Empirical transverse charge densities in the deuteron

Using the recent empirical information on the deuteron electromagnetic form factors we map out the transverse charge density in the deuteron as viewed from a light front moving towards the deuteron. The charge densities for a transversely polarized deuteron are characterized by monopole, dipole and quadrupole patterns.     

Electromagnetic nucleon-to-delta transition in chiral effective-field theory

We perform a relativistic chiral effective-field theory calculation of pion electroproduction off the nucleon (e- N --> e- N(pi)) in the delta(1232)-resonance region. After fixing the three low-energy constants, corresponding to the magnetic (M1), electric (E2), and Coulomb (C2) gammaNdelta couplings, our calculation provides a prediction for the momentum transfer and pion-mass dependence of the gammaNdelta form factors. The prediction for the pion-mass dependence resolves the discrepancy between the recent lattice QCD results and the experimental value for the "C2/M1 ratio" at low Q2.     

Charge transition densities for the excitation and nucleon decay of the giant dipole resonance in16O

Predictions on charge transition densities in¹⁶O for the excitation of the giant dipole resonance are given within a continuum self-consistent RPA-SK3 theory. The nuclear states are allowed to decay with proton or neutron ejection. The discussion is focused on the analysis of the radial behaviour of transition densities in terms of their microscopic structure. The rôle of RPA ground state correlations is clarified. The surface properties of resonant nuclear states extracted from photonuclear and (e, e′ x) reactions at low momentum transfer are confronted with the full radial dependence of the resonant structure shown in charge transition densities.     

A new evaluation of polarized parton densities in the nucleon

We present a new leading and next-to-leading QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed. Received: 23 November 2001 / Revised version: 10 January 2002 Published online: 22 February 2002     

Calculation of charge and transition charge densities in some even mass Ge isotopes from microscopic nuclear structure wave functions

Microscopic nuclear structure wave functions obtained within the EXCITED FED VAMPIR approach are used to calculate the charge densities for the ground states as well as the transition charge densities for the transitions from the ground to the first and second 2⁺ states in some doubly even Ge isotopes. The results are compared with the data extracted from elastic and inelastic electron scattering experiments. Except for the heavier isotopes, where the calculations fail to yield enough collectivity, rather nice agreement is obtained. This result strongly supports the theoretically predicted shape coexisting structures in the low spin states of the nuclei in this mass region.     

Spin densities in the transverse plane and generalized transversity distributions

We show how generalized quark distributions in the nucleon describe the density of polarized quarks in the impact parameter plane, both for longitudinal and transverse polarization of the quark and the nucleon. This density representation entails positivity bounds including chiral-odd distributions, which tighten the known bounds in the chiral-even sector. Using the quark equations of motion, we derive relations between the moments of chiral-odd generalized parton distributions of twist two and twist three. We exhibit the analogy between polarized quark distributions in impact parameter space and transverse momentum dependent distribution functions.Received: 25 April 2005, Published online: 27 July 2005     

On the calculation of charge densities in crystals

A general method is given for determining the spatial charge distribution of a filled electronic band using Bloch state charge distributions determined at very few k points. Formulae are given for several important cases.     

Meson polarized distribution function and mass dependence of the nucleon parton densities

The polarized distribution functions of mesons,including pion,kaon and eta,using the proton structure function,are calculated.We are looking for a relationship between the polarized distribution of mesons and the polarized structure of nucleons.We show that the meson polarized parton distributions leads to zero total spin for the concerned mesons,considering the orbital angular momentum of quarks and gluons inside the meson.Two separate Monte Carlo algorithms are applied to compute the polarized parton distributions of the kaon.Via the mass dependence of quark distributions,the distribution function of the eta meson is obtained.A new method by which the polarized sea quark distributions of protons are evolved separately-which cannot be performed easily using the standard solution of DGLAP equations-is introduced.The mass dependence of these distributions is obtained,using the renormalization group equation which makes their evolutions more precise.Comparison between the evolved distributions and the available experimental data validates the suggested solutions for separated evolutions.     

Meson polarized distribution function and mass dependence of the nucleon parton densities

The polarized distribution functions of mesons, including pion, kaon and eta, using the proton structure function, are calculated. We are looking for a relationship between the polarized distribution of mesons and the polarized structure of nucleons. We show that the meson polarized parton distributions leads to zero total spin for the concerned mesons, considering the orbital angular momentum of quarks and gluons inside the meson. Two separate Monte Carlo algorithms are applied to compute the polarized parton distributions of the kaon. Via the mass dependence of quark distributions, the distribution function of the eta meson is obtained. A new method by which the polarized sea quark distributions of protons are evolved separately which cannot be performed easily using the standard solution of DGLAP equations - is introduced. The mass dependence of these distributions is obtained, using the renormalization group equation which makes their evolutions more precise. Comparison between the evolved distributions and the available experimental data validates the suggested solutions for separated evolutions.     

