Model Of Weak Interactions Research Articles

Measurement of the antineutrino escape asymmetry with respect to the spin of the decaying neutron

The result of a new run of measurements of the antineutrino escape asymmetry with respect to the spin of the decaying neutron is presented. The asymmetry coefficient is B=0.9821±0.0040, which is consistent with the prediction of the standard model of weak interactions. The prospects for increasing the accuracy of the measurements are discussed.

The Gerasimov-Drell-Hearn sum rule and the infinite-momentum limit

We study the current-algebra approach to the Gerasimov-Drell-Hearn sum rule, paying particular attention to the infinite-momentum limit. Employing the order-alpha^2 Weinberg-Salam model of weak interactions as a testing ground, we find that the legitimacy of the infinite-momentum limit is intimately connected with the validity of the naive equal-times algebra of electric charge densities. Our results considerably reduce the reliability of a recently proposed modification of the Gerasimov-Drell-Hearn sum rule, originating from an anomalous charge-density algebra.

Atomic Parity Experiment Has Its Moment

For over eight years, researchers at JILA and the University of Colorado, Boulder, have worked patiently and painstakingly to improve the precision with which they can detect a rare, parity‐violating atomic transition. The group, led by Carl Wieman, has finally been rewarded with a measurement of the transition amplitude that is precise to 0.35%, a factor of seven better than their 1988 measurement of the same transition. The dominant uncertainty in the value of this term is now the uncertainty in the atomic theory, which reached 1.2% in the early 1990s. The combined uncertainties bring the data into the realm where they place useful constraints on the Standard Model of electro weak interactions. As icing on the cake, the Boulder experiment also gives the first good evidence for a nuclear feature predicted years ago: the nuclear anapole moment.

Finite volume model of weak shock interaction with lung tissue.

The lung and other organs with high gas content tend to be the most susceptible to damage by lithotripter shock waves. Since the gas volume is large, the damage processes most likely differ from traditional cavitation mechanisms. A finite volume model has previously been developed to investigate the interaction of shock waves with single, isolated bubbles. This model has been modified to explore other possible mechanisms of lung tissue damage. In the model, the single bubble is replaced with a layer of cylindrical bubbles, and a shock wave is incident normal to this bubble layer. The affect of bubble spacing on the shock wave propagation through the layer and the resulting bubble dynamics is determined.

Weakly bonded clusters of H 2S

A weak interaction model has been used to examine the potential energy surfaces of weakly bound dimers, that include a hydrogen sulfide molecule. The comparison with corresponding water clusters shows certain structural similarities but significantly different energetics. Interconversion barriers are mostly smaller for H 2S complexes than for the corresponding water complexes. This is attributed in part to the size of sulfur relative to oxygen, leading to greater equilibrium separations from bonding partners and thereby decreased electrical stabilization. Values are reported for rotational constants, dipole moments, and interconversion barriers.

Interactions of α-chymotrypsinogen A with alkylureas

Solvation of α-chymotrypsinogen A (α-ctg A) in aqueous urea, methylurea, N,N′-dimethylurea and ethylurea was studied by density measurements. From the densities at constant molality and at constant chemical potential the preferential solvation parameters were determined. In urea and methylurea preferential solvation was observed, whereas in N,N′-dimethylurea and ethylurea at higher concentration water is preferentially bound. From preferential solvation data Gibbs free energy of transfer of α-ctg A from water to urea and alkylurea solutions were calculated. Since the enthalpies of transfer were determined previously, the entropies of transfer could also be obtained so that a complete thermodynamic description is available. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions involved in solvation as well as to calculate the exchange constant by using the model of weak interactions. In solvation of alkylureas the hydrophobic nature of the alkyl groups is clearly reflected.

