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Shi-Lin Zhu

Publications and source records attributed to Shi-Lin Zhu.

At least 307 records · Page 17Linked to original sources
arXiv2002

What Do We Know About the Strange Magnetic Radius?

We analyze the q^2-dependence of the strange magnetic form factor, \GMS(q^2), using heavy baryon chiral perturbation theory (HBChPT) and dispersion relations. We find that in HBChPT a significant cancellation occurs between the O(p^2) and O(p^3) loop contributions. Consequently, the slope of \GMS at the origin displays an enhanced sensitivity to an unknown O(p^3) low-energy constant. Using dispersion theory, we estimate the magnitude of this constant, show that it may have a natural size, and conclude that the low-q^2 behavior of \GMS could be dominated by nonperturbative physics. We also discuss the implications for the interpretation of parity-violating electron scattering measurements used to measure \GMS(q^2).

hep-ph↗
arXiv2002

Recoil Order Chiral Corrections to Baryon Octet Axial Currents and Large $N_c$ QCD

We compute the chiral corrections to octet baryon axial currents through ${\cal O}(p^3)$ in heavy baryon chiral perturbation theory, including both octet and decuplet baryon intermediate states. We include the latter in a consistent way by using the small scale expansion. We find that, in contrast to the situation at ${\cal O}(p^2)$, there exist no cancellations between octet and decuplet contributions at ${\cal O}(p^3)$. Consequently, the ${\cal O}(p^3)$ corrections spoil the expected scaling behavior of the chiral expansion. We discuss this result in terms of the $1/N_c$ expansion. We also consider the implications for determination of the strange quark contribution to the nucleon spin from polarized deep inelastic scattering data.

hep-ph↗
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.

hep-ph↗
arXiv2001

Parity Violating Photoproduction of $π^\pm$ on the $Δ$ Resonance

We analyze the real photon asymmetry $A^\pm_γ$ for the parity violating (PV) $π^\pm$ production on the $Δ$ resonance via the reactions ${\vec γ} + p \to Δ^+ \to π^+ + n$ and ${\vec γ} + d \to Δ^0 + p \to π^- + p + p$. This asymmetry is nonvanishing due to a PV $γN Δ$ coupling constant, $d^\pm_Δ$. We argue that an experimental determination of this coupling would be of interest for hadron dynamics, possibly shedding light on the S-wave/P-wave puzzle in the hyperon nonleptonic decays and the violation of Hara's theorem in weak radiative hyperon decays.

hep-ph↗
arXiv2001

Electroweak Radiative Corrections to Parity-Violating Electroexcitation of the $Δ$

We analyze the degree to which parity-violating (PV) electroexcitation of the $Δ(1232)$ resonance may be used to extract the weak neutral axial vector transition form factors. We find that the axial vector electroweak radiative corrections are large and theoretically uncertain, thereby modifying the nominal interpretation of the PV asymmetry in terms of the weak neutral form factors. We also show that, in contrast to the situation for elastic electron scattering, the axial $N\toΔ$ PV asymmetry does not vanish at the photon point as a consequence of a new term entering the radiative corrections. We argue that an experimental determination of these radiative corrections would be of interest for hadron structure theory, possibly shedding light on the violation of Hara's theorem in weak, radiative hyperon decays.

hep-ph↗
arXiv2001

Subleading corrections to parity violating pion photoproduction

We compute the photon asymmetry $B_γ$ for near threshold parity violating (PV) pion photoproduction through sub-leading order. We show that sub-leading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to $B_γ$ -- obtained from the PV $γ$-decay of $^{18}$F -- suggest that the impact of the subleading contributions may be more significant than expected from naturalness argumen

hep-ph↗
arXiv2000

$πΔΔ$ coupling constant

We calculate the $πΔΔ$ coupling $g_{π^0Δ^{++}Δ^{++}}$ using light cone QCD sum rule. Our result is $g_{π^0Δ^{++}Δ^{++}}=(11.8\pm 2.0)$.

nucl-th↗
arXiv2000

Excited heavy baryon masses in HQET QCD sum rules

We construct the interpolating currents for the fourteen p-wave excited heavy baryons in the framework of heavy quark effective theory (HQET). At the leading order in the 1/m_Q expansion these interpolating currents do not mix different states with the same J^P with each other. We use QCD sum rule to calculate the masses of the p-wave excited J=1/2 spin doublet heavy baryons in the m_Q~infinity limit. We discuss some implications of our results.

