arXiv subjects

Qi-Shu Yan

Publications and source records attributed to Qi-Shu Yan.

At least 73 records · Page 4Linked to original sources

arXiv2009

The pseudoscalar glueball in a chiral Lagrangian model with instanton effect

We study the pseudoscalar glueball candidates in a chiral effective Lagrangian model proposed by 't hooft, motived by taking into account the instanton effects, which can describe not only the chiral symmetry breaking, but also the solution of $U_A(1)$. We study the parameter space allowed by constraints from vacuum conditions and unitary bounds. By considering two scenarios in $0^{++}$ sector, we find that parameter space which can accommodate the $0^{-+}$ sector is sensitive to the conditions in $0^{++}$ sector. From our analysis, it is found that three $η$ states, i.e. $η(1295)$, $η(1405)$, $η(1475)$, can be glueball candidates if we assume that the lightest $0^{++}$ glueball has a mass 1710 MeV. While there is no $0^{-+}$ glueball candidate found in experiments if we assume that the lightest $0^{++}$ glueball has a mass 660 MeV.

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arXiv2009

Scalar Mesons and glueballs in $Dp-Dq$ hard-wall models

We investigate light scalar mesons and glueballs in the $Dp-Dq$ hard-wall models, including $D3-Dq$, $D4-Dq$, and $D6-Dq$ systems. It is found that only in the $D4-D6$ and $D4-D8$ hard wall models, the predicted masses of the ${\bar q} q$ scalar meson $f_0$, scalar glueball are consistent with their experimental or lattice results. This indicates that $D4-D6$ and $D4-D8$ hard-wall models are favorite candidates of the realistic holographic QCD model.

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arXiv2008

Charged Higgs in the NMSSM

The charged Higgs boson decays $H^\pm\to W^\pm A_1$ and $H^\pm\to W^\pm h_i$ are studied in the framework of the next-to Minimal Supersymmetric Standard Model (NMSSM). It is found that the decay rate for H^\pm\to W^\pm A_1 can dominate both below and above the top-bottom threshold. We suggest that p p\to H^\pm A_1 is a promising discovery channel for a light charged Higgs boson in the NMSSM with small or moderate \tanβand dominant decay mode H^\pm \to W^\pm A_1 which leads to W^\pm A_1 A_1. This W^\pm A_1 A_1 signature can also arise from the Higgsstrahlung process pp\to W^\pm h_1 followed by the decay h_1\to A_1 A_1. It is shown that there exist regions of parameter space where these processes can have comparable cross sections and we suggest that their respective signals can be distinguished at the LHC by using appropriate reconstruction methods.

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arXiv2008

Confront Holographic QCD with Regge Trajectories of vectors and axial-vectors

We derive the general 5-dimension metric structure of the $Dp-Dq$ system in type II superstring theory, and demonstrate the physical meaning of the parameters characterizing the 5-dimension metric structure of the \textit{holographic} QCD model by relating them to the parameters describing Regge trajectories. By matching the spectra of vector mesons $ρ_1$ with deformed $Dp-Dq$ soft-wall model, we find that the spectra of vector mesons $ρ_1$ can be described very well in the soft-wall $D3-Dq$ model, i.e, $AdS_5$ soft-wall model. We then investigate how well the $AdS_5$ soft-wall model can describe the Regge trajectory of axial-vector mesons $a_1$. We find that the constant component of the 5-dimension mass square of axial-vector mesons plays an efficient role to realize the chiral symmetry breaking in the vacuum, and a small negative $z^4$ correction in the 5-dimension mass square is helpful to realize the chiral symmetry restoration in high excitation states.

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arXiv2008

Production and decays of the light pseudoscalar boson $η$ at the LHC in the simplest little Higgs model

In many extensions of the standard model, the Higgs sector often contains an additional pseudoscalar boson. A good example is the SU(3) simplest little Higgs model, which accommodates a light pseudoscalar boson $η$ with quite different characteristics from those in other multi-Higgs-doublet models. We study various phenomenological signatures of the $η$ at the LHC. In particular, we calculate in details both production and decays in the Drell-Yan type channel $q \bar{q} \to Z/Z' \to h η$, and in the associated production with a $t\bar t$ pair, $gg (q\bar q) \to t \bar t η$. We emphasize the $τ^+ τ^-$ decay mode of the $η$ boson when its mass is below the $b\bar b$ threshold. We show that $t\bar t η$ production is in fact large enough to give a sizable number of events while suppressing the backgrounds. We also comment on the direct gluon fusion process and the indirect decay from the heavy $T$ quark ($T \to t η$)

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arXiv2008

Charged Higgs bosons in the Next-to MSSM (NMSSM)

