Fundamental Weak Interactions Research Articles

Theoretical investigations on the nitro-explosive sensing process of a MOF sensor: Roles of hydrogen bond and π-π stacking

Hydrogen bond and π-π stacking are fundamental weak interactions which play unknown roles during the luminescent sensing processes of MOF sensors. Roles of them are uncovered by studying the nitro-explosive detecting mechanism of a typical MOF-based sensor. Photo-induced electron transfer from the MOF sensor to nitrobenzene is proved to induce the experimentally observed luminescence quenching. Hydrogen bond and π-π stacking between the analyte and sensor are proved to induce large orbital overlaps which facilitate the electron transfer process. Two pathways for the electron transfer process are put forward during which hydrogen bond and π-π stacking play key roles.

Superallowed 0+ → 0+ β decay and CKM unitarity: A new overview including more exotic nuclei

The ft values for superallowed 0+ → 0+ nuclear β transitions are nearly independent of nuclear-structure ambiguities and depend uniquely on the vector part of the weak interaction. They thus provide access to clean tests of some of the fundamental precepts of weak-interaction theory and can even probe physics beyond the standard model. We have just completed a new survey and overview of world data on such transitions, including not just the nine cases considered in the past, but also eleven more from T = 1 parents: even-even Tz = - 1 nuclei from 18Ne to 42Ti; and odd-odd nuclei from 62Ga to 74Rb. These new cases all involve more exotic nuclei and, to yield comparable precision, present real experimental challenges. Nevertheless, three of these new cases are already known well enough to contribute - together with the nine well known transitions - to the setting of limits on fundamental weak-interaction parameters. The remaining eight cases show promise for making important contributions in future.

Λ hyperon as helicity analyser of s quark in B decay

We explore how well one can probe the s quark chirality of the fundamental weak interaction of nonleptonic B decay using the spin-analysing property of the Λ hyperon. We present the prediction of the standard model as quantitatively as possible in a perturbative QCD picture avoiding detailed form-factor calculation involving quark mass corrections. A clean test of chirality will be possible with B̄ → ΛX when X is an antibaryon or its excited state.

Experimental value of G A/GV from a measurement of both P-odd correlations in free-neutron decay

A new experimental value of the fundamental weak-interaction parameter λ=GA/GV (−1.2686±0.0046) is obtained for the first time by an original method that consists in measuring both P-odd correlations in free-neutron decay.

Laser applications to fundamental weak interaction studies.

The possibility of performing weak interaction experiments usingspectroscopic techniques is discussed. In such an experiment, a laser is tunedto an electronic transition of the daughter, and a signal whose strength isproportional to the number of recoil atoms is monitored, such as fluorescence,absorption, or anisotropy induced in radiation emitted in a subsequent nucleardecay. As a specific example of this technique, we consider measuring theangular correlation between the momenta of the electron and the antineutrinoemitted in the decay/sup 85/Kr/r arrow//sup 85/Rb/sup m/+..beta../sup /minus//+/nu/bar //using the laser-induced nuclear orientation technique. Such anexperiment is currently under way.

Fluctuation kinetics of reactions

The fluctuation kinetics of reactions corresponds to a description of the reacting systems at a mesoscopic level. In this approach, a description is written in terms of concentration distributions which are continuous but fluctuating. The basic principles and methods of fluctuation kinetics are illustrated by several specific examples. Particular emphasis is placed on cases in which powerful mechanisms intensify microscopic fluctuations associated with the atomistic nature of the individual reaction events to the point that they determine the outcome of events at macroscopic scales. The situation is analogous to macroscopic quantum effects. In the first main section of the paper, the induction period of a branching chemical reaction is calculated under the assumption of a complete mixing of the reactants and also for the case with spatially inhomogeneous fluctuations. The second section of the paper discusses fluctuations in the course of a two-particle recombination reaction. The third section takes up the spontaneous breaking of chiral symmetry in the course of biological evolution and a possible role of fundamental weak interactions. Appendix I gives the solution of the general problem in which the point of a second-order phase transition in a distributed system is traversed at a finite rate. Appendix II describes mathematical methods of the fluctuation kinetics of reactions.

The structure of weak interactions for composite quarks and leptons

We consider a model of quarks and leptons as quasi-Goldstone fermions which is based on an underlying supersymmetric SU(2) HC × SU(2)′ HC preon theory. The spontaneous breakdown of a global U(6) × U(6)′ × U(1) symmetry to U(4) × U(4)′ × SU(2) diag creates both quarks and leptons and at the same time allows for the possibility of having either residual or fundamental weak interactions. Effective lagrangians in the confining phase of the theory are compared to those emerging from a complementary picture and the problems connected with the nature of the weak interactions are discussed in this context also.

