Isospin Symmetry Breaking in the Chiral Quark Model

We discuss the isospin symmetry breaking (ISB) of the valence- and sea-quark distributions between the proton and the neutron in the framework of the chiral quark model. We assume that isospin symmetry breaking is the result of mass differences between isospin multiplets and then analyze the effects of isospin symmetry breaking on the Gottfried sum rule and the NuTeV anomaly. We show that, although both flavor asymmetry in the nucleon sea and the ISB between the proton and the neutron can lead to the violation of the Gottfried sum rule, the main contribution is from the flavor asymmetry in the framework of the chiral quark model. We also find that the correction to the NuTeV anomaly is in an opposite direction, so the NuTeV anomaly cannot be removed by isospin symmetry breaking in the chiral quark model. It is remarkable that our results of ISB for both valence- and sea-quark distributions are consistent with the Martin-Roberts-Stirling-Thorne parametrization of quark distributions.Comment: 14 latex pages, 3 figures, final version for journal publicatio

Perceived Barriers to Higher Education in STEM Among Disadvantaged Rural Students: A Case Study

This case study examined the perceptions of scholarship recipients participating in Southwest Virginia Community College’s (SWCC’s) S-STEM scholarship program which examined whether the program helped remove barriers to students’ educational goals and STEM career aspirations. The study used a focus group and a survey to elicit responses from student participants in the SWCC S-STEM program. Participants were low-income residents of rural Appalachia, and many were first generation college students. Results indicated that students in the SWCC S-STEM program experienced a wide variety of barriers to STEM educational and career success, including economic, geographic, social, and educational barriers, and that the S-STEM program assisted students in overcoming these barriers. This study may inform efforts to further increase the number of underrepresented students who enroll in and complete STEM education programs

A photoelectron imaging and quantum chemistry study of the deprotonated indole anion

Indole is an important molecular motif in many biological molecules and exists in its deprotonated anionic form in the cyan fluorescent protein, an analogue of green fluorescent protein. However, the electronic structure of the deprotonated indole anion has been relatively unexplored. Here, we use a combination of anion photoelectron velocity-map imaging measurements and quantum chemistry calculations to probe the electronic structure of the deprotonated indole anion. We report vertical detachment energies (VDEs) of 2.45 ± 0.05 eV and 3.20 ± 0.05 eV, respectively. The value for D₀ is in agreement with recent high-resolution measurements whereas the value for D₁ is a new measurement. We find that the first electronically excited singlet state of the anion, S₁(ππ*), lies above the VDE and has shape resonance character with respect to the D₀ detachment continuum and Feshbach resonance character with respect to the D₁ continuum

The Quark/Antiquark Asymmetry of the Nucleon Sea

Although the distributions of sea quarks and antiquarks generated by leading-twist QCD evolution through gluon splitting $g \rightarrow \bar q q$ are necessarily CP symmetric, the distributions of nonvalence quarks and antiquarks which are intrinsic to the nucleon's bound state wavefunction need not be identical. In this paper we investigate the sea quark/antiquark asymmetries in the nucleon wavefunction which are generated by a light-cone model of energetically-favored meson-baryon fluctuations. The model predicts striking quark/antiquark asymmetries in the momentum and helicity distributions for the down and strange contributions to the proton structure function: the intrinsic $d$ and $s$ quarks in the proton sea are predicted to be negatively polarized, whereas the intrinsic $\bar d$ and $\bar s$ antiquarks give zero contributions to the proton spin. Such a picture is supported by experimental phenomena related to the proton spin problem and the violation of the Ellis-Jaffe sum rule. The light-cone meson-baryon fluctuation model also suggests a structured momentum distribution asymmetry for strange quarks and antiquarks which could be relevant to an outstanding conflict between two different determinations of the strange quark sea in the nucleon. The model predicts an excess of intrinsic $d \bar d$ pairs over $u \bar u$ pairs, as supported by the Gottfried sum rule violation. We also predict that the intrinsic charm and anticharm helicity and momentum distributions are not identical.Comment: LaTex 18 pages, 4 figures. To obtain a copy, send e-mail to [email protected]

