arXiv subjects

Chao-Shang Huang

Publications and source records attributed to Chao-Shang Huang.

At least 55 records · Page 3Linked to original sources

arXiv2001

Damped $\sin(β-α)$ of Higgs couplings and the lightest Higgs production at $γγ$ colliders in MSSM

In the decoupling limit, $M^2_{A^0} \gg M^2_Z$, the heavy CP-even, CP-odd and charged Higgs boson masses are nearly degenerate, $\sin(β-α)$ approaches 1, and the lightest CP-even Higgs boson almost displays the same properties as the Standard Model Higgs boson. But the stop and sbottom sector can change this pattern through radiative corrections. We find that there are parameter regions at small, moderate and large $\tanβ$ in MSSM under experimental constraints of $(g-2)_μ$ and $b\to sγ$, where $\sin^2(β-α)$ is damped (say below 0.8), which has a significant effect on Higgs couplings $g_{h^0VV} (V=W^\pm,Z^0)$ and $g_{h^0γγ}$. We discuss its impact on the lightest CP-even Higgs production at $γγ$ colliders.

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arXiv2001

Λ_b Lifetime from the HQET Sum Rule

The HQET sum rule analysis for the Λ_b matrix element of the four-quark operator relevant to its lifetime is reported. Our main conclusion is that the lifetime ratio τ(Λ_b)/τ(B^0) can be as low as 0.91.

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arXiv2001

g-2 in composite models of leptons

Based on the bound state description of the muon and general relativistic covariant quantum field theory, we illustrate with a simple composite model that the observed deviation of (g-2)_μcan be a demonstration of the substructure of the muon and give the constraints on the radius of the muon in different cases of light constituents and heavy constituents.

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arXiv2001

B_s \to \ell^+ \ell^- in a model II 2HDM and MSSM

In this paper we analyze the process $B_s \to \ell^+ \ell^-$ in a model II 2HDM and MSSM. All the leading terms of Wilson coefficients relevant to the process are given in the large tan$β$ limit. It is shown that the decay width for $B_s \to \ell^+ \ell^-$ depends on all parameters except $m_{A^0}$ in the 2HDM. The branching ratio of $B_s \to μ^+ μ^-$ can reach its experimental bound in some large tan$β$ regions of the parameter space in MSSM because the amplitude increases like tan$^3β$ in the regions. For l=$τ$, the branching ratio can even reach $10^{-4}$ in the regions. Therefore, the experimental measurements of leptonic decays of $B_s$ could put a constraint on the contributions of neutral Higgs bosons and consequently the parameter space in MSSM.

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arXiv2001

Search for new physics via CP violation in $B_{d,s} \to l^+ l^-

It is shown that in the approximation of $|\frac{q}{p}|$=1 the CP violation in $B^0_{d,s} \to l^+ l^-$ decays vanishes in SM. In a 2HDM with CP violating phases and MSSM the CP asymmetries depend on the parameters of models and can be as large as 40% for $B^0_d$ and 3% for $B^0_s$. An observation of CP asymmetry in the decays would unambiguously signal the existence of new physics.

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arXiv2001

CP Violation and Extra Dimensions

It is shown that the new sources of CP violation can be generated in the models with more than one extra dimensions. In the supersymmetric models on the space-time $M^4\times T^2/Z_2$, where the radius moduli have auxiliary vacuum expectation values and the supersymmetry breaking is mediated by the Kaluza-Klein states of gauge supermultiplets, we analyze the gaugino masses and trilinear couplings for two scenarios and obtain that there exist relative CP violating phases among the gaugino masses and trilinear couplings.

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arXiv2001

Renormalizaion group equations and infrared quasi fixed point behaviors of non-universal soft terms in MSSM

The renormalization group equations(RGEs) of non-universal soft supersymmetric breaking terms with CP violating phases are analyzed in this paper. We obtain the analytic solutions of RGEs by directly solving the RGEs themselves. Compared with the method of spurion expansion our approach proves to be simple and succinct, and easy to extend to the case of complex parameters. With the analytical forms of the solutions we obtained the infrared quasi fixed point behavior of soft terms are analyzed and it turns out to support the notion in scenarios with CP violating phases.