Mechanism of " I=1/2 Enhancement" in the Relativistic Quark Model

In the analysis of weak non-leptonic decays (abbreviated as NLD's) of hadrons various ingredients and effects should be taken into consideration, even when the theory provides the fundamental form of the weak interaction among the constitu­ ents. It is necessary to clarify the respective roles of these ingredients in order to make a correct estimation of the physical transition amplitudes. Now it is widely believed that the fundamental weak interaction of non-lepton­ lC decay of ordinary hadrons at lower energies is given by the New-Nagoya-GIM modelll (or its extension to six-quark KM model)) with the left-handed charged currents. Then the main problems concerning NLD of ordinary hadrons can be summarized as follows: (a) to understand what is called enhancement of the LII = 1/2 amplitudes and suppression of the LII = 3/2 ones; (b) to understand consistently the observed features of the S and P waves of hyperon decays as well as kaon decays. It has long been pointed outJ that, as far as the non-leptonic weak interac­ tion H wNL is a product of color-singlet V-A currents, only the flavor-anti­ symmetric component contributes to the one- (low-lying) baryon matrix elements (B' IHwNL[B) leading to the JJ = 1/2 rule for hyperon decays in the framework of PCAC and current-algebra technique. For the recent few years some progress has been made from two different sides. First the strong interaction effects at short distances are investigated on the effective weak Hamiltonian where we meet the operators containing a certain kind of right-handed current.'J Secondly, the mag­ nitude of (B' IHnlC[B) has been discussed by using the composite model and the effect of the confinement has been argued to be large enough to account for the observed magnitude of the LII = 1/2 amplitude of hyperon decays. 5)

FUTURE OF WEAK INTERACTIONS*

A review is given of the particles and processes involved in weak interactions in order to shed light on future possibilities of such research. The predicted spectrum of weak intermediaries, the possibilities of finding a large and perhaps simple gauge group G that includes both the isochromatic weak interactions and the metachromatic strong, the possibility of no fundamental weak interactions at all, and the properties of maons are noted as future prospects. (JFP)

29.—The Possibility of Second-Class Currents in Gamow-Teller β-Decay

SynopsisMirror Gamow-Teller β-decay takes place from members of isospin multiplets to a common final state or to final states that are mirrors of each other. It is found that in these cases the intrinsic speed of the positon emission is systematically lower, by 10–15 per cent, than that of the mirror negaton emission. This difference could be due to a fundamental weak interaction effect, a second-class term in the weak hadronie current, or to a failure of exact symmetry in the nuclear structure. The influence of binding energy differences is studied in the latter context and it is concluded that they cannot be responsible for the empirical asymmetry. The effects of changes of configurational mix across the multiplets is also considered; very few estimates have ben explicitly made but it would be surprising if this effect turned out to be of constant sign and magnitude over the wide range of A involved. No present firm conclusion can be made but none of the empirical evidence is inconsistent with the reality of a largely momentum-transfer-independent second-class current.

FtAsymmetry in Mirror Gamow-TellerβDecay: Binding-Energy Effects

It is shown that the systematic asymmetry observed between positron and negatron emitters in mirror Gamow-Teller $\ensuremath{\beta}$ decay is not due to binding-energy differences between the respective $\ensuremath{\beta}$-transforming nucleons; it must be due either to a fundamental weak interaction effect or to a nuclear structure effect of some type not yet quantitatively discussed.

Universality of Weak Bilinear Transitions and Its Relation to the Fundamental Weak Interactions

Universality of Weak Bilinear Transitions and Its Relation to the Fundamental Weak Interactions

Universality of Weak Bilinear Transition and Its Relation to the Fundamental Weak Interaction

Universality of Weak Bilinear Transition and Its Relation to the Fundamental Weak Interaction

Pole Model of Nonleptonic Hyperon Decays, and Model of Hadrons and Their Fundamental Weak Interaction

The pole model of nonleptonic hyperon decays proposed by Kawasaki, Imoto and Furui (KIF) and Lee and Swift is reexamined for the purpose of establishing connection between the phenomenology and subnuclear structure of hadrons and their weak interaction. It is assumed that there exist three urbaryons which play an essential role in composing hadrons. Baryons are assumed to be nonrelativistic bound states of such three urbaryons. Two types of hyperon models are considered: One is the quartet-like model (ModelI), and the other is the quark-like model (ModelII). The effective two-body weak Hamiltonian between baryons becomes parity-conserving, and in a simplified limit in which all strong interaction corrections are neglected this Hamiltonian is of the D or F type for ModelI or II, respectively. In general, matrix elements of nonleptonic hyperon decays are written by using effectively five parameters. η (or η′), a member of the parameters, is introduced which is regarded as a measure of departure from the simplified limit. For any value of η (or η′), one can reproduce all the experimental data on nonleptonic hyperon decays including decay probabilities. This is possible only when the F/Dratio (a member of the five parameters) of the strong baryon-pseudoscalar-meson interaction is equal to ~ (0.5 ~ 0.6). Consistency of the values of adjusted parameters with other phenomena is investigated. It is concluded that to regard the weak Jp·Jp+ interaction as the only fundamental interaction responsible for nonleptonic decays is unlikely, where Jp stands for an appropriate urbaryonic or Cabibbo-like current. It seems difficult at present to determine which of the two Models is superior owing especially to the lack of knowledge of the parity-nonconserving amplitude.