arXiv subjects

Xuemin Jin

Publications and source records attributed to Xuemin Jin.

28 records · Page 2Linked to original sources

arXiv1995

New QCD Sum Rules for In-Medium Nucleons

New QCD sum rules for nucleons in nuclear matter are derived from a mixed correlation function of spin-1/2 and spin-3/2 interpolating fields. These sum rules allow a determination of the scalar self-energy of the nucleon independent of the poorly known four-quark condensates. An analysis of these new sum rules in concert with previous nucleon sum rules from spin-1/2 interpolators indicates consistency with the expectations of relativistic mean-field phenomenology. We find $M^* = 0.68 \pm 0.08$ GeV and $Σ_v = 0.31 \pm 0.06$ GeV at nuclear matter saturation density.

nucl-th↗

arXiv1995

Valid QCD Sum Rules for Vector Mesons in Nuclear Matter

QCD sum rules for vector mesons (rho, omega, phi) in nuclear matter are reexamined with an emphasis on the reliability of various sum rules. Monitoring the continuum contribution and the convergence of the operator product expansion plays a crucial role in determining the validity of a sum rule. The uncertainties arising from less than precise knowledge of the condensate values and other input parameters are analyzed via a Monte-Carlo error analysis. Our analysis leaves no doubt that vector-meson masses decrease with increasing density. This resolves the current debate over the behavior of the vector-meson masses and the sum rules to be used in extracting vector meson properties in nuclear matter. We find a ratio of rho-meson masses of $m_{ρ^*}/m_ρ= 0.78\pm0.08$ at nuclear matter saturation density.

nucl-th↗

arXiv1995

Baryon QCD sum rules in an external isovector-scalar field and baryon isospin mass splittings

Within the QCD sum-rule approach in an external field, we calculate the baryon matrix element of isovector-scalar current, $H_{\rm B}=\langle B|\overline{u}u- \overline{d}d|B\rangle/2M_{\rm B}$, for octet baryons, which appears in the response of the correlator of baryon interpolating fields to a constant isovector-scalar external field. The sum rules are obtained for a general baryon interpolating field with an appropriate form for the phenomenological ansatz of the spectral density. The key phenomenological input is the response of the quark condensates to the external field. To first order in the quark mass difference $δm=m_d-m_u$, the non-electromagnetic part of the baryon isospin mass splitting is given by the product of $δm$ and $H_{\rm B}$. Therefore, QCD sum-rule calculation of $H_{\rm B}$ leads to an estimate of the octet baryon isospin mass splittings. The resulting values are comparable to the experimental values; however, the sum-rule predictions for $H_{\rm B}$ are sensitive to the values of the response of the quark condensates to the external source, which are not well determined.

hep-ph↗

arXiv1995

QCD Sum Rules and Applications to Nuclear Physics

Applications of QCD sum-rule methods to the physics of nuclei are reviewed, with an emphasis on calculations of baryon self-energies in infinite nuclear matter. The sum-rule approach relates spectral properties of hadrons propagating in the finite-density medium, such as optical potentials for quasinucleons, to matrix elements of QCD composite operators (condensates). The vacuum formalism for QCD sum rules is generalized to finite density, and the strategy and implementation of the approach is discussed. Predictions for baryon self-energies are compared to those suggested by relativistic nuclear physics phenomenology. Sum rules for vector mesons in dense nuclear matter are also considered.

hep-ph↗

arXiv1994

QCD sum rules for $Δ$ isobar in nuclear matter

The self-energies of $Δ$ isobar propagating in nuclear matter are calculated using the finite-density QCD sum-rule methods. The calculations show that the Lorentz vector self-energy for the $Δ$ is significantly smaller than the nucleon vector self-energy. The magnitude of the $Δ$ scalar self-energy is larger than the corresponding value for the nucleon, which suggests a strong attractive net self-energy for the $Δ$; however, the prediction for the scalar self-energy is very sensitive to the density dependence of certain in-medium four-quark condensate. Phenomenological implications for the couplings of the $Δ$ to the nuclear scalar and vector fields are briefly discussed.

hep-ph↗

arXiv1994

Stranger in the Light: The Strange Vector Form Factors of the Nucleon

A model combining vector meson dominance, $ω- ϕ$ mixing and a kaon cloud contribution is used to estimate the strangeness vector form factors of the nucleon in the momentum range of the planned measurements at MIT-Bates and CEBAF. We compare our results with some other theoretical estimates and discuss the nucleon strangeness radius in models based on dynamically dressed, extended constituent quarks. For a quantitative estimate in the latter framework we use the Nambu-Jona-Lasinio model.

hep-ph↗

arXiv1994

Constraints on the Fiite-Density Spectral Densities of Vector Channel

Sum rules for the variation of finite-density spectral density of vector channel with baryon density are derived based on dispersion relations and the operator product expansion. These sum rules may serve as constraints on the phenomenological models for the finite-density spectral densities used in the approaches motivated from QCD. Applying these sum rules to the rho meson in nuclear medium with a simple pole-plus-continuum ansatz for the spectral densities, we found that the qualitative features of the QCD sum-rule predictions for the spectral parameters are consistent with these sum rules; however, the quantitative QCD sum-rule results violate the sum rules to certain degree.

hep-ph↗

arXiv1994

Relations among Zero Momentum Correlators for Heavy-Light Systems in QCD

Relations connecting various zero momentum correlators of interpolating fields for pseudoscalar and scalar channel, containing one heavy and one light quark field, are derived from the Euclidean space formulation of the QCD functional integral. These relations may serve as constraints on the phenomenological models or approaches motivated from QCD, and suggest a method to extract the chiral quark condensates. It is also found that the correlator for pseudoscalar channel differs from that for scalar channel even in the large heavy quark mass limit.

hep-ph↗

arXiv1994

QCD Sum Rules for $Σ$ Hyperons in Nuclear Matter

Within finite-density QCD sum-rule approach we investigate the self-energies of $Σ$ hyperons propagating in nuclear matter from a correlator of $Σ$ interpolating fields evaluated in the nuclear matter ground state. We find that the Lorentz vector self-energy of the $Σ$ is similar to the nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the $Σ$ is also close to the corresponding value for nucleon; however, this prediction is sensitive to the strangeness content of the nucleon and to the assumed density dependence of certain four-quark condensate. The scalar and vector self-energies tend to cancel, but not completely. The implications for the couplings of $Σ$ to the scalar and vector mesons in nuclear matter and for the $Σ$ spin-orbit force in a finite nucleus are discussed.

hep-ph↗

arXiv1994

Disoriented Chiral Condensates and Quantum Mechanical Isospin Correlation

Classical considerations suggest that the probability distribution $P(R)$, where $R$ is the ratio of neutral pions to total pions emitted from a disoriented chiral condensate (which has been hypothesized to form in heavy ion reactions) is $R^{-1/2}/2$. Quantum mechanical isospin correlations between the condensate and the remainder of the system can alter this. Moments of the P(R) distribution can be expressed in terms of expectation values of $(I^2/N^2)^m$ where $I$ is the isospin carried by the condensate, $N$ is the number of pions emitted and m is an arbitrary integer. We find that the probability distribution is very similar to the classical distribution for $0.1 < R < 0.9$ unless the isospin carried by the condensate is very large.

hep-ph↗