cosmic-rays physics and astrophysics.

hep-ph↗

arXiv1996

Multiscale Technicolor and $b \to s γ$

Correction to the $b\rightarrow sγ$ branching ratio in the multiscale walking technicolor model (MWTCM) is examined. For the original MWTCM, the correction is too large to explain the recent CLEO data. We show that if topcolor is further introduced, the branching ratio in the topcolor assisted MWTCM can be in agreement with the CLEO data for a certain range of the parameters.

hep-ph↗

arXiv1996

A study on the rare radiative decay $B_c \to D_s^*γ$ in technicolor with scalars

Applying the perturbative QCD (PQCD), we study the process $B_c\rightarrow D_s^*γ$ in the technicolor with a massless scalar doublet model (TCMLSM) recently presented by C. D. Carone and H. Georgi; and compare the results with that estimated in the standard model (SM). There are two mechanisms which contribute to the $B_c\rightarrow D_s^* γ$ process. One proceeds through the short distance $b\rightarrow s γ$ transition, the other through weak annihilation accompanied by a photon emission. In the SM, these two processes are found to contribute with the same order of magnitude. In the TCMLSM, the modification of $B_c\rightarrow D_s^*γ$ from $π_p$ (the physical pions in this model) is small for the allowed mass of $π_p$.

hep-ph↗

arXiv1996

Study on the rare radiative decay $B_c \to D_s^*γ$ in the standard model and multiscale walking technicolor model

Applying the perturbative QCD ( PQCD ) method, we study the decay $B_c\rightarrow D_s^*γ$ in the standard model and multiscale walking technicolor model. In the SM, we find that the contribution of weak annihilation is more important than that of the electromagnetic penguin. The presence of Pseudo-Goldstone-Bosons in the MWTCM leads to a large enhancement in the rate of $B_c\rightarrow D_s^*γ$, but this model is in conflict with the branching ratio of $Z\rightarrow b\overline b$ ( $R_b$ ) and the CLEO data on the branching ratio BR ( $b\rightarrow sγ$ ). If topcolor is further introduced, the calculated results in the topcolor assisted MWTCM can be suppressed and be in agreement with the CLEO data for a certain range of the parameters.

hep-ph↗