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arXiv2000

Rare decays $B\to X_sl^+l^-$ and $B\to K^{(*)}l^+l^-$ in SM and beyond

After a brief review of the inclusive and exclusive rare semileptonic decays of B mesons in the standard model (SM), an overview of recent theoretical developments in this field is given. New physics effects on various observables such as branching ratio, backward-forward asymmetry, polarization of lepton and CP violation in the decays are anlyzed in models beyond SM (supersymmetric models and two Higgs doublet models).

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arXiv2000

Constraints on the Mass and Mixing of the 4th Generation Quark From Direct CP Violation$ε^{\prime}/ε$ and Rare K Decays

We investigate the $ε^{\prime} /ε$ for $K\to ππ$ in a sequential fourth generation model. By giving the basic formulae for $ε^{\prime}/ε$ in this model, we analyze the numerical results which are dependent of $m_{t^{\prime}}$ and imaginary part of the fourth CKM factor, ${Im}V^{*}_{t^{'}s}V_{t^{'}d}$ (or $V^{*}_{t^{'}s}V_{t^{'}d}$ and the fourth generation CKM matrix phase $θ$). We find that, unlike the SM, when taking the central values of all parameters for $ε^{\prime}/ε$, the values of $ε^{\prime}/ ε$ can easily fit to the current experimental data for all values of hadronic matrix elements estimated from various approaches. Also, we show that the experimental values of $ε^{\prime}/ε$ and rare K decays can provide a strong constraint on both mass and mixing of the fourth generation quark. When taking the values of hadronic matrix elements from the lattice or 1/N expansion calculations, a large region of the up-type quark mass $m_{t^{\prime}}$ is excluded.

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arXiv2000

Exclusive semileptonic rare decays $B ->_ ($K,K^*) \ell^+ \ell^- in supersymmetric theories

The invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes $B\to K(K^*)\ell^+ \ell^-, \ell=μ, τ$ are analyzed under supersymmetric context. Special attention is paid to the effects of neutral Higgs bosons (NHBs). Our analysis shows that the branching ratio of the process $\bkm$ can be quite largely modified by the effects of neutral Higgs bosons and the forward-backward asymmetry would not vanish. For the process $\bksm$, the lepton transverse polarization is quite sensitive to the effects of NHBs, while the invariant mass spectrum, forward-backward asymmetry, and lepton longitudinal polarization are not. For both $\bkt$ and $\bkst$, the effects of NHBs are quite significant. The partial decay widths of these processes are also analyzed, and our analysis manifest that even taking into account the theoretical uncertainties in calculating weak form factors, the effects of NHBs could make SUSY shown up.

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arXiv2000

1/m_Q Corrections to the Heavy-to-Light-Vector Transitions in the HQET

Within the HQET, the heavy to light vector meson transitions are systematically analyzed to the order of 1/m_Q. Besides the four universal functions at the leading order, there are twenty-two independent universal form factors at the order of 1/m_Q. Both the semileptonic decay B->ρwhich is relevant to the |V_{ub}| extraction, and the penguin induced decay B -> K^* which is important to new physics discovering, depend on these form factors. Phenomenological implications are discussed.

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arXiv2000

The Electric Dipole Moment and CP Violation in $B \to X_s l^+ l^-$ in SUGRA Models with Nonuniversal Gaugino Masses

The constraints of electric dipole moments (EDMs) of electron and neutron on the parameter space in supergravity (SUGRA) models with nonuniversal gaugino masses are analyzed. It is shown that with a light sparticle spectrum, the sufficient cancellations in the calculation of EDMs can happen for all phases being order of one in the small tan$β$ case and all phases but $ϕ_μ$ ($|ϕ_μ| <\sim π/6$) order of one in the large tan$β$ case. This is in contrast to the case of mSUGRA in which in the parameter space where cancellations among various SUSY contributions to EDMs happen $|ϕ_μ|$ must be less than $π/10$ for small $tanβ$ and ${\cal{O}}(10^{-2})$ for large $tanβ$. Direct CP asymmetries and the T-odd polarization of lepton in $B\to X_s l^+l^-$ are investigated in the models. In the large tan$β$ case, $A_{CP}^2$ and $P_N$ for l=$μ$ ($τ$) can be enhanced by about a factor of ten (ten) and ten (three) respectively compared to those of mSUGRA.

