Parity-violating Interaction Research Articles

Non-mesonic decay modes of hypernuclei

The present status of theoretical descriptions of non-mesonic ( ΛN → NN) decay modes of hypernuclei is reviewed. One model, which evaluates a strangeness-changing, parity-violating weak interaction “potential” in nuclear matter, is examined in detail to exemplify the physics which can be learned and the problems which must be confronted. The importance of measuring the different isospin decay channels and separating the parity-conserving and parity-violating modes is stressed. Finally, this model is briefly compared and contrasted with other existing calculations.

Preferential stabilization of the D-sugar series by the parity-violating weak interactions

Hydrated D-glyceraldehyde is stabilized relative to its corresponding L-enantiomer by the parity-violating weak interactions.

Parity-violating energy differences between chiral conformations of tetrahydrofuran, a model system for sugars

The C2-endo conformations of tetrahydrofuran are stabilized relative to their C3-endo enantiomers by the parity-violating weak interactions.

Enhancement of Parity Violation for Overlapping Nuclear Resonances

Proton scattering from a medium weight nucleus and the possibility of finding tWQ resonances, with the same spin but opposite parity, overlapping is studied. As a guide to the experimental study of this possibility we have constructed a simple separable potential model involving spin ~-spin 0 scattering that contains the required resonances for adjacent I values in the absence of a parity-violating (PV) interaction. A phenomenological PV interaction is then introduced and the magnitude of the longitudinal asymmetry is studied as a function of the model parameters. It is found that the magnitude of the asymmetry is greatest at zero separation for the case of narrow resonance levels.

Parity Violation from SUSY Vertex Corrections in Deep Inelastic Scattering

Corrections to the eey and qqy vertices, at the one loop level, from intermediate supersymmetric (SUSY) states are calculated. The induced parity-violating interaction between electrons and nucleons is applied to the calculation of the lowest order SUSY contribution to the asymmetry in deep inelastic e + deuteron scattering in both the 'tree-breaking' (TB) and 'renormalisation-group' (RG) supergravity models. The results indicate that, for a wide range of sparticle masses, the SUSY contributions lie well within constraints implied by present measurements.

Parity-violating energy differences of chiral minerals and the origin of biomolecular homochirality

The biochemistry of terrestrial organisms is based on chiral (handed) molecules, with one of the two possible series of enantiomers (mirror-image isomers) being predominant. Specifically, terrestrial biochemistry is homochirally supported by L-α-amino acids and D-sugars to the almost complete exclusion of the enantiomeric D-α-amino acids and L-sugars. This particular homochiral selection may be a result of very small differences between the electronic energies of enantiomeric prebiotic molecules due to the parity-violating weak interactions. The energy differences are, however, so small for simple chiral molecules, that the propagation of homochirality would require a dissymmetry amplification mechanism involving both large quantities of reactants and a long reaction time. An alternative theory, presented here, considering the effects of the parity-violating weak interactions in crystalline enantio-selective prebiotic catalysts, such as the clay silicates, may require considerably less amplification.

The effects of parity violation of molecular structure

Through the action of the parity-violating weak interactions, a chiral molecule and its enantiomer are expected to have equilibrium structures which slightly deviate from an exact mirror-image relationship. It is found that such deviations, and the resulting small differences in the electromagnetic interactions within enantiomeric molecules, are insufficient to perturb significantly or counteract the inherent parity-violating energy differences between enantiomers.

Origins of biomolecular handedness.

Classical mechanisms proposed for the transition from racemic geochemistry to homochiral biochemistry in terrestrial evolution generally ascribe to chance the particular handed choice of the L-amino acids and the D-sugars by self-replicating systems. The parity-violating weak neutral current interaction gives rise to an energy difference between a chiral molecule and its mirror-image isomer, resulting in a small stabilization of the L-amino acids and the L-peptides in the alpha-helix and the beta-sheet conformation relative to the corresponding enantiomer. The energy difference suffices to break the chiral symmetry of autocatalytic racemic reaction sequences in an open non-equilibrium system.

Some general properties of theO(α)corrections to parity violation in atoms

The model-dependent contributions to the parity-violating electron-nucleon interaction arising from $\ensuremath{\gamma}Z$ box diagrams are discussed on the basis of a formulation in which the hadronic parts of the amplitude are treated exactly ab initio. This leads to a derivation of general properties and more refined estimates of these effects. A method to take into account the large-distance part of the hadronic contributions to the $\ensuremath{\gamma}Z$ mixing diagrams using experimental information on ${e}^{+}+{e}^{\ensuremath{-}}$\ensuremath{\rightarrow}hadrons is briefly discussed. Predictions for the ${C}_{\mathrm{iN}} (i=1,2, N=p,n)$ are updated taking into account the more detailed estimates of this paper.