The charged Higgs boson decays $H^\pm\to W^\pm A_1$ and $H^\pm\to W^\pm h_i$ are studied in the framework of the next-to Minimal Supersymmetric Standard Model (NMSSM). It is found that the decay rate for $H^\pm\to W^\pm A_1$ can exceed the rates for the $τ^\pmν$ and $tb$ channels both below and above the top-bottom threshold. The dominance of $H^\pm\to W^\pm A_1$ is most readily achieved when $A_1$ has a large doublet component and small mass. We also study the production process $pp\to H^\pm A_1$ at the LHC followed by the decay $H^\pm\to W^\pm A_1$ which leads to the signature $W^\pm A_1 A_1$. We suggest that $p p\to H^\pm A_1$ is a promising discovery channel for a light charged Higgs boson in the NMSSM with small or moderate $\tanβ$ and dominant decay mode $H^\pm \to W^\pm A_1$. This $W^\pm A_1 A_1$ signature can also arise from the Higgsstrahlung process $pp\to W^\pm h_1$ followed by the decay $h_1\to A_1 A_1$. It is shown that there exist regions of parameter space where these processes can have comparable cross sections and we suggest that their respective signals can be distinguished at the LHC by using appropriate reconstruction methods.

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arXiv2007

Constraints on the electroweak chiral Lagrangian from the precision data

In the framework of the effective field theory method, we use the experimental data and the perturbative unitarity bounds to determine the values and uncertainty of all the 11 chiral coefficients ($\al_i, i=0, ..., 10$) of the standard electroweak chiral Lagrangian. Up to linear terms in $\al_i$, we provide the one-loop renormalization group equations of all the chiral coefficients, which are calculated in the Feynman-'t Hooft gauge using the modified minimal subtraction scheme. With the improved renormalization group equations to sum over the logarithmic corrections, we analyze the current experimental uncertainty of oblique correction parameters, $S(Λ)$ and $T(Λ)$. We find that, due to the large uncertainty in the triple gauge-boson coupling measurements, the parameter space of positive $S(Λ)$ for $Λ> 1$ TeV is still allowed by the current experimental data. $T(Λ)$ tends to increase with $Λ$ even in the presence of the operators that contribute to the triple and quartic gauge-boson couplings.

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arXiv2007

Roles of Higgs decay into two pseudoscalar bosons in the search of intermediate-mass Higgs Boson

The dominance of $h\to ηη$ decay mode for the intermediate mass Higgs boson is highly motivated to solve the little hierarchy problem and to ease the tension with the precision data. However, the discovery modes for $m_h \alt 150$ GeV, $h \to γγ$ and $W/Z h \to (\ellν/\ell \bar \ell) (b\bar b)$, will be substantially affected. We show that $h \to ηη\to 4b$ is complementary and we can use this decay mode to detect the intermediate Higgs boson at the LHC, via $Wh$ and $Zh$ production. Requiring at least one charged lepton and 4 $B$-tags in the final state, we can identify a clean Higgs boson signal for $m_h \alt 150$ GeV with a high significance and with a full Higgs mass reconstruction. We use the next-to-minimal supersymmetric standard model and the simplest little Higgs model for illustration.

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arXiv2007

Spectra, triple and quartic gauge couplings in a Higgsless model

Spectra, triple and quartic gauge couplings of the Higgsless model with gauge group $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ defined in warped space are explored with numerical method. We extend the equation of motions, boundary conditions and formalism of multi-gauge-boson vertices to the Hirn-Sanz scenario. By assuming the ideally delocalized fermion profile, we study the spectra of vector bosons as well as the triple and quartic gauge couplings among vector bosons. It is found that mass spectra can be greatly modified by the parameters of QCD power corrections. Meanwhile, the triple and quartic gauge couplings can deviate from the values of the standard model to at least $\pm 10%$ and can saturate the LEP2 bounds. We find the triple gauge couplings of $Z{\bar W}W$ can be $ 50 %$ smaller than the unitarity bounds. While the triple gauge couplings of ${\bar Z}WW$ is 20% smaller than the unitarity bounds, which might challenge the detection of ${\bar Z}$ via s channel at LHC if $m_{\bar Z}> 500$ GeV.

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arXiv2007

Role of h --> eta eta in Intermediate-Mass Higgs Boson Searches at the Large Hadron Collider

The dominance of $h\to ηη$ decay mode for the intermediate mass Higgs boson is highly motivated to solve the little hierarchy problem and to ease the tension with the precision data. However, the discovery modes for $m_h \alt 150$ GeV, $h \to γγ$ and $W/Z h \to (\ellν/\ell \bar \ell) (b\bar b)$, will be substantially affected. In this Letter, we show that $h \to ηη\to 4b$ is complementary and we can use this decay mode to detect the intermediate Higgs boson at the LHC, via $Wh$ and $Zh$ production. Requiring at least one charged lepton and 4 $B$-tags in the final state, we can identify a clean Higgs boson signal for $m_h \alt 150$ GeV with a high significance and with a full Higgs mass reconstruction. We use the next-to-minimal supersymmetric standard model and the simplest little Higgs model for illustration.

