Fernanda Monti Steffens

Dynamical symmetry breaking in the sea of the nucleon

We derive the nonanalytic chiral behavior of the flavor asymmetry d - u. Such behavior is a unique characteristic of Goldstone boson loops in chiral theories, including QCD, and establishes the unambiguous role played by the Goldstone boson cloud in the sea of the proton. Generalizing the results to the SU(3) sector, we show that strange chiral loops require that the s - s distribution be nonzero.

Mesonic corrections to the shape of quark distributions

Abstract We compute the full x dependence of the proton and neutron spin structure functions in the MIT bag model, including the effect of gluon exchange and the meson cloud. Impressive agreement is found for x larger than 0.1, where polarised gluons are not expected to play a significant role.

Heavy-quark axial charges to nonleading order

We combine Wittens renormalization group with the matching conditions of Bernreuther and Wetzel to calculate at next-to-leading order the complete heavy-quark contribution to the neutral-current axial-charge measurable in neutrino-proton elastic scattering. Our results are manifestly renormalization group invariant.

Thermodynamics of quasi-particles at finite chemical potential

Abstract We present in this work a generalization of the solution of Gorenstein and Yang to the inconsistency problem of thermodynamics for systems of quasi-particles whose masses depend on both the temperature and the chemical potential. We work out several solutions for an interacting system of quarks and gluons and show that there is only one type of solution that reproduce both perturbative and lattice QCD.

A New analysis of charge symmetry violation in parton distributions

Abstract To date, the strongest indication of charge symmetry violation in parton distributions has been obtained by comparing the F 2 structure functions from CCFR neutrino data and NMC muon data. We show that in order to make precise tests of charge symmetry with the neutrino data, two conditions must be satisfied. First, the nuclear shadowing calculations must be made explicitly for neutrinos, not simply taken from muon data on nuclei. Second, the contribution of strange and charm quarks should be calculated explicitly using next-to-leading order (NLO) QCD, and the “slow rescaling” charm threshold correction should not be applied to the neutrino data. When these criteria are satisfied, the comparison is consistent with charge symmetry within the experimental errors and the present uncertainty in the strange quark distribution of the nucleon.

A study of quark-parton distributions in a simple quark model

Abstract We examine the quark-parton momentum distributions calculated from a simple quark model using two recently proposed methods. It is seen that the distributions predicted at large values of Bjorken x are especially sensitive to the approximation made. In particular it is essential to guarantee the correct support.

Thermodynamics of quasi-particles

Abstract We present in this work a generalization of the solution of Gorenstein and Yang for a consistent thermodynamics for systems with a temperature dependent Hamiltonian. We show that there is a large class of solutions, work out three particular ones, and discuss their physical relevance. We apply the particular solutions for an ideal gas of quasi-gluons, and compare the calculation to lattice and perturbative QCD results.

Flavor asymmetry of the nucleon sea

We reexamine the effects of antisymmetry on the antiquarks in the nucleon sea arising from gluon exchange and pion exchange between confined quarks. While the effect is primarily to suppress down relative to up antiquarks, this is numerically insignificant for the pion terms. {copyright} {ital 1997} {ital The American Physical Society}

A Study of Structure Functions for the Bag Beyond Leading Order

There has recently been surprising progress in understanding the spin and flavor dependence of deep inelastic structure functions in terms of the same physics needed in the simple quark models used for hadronic spectroscopy. However, the corresponding scale is usually very low, casting doubt on the use of leading order

Computation of parton distributions from the quasi-PDF approach at the physical point

QCD