Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon-meson pairs such as $\Lambda K$ and $\Sigma K$, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-$x$ region, the perturbative contributions are more significant in the small-$x$ region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of $x$. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region $0.02 < x < 0.03$. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with NNPDF global analysis added, accepted for publication in EPJ

Charge Symmetry Violation Corrections to Determination of the Weinberg Angle in Neutrino Reactions

We show that the correction to the Paschos-Wolfenstein relation associated with charge symmetry violation in the valence quark distributions is essentially model independent. It is proportional to a ratio of quark momenta that is independent of Q^2. This result provides a natural explanation of the surprisingly good agreement found between our earlier estimates within several different models. When applied to the recent NuTeV measurement, this effect significantly reduces the discrepancy with other determinations of the Weinberg angle.Comment: 7 pages, no figures; expanded discussion of N.ne.Z correction

The flavour asymmetry and quark-antiquark asymmetry in the Σ+\Sigma^+-sea

The sea quark content of the $\Sigma^+$ baryon is investigated using light-cone baryon-meson fluctuation model suggested by Brodsky and Ma. It is found that the $\Sigma^+$ sea is flavour asymmetric (\dbar > \ubar > \sbar) and quark-antiquark asymmetric (q \not= \qbar). Our prediction for the flavour asymmetry, \dbar > \ubar > \sbar, is significantly different from the SU(3) prediction (\dbar < \ubar < \sbar), while our prediction for the $d$-\dbar asymmetry is consistent with the SU(3) prediction.Comment: RevTex, 12 pages, 4 Postscript figures. The effects from the input parton distribution evolution are discussed. Conclusions remain. Version to appear in Phys. Lett.

Non-perturbative structure of the polarized nucleon sea

We investigate the flavour and quark-antiquark structure of the polarized nucleon by calculating the parton distribution functions of the nucleon sea using the meson cloud model. We find that the SU(2) flavor symmetry in the light antiquark sea and quark-antiquark symmetry in the strange quark sea are broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar. The polarization of the strange sea is found to be positive, which is in contradiction to previous analyses. We predict a much larger quark-antiquark asymmetry in the polarized strange quark sea than that in the unpolarized strange quark sea. Our results for both polarized light quark sea and polarized strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure

Rashba interferometers: Spin-dependent single and two-electron interference

Quantum transport in semiconductor nanostructures can be described theoretically in terms of the propagation and scattering of electron probability waves. Within this approach, elements of a phase-coherent electric circuit play a role similar to quantum-optical devices that can be characterised by scattering matrices. Electronic analogues of well-know optical interferometers have been fabricated and used to study special features of charge carriers in solids. We present results from our theoretical investigation into the interplay between spin precession and quantum interference in an electronic Mach-Zehnder interferometer with spin-orbit coupling of the Rashba type. Intriguing spin-dependent transport effects occur, which can be the basis for novel spintronic devices such as a magnet-less spin-controlled field-effect transistor and a variety of single-qubit gates. Their functionality arises entirely from spin-dependent interference of each single input electron with itself. We have also studied two-electron interference effects for the spin-dependent Mach-Zehnder interferometer, obtaining analytical expressions for its two-fermion-state scattering matrix. Using this result, we consider ways to generate two-electron output states for which the Rashba spin-subband quantum number and the output-arm index are entangled. Combining spin-dependent interference in our proposed Mach-Zehnder interferometer with a projective charge measurement at the output enables entanglement generation. As our particular scheme involves tuneable spin precession, electric-field control of entanglement production can be achieved.Comment: 7 pages, 5 figures, Elsevier style, submitted to special issue of Solid State Communications, v2: replacement to rectify formatting problems, v3: minor changes + 3 references adde

Role of the Delta (1232) in DIS on polarized 3^3He and extraction of the neutron spin structure function g1n(x,Q2)g_{1}^{n}(x,Q^2)

We consider the effect of the transitions $n \to \Delta^{0}$ and $p \to \Delta^{+}$ in deep inelastic scattering on polarized $^3$He on the extraction of the neutron spin structure function $g_{1}^{n}(x,Q^2)$. Making the natural assumption that these transitions are the dominant non-nucleonic contributions to the renormalization of the axial vector coupling constant in the A=3 system, we find that the effect of $\Delta$ increases $g_{1}^{n}(x,Q^2)$ by $10 \div 40$% in the range $0.05 \le x \le 0.6$, where our considerations are applicable and most of the data for $g_{1}^{n}(x,Q^2)$ exist.Comment: 23 pages, 6 figures, revte

The influence of direct DD-meson production to the determination on the nucleon strangeness asymmetry via dimuon events in neutrino experiments

Experimentally, the production of oppositely charged dimuon events by neutrino and anti-neutrino deep inelastic scattering (DIS) is used to determine the strangeness asymmetry inside a nucleon. Here we point out that the direct production of $D$-meson in DIS may make substantial influence to the measurement of nucleon strange distributions. The direct $D$-meson production is via the heavy quark recombination (HQR) and via the light quark fragmentation from perturbative QCD (LQF-P). To see the influence precisely, we compute the direct $D$-meson productions via HQR and LQF-P quantitatively and estimate their corrections to the analysis of the strangeness asymmetry. The results show that HQR has stronger effect than LQF-P does, and the former may influence the experimental determination of the nucleon strangeness asymmetry.Comment: 9 latex pages, 7 figure

Asymmetry of Strange Sea in Nucleons

Based on the finite-temperature field theory, we evaluate the medium effects in nucleon which can induce an asymmetry between quarks and antiquarks of the strange sea. The short-distance effects determined by the weak interaction can give rise to $\delta m\equiv \Delta m_s-\Delta m_{\bar s}$ where $\Delta m_{s(\bar s)}$ is the medium-induced mass of strange quark by a few KeV at most, but the long-distance effects by strong interaction are sizable. Our numerical results show that there exists an obvious mass difference between strange and anti-strange quarks, as large as 10-100 MeV.Comment: 15 latex pages, 3 figures, to appear in PR

Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering

We investigate the possibility of identifying an explicit pionic component of the nucleon through measurements of polarized $\Delta^{++}$ baryon fragments produced in deep-inelastic leptoproduction off polarized protons, which may help to identify the physical mechanism responsible for the breaking of the Gottfried sum rule. The pion-exchange model predicts highly correlated polarizations of the $\Delta^{++}$ and target proton, in marked contrast with the competing diquark fragmentation process. Measurement of asymmetries in polarized $\Lambda$ production may also reveal the presence of a kaon cloud in the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in Zeit. Phys.

Structure functions in the bag model

In this paper we present calculations of nucleon structure functions in the three-dimensional MIT bag model. The nucleon wave functions are modified by the Peierls Yoccoz projection in order to give eigenstates of the total momentum operator. Pair creation by the probe is taken into account. Without this the quark distributions would not obey normalization requirements. The quark distributions have vanishing support for x>1. The effect of one-gluon exchange, yielding the N−Δ mass splitting, is incorporated. This has significant effects on the du ratio as well as the spin-dependent g1(x) of the neutron. Finally, the results are compared to data after allowing for perturbative QCD evolution.A. W. Schreiber, A. I. Signal, and A. W. Thoma