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arXiv2007

Constrained Electroweak Chiral Lagrangian

We update the uncertainty analysis on $S$ parameter of the electroweak chiral Lagrangian (EWCL) by including the LEP-II W pair production data. We find that experimental data still allow a positive $S^{EXP}(1\textrm{TeV})$.

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arXiv2006

Electroweak symmetry breaking and precision data

We study the impact of LEP2 constraints on the dimensionless coefficients of the electroweak chiral Lagrangian on the precision observables using the improved renormalization group equations. We find that the current uncertainty in the triple and quartic gauge boson couplings can accommodate electroweak symmetry breaking models with $S(Λ=1 \textrm{TeV}) > 0$.

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arXiv2005

A correct renormalization procedure for the electroweak chiral Lagrangian

We perform a systematic one-loop renormalization to the standard model with a nonlinearly realized Higgs boson field and the electroweak chiral Lagrangian up to $O(p^2)$ order. We find even in the nonlinear form, the Higgs model of the standard model is renormalizable in our procedure. We also examine $β$ functions of gauge couplings for the standard model and $β$ functions for anomalous couplings in the electroweak chiral Lagrangian up to $O(p^2)$ order, and find our results agree with all well-known results. Based on these observations, we conclude that our calculation procedure could be a correct one to systematically construct the divergences of the electroweak chiral Lagrangian when $O(p^4)$ operators are included.

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arXiv2005

Renormalization of the EWCL and its Application to LEP2

We perform a systematic one-loop renormalization on the electroweak chiral Lagrangian (EWCL) up to $O(p^4)$ operators and construct the renormalization group equations (RGE) for the anomalous couplings. We examine the impact of the triple gauge coupling (TGC) measurement from LEP2 to the uncertainty of the $S-T$ parameter at the $Λ=1 TeV$, and find that the uncertainty in the TGC measurements can shift $S(Λ)$ at least $3.3 σ$.

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arXiv2004

The radiative corrections of the electroweak chiral Lagrangian with renormalization group equations

We show the computational procedure of the renormalization of the electroweak chiral Lagrangian (the 4D Higgsless standard model), and provide one simplified version of its one-loop renormalization group equations, which we demonstrate its simplicity and reliability. By analyzing the solutions of the one-loop renormalization group equations of the electroweak chiral Lagrangian, we study the parameter space of the precision test parameters at ultraviolet cutoff with the current low energy experimental constraints. We find that the region of the permitted parameter space can be greatly amplified (1 to 2 order) by the radiative corrections of those undetermined anomalous couplings.

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arXiv2004

One-loop anomalous couplings and matching conditions in the nonlinear realization of the SU(2) Higgs Model

We study the renormalization of the nonlinear realization of the SU(2) Higgs model in the modified minimal subtraction renormalization scheme. We propose that the effective field method with truncated operator series is trustworthy even when the Higgs boson is relatively light. Using the technique of background field method in the coordinate space, we derive the matching conditions at tree and one loop order, both in the regions where the Higgs boson is heavy and where it is light. We obtain the complete one-loop anomalous couplings up to ${\Large O} (p^4)$ in the SU(2) Higgs model. We observe that the contribution of the gauge bosons and the Goldstone bosons to the anomalous couplings at the one-loop level is significant. By establishing the correspondence between our coordinate space calculation and the momentum space calculation that exists in the literature, we find agreement in all the matching conditions in the heavy Higgs boson limit.

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arXiv2003

The Contributions of Neutral Higgs Bosons to Charmless Nonleptonic B Decays in MSSM

We investigate the contributions of neutral Higgs bosons to nonleptonic transition $b \to q \bar{s} s, q=d, s$ under the supersymmetric context. Their effects to decay width and CP violation in corresponding exclusive decays are explored. The anomalous dimension matrices of the operators which have to be incorporated to include the contributions of neutral Higgs bosons are given. We find that when tan$β$ is large (say, 50) and neutral Higgs bosons are not too heavy (say, 100 GeV), contributions of neutral Higgs penguin can dominate electroweak penguin contributions, and for some processes, they can greatly modify both decay width and CP asymmetry.

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arXiv2002

The one loop renormalization of the effective Higgs sector and its implications

We study the one-loop renormalization the standard model with anomalous Higgs couplings ($O(p^2)$) by using the background field method, and provide the whole divergence structure at one loop level. The one-loop divergence structure indicates that, under the quantum corrections, only after taking into account the mass terms of Z bosons ($O(p^2)$) and the whole bosonic sector of the electroweak chiral Lagrangian ($O(p^4)$), can the effective Lagrangian be complete up to $O(p^4)$.

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