Parton Sum Rules and Improved Scaling Variable

The effect from quark masses and transversal motion on the Gottfried, Bjorken, and Ellis-Jaffe sum rules is examined by using a quark-parton model of nucleon structure functions based on an improved scaling variable. Its use results in corrections to the Gottfried, Bjorken, and Ellis-Jaffe sum rules. We use the Brodsky-Huang-Lepage prescription of light-cone wavefunctions to estimate the size of the corrections. We constrain our choice of parameters by the roughly known higher twist corrections to the Bjorken sum rule and find that the resulting corrections to the Gottfried and Ellis-Jaffe sum rules are relevant, though not large enough to explain the observed sum rule violations.Comment: latex, with 1 postscript figure, to be published in Phys.Lett.

Asymmetric Quark/Antiquark Hadronization in e+e- Annihilation

We point out that the fragmentation of a strange quark into nucleons versus antinucleons is not necessarily identical $D_{p/s}(z,Q^2) \neq D_{\bar p/s}(z,Q^2)$, even though the perturbative contributions from gluon splitting and evolution are $p \leftrightarrow \bar p$ symmetric. The observation of such asymmetries in the hadronization of strange and other heavy quarks can provide insight into the nonperturbative mechanisms underlying jet fragmentation in QCD.Comment: Latex, 12 page

Intrinsic quadrupole moment of the nucleon

We address the question of the intrinsic quadrupole moment Q_0 of the nucleon in various models. All models give a positive intrinsic quadrupole moment for the proton. This corresponds to a prolate deformation. We also calculate the intrinsic quadrupole moment of the Delta(1232). All our models lead to a negative intrinsic quadrupole moment of the Delta corresponding to an oblate deformation.Comment: 17 pages, 5 figure

Sigma Meson Cloud and Proton's Light Flavor Sea Quarks

We take into account the sigma meson cloud effect in the meson cloud model to calculate the distributions of light flavor sea quarks in the proton. Our calculation gives a better description of the data for $\bar{d}(x)/\bar{u}(x)$. We also provide a picture that the probability of finding a physical proton in a Fock state $|N\omega>$ is reasonable small with a smaller cutoff $\Lambda_{\omega}$.Comment: 10 latex pages, 4 figures. Version to appear in PL

CP-violating asymmetries in top-quark production and decay in e+e−e^+ e^- annihilation within the MSSM

We obtain analytic formulae for the cross section of the sequential processes of $e^+ e^- \to t \bar t$ and $t \to b l \nu$ in the laboratory frame where the dependence on triple product correlations of the type (\hat(q}_1 x \hat{q}_2 . \hat{q}_3), induced by CP violation both in the production and the decay are explicitely shown. Different observables sensitive to CP violation are defined and calculated in the Minimal Supersymmetric Standard Model (MSSM). The observables sensitive to CP violation are of the order of $10^-3$. The dependence on the masses of the supersymmetric particles is also shown.Comment: 17 pages of LateX plus five uuencoded Postscript figures, LateX file and PS-figures are also available via anonymous ftp at ftp://info.oeaw.ac.at/pub/hephy-pub/62

Real Space Renormalization Group for Langevin Dynamics in Absence of Translational Invariance

A novel exact dynamical real space renormalization group for a Langevin equation derivable from a Euclidean Gaussian action is presented. It is demonstrated rigorously that an algebraic temporal law holds for the Green function on arbitrary structures of infinite extent. In the case of fractals it is shown on specific examples that two different fixed points are found at variance with periodic structures. Connection with growth dynamics of interfaces is also discussed.Comment: 22 pages, RevTex 3.0, 5 figures available upon request from [email protected], to be published in J.Stat.Phy