arXiv subjects
Publications and source records attributed to Shi-Lin Zhu.
The pionic coupling constants in the decays of the $1^{-+}$ hybrid meson are calculated. The double Borel transformation is invoked and continuum contribution is subtracted. The decay widths of the processes $1^{-+}\to ρπ, f_1 π, πγ$ are around $40, 100, 0.3$ MeV respectively.
We first derive the mass sum rules for the heavy hybrid mesons to obtain the binding energy and decay constants in the leading order of HQET. The pionic couplings between the lightest $1^{-+}$ hybrid $(Q\bar q g)$ and the lowest three heavy meson doublets are calculated with the light cone QCD sum rules. With $SU_f (3)$ flavor symmetry we calculate the widths for all the possible two-body decay processes with a Goldstone boson in the final state. The total width of the $1^{-+}$ hybrid is estimated to be 300 MeV. We find the dominant decay mode of the $1^{-+}$ hybrid is $1^{-+}\to π+ 1^+$ where the $1^+$ heavy meson belongs to the $(1^+,2^+)$ doublet. Its branching ratio is about 80% so this mode can be used for the experimental search of the lowest heavy hybrid meson.
The light cone QCD sum rules are derived for $ωNN$ vector and tensor couplings simultaneously. The vacuum gluon field contribution is taken into account. Our results are $g_ω=(18\pm 8), κ_ω=(0.8\pm 0.4)$.
The radiative decays of heavy baryons and lowest three doublets of heavy mesons are studied with the light cone QCD sum rules in the leading order of heavy quark effective theory.
The light cone QCD sum rules are derived for the $K^\ast Kπ$ coupling $g_{K^\ast Kπ} $ and the $ρππ$ coupling $g_{ρππ}$. 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 $g_{K^\ast Kπ}=(8.7\pm 0.5)$ and $g_{ρππ}=(11.5\pm 0.8)$ is in good agreement with the experimental value.
We study the two point correlation function of two nucleon currents sandwiched between the vacuum and the rho meson state. The light cone QCD sum rules are derived both for $ρNN$ vector and tensor couplings simultaneously. 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 results are $g_ρ=(2.5\pm 0.2)$, $κ_ρ=(8.0\pm 2.0), in good agreement with the values used in the nuclear forces.
The light cone QCD sum rules are employed to calculate the $πN N(1535)$ coupling $g_{πN N^\ast}$. We study the two point correlation function of two nucleon currents sandwiched between the vacuum and the pion state. The contribution from the excited states and the continuum is subtracted cleanly through double Borel transformation with respect to the nucleon and N(1535) momenta, $p_1^2$, $p_2^2=(p-q)^2$. Our calculation shows that the $πN N(1535)$ coupling is strongly suppressed.
The light cone QCD sum rules are derived for the $πNN$ coupling $g_{πNN}$ and $πNN(1535)$ coupling $g_{πNN^\ast}$. The contribution from the excited states and continuum is subtracted cleanly through double Borel transformation. We first improve the original sum rule for $g_{πNN}$ and determine the value of the pion wave function at the middle point $ϕ_π(u_0 ={1\over 2})=(1.5\pm 0.2)$ at $μ=1$GeV, which is a fundamental nonperturbative quantity like the quark condensate. Our calculation shows that the $πN N(1535)$ coupling is strongly suppressed.
The couplings and decay widths of the proceses (1^+,2^+)->(0^-,1^-)+rho are studied with ligh-cone QCD sum rules in the leading order of heavy quark effective theory. These processes are employed to estimate the two pion transition widths of the (1^+,2^+) doublet through the low mass tail of the rho resonance. Our calculation shows that the two pion decay widths are much smaller than the single pion decay widths. However, B_1 and B_2^* mesons should also have significant two pion decay widths around 1.5 MeV.
We first improve the previous results on the masses of the doublets (0^+,1^+) and (1^+,2^+) with QCD sum rules up to the order of O(1/m_Q) in the framework of HQET and calculate the O(1/m_Q) correction to the decay constants f_{-,1/2} and f_{+,3/2}. With the mass matrix of the two 1^+ states, we obtain the mixing angle for the two states and the interpolating currents, which couple to only one of the two eigenstates up to the order of O(1/m_Q). Using these results we derive the light-cone sum rules for the amplitudes of the pionic decay of B_1 and B_2^* up to the order of O(1/m_Q) in HQET. The O(1/m_Q) correction to the decay amplitude of B_1 and B_2^* are found to be small. When applied to D_1 and D_2^* the theoretical results are in good agreement with experimental data though the theoretical uncertainty is sizeable for D system.
The couplings of pions with lowest three doublets (0^-,1^-), (0^+,1^+) and (1^+,2^+) of heavy mesons are studied with ligh cone QCD sum rules in the leading order of heavy quark effective theory. The ambiguity due to the presence of two distinct 1^+ states are solved.
The couplings of pions with heavy baryons g_2 (Σ^*, Σ) and g_3(Σ^*, Λ) are studied with light-cone QCD sum rules in the leading order of heavy quark effective theory. Both sum rules are stable. Our results are g_2=(1.56\pm 0.3), g_3=(0.94\pm 0.06).
We use a solvable model to perform modified dyson mapping and reveal the unphysical-state effects in the original Random Phase Approximation (RPA). We then propose a method to introduce the RPA and improve it based on a Boson mapping.
We calculate the on-shell $Σ^0$-$Λ$ mixing parameter $θ$ with the method of QCD sum rule. Our result is $θ(m^2_{Σ^0}) =(-)(0.5\pm 0.1)$MeV. The electromagnetic interaction is not included.
The method of QCD sum rules in the presence of external elctromagnetic fields is used to calculate the $Ω$ magnetic moment $μ_{Ω^-}$ and $Σ^0$-$Λ$ transition magnetic moment $μ_{Σ^0Λ}$, with the susceptibilities obtained previously from the study of octet baryon magnetic moments. The results $μ_{Ω^-}=-1.92μ_N$ and $μ_{Σ^0Λ}=1.5μ_N$ are in good agreement with the recent experimental data.
We use QCD spectral sum rules to extract the Sigma_c and Lambda_c magnetic moments. The elctromagnetic field is treated as the external field. We adopt the value of the susceptibility chi=-4.5 GeV^{-2}, which is determined from an overall analysis of the octet baryon magnetic moments. Our result for Sigma_c is in agreement with the quark model prediction, while slight deviation exists from the Lambda_c.