Higher-order effects in Fermi-type charged current theory of weak interactions: Semi-leptonic neutral currents

In a convergent field theory rescattering graphs lead to neutral-current effects of the observed magnitude if the effective cut-off momentum is $\text{～G}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{≈ 300}\text{GeV}$. A perturbation expansion is justified owing to the value f=0.18 of the resulting expansion parameter.     

Parity violations by neutral currents in muonic atoms

The 2S-1S transition in low Z muonic atoms is shown to be extremely sensitive to possible parity violation, such as may introduced by neutral currents. The most striking effects of parity violation are found in the case of muonic Li and Be where they are estimated to be of the order of 10% on the basis of current models.     

Testing the structure of weak neutral currents by inelastic neutrino scattering from nuclei

By using selected nuclear transitions specific pieces of the weak neutral current may be greatly enhanced, leading to widely different results for different models of the weak neutral current. Predictions for low-energy inelastic neutrino scattering from ¹²C are examined within the framework of a variety of SU(2)_W × U(1) gauge theory models.     

Exchange currents in electron scattering from light nuclei

Effects of meson exchange currents on elastic and inelastic electron scattering from nuclei are considered with specific applications to ³He, ⁶Li, ⁷Li, ⁹Be and ¹⁰B. The one-pion exchange approximation is employed (with “pair” and “pionic” graphs) in the non-relativistic limit, where only transverse isovector multipoles are allowed. This approach is shown to be consistent with current conservation. Form factors are calculated with and without exchange currents for a wide range of momentum transfers (up to 1 GeV/c) and for a variety of nuclear transitions to determine where exchange-current effects are large. The relevance of these calculations to experiment is discussed.     

Weak neutral currents in the U3(W)-gauge theory of weak and electromagnetic interactions

A discussion is given of the implications of the recently proposed U₃(W)-gauge theory of weak and electromagnetic interactions (Pandit 1976) for some phenomena resulting from its weak neutral currents: (1) neutrino-electron scattering, (2) neutrino-nucleon elastic and inelastic scattering, (3) coherent neutrino-nucleus scattering (4) weak interaction effects ine ⁺ e ⁻→μ⁺μ⁻ and (5) parity-violation in atomic physics. The theory agrees quite well with the available experimental results on neutrino processes. We find the coherent neutrino-nucleus cross-section for Fe⁵⁶ to be about 6 times larger than that in the WS-GIM theory giving some hope of accounting for supernova explosion by the resulting neutrino-radiation pressure.     

Space-time structure of weak neutral currents: (II). Elastic scattering

The elastic scattering of neutrinos and antineutrinos on nucleons in which the initial and final nucleon polarizations are measured, is studied from the point of view of the space-time properties of the currents. Structure functions are defined and experimentally measurable quantities which can be usual to disentangle the Lorentz structure of the currents are given. Second class current effects are also examined.     

Parity conserving neutral currents and right-handed neutrinos

Interpreting the leptons as a fourth color degree of freedom, we study a unique theory of the weak and electromagnetic interactions involving two neutral massive intermediate bosons. The neutral current interaction conserves parity. Implications of a university of weak, electromagnetic and strong interactions are discussed.     

Parity violation in electron scattering

By comparing the cross sections for left- and right-handed electrons scattered from various unpolarized nuclear targets, the small parity-violating asymmetry can be measured. These asymmetry data probe a wide variety of important topics, including searches for new fundamental interactions and important features of nuclear structure that cannot be studied with other probes. A special feature of these experiments is that the results are interpreted with remarkably few theoretical uncertainties, which justifies pushing the experiments to the highest possible precision. To measure the small asymmetries accurately, a number of novel experimental techniques have been developed.     

Parity violation in electron scattering

Approximations based on the 2PI effective action are used to investigate the process of equilibration in ϕ⁴ theory in 3+1 dimensions, both in the symmetric and broken phase. A special emphasis is put on the study of the kinetic and chemical equilibration.     

Parity violations in hydrogen and the fundamental structure of the weak current

Experiments in progress with hydrogen and deuterium may in practice determine the fundamental parameters and constituents of the weak interaction within the framework of unified gauge theories. In particular, for SU (2) × U (1) theories, from the results of these experiments one can infer the masses of the charged and neutral weak vector bosons (and thus sin²θ_W), and the isospin classification of the right-handed portions of the electron and the u- and d-quarks. Non-singlet assignments for e_R, u_R and d_R would imply the existence of additional leptons and/or quarks. Hydrogen/deuterium data also may be used to discriminate between SU (2) × U (1) models and various models based on larger gauge groups.     

