arXiv subjects

Chong Sheng Li

Publications and source records attributed to Chong Sheng Li.

At least 109 records · Page 6Linked to original sources

arXiv2002

Supersymmetric Electroweak Corrections to Heavier Top Squark Decay into Lighter Top Squark and Neutral Higgs Boson

We calculate the Yukawa corrections of order ${\cal O}(α_{ew}m_{t(b)}^2/m_W^2)$, ${\cal O}(α_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal O}(α_{ew}m_{t(b)}^4/m_W^4)$ to the widths of the decays $\tilde t_2\to \tilde t_1 + (h^0,H^0,A^0)$ in the Minimal Supersymmetric Standard Model, and perform a detailed numerical analysis. We also compare the results with the ones presented in an earlier literature, where the ${\cal O}(α_{s})$ SUSY-QCD corrections to the same three decay processes have been calculated. Our numerical results show that for the decays $\tilde t_2\to \tilde t_1 + h^{0}$, $\tilde t_2\to \tilde t_1 + H^{0}$, the Yukawa corrections are significant in most of the parameter range, which can reach a few ten percent, and for the decay $\tilde t_2\to\tilde t_1 + A^{0}$, the Yukawa corrections are relatively smaller, which are only a few percent. The numerical calculations also show that using the running quark masses and the running trilinear coupling $A_t$, which include the QCD, SUSY-QCD, SUSY-Electroweak effects and resume all high order ($\tanβ$)-enhanced effects, can vastly improve the convergence of the perturbation expansion. We also discuss the effects of the running of the higgsino mass parameter $μ$ on the corrections, and find that they are significant, too, especially for large $\tanβ$.

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arXiv2002

$B \to π^+ π^-, K π, K \etap$ decays and new physics effects in the general two-Higgs-doublet model: an update

In this paper, we reexamine the new physics contributions to seven well measured $B \to PP$ decays in the standard model (SM) and the general two-Higgs-doublet model (model III) and compare the theoretical predictions with the new data. Within the considered parameter space we found that: (a) the measurements of the branching ratios for $B\to π^+ π^-, K^- π^+$ and $K^0 π^+$ lead to a strong constraint on the form factor $F_0^{Bπ}(0)$: $F_0^{Bπ}(0)=0.24 \pm 0.03$; (b) the new physics enhancements to the penguin-dominated $B \to K π$ and $K \etap$ decays are significant in size, $\sim (40-65)%$ $w.r.t$ the SM predictions, and play an important role in restoring the consistency between the data and the theory.

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arXiv2002

$\etap K$ puzzle of B meson decays and new physics effects in the general two-Higgs-doublet model

we calculate the new physics contributions to seven measured decays $B \to π^+ π^-, K π$ and $ K \etap$ in the general two-Higgs-doublet model (Model III). Within the considered parameter space, we find that: (a) the CLEO/BaBar measurement of $B\to π^+ π^-$ decay prefers a small $F_0^{Bπ}(0)$: $F_0^{Bπ}(0)=0.25 \pm 0.03$; (b) the new physics enhancements to the penguin-dominated $B \to Kπ$ and $B\to K \etap$ decays are significant in size, $\sim (40-70)%$ $w.r.t$ the standard model predictions; and (c) the new physics enhancements can boost the branching ratios ${\cal B}(B \to K^+ \etap)$ and ${\cal B}(B \to K^0 \etap)$ to be consistent with the data within one standard deviation, and hence lead to a simple and plausible new physics interpretation for the $\etap K$ puzzle.

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arXiv2001

Supersymmetric Electroweak Corrections to Sbottom Decay into Lighter Stop and Charged Higgs Boson

The Yukawa corrections of order ${\cal O}(α_{ew}m_{t(b)}^2/m_W^2)$, ${\cal O}(α_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal O}(α_{ew}m_{t(b)}^4/m_W^4)$ to the width of sbottom decay into lighter stop plus charged Higgs boson are calculated in the Minimal Supersymmetric Standard Model. These corrections depend on the masses of charged Higgs boson and lighter stop, and the parameters $\tanβ$ and $μ$. For favorable parameter values, the corrections decrease or increase the decay widths significantly. Especially for high values of $\tanβ$(=30) the corrections exceed at least 10% for both $\tilde b_1$ and $\tilde b_2$ decay. But for low values of $\tanβ$(=4,10) the corrections are small and the magnitudes are less than 10%. The numerical calculations also show that using the running bottom quark mass which includes the QCD effects and resums all high order $\tanβ$-enhanced effects can improve much the convergence of the perturbation expansion.