Investigation of Higgs and Heavy Fermion Masses in Yukawa Models on a Parallel Computer

The Standard Model of electromagnetic and weak interactions of elementary particles has been applied successfully to a wide variety of phenomena. Most of the phenomenological applications are made in the framework of perturbation theory, which appears to be a good approximation since most of the couplings are small. In the Standard Model the masses of particles, including the W- and Z-bosons, quarks and the yet to be discovered Higgs particle, are generated by means of the Higgs mechanism. As a result the masses are related to the coupling constants in a definite way. In particular the Higgs mass can be expressed as

Lepton flavor violation and the tau neutrino mass.

We point out that, in the left-right symmetric model of weak interaction, if $\nu_\tau$ mass is in the keV to MeV range, there is a strong correlation between rare decays such as $\tau \rightarrow 3 \mu, \tau \rightarrow 3 e$ and the $\nu_\tau$ mass. In particular, we point out that a large range of $\nu_\tau$ masses are forbidden by the cosmological constraints on $m_{\nu_\tau}$ in combination with the present upper limits on these processes.

No parity violation without R-parity violation.

In a class of supersymmetric left-right models (SUSYLR) of weak interactions where R-parity is automatically conserved, we show that spontaneous breakdown of parity CANNOT occur without spontaneous breakdown of R-parity. This intriguing result connects two physically different scales in supersymmetric models.

Phase separation of grafted polymers under strong demixing interaction

The phase separation of grafted homopolymers of two different kinds (A and B) under strong demixing interaction is investigated, with demixing energy far greater than kT per chain. A stable self-consistent model for the phase-separated state will all the chains end at the same height is successfully constructed. The configuration contains pure A and B monomer regions and inevitable A-B mixed regions. The composition and magnitude of the free energy of the system were studied, the size of the periodic regions and its dependence on the demixing interaction strength were calculated. The system with distributed end density profile is further studied. Comparison is made with results obtained from the previous weak interaction model using second order correlation function under mean field approximation

Decomposition of weak hypercharge number and electroweak interaction model.

The lack of simplicity of the weak hypercharge [ital Y] values in the standard electroweak model suggests the possibility that [ital Y] may not be a truly fundamental number and may be expressed as the sum of the baryon number, lepton number, [ital I][sub 3][sup [ital L]], and [ital I][sub 3][sup [ital R]]. Such an idea will lead to an SU(2)[sub [ital L]][times]U(1)[sub leptons][times]U(1)[sub baryon][times]U(1)[sub [ital R]] electroweak model, where the lepton and baryon numbers have short-range dynamical effects, and new weak neutral vector particles of unusual coupling properties arise.

Electronic transport properties of amorphous W/Si multilayers

The temperature dependence of the sheet resistance of e-beam evaporated W/Si multilayers was investigated. A positive temperature coefficient of resistivity (TCR) 190–600 ppm/K was obtained for multilayers with crystalline tungsten layers ( d w > 4 nm). Multilayers with amorphous tungsten layers 1–4 nm thick revealed nom-metallic resistivity behaviour with a negative TCR, -(100–300) ppm/K in the temperature range 1.8–300 K, and were superconducting with the superconducting transition temperature T c up to 4.21 K. The resistivity behaviour of the amorphous W/Si multilayers with Si layer thicknesses 1–10 nm can be described within the framework of 3D weak localization and interaction models. At temperatures close to T c superconducting fluctuations decrease the resistance of these samples. At temperatures above T c both effects can be comparable, resulting in a maximum in the temperature dependence of the resistance. A relatively strong coupling between metallic layers was observed. This coupling could originate from mixing at the W/Si interfaces and interdiffusion during the deposition and subsequent annealing. The different resistivity behaviour of amorphous tungsten monolayers strongly supports this assumption.