Charge densities and charge noise in mesoscopic conductors

We introduce a hierarchy of density of states to characterize the charge distribution in a mesoscopic conductor. At the bottom of this hierarchy are the partial density of states which represent the contribution to the local density of states if both the incident and the out-going scattering channel is prescribed. The partial density of states play a prominent role in measurements with a scanning tunneling microscope on multiprobe conductors in the presence of current flow. The partial density of states determine the degree of dephasing generated by a weakly coupled voltage probe. In addition the partial density of states determine the frequency-dependent response of mesoscopic conductors in the presence of slowly oscillating voltages applied to the contacts of the sample. The partial density of states permit the formulation of a Friedel sum rule which can be applied locally. We introduce the off-diagonal elements of the partial density of states matrix to describe charge fluctuation processes. This generalization leads to a local Wigner-Smith life-time matrix.     

Collective transition densities in neutron-rich nuclei

Quadrupole transition densities in neutron-rich nuclei in the vicinity of the neutron drip-line are calculated in the framework of the Random Phase Approximation. The continuum is treated by expansion in oscillator functions. We focus on the states which contribute to the usual Giant Quadrupole Resonance, and not on the low-lying strength which is also expected in such nuclei and whose collective character is still under debate. We find that, due to the large neutron skin in these nuclei, the isoscalar and isovector modes are in general strongly mixed. We further show that the transition densities corresponding to the GQR states can be reasonably well described by the collective model in terms of in phase and out of phase oscillations of neutron and proton densities which have different radii.     

Signatures of chiral dynamics in the nucleon to Delta transition⋆

Utilizing the methods of chiral effective field theory we present an analysis of the electromagnetic NΔ-transition current in the framework of the non-relativistic “small scale expansion” (SSE) to leading-one-loop order. We discuss the momentum dependence of the magnetic dipole, electric quadrupole and Coulomb quadrupole transition form factors up to a momentum transfer of Q² < 0.3GeV^2. Particular emphasis is put on the identification of the role of chiral dynamics in this transition. Our analysis indicates that there is indeed non-trivial momentum dependence in the two quadrupole form factors at small Q² < 0.15GeV^2 arising from long-distance pion physics, leading, for example, to negative radii in the (real part of the) quadrupole transition form factors. We compare our results with the EMR(Q²) and CMR(Q²) multipole ratios from pion-electroproduction experiments and find a remarkable agreement up to four-momentum transfer of Q² ≈ 0.3GeV^2. Finally, we discuss the chiral extrapolation of the three transition form factors at Q² = 0, identifying rapid changes in the (real part of the) quark mass dependence of the quadrupole transition moments for pion masses below 200MeV, which arise again from long-distance pion dynamics. Our findings indicate that dipole extrapolation methods currently used in lattice QCD analyses of baryon form factors are not applicable for the chiral extrapolation of NΔ quadrupole transition form factors.     

Structure of weak nucleon currents and charge asymmetry in nuclear beta decay

Structure of weak nucleon currents is studied from the beta decays in the A=12 system. We have investigated the experimental data on the beta-ray angular distribution in the aligned ¹²B and ¹²N recently given by the Osaka group with our formulas to find a new limit for the induced tensor current. A possible difference of the ratio y of the axial charge to Gamow-Teller matrix elements between the beta decays of ¹²B and ¹²N is calculated theoretically in connection with the ft-value asymmetry, since it affects the evaluation of the strength of the induced tensor current.     

Parametrization of the 1S0 two nucleon transition matrix

The ¹S₀ two-nucleon transition matrix T is constructed from the symmetric part σ of its half-shell elements. The on-shell component of σ is given by the phase shift, while a wide class of parametrizations is suggested for the off-shell part. Restrictions on the off-shell part of σ arising from the short range and the proper one-pion-exchange tail of the nucleon-nucleon interaction are investigated. Using σ in the ¹S₀ and the Reid soft-core potential in the other partial waves, the binding energy per particle in nuclear matter and ¹⁶O and the ¹⁸O shell-model spectrum are computed. The sensitivity of these nuclear-structure results is tested with respect to (i) smooth off-shell changes in σ, (ii) various assumptions on the high-energy phase shift, (iii) the charge dependence of the phase shift, and (iv) experimental uncertainties in the phase shift.