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arXiv2001

Branching ratios and CP-violating asymmetries of $B_s \to h_1 h_2 $ decays in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to branching ratios and CP-violating asymmetries of the charmless hadronic decays $B_s \to h_1 h_2$ in the standard model and the general two-Higgs doublet models (models I, II, and III). Within the considered paramter space, we find the following. (a) In models I and II, the new physics corrections are always small in size and will be masked by other larger known theoretical uncertainties. (b) In model III, the new physics corrections to the branching ratios of those QCD penguin-dominated decays $\ov B_s \to K^0\etapp, K^+ K^{-*}, etc.$, are large in size and insensitive to the variations of $\mhp$ and $\nceff$. For tree- or electroweak penguin-dominated decay modes, however, the new physics corrections are very small in size. (c) For $\ov B_s \to K^+ K^{-*}$ and other seven decay modes, the branching ratios are at the level of $(1-3)\times 10^{-5}$ and will be measurable at the future hadron colliders with large $b$ production. (d) Among the studied thirty nine $B_s$ meson decay modes, seven of them can have a CP-violating asymmetry ${\cal A}_{CP}$ larger than 20% in magnitude. The new physics corrections are small or moderate in magnitude. (e) Because of its large and $\nceff$ stable branching ratio and CP violating asymmetry, the decay $\ov B_s \to K^+ K^{-*}$ seems to be the "best" channel to find CP violation of $B_s$ system through studies of two-body charmless decays of $B_s$ meson.

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arXiv2000

Charmless hadronic decays $B \to PP, PV, VV$ and new physics effects in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to the branching ratios of the two-body charmless hadronic decays of $B_u$ and $B_d$ mesons induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs doublet models (models I, II and III). Within the considered parameter space, we find that: (a) the new physics effects from new gluonic penguin diagrams strongly dominate over those from the new $γ$- and $Z^0$- penguin diagrams; (b) in models I and II, new physics contributions to most studied B meson decay channels are rather small in size: from -15% to 20%; (c) in model III, however, the new physics enhancements to the penguin-dominated decay modes can be significant, $\sim (30 -200)%$, and therefore are measurable in forthcoming high precision B experiments; (d) the new physics enhancements to ratios ${\cal B}(B \to K \etap)$ are significant in model III, $\sim (35 -70)%$, and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B \to K \etap $ decay rates; (e) the theoretical predictions for ${\cal B}(B \to K^+ π)$ and ${\cal B}(B \to K^0 π^+)$ in model III are still consistent with the data within $2σ$ errors; (f) the significant new physics enhancements to the branching ratios of $B \to K^0 π^0, K^* η, K^{*+} π^-, K^+ ϕ, K^{*0} ω, K^{*+} ϕ$ and $K^{*0} ϕ$ decays are helpful to improve the agreement between the data and the theoretical predictions; (g) the theoretical predictions of ${\cal B}(B \to PP, PV, VV)$ in the 2HDM's are generally consistent with experimental measurements and upper limits ($90% C.L.$)

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arXiv2000

Electroweak Corrections to the Deacy $H^+\to W^+h$ in the Minimal Supersymmetric Model

We calculate the $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ and $O(α_{ew} m_{t(b)}^4/m_W^4)$ supersymmetric electroweak corrections to the process $H^+\to W^+h$ in the Minimal Supersymmetric Model. These corrections arise from the virtual effects of the third family quaurks (top and bottom) and squarks (top-squark and bottom-squark). We find that for $m_{H^+}>200$GeV at low $\tanβ(\leq 3)$, the corrections can increase the tree-level decay widths and the branching radios more than 20% and 40%, respectively.