Search for neutral currents in 30P and 23Na nuclei

The parity-forbidden M1 + E2 γ-decays from 30 P∗(J π = 2 − ; E x = 4.144 MeV) to 30 P∗(J π = 1 + ; E x = 0.709 MeV) and from 23 Na∗ (J π = 5 2 − ; T = 1 2 ; E x = 3.848 MeV) to 23Na(g.s.) have been investigated theoretically. Considering various strong- and weak-interaction models the circular polarizations ( P γ ) of 3.43 MeV gamma rays emitted by 30P∗ and of 3.85 MeV gamma rays emitted by 23Na∗ have been calculated. The results determine a range of P γ values from which we selected the most probable values: P γ = 0.7 × 10 −3 for 30P and P γ = 0.6 × 10 −4 for 23Na.

Renormalization of Fermionic Theories in Stochastic Quantization

>~ 4 > Various aspects, ranging from its usefulness as a scheme for numerical computations in quantum field theory to its viability· as an alternative and perhaps a more flexible scheme for quantizing field theories, have been studied. In order to be able to consider SQM as a complete scheme for quantizing field theories, it becomes necessary to examine the renormalization programme within the framework of SQM. Here by renormalizability of a given theory we mean that the higher order corrections do not alter the structure of the stochastic equations one started out with. This question assumes particular importance in the context of physically relevant theories such as Yang-Mills field theory, quantum electrodynamics and unified models of weak and electromagnetic interactions, where SQM not only permits but also requires introduc­ tion of certain features, such as stochastic gauge fixing, 5 > not present in the conven­ tional field theories and thereby precludes the possibility of any conclusions to be drawn regarding the renormalizability or otherwise of such theories within the framework of SQM on the basis of the results established in the conventional frame­ work. It is, therefore, necessary to study renormalization entirely within the frame­ work of SQM and to develop the necessary techniques so as to have a better intuition about the behaviour of ultra-violet (UV) divergences in SQM which could be useful in discussing quantization of non-holonomic systems which fall outside the realm of ·conventional quantization methods. So far, the renormalizability, within SQM, of only the ¢ 4 theory 6 > and gauge theories with stochastic gauge fixing 7 > has been inves­ tigated. The present investigation is devoted to the study of renormalization of fermionic theories in SQM. It is now known that the fermionic theories in SQM without a non-trivial kernel require new counterterms not present in the original unrenormal­ ized formulation. It is, therefore, important that the renorma_Iizability properties of fermionic theories in SQM be studied and understood. The formalism of SQM offers

Parity mixing in36Cl investigated via circular polarization of the 1.95105 MeV gamma-rays

TheM1+E2 parity-forbidden γ-decay from36Cl (Jπ=2+;T=1;Ex=1.95105 MeV) to36Cl (g.s.) has been thoroughly investigated theoretically. Considering various strong- and weak-interaction models the circular polarizationPγ of 1.95105 MeV gamma-ray has been calculated. The range of the calculated values ofPγ is lying between 0.3·10−4 and 1.3·10−4.

Photon-electron directional correlation in muonic atoms and weak-interaction models

Measurements of photon-electron directional correlation in muonic atoms may provide useful information on the low-energy neutral-current effective interaction of charged leptons with light quarks, significantly complementing the information obtainable from other low-energy parity-violation experiments. We calculate the expectations for the correlation coefficients in conventional extended gauge models, such as to test for possible deviations with respect to the standard model. We discuss sources of uncertainty in the estimate of such deviations. The physical relevance of this analysis is exhibited in a number of graphs which illustrate how such experiments, at presumably attainable precision, would significantly improve the bounds on the effective lagrangian as obtained from other sets of data (including LEP).

Rare muon decays and physics beyond the standard model

Rare muon processes such as muonium to antimuonium conversion, μ→eγ and μ→3e provide sensitive tests of new physics beyond the standard model. Specifically the left-right symmetric models of weak interaction with a low scale for the right-handedW R boson (in the TeV range) provide a whole range of rare muon processes which are experimentally accessible. In this talk, I discuss the implications of the left-right symmetric models for rare muon processes and also briefly touch on the SUSY models with R-parity violation and their implications for these processes.