hep-ph↗
arXiv2000

Recoil Order Chiral Corrections to Baryon Octet Axial Currents

We calculate chiral corrections to the octet axial currents through ${\cal O}(p^3)$ using baryon chiral perturbation theory (BCPT). The relativistic BCPT framework allows one to sum an infinite series of recoil corrections at a given order in the chiral expansion. We also include SU(3)-breaking operators occuring at ${\cal O}(p^2)$ not previously considered. We determine the corresponding low-energy constants (LEC's) from hyperon semileptonic decay data using a variety of infrared regularization schemes. We find that the chiral expansion of the axial currents does not display the proper convergence behavior, regardless of which scheme is chosen. We explore the implications of our analysis for determinations of the strange quark contribution to the nucleon spin, $Δs$.

hep-ph↗
arXiv2000

Octet Baryon Charge Radii, Chiral Symmetry and Decuplet Intermediate States

We compute the octet baryon charge radii to O(1/Heavy^3) in heavy baryon chiral perturbation theory. We examine the effect of including the decuplet of spin-3/2 baryons explicitly. We find that it does no t improve the level of agreement between the HBchiPT and experimental values for the Sigma^- charge radius.

hep-ph↗
arXiv2000

Chiral Symmetry and the Parity-Violating $NNπ$ Yukawa Coupling

We construct the complete SU(2) parity-violating (PV) $π, N, Δ$ interaction Lagrangian with one derivative, and calculate the chiral corrections to the PV Yukawa $NNπ$ coupling constant $h_π$ through ${\cal O}(1/Λ_χ^3)$ in the leading order of heavy baryon expansion. We discuss the relationship between the renormalized $\hpi$, the measured value of $\hpi$, and the corresponding quantity calculated microscopically from the Standard Model four-quark PV interaction.

hep-ph↗
arXiv2000

The $ηNN$ coupling constant

We derive the light cone QCD sum rule for the $ηNN$ coupling constant $g_{ηNN} $. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with respect to the two external momenta, $p_1^2$, $p_2^2=(p-q)^2$. Our result is $α_{ηNN}=(0.3\pm 0.15)$, which favors small values used in literatures.

nucl-th↗
arXiv2000

The Nucleon Anapole Moment and Parity-Violating ep Scattering

Parity-violating (PV) interactions among quarks in the nucleon induce a PV $γNN$ coupling, or anapole moment (AM). We compute electroweak gauge-independent contributions to the AM through ${\cal O}(1/\lamchis)$ in chiral perturbation theory. We estimate short-distance PV effects using resonance saturation. The AM contributions to PV electron-proton scattering slightly enhance the axial vector radiative corrections, R_A^p, over the scale implied by the Standard Model when weak quark-quark interactions are neglected. We estimate the theoretical uncertainty associated with the AM contributions to R_A^p to be large, and discuss the implications for the interpretation PV of ep scattering.

hep-ph↗
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.

hep-ph↗
arXiv2000

Strong and electromagnetic decays of p-wave heavy baryons $Λ_{c1}, Λ^*_{c1}$

We first calculate the binding energy, the pionic and electromagnetic couping constants of the lowest lying p-wave heavy baryon doublet $Λ_{c1}$, $Λ_{c1}^*$ in the leading order of the heavy quark expansion. Then we calculate the two-body decay widths with these couplings and compare our results with other approaches. Our results are $Γ(Λ_{c1}\to Σ_c π, Σ_c γ, Σ^*_c γ) =2.7, 0.011, 0.001$ MeV and $Γ(Λ^*_{c1}\to Σ_c π, Σ_c γ, Σ^*_c γ, Λ_{c1} γ) =33, 5, 6, 0.014$ keV respectively. We find $Λ_{c1}, Λ^*_{c1}\to Λ_c γ$ is strictly forbidden in the leading order of the heavy quark expansion. At the order of ${\cal O} (1/m_c)$ their widths are $36, 48$ keV respectively.

hep-ph↗
arXiv1999

Hybrid quarkonium masses up to the order of ${\cal O}(1/m_Q)$

We have calculated the binding energy of the hybrid quarkonium up to the order of ${\cal O}(1/m_Q)$ and found their decay constants scale like $m_Q^{5/4}$ as $m_Q\to \infty$. The $0^{--}$ and $0^{++}$ hybrid quarkonium is exactly degenerate in the limit of $m_Q\to\infty$ while the ${\cal O}(1/m_Q)$ correction renders the $0^{--}$ mass lower than that for $0^{++}$. The $1^{-+}$ and $1^{+-}$ hybrid is nearly degenerate and lies 0.7 GeV lower than $0^{--}$. With $m_b=4.8$GeV the mass of $1^{-+}$ $b\bar b g$ state is $(10.75\pm 0.10)$, which is the lightest exotic hybrid quarkonium.

hep-ph↗