A theoretical analysis of parity violation induced by neutral currents in atomic cesium

In this paper we give a theoretical analysis of the parity violation phenomena in nS − n′S transitions in atomic cesium induced by the electron-nucleus neutral-current interaction. The actual observation of parity violation consists in the measurement of an interference between the p.v. electric dipole amplitude E l pv with the electric amplitude induced by a static electric field. Our theoretical work must then include a calculation of the diagonal and non-diagonal polarizabilities of the states of atomic cesium. We have used a one-electron model proposed by Norcross which incorporates some many-body effects like the electric screening induced by the core polarization in a semi-empirical way. Our calculated values of the diagonal and non-diagonal polarizabilities of the nS states are in good agreement with the existing measurements; this confirms the already well-established success of the model in predicting the radiative transitions in cesium. We present theoretical arguments supported by detailed numerical computations showing that the one-particle matrix element of the parity-violating electron-nucleus interaction and the parity-violating electric dipole amplitude E l pv itself weakly depend on the shape of the one-electron potential provided the binding energies of the valence states are reproduced accurately. Furthermore it turns out that because of a compensation mechanism, the parity-violating transition is induced by the radiation field outside the ion core region where the screening can be described simply in terms of the measurable cesium ion polarizability. Our results are then used to extract, from the Ecole Normale Supérieure experiment, a value of the weak charge Q w = −57.1 ± 9.4 (r.m.s. statistical deviation) ± 4.7 (systematic uncertainty). This number is to be compared with the prediction of the Weinberg-Salam model with electro-weak radiative corrections: Q w = −68.6 ± 3.0. A general discussion of the uncertainties of the atomic physics calculations leads to the conclusion that the theoretical error which affects the determination of Q w is not likely to exceed 10 to 15%.

Radiative corrections to atomic parity violation

Electroweak radiative corrections to the $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ parity-violating electron-quark interaction are presented, including axial-vector isoscalar effects induced at the one-loop level. Implications of our results for parity-violation searches in ordinary hydrogen, deuterium, and heavy atoms are discussed.

Energy inequivalence of peptide enantiomers from parity non-conservation

L-Alanine and L-peptides in the α-helix and β-sheet conformation are stabilized relative to the corresponding enantiomer by the weak parity-violating interaction.

Instability of parametrization of fermion mixings in the presence of parity-violating interactions

If parity is not conserved, fermion mixings cannot be parametrized by mass matrices only. If two fermion fields are mixed, the poles of the propagators are given as roots of a cubic equation and the situation is singular in the limit of the parity nonconservation parameters tending to zero.

Electroweak effects in a superconductor

We show that mixing of the electroweak gauge bosons may occur in a superconductor, resulting in an enhanced neutral current with long-range electromagnetic parity-violating interactions or electric charge non-conserving processes.

Analytical properties and resonant structure of theS-matrix in case of noncentral and parity-violating interactions

The analytical properties and the resonant structure of the nonrelativisticS-matrix are investigated for elastic scattering with absorption for central, noncentral and parity-violating interactions and when the equations of motion for particles inside a sphere with finite radius are unknown. The conditions for the completeness of wave functions outside the interaction sphere, for the symmetry and for the generalized unitarity of theS-matrix are used. The conditions of micro- and macrocausality for the obtained results are investigated.

Parity-violating electromagnetic interaction in the vector-meson-dominance model

We discuss how the parity-violating (PV) photon-nucleon ($\ensuremath{\gamma}\mathrm{NN}$) coupling (or, more generally, any PV $\ensuremath{\gamma}B{B}^{\ensuremath{'}}$ vertex) can be calculated consistently in the vector-meson-dominance model. Gauge invariance gives rise to useful constraints among the weak $\mathrm{VNN}$ coupling constants ($V=\ensuremath{\rho},\ensuremath{\omega},\ensuremath{\varphi}$). Our estimates indicate that effects caused by the PV $\ensuremath{\gamma}\mathrm{NN}$ vertex could be as important as those caused by radiative corrections due to two-boson exchange.

Cancellation of equilibrium parity-violating currents

It has recently been shown that in a rotating equilibrium system there exist neutrino and antineutrino currents parallel to the rotation axis. This suggests that particles other than neutrinos can also develop equilibrium currents if parity-violating weak interactions are taken into account. This possibility is examined using quantum field theory at finite temperature, density, and angular velocity. Regularization and renormalization of such a theory are discussed. The result obtained is negative. It is found that in the model considered the equilibrium current vanishes in the lowest order of perturbation theory. This is a surprising result, since the existence of a nonzero current is not forbidden by the symmetries of the Lagrangian. The question naturally arising from this result is whether a nonzero current appears in higher orders of perturbation theory or in different models or there is some deep physical reason which makes the equilibrium current equal to zero for all particles except neutrinos.

Equilibrium parity-violating current in a magnetic field

It is argued that if the Hamiltonian of a system of charged fermions does not conserve parity, then an equilibrium electric current parallel to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ can develop in such a system in an external magnetic field $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$. The equilibrium current is calculated (i) for noninteracting left-handed massless fermions and (ii) for a system of massive particles with a Fermitype parity-violating interaction. In the first case a nonzero current is found, while in the second case the current vanishes in the lowest order of perturbation theory. The physical reason for the cancellation of the current in the second case is not clear and one cannot rule out the possibility that a nonzero current appears in other models.

Parity-violating electric-dipole transitions in helium

The paper examines parity-violating electric-dipole transitions in He in order to gain insight into the reliability of approximate calculations which are carried out for transitions in many-electron atoms. The contributions of the nearest-lying states are computed with a variety of wave functions, including very simple product wave functions, Hartree-Fock functions and Hylleraas-type wave functions with up to 84 parameters. It is found that values of the matrix elements of the parity-violating interaction can differ considerably from the values obtained from the good wave functions, even when these simple wave functions give accurate values for the matrix elements in question

Parity-violating effects of weak interactions in molecules

Effects of neutral-current parity-violating weak interactions in molecules are investigated. Asymmetries in the spectra of optically active mirror systems are estimated. The activity induced by weak interactions in rotational and vibrational transitions of nonactive molecules is computed.