Parity and isospin nonconservation in 16O investigated via [formula omitted] resonance reaction

The parity- and partially isospin-forbidden α 0-decay from O ∗ ( J π = 2 −, T = 1; E x = 12.9686 MeV) to 12C(g.s.) has been thoroughly investigated theoretically. Considering various strong and weak interaction models, the longitudinal A L and the irregular transverse A b analyzing powers of the reaction 15 N( p , α 0) 12 C have been calculated in the energy range around the 2 − resonance in 16O ∗. The isospin impurity due to the coupling with 2 −, E x = 12.53 MeV excited level in 16O ∗, which has mainly a T = 0 component, have been considered in the calculations. Energy anomalies for the expected interference effects, relevant for the experiments, have been found to be A L ≈ 2.0×10 −5 and A b ≈ 0.4×10 −5.

Isovector parity mixing in 16O investigated via the 15N(p

The parity- and isospin-forbidden {alpha}{sub 0} decay from {sup 16}O{sup *}({ital J}{sup {pi}}=2{sup {minus}}, {ital T}=1, {ital E}{sub {ital x}}=12.9686 MeV) to {sup 12}C(g.s.) has been investigated theoretically. Considering various strong and weak interaction models the longitudinal {ital A}{sub {ital L}} and the irregular transverse {ital A}{sub {ital b}} analyzing powers of the reaction {sup 15}N({ital {rvec p}},{alpha}{sub 0}){sup 12}C have been calculated in the energy range of the 2{sup {minus}} resonance in {sup 16}O{sup *}. Energy anomalies for the expected interference effects, relevant for experiments, have been found to be {ital A}{sub {ital L}}=1.1{times}10{sup {minus}5} and {ital A}{sub {ital b}}=0.9{times}10{sup {minus}5} at {theta}=90{degree} and {ital A}{sub {ital L}}=1.4{times}10{sup {minus}5} and {ital A}{sub {ital b}}=0.2{times}10{sup {minus}5} at {theta}=150{degree} based on a conservative value of 0.1 eV for the parity-nonconservation matrix element. A proposal for an experimental investigation is sketched.

Pseudopotential multireference single and double excited configuration interaction calculations of nickel-containing molecules. 4. HNiSiH3 and HNiAlH3 as minimum models of hydrogen atoms chemisorption on a supported nickel atom

The chemisorption of atomic H on a Ni atom bound to SiH{sub 3} or AlH{sub 3} supporting fragments has been investigated by means of pseudopotential CI calculations. The two systems investigated, H-Ni-SiH{sub 3} and H-Ni-AlH{sub 3}, can be considered as minimum models of strong (SMSI) and weak (WMSI) metal-support interactions, respectively. It is found that the presence on the SiH{sub 3} support of a singly occupied dangling bond, not present on AlH{sub 3}, is the key factor determining the strong metal-support interaction. By this interaction, the Ni atom binds the adsorbed H atom less strongly than in the free NiH molecule. The chemisorption of H decreases also the Ni-substrate bond strength. This result, however, is found only after inclusion of correlation effects. Uncorrelated calculations show the opposite trend, that is, a reinforcement of both Ni-H and Ni-support bonds by H chemisorption. This contradictory result is probably the consequence of the different SCF and CI energy separation between the Ni 3d{sup 8}4s{sup 2} and 3d{sup 9}4s{sup 1} configurations. The formation of two covalent bonds, as in H-Ni-SiH{sub 3}, implies that the metal atom assumes a 3d{sup n}4s{sup 2}-like configuration more suitable to form directional 4sp hybrid orbitals. The case of Nimore » is compared with the limiting situations of Fe (3d{sup 6}4s{sup 2}) and Cu (3d{sup 10}4s{sup 1}) to generalize the conclusions about the electronic mechanisms with the limiting situations of Fe (3d{sup 6}4s{sup 2}) and Cu (3d{sup 10}4s{sup 1}) to generalize the conclusions about the electronic mechanisms