Axial polarizability and weak currents in nuclei

The effect of the isobaric excitations on the weak axial coupling constants in nuclei is studied through P.C.A.C. We first establish the Klein-Gordon equation for the virtual pion field in the nucleus; it takes into account pion rescattering. The influence of isobar excitation is contained in the axial polarizability coefficient which is linked to the p-wave π-N scattering volume. The derivation of this equation stresses its analogies with electromagnetism. We give then a basic relation between the axial current and the pionic field. It incorporates the effects of the isobars in the axial polarizability, which leads naturally to an electromagnetic analog. We show that this relation leads in heavy nuclei to a quenching of the axial coupling constant by the Lorentz-Lorenz factor, which may originate from the short range or the Pauli correlations, depending on the range of the π-N forces. Hence this quenching may have a different origin than the existence of short-range correlations and may arise from a Pauli blocking effect. On the other hand, the pseudoscalar coupling constant is found to be strongly suppressed. In finite nuclei, these basic quenchings can be masked by surface effects, the general features of which are studied with the help of a solvable model. This model is further used to obtain the asymptotic pion field which is linked to the effective pion-nucleus coupling constant and can be determined experimentally through π-nucleus dispersion relations. We find that this quantity is quenched, in agreement with recent experimental data.     

Right-handed weak currents in neutrino scattering

We investigate transition strengths of right-handed weak charged currents in deep inelastic neutrino scattering, exploiting the dominance of p, n valence quarks in the nucleon. The energy dependence of σ_t and the average quantities 〈y〉 and 〈Q²〉 are shown to provide sensitive measures of new quark production thresholds and right-handed currents in $\text{ν}\text{N}$ scattering. With our analysis, the present data give an upper bound on the right to left hand structure function ratio of $\text{F}{}_{\mathrm{<mtext>R</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{F}{}_{\mathrm{<mtext>L</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{≈}\text{1}\text{2}$, above a threshold of W≈7.5 GeV.     

Effects of neutral weak currents in annihilation

General cross-sections are given for annihilation via one photon and W⁰ exchange. Effects of the W⁰ in the special cases e⁺e^?→μ⁺μ^? and $\text{p}\text{p}\text{→?}{}^{\mathrm{+}}\text{?}{}^{\mathrm{?}}$ at high energies are discussed. These effects are estimated to be comparable to the effects from one γ exchange at energies accesible in NAL and SPS.     

Contributions to the exchange currents to elastic electron scattering from nuclei

We have investigated the effects of the meson exchange currents on the charge form factor, the charge density and the rms radius of ⁴⁰Ca. It turns out that the effects of the one-pion-exchange currents are appreciably large while the -π exchange current gives small effects compared with those of the neutron.     

Parity violation in polarised electron deuteron scattering

Preliminary calculations show that the parity violating asymmetry in polarised electron deuteron elastic scattering can be as large as observed in the SLAC experiment even in the intermediate energy region. We propose that experiments should be done to search for these asymmetries.     

Weak neutral currents and neutrino electromagnetic properties

The phenomenological Hamiltonian for weak lepton interaction that contains, along with a charged current V-A interaction, a neutral current V-A interation and the dispersion method are used to study the effect of lepton and nucleon currents on the electromagnetic properties of the neutrino. Expressions are obtained for the neutrino formfactor F(q²) when it satisfies the dispersion relations without subtraction and with one subtraction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 43–48, May, 1977.     

Parity-violating electron deuteron scattering and the proton's neutral weak axial vector form factor

We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions.     

Parity violating neutral currents in a left-right symmetric gauge model

We consider parity violating effects in the neutral sector of a left-right symmetric SU(2)_L × SU(2)_R × U(1) gauge model of weak and electromagnetic interaction. With four quarks and four leptons, the parity violating optical rotation in atoms is estimated to be about an order of magnitude smaller (and of opposite sign) compared to the Salam-Weinberg (SW) model prediction. However, with new quarks and leptons this effect can be arranged to be even smaller. Weak-electromagnetic interference effects are quantitatively different from those found in the SW model. A unified gauge theory which embeds the left-right symmetric gauge model is briefly discussed.     

Parity conserving weak neutral current effects in fundamental bound systems

The effects induced by the Z-boson exchange in the hyperfine structure and Lamb shift of some fundamental bound systems is analyzed. The hfs of muonium appears as a promising test of the Weinberg-Salam theiry.     

Weak neutral currents in elastic muon-nucleon scattering

Elastic polarized muon scattering is considered as an independent source of information on weak neutral currents involving muons. At low energies and high intensities cross section asymmetries are measurable which are sensitive to the right-handed weak muon charge, involve new combinations of coupling constants and depend remarkably on the details of weak nucleon form factors.