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arXiv2000

Supersymmetric Electroweak Corrections to $W^{\pm}H^{\mp}$ Associated Production at the CERN Large Hadron Collider

The $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ and $O(α_{ew} m_{t(b)}^4/m_W^4)$ supersymmetric electroweak corrections to the cross section for $W^{\pm}H^{\mp}$ associated production at the LHC are calculated in the minimal supersymmetric standard model. Those corrections arise from the quantum effects which are induced by the Yukawa couplings from the Higgs sector and the genuine supersymmetric electroweak couplings involving supersymmetric particles, i.e. chargino-top(bottom)-sbottom(stop) couplings, neutralino-top(bottom)-stop(sbottom) couplings and charged Higgs-stop-sbottom couplings. The Yukawa corrections can decrease the total cross sections significantly for low $\tanβ(<4)$ when $m_{H^+}<300$GeV, which exceed -12%. For high $\tanβ$ the Yukawa corrections become negligibly small. The genuine supersymmetric electroweak corrections can increase or decrease the total cross sections depending on the supersymmetric parameters, which are at most a few percent, except the region near the threshold. We also show that the genuine supersymmetric electroweak corrections depend strongly on the choice of $\tanβ$, $A_t$, $M_{\tilde Q}$ and $μ$. For large values of $A_t$, or large values of $μ$ and $\tanβ$, one can get larger corrections. The corrections can become very small, in contrast, for larger values of $M_{\tilde Q}$.

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arXiv2000

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

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.

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arXiv2000

Supersymmetric Electroweak Corrections to Charged Higgs Boson Production in Association with a Top Quark at Hadron Colliders

We calculate the $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ and $O(α_{ew} m_{t(b)}^4/m_W^4)$ supersymmetric electroweak corrections to the cross section for the charged Higgs boson production in association with a top quark at the Tevatron and the LHC. These corrections arise from the quantum effects which are induced by potentially large Yukawa couplings from the Higgs sector and the chargino-top(bottom)-sbottom(stop) couplings, neutralino-top(bottom)-stop(sbottom) couplings and charged Higgs-stop-sbottom couplings. They can decrease or increase the cross section depending on $\tanβ$ but are not very sensitive to the mass of the charged Higgs boson for high $\tanβ$. At low $\tanβ(=2)$ the corrections decrease the total cross sections significantly, which exceed -12% for $m_{H^{\pm}}$ below $300GeV$ at both the Tevatron and the LHC, but for $m_{H^{\pm}}>300GeV$ the corrections can become very small at the LHC. For high $\tanβ(=10,30)$ these corrections can decrease or increase the total cross sections, and the magnitude of the corrections are at most a few percent at both the Tevatron and the LHC.

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arXiv1999

Gluon penguin enhancements to inclusive charmless decays of b quark in the 2HDM with flavor changing couplings

We calculate the enhancements to the inclusive charmless decays of b quark, $b \to s g, s q\bar{q}, sgg$, from gluon penguin diagrams induced by the charged and neutral Higgs bosons $(H^{\pm}, h^0, H^0$, and A^0) in the Two-Higgs-Doublet Model with flavor-changing couplings. Within the considered parameter space, the new contributions from charged Higgs boson are dominant. After including the new contributions, the branching ratio $BR(b \to sg)$ (q^2 =0) can be increased form $\sim 0.2%$ in the standard model to 4.4% and 2.6% in the two-Higgs-doublet model for $m_{H^+}=100$ and 200 GeV, respectively. The new contribution to the decay mode $b \to s q \bar{q}$ with q=(u,d,s) is, however, numerically small and peaked at the lower q^2 region. The new contribution to $b \to s gg$ can also be neglected.

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arXiv1999

Yukawa Corrections to Charged Higgs Boson Production in Association with a Top Quark at Hadron Colliders

We calculate the Yukawa corrections of order $O(α_{ew}m_{t(b)}^{2}/m_{W}^{2})$ to charged Higgs boson production in association with a top quark at the Tevatron and the LHC. The corrections are not very sensitive to the mass of the charged Higgs boson and can exceed -20% for low values of $\tanβ$, where the contribution of the top quark is large, and high values of $\tanβ$ where the contribution of the bottom quark becomes large. These Yukawa corrections could be significant for charged Higgs boson discovery searches based on this production process, particularly at the LHC where the cross section is relatively large.

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arXiv1999

SUSY-QCD Effect on Top-Charm Associated Production at Linear Collider

We evaluate the contribution of SUSY-QCD to top-charm associated production at next generation linear colliders. Our results show that the production cross section of the process $e^+e^-\to t\bar c{or}\bar t c$ could be as large as 0.1 fb, which is larger than the prediction of the SM by a factor of $10^8$.

