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Chun Liu

Publications and source records attributed to Chun Liu.

At least 181 records · Page 10Linked to original sources
arXiv2001

Stau LSP and comparison with H^+(-) phenomenology

In supersymmetric models with explicit breaking of R-parity the lightest supersymmetric particle (LSP) may be the lightest stau, $\stau_1$. Such a scenario would provide a clear sign of R-parity violating SUSY, although its phenomenology may resemble that of a charged Higgs boson, $H^\pm$. We discuss various ways of distinguishing a LSP $\stau_1$ from $H^\pm$ at future colliders, and address the case of $\stau_1$ mimicking the signal for $H^\pm$. As an example we suggest that the recent L3 signal for $H^+H^-\to qq'qq'$ and $H^+H^-\to qq'τν_τ$ could be more easily explained by a LSP $\stau_1$.

hep-ph↗
arXiv2001

A Model for Neutrino Warm Dark Matter and Neutrino Oscillations

The muon- and tau-neutrinos with the mass in the keV range, which are allowed in a low reheating temperature cosmology, can compose the warm dark matter of the universe. A model of four light neutrinos including the keV scale $ν_μ$ and $ν_τ$ is studied, which combines the seesaw mechanism and the Abelian flavor symmetry. The atmospheric neutrino anomaly is due to the $ν_μ-ν_τ$ oscillation. The solar neutrino problem is answered by the oscillation into the light sterile neutrino, where the SMA, LMA, and LOW-QVO solutions can be accommodated in our scenario.

hep-ph↗
arXiv2001

Scenario of Light Sterile Neutrinos with A Heavy Tau Neutrino in A Supersymmetric Model

Three light sterile neutrinos (ν_e^s, ν_μ^s and ν_τ^s) are introduced to accommodate all the available neutrino data: the atmospheric neutrino anomaly is explained by ν_μ-ν_μ^s oscillation with maximal mixing; the solar one is due to ν_e-ν_e^s oscillation of small angle Mikheyev-Smirnov-Wolfenstein type; the Liquid Scintillation Neutrino Detector data is from ν_e -ν_μoscillations, so that the neutrinos can be the hot component of the dark matter. The big bang nucleosynthesis constraint is satisfied by taking the tau neutrino to be 10 MeV heavy. The ν_τdecay is discussed in a model of gauge mediated supersymmetry breaking. The decay mode ν_τ\to\tilde{G}γwith \tilde{G} being the gravitino is proposed. The ν_τhas a rather long lifetime \sim 10^3-10^{13} sec. Its implication to the Gamma-ray Burst is discussed.

hep-ph↗
arXiv2000

Leading Isgur-Wise form factor of $Λ_b\toΛ_{c1}$ transition using QCD sum rules

The leading Isgur-Wise form factor $ξ(y)$ parametrizing the semileptonic transitions $Λ_b\toΛ^{1/2}_{c1}\ell\barν$ and $Λ_b\toΛ^{3/2}_{c1}\ell\barν$ is calculated by using the QCD sum rules in the framework of heavy quark effective theory, where $Λ^{1/2}_{c1}$ and $Λ^{3/2}_{c1}$ is the orbitally excited charmed baryon doublet with $J^P=(1^-/2,3^-/2)$. The interpolating currents with transverse covariant derivative are adopted for $Λ^{1/2}_{c1}$ and $Λ^{3/2}_{c1}$ in the analysis. The slope parameter $ρ^2$ in linear approximation of the Isgur-Wise function is obtained to be $ρ^2=2.01$, and the interception to be $ξ(1)=0.29$. The decay branching ratios are estimated.

hep-ph↗
arXiv2000

Excited Heavy Baryon Masses from the 1/N_c Expansion of HQET

The mass spectra of the L=1 orbitally excited heavy baryons with light quarks in both the spin-flavor symmetric and the mixed representations are studied by the $1/N_c$ expansion method in the framework of the heavy quark effective theory. The mixing effect between the baryons in the two representations is also considered. The general pattern of the spectrum is predicted which will be verified by the experiments in the near future.

hep-ph↗
arXiv2000

$1/m_Q$ and $1/N_c$ Expansions for Excited Heavy Baryons with Light Quarks in the Spin-Flavor Symmetric Representation

The mass spectrum of the L=1 orbitally excited heavy baryons with light quarks in the spin-flavor symmetric representation is studied by the $1/N_c$ expansion method in the framework of the heavy quark effective theory. The mixing effect from the baryons in the mixed representation is considered. The general pattern of the spectrum is predicted which will be verified by the experiments in the near future. The $1/m_Q$ and SU(3) corrections are also considered. Mass relations for the baryons $Λ_{c1}^{(*)}$, $Σ_{c1}^{(*)}$, $Ξ_{c1}^{(')(*)}$, and $Ω_{c1}^{(*)}$ are derived.

hep-ph↗
arXiv2000

1/m_Q Corrections to the Heavy-to-Light-Vector Transitions in the HQET

Within the HQET, the heavy to light vector meson transitions are systematically analyzed to the order of 1/m_Q. Besides the four universal functions at the leading order, there are twenty-two independent universal form factors at the order of 1/m_Q. Both the semileptonic decay B->ρwhich is relevant to the |V_{ub}| extraction, and the penguin induced decay B -> K^* which is important to new physics discovering, depend on these form factors. Phenomenological implications are discussed.

hep-ph↗
arXiv2000

Supersymmetry for Flavors

An understanding of the lepton masses within the framework of SUSY is presented. A family symmetry is introduced. Sneutrino VEV breaks this symmetry. The tau mass is due to the Higgs VEV, and muon mass purely from the sneutrino VEV. A viable model is constructed, which predicts (1-10) MeV tau-neutrino.

