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Chun Liu

Publications and source records attributed to Chun Liu.

191 records · Page 11Linked to original sources
arXiv1998

Four-quark Operators Relevant to B Meson Lifetimes from QCD Sum Rules

At the order of 1/m_b^3, the B meson lifetimes are controlled by the hadronic matrix elements of some four-quark operators. The nonfactorizable magnitudes of these four-quark operator matrix elements are analyzed by QCD sum rules in the framework of heavy quark effective theory. The vacuum saturation for color-singlet four-quark operators is justified at hadronic scale, and the nonfactorizable effect is at a few percent level. However for color-octet four-quark operators, the vacuum saturation is violated sizably that the nonfactorizable effect cannot be neglected for the B meson lifetimes. The implication to the extraction of some of the parameters from B decays is discussed. The B meson lifetime ratio is predicted as τ(B^-)/τ(B^0)=1.09\pm 0.02. However, the experimental result of the lifetime ratio τ(Λ_b)/τ(B^0) still cannot be explained.

hep-ph↗
arXiv1998

Excited Heavy Mesons from QCD Sum Rules

Orbitally excited L=1 charm mesons are studied by QCD sum rules in the framework of heavy quark effective theory. The meson masses and the strong decay widths are obtained. This talk is based on our works of refs. 1 and 2 collaborated with Y.B. Dai, C.S. Huang, M.Q. Huang and H.Y. Jin.

hep-ph↗
arXiv1997

1/N_c Expansion of the Heavy Baryon Isgur-Wise Functions

The 1/N_c expansion of the heavy baryon Isgur-Wise functions is discussed. Because of the contracted SU(2N_f) light quark spin-flavor symmetry, the universality relations among the Isgur-Wise functions of Λ_b to Λ_c and Σ_b^{(*)} to Σ_c^{(*)} are valid up to the order of 1/N_c^2.

hep-ph↗
arXiv1997

Some Remarks on the Baryon-Meson Couplings in the 1/N_c Expansion

The original results for the baryon-pion couplings in the large $N_c$ QCD can be understood in a simpler way in the Hartree-Fock picture. The large $N_c$ relation and its $1/N_c$ correction between the heavy baryon-meson coupling and the light baryon-meson coupling are emphasized. Application to the baryon-$ρ$ meson interactions is straightforward. The implications of recent experimental result for the strong coupling constants of the heavy baryon chiral lagrangian are discussed.

hep-ph↗
arXiv1997

Phenomenology of A Supersymmetric Model for Fermion Mass Hierarchy

Some phenomenological aspects of a supersymmetric model for fermion mass hierarchy proposed previously are discussed. It is required that the lepton universality violation is near to its current experimental bound. The lepton number violation decay modes $τ\to 2eμ$ and $3μ$ maybe observable in the near future. The Majorana mass of electron-neutrino is predicted to be about 0.1 eV. The fine-tuning problem is discussed.

hep-ph↗
arXiv1996

Heavy Baryon Masses in Large N_c HQET

We argue that in the large N_c HQET, the masses of the s-wave low-spin heavy baryons equal to the heavy quark mass plus proton mass approximately. To the subleading order, the heavy baryon mass 1/N_c expansion not only has the same form, but also has the same coefficients as that of the light baryon. Based on this, numerical analysis is made.

hep-ph↗
arXiv1996

QCD Sum Rules for Masses of Excited Heavy Mesons

The masses of excited heavy mesons are studied with sum rules in the heavy quark effective theory. A set of interpolating currents creating (annihilating) excited heavy mesons with arbitrary spin and parity are proposed and their properties are discussed. Numerical results at the leading order of the {\cal O}(1/m_Q) expansion are obtained for the lowest doublets (0^+, 1^+) and (1^+, 2^+).

hep-ph↗
arXiv1996

QCD Sum Rule Analysis for the Λ_b to Λ_c Semileptonic Decay

The 1/m_c and 1/m_b corrections to the Λ_b to Λ_c semi- leptonic decay are analyzed by QCD sum rules. Within the framework of heavy quark effective theory,the subleading baryonic Isgur-Wise func- tion of Λ_b to Λ_c has been calculated. It is shown that the corrections due to the 1/m Lagrangian insertion are negligibly small. The sizable 1/m_Q effect to the decay lies only in the weak current. The decay spectrum and the branching ratio are given.

hep-ph↗
arXiv1995

Quark Mass Hierarchy and CP Violation in Low Energy Supersymmetry

A pattern of quark mass hierarchy and CP violation within the framework of low energy supersymmetry is described. By assuming some discrete symmetry among the three families, the quarks of the third family obtain masses at tree level. The second family obtains masses radiatively at one-loop level due to the soft breaking of the family symmetry. At this level, the first family remains massless by some degeneracy conditions of the squarks. As a result of R-parity violation, the sneutrino vacuum expectation values are nonvanishing. CP violation occurs through the superweak sneutrino exchange. This picture is consistent with the experiments on the flavor changing neutral current.

hep-ph↗
arXiv1995

Cyclic Family Symmetry and Lepton Hierarchy in Supersymmetry

A cyclic symmetry among the left-handed doublets of the three families is proposed. This symmetry can naturally result in a realistic hierarchical pattern of the fermion masses within the framework of supersymmetry with nonvanishing sneutrino vacuum expectation values.

hep-ph↗