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arXiv2000

Supersymmetric CP Violation in $B \to X_s l^+ l^-$ in Minimal Supergravity Model

Direct CP asymmetries and the CP violating normal polarization of lepton in inclusive decay B \to X_s l^+ l^- are investigated in minimal supergravity model with CP violating phases. The contributions coming from exchanging neutral Higgs bosons are included. It is shown that the direct CP violation in branching ratio, A_{CP}^1, is of {\cal{O}}(10^{-3}) for l=e, μ, τ. The CP violating normal polarization for l=μcan reach 0.5 percent when tanβis large (say, 36). For l=τand in the case of large \tanβ, the direct CP violation in backward-forward asymmetry, A_{CP}^2, can reach one percent, the normal polarization of τcan be as large as a few percent, and both are sensitive to the two CP violating phases, ϕ_μand ϕ_{A_0}, and consequently it could be possible to observe them (in particular, the normal polarization of τ) in the future B factories.

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arXiv2000

$B\to X_sτ^+τ^-$ in a CP spontaneously broken two Higgs doublet model

The differential branching ratio, CP asymmetry and lepton polarization $P_N$ for $B\to ^M X_sτ^+τ^-$ in a CP spotaneously broken two Higgs doublet model are compute d. ^M It is shown that contributions of neutral Higgs bosons to the decay are ^M quite significant when $\tanβ$ is large and $P_N$ can reach five persent.

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arXiv2000

Reanalysis of the Four-Quark Operators Relevant to Λ_b Lifetime from QCD Sum Rule

Λ_b matrix element of four-quark operator relevant to its lifetime is reanalyzed by QCD sum rule. The new ingredients introduced are that (1) more vacuum condensates are considered; (2) different quark-hadron duality is adopted; and (3) the possible deviation from the vacuum saturation assumption for the four quark condensates is considered. With κ_1=4 the related hadronic parameter r is calculated to be 3.6 \pm 0.9, and the lifetime ratio τ(Λ_b)/τ(B^0) = 0.83 \pm 0.04, which is consistent with the experimental data.

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arXiv1999

$B\to X_sτ^+τ^-$ in a CP softly broken two Higgs doublet model

The differential branching ratio, forward-backward asymmetry, CP asymmetry and lepton polarization for a B-meson to decay to strange hadronic final states and a $τ^+τ^-$ pair in a CP softly broken two Higgs doublet model are computed. It is shown that contributions of neutral Higgs bosons to the decay are quite significant when $\tanβ$ is large. And it is proposed to measure the direct CP asymmetry in back-forward asymmetry.

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arXiv1999

The $B\to X_sl^+l^-$ and $B\to X_s γ$ decays with the fourth generation

If the fourth generation fermions exist, the new quarks could influence the branching ratios of the decays of $B\to X_s γ$ and $B\to X_sl^+l^-$. We obtain two solutions of the fourth generation CKM factor $V^{*}_{t^{'}s}V_{t^{'}b}$ from the decay of $B\to X_s γ$. We use these two solutions to calculate the new contributions of the fourth generation quark to Wilson coefficients of the decay of $B\to X_sl^+l^-$. The branching ratio and the forward-backward asymmetry of the decay of $B\to X_sl^+l^-$ in the two cases are calculated. Our results are quite different from that of SM in one case, almost same in another case. If Nature chooses the formmer, the $B$ meson decays could provide a possible test of the forth generation existence.

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arXiv1999

Exclusive Rare Decays of Heavy Baryons to Light Baryons: $Λ_b \ri ghtarrow Λγ$ and $Λ_b \to Λl^{+} l^{-}$

Rare decays $Λ_b \to Λγ$ and $Λ_b \to Λl^{+} l^{-}$ (l= e, $μ$) are examined. We use QCD sum rules to calculate the hadronic matrix elements governing the decays. The $Λ$ polarization in the decays is analyzed and it is shown that the polarization parameter in $Λ_b \to Λγ$ does not depends on the values of hadronic form factors. And the energy spectrum of $Λ$ in $Λ_b \to Λl^{+} l^{-}$ is given.

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