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

QCD sum rule analysis of excited $Λ_c$ mass parameter

The mass parameter of orbitally excited $Λ_c$ baryons is calculated by using QCD sum rule in the framework of heavy quark effective theory. Two kinds of interpolating current for the excited heavy baryons are introduced. It is obtained that $\barΛ=1.08^{+0.095}_{-0.104}$ GeV for the non-derivative current and $\barΛ=1.06^{+0.090}_{-0.107}$ GeV for the current with derivative. These results are consistent with experimental data.

hep-ph↗
arXiv1999

Topcolor-Assisted Supersymmetry

It has been known that the supersymmetric flavor changing neutral current problem can be avoided if the squarks take the following mass pattern, namely the first two generations with the same chirality are degenerate with masses around the weak scale, while the third generation is very heavy. We realize this scenario through the supersymmetric extension of a topcolor model with gauge mediated supersymmetry breaking.

hep-ph↗
arXiv1999

$Λ_b\toΣ_c^{(*)}πl{\barν}$ in the heavy quark, chiral, and large $N_c$ limits

The decay of $Λ_b\toΣ_c^{(*)}πl{\barν}$ processes are calculated in the framework of heavy baryon chiral perturbation theory with help of the $1/N_c$ expansion. The decay rate distributions over $v\cdot v^{\prime}$ where $v$ and $v^{\prime}$ are the 4-vector velocities of $Λ_b$ and $Σ_c^{(*)}$ respectively, and over the pion and lepton energies are given. The decay branching ratios amount to about $1.21(0.971)%$ for $Λ_b\toΣ_cπl{\barν}$ and $0.798(0.640)%$ for $Λ_b\toΣ_c^*πl{\barν}$ by using the baryonic Isgur-Wise function predicted by QCD sum rule (large $N_c$ QCD).

hep-ph↗
arXiv1999

Four Light Neutrinos in Singular Seesaw Mechanism with Abelian Flavor Symmetry

The four light neutrino scenario, which explains the atmosphere, solar and LSND neutrino experiments, is studied in the framework of the seesaw mechanism. By taking both the Dirac and Majorana mass matrix of neutrinos to be singular, the four neutrino mass spectrum consisting of two almost degenerate pairs separated by a mass gap $\sim 1$ eV is naturally generated. Moreover the right-handed neutrino Majorana mass can be at $\sim 10^{14}$ GeV scale unlike in the usual singular seesaw mechanism. Abelian flavor symmetry is used to produce the required neutrino mass pattern. A specific example of the flavor charge assignment is provided to show that maximal mixings between the $ν_μ-ν_τ$ and $ν_e-ν_s$ are respectively attributed to the atmosphere and solar neutrino anomalies while small mixing between two pairs to the LSND results. The implication in the other fermion masses is also discussed.

hep-ph↗
arXiv1999

Electroweak Symmetry Breaking due to Confinement

Within the framework of gauge mediated supersymmetry breaking, we consider an electroweak symmetry breaking pattern in which there is no conventional $μ$ term. The pattern is made appealing through realizing it as low energy effective description of a supersymmetric Yang-Mills theory which is of confinement. Phenomenological implications are discussed.

hep-ph↗
arXiv1998

MeV Tau Neutrino in Gauge Mediated Supersymmetry Breaking Model

A supersymmetric model which naturally accommodates MeV tau neutrino within the framework of gauge mediated supersymmetry breaking is described. The lepton number violation is originally introduced in the messenger sector of the theory. A large slepton-Higgs mixing mass and a small lepton-higgsino mixing mass are generated at one-loop. Scalar tau neutrino has non-vanishing vacuum expectation value. These result in a non-zero ν_τ mass which is in the range of (1-10) MeV.

hep-ph↗
arXiv1998

Excited Heavy Baryon Spectrum in Large N_c Heavy Quark Effective Theory

L=1 excited heavy baryon masses are analyzed by heavy quark and large N_c expansions. In heavy quark limit, mass is parameterized by Λ-bar and it is expanded further by spin-flavor breaking operators to the zeroth order of 1/N_c. Expanding coefficients will be fixed by more data on the excited baryons in the near future.

hep-ph↗
arXiv1998

Analysis of Lambda_b to Lambda_c Weak Decays in Heavy Quark Effective Theory

The Lambda_b to Lambda_c semileptonic decay is analyzed in the framework of heavy quark effective theory to the order of 1/m_c and 1/m_b. The QCD sum rule and large N_c predictions to the decay form factors are applied. It argues that the subleading baryonic Isgur-Wise function in the large N_c limit vanishes. The decay rates, distributions and asymmetry parameters are calculated numerically. Some of the nonleptonic decay modes are discussed in the end.

hep-ph↗