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arXiv1999

O(α_s) QCD Corrections to Spin Correlations in $e^- e^+ \to t \bar t$ process at the NLC

Using a Generic spin basis, we present a general formalism of one-loop radiative corrections to the spin correlations in the top quark pair production at the Next Linear Collider, and calculate the O(α_s) QCD corrections under the soft gluon approximation. We find that: (a) in Off-diagonal basis, the $O(α_s)$ QCD corrections to $e_L^- e^+$ ($e_R^- e^+$) scattering process increase the differential cross sections of the dominant spin component $t_{\uparrow}\bar{t}_{\downarrow}$ ($t_{\downarrow}\bar{t}_{\uparrow}$) by $\sim 30%$ and $\sim (0.1%-3%)$ depending on the scattering angle for $\sqrt{s}=400 GeV$ and 1 TeV, respectively; (b) in {Off-diagonal basis} (Helicity basis), the dominant spin component makes up 99.8% ($\sim 53%$) of the total cross section at both tree and one-loop level for $\sqrt{s}=400 GeV$, and the Off-diagonal basis therefore remains to be the optimal spin basis after the inclusion of $O(α_s)$ QCD corrections.

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arXiv1998

Leading Electroweak Corrections to the Neutral Higgs Boson Production at the Fermilab Tevatron

We calculate the leading electroweak corrections to the light neutral Higgs boson production via $q\bar q'\to WH$ at the Fermilab Tevatron in both the standard model and the minimal supersymmetric model, which arise from the top-quark and Higgs boson loop diagrams. We found that the leading electroweak corrections can exceed the QCD corrections for favorable values of the parameters in the MSSM, but such corrections are only about $-1% \sim -2%$ in the SM, which are much smaller than the QCD corrections. For the mass region of $90 < m_{h_0} < 120$ GeV, the leading electroweak corrections can reach -10% for large $\tanβ$, and these corrections may be observable at a high luminosity Tevatron; at the least, new constraints on the $\tanβ$ can be established.

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arXiv1998

Signatures of the light gluino in the top quark production

If a light gluino, with a mass of the order of GeV, exists in the minimal supersymmetric extension of the Standard Model, then it can contribute to the production rate of the top quark pairs at hadron colliders via the process gluino + gluino --> t + tbar. Because the top quark is heavy, the masses of the superpartners of the left-handed and right-handed top quarks can be very different such that a parity-violating observable can be induced at the tree level. We discuss the phenomenology of this parity violating asymmetry at the CERN Large Hadron Collider.

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arXiv1998

Squarks Loop Corrections to the Charged Higgs Boson Pair Production in Photon-Photon Collisions

We calculate the squarks one-loop corrections to the cross sections of the chared Higgs boson pair production in photon-photon collisions in the minimal supersymmetric extension of standard model(MSSM). In general, in case of the large splitting in the masses of left-top squark and the right-top squark and for $\tanβ$ near 1.5, the corrections can reduce the cross sections by more than 10% for a wide range of the charged Higgs boson mass, depending on the $e^+e^-$ center-of-mass energy. But in other cases, the corrections are at most only a few percent. Those corrections can be comparable to the $O(αm_t^2/m_W^2)$ Yukawa corrections in previous literature.

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arXiv1998

Lightest Neutral Higgs Pair Production in Photon-photon Collisions in the Minimal Supersymmetric Standard Model

The cross sections for the lightest neutral Higgs pair production at the one-loop level in photon-photon collisions are calculated in the Minimal Supersymmetric Standard Model(MSSM). We find that the contributions to the lightest Higgs boson pair production cross sections arising from the genuine supersymmetric virtual particles dominate over that arising from the virtual particles in the two-Higgs-doublet model (2HDM) if there are mixing between the right- and left-handed stops, otherwise, the contributions from ones in the 2HDM are dominant. We present the detailed numerical results of the cross sections of the process $e^+e^-\to γγ\to h_0h_0$ in both beamstrahlung and laser back scattering photon modes at the Next Linear Collider (NLC). The cross sections are typically in the range of $10^{-3}fb $ to $10^5 fb$ depending on the choice of the mass of the lightest neutral Higgs boson, $\tanβ$ and photon collision modes, especially whether there are mixing between the stops.

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