arXiv subjects

Qi-Shu Yan

Publications and source records attributed to Qi-Shu Yan.

84 records · Page 5Linked to original sources

arXiv2002

The renormalization of the effective gauge Lagrangian with spontaneous symmetry breaking: the U(1) case

We study the renormalization of the nonlinear effective U(1) Lagrangian up to $O(p^4)$ with spontaneous symmetry breaking. The problems of the quartic divergences and of the truncation of infinite divergence tower are addressed. The renormalization group equations of the effective Lagrangian are derived, which make it possible to get the leading logarithm corrections of the heavy degree of freedom, even if the effective and full theories are matched at tree level. The method we use in the U(1) case can easily be extended to study the non-Abelian effective theories and the electroweak chiral Lagrangian.

hep-ph↗

arXiv2002

The renormalization of the effective Lagrangian with spontaneous symmetry breaking: the SU(2) case

We study the renormalization of the nonlinear effective SU(2) Lagrangian up to $O(p^4)$ with spontaneous symmetry breaking. The Stueckelberg transformation, the background field gauge, the Schwinger proper time and heat kernel method, and the covariant short distance expansion technology, guarantee the gauge covariance and incooperate the Ward indentities in our calculations. The renormalization group equations of the effective couplings are derived and analyzed. We find that the difference between the results gotten from the direct method and the renormalization group equation method can be quite large when the Higgs scalar is far below its decoupling limit.

hep-ph↗

arXiv2002

Brane fluctuation and the electroweak chiral Lagrangian

We use the external field method to study the electroweak chiral Lagrangian of the extra dimension model with brane fluctuation. Under the assumption that the contact terms between the matters of the standard model and KK excitations are heavily suppressed, we use the standard procedure to integrate out the quantum fields of KK excitations and the equation of motion to eliminate the classic fields of KK excitations. At one-loop level, we find that up to the order $O(p^4)$, due to the momentum conservation of the fifth dimension and the gauge symmetry of the zero modes, there is no constraint on the size of extra dimension. This result is consistent with the decoupling theorem. However, meaningful constraints can come from those operators in $O(p^6)$, which can contribute considerably to some anomalous vector couplings and can be accessible in the LC and LHC.

hep-ph↗

arXiv2002

Is the truncated SU(N) non-Abelian gauge theory in extra dimensions renormalizable?

In this letter we show that in the extra dimension model, contrary to the widely accepted conception, the simply truncated $ϕ^4$ and non-Abelian SU(N) Kaluza-Klein theories are not renormalizable, i.e. the tree level relations of the effective theories can not sustain the quantum corrections. The breaking down of the tree level relations of the effective theories can be traced back to several factors: the breaking of the higher dimension Lorentz symmetry and higher dimension gauge symmetry, interactions assumed in the underlying Lagrangians, and the dimension reduction and rescaling procedure.

hep-th↗

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.

hep-ph↗

arXiv2001

Radiative electroweak symmetry breaking in the extra dimensions scenarios

We study the radiative spontaneous electroweak symmetry breaking in the extra dimensions scenarios of the standard model extension proposed by Antoniadis {\it et al}, Dienes {\it et al.} and Pomarol {\it et al.}. In the framework of multi-scale effective theory when viewing from the ultraviolet cutoff scale down to the low energy scale, we find that the effects of Kaluza-Klein excitations of bosons can change the sign of the Higgs mass term of the standard model from positive to negative and therefore trigger the electroweak symmetry breaking at 1.6 (2) TeV or so when the compactification scale is assumed to be 0.8 (1.5) TeV or so. New particle contents beyond the SM or supersymmetry are not necessary for this mechanism. We conclude that in the extra dimension scenarios, the radiative correction can naturally induce the desired electroweak symmetry breaking.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv1999

Scales, Couplings Revisited and Low Energy Phenomenology in M-theory on $S^1/Z_2$

We revisit the eleven dimension Planck scale, the physical scale of the eleventh dimension, the physical scale of Calabi-Yau manifold and coupling in hidden sector in M-theory on $S^1/Z_2$. And we discuss the reasonable bound on them. Considering F-term of dilaton and moduli SUSY breaking and choosing two repersentative points which correspond to scalar quasi-massless scenario and dilaton dominant SUSY breaking scenario respectively, we analyze experimental constraints to the parameter space. The sparticle spectrum and some phenomenological predictions are also given.

hep-ph↗

arXiv1998

The Promising Process to Distinguish Supersymmetric Models with Large tan$β$ from the Standard Model: $B\to X_sμ^{+}μ^{-}$

It is shown that in supersymmetric models (SUSYMs) the large supersymmetric contributions to $B \to X_sμ^{+}μ^{-}$ come from the Feynman diagrams which consist of exchanging neutral Higgs bosons (NHBs) and the chargino-stop loop and are proportional to $m_b m_μ$tan$^3β/m_{h}^2$ when tan$β$ is large and the mass of the lightest neutral Higgs boson m$_h$ is not too large (say, less than 150 Gev). Numerical results show that the branching ratios of $B \to X_sμ^{+}μ^{-}$ can be enhanced by more than 100% compared to the standard model (SM) and the backward-forward asymmetry of lepton is significantly different from that in SM when tan$β\geq 30$.

hep-ph↗

arXiv1998

$B \to X_{s} τ^{+} τ^{-}$ in the flipped SU(5) model

We perform a detailed study of the inclusive branching ratio and the forward-backward asymmetry of the rare B decay process $B \longrightarrow X_{s} τ^{+} τ^{-}$ in the flipped SU(5) model, a predictive model which has only two free parameters, plus the sign of the higgs mixing mass $μ$, to describe mass spectrum and mixings of about 30 sparticles. In contrast to other works dealing with such a topic, our study has included the contributions of the neutral higgs bosons through penguin diagrams to this process under the context of supersymmetry. In some regions of the parameter space, due to the substantial enhancement effects coming from supersymmetry, these contributions become quite significant and could make the flavor change process $B \longrightarrow X_{s} τ^{+} τ^{-}$ a microscope to probe the regions of large tan$β$ and a window to gain an insight into new physics beyond the standard model(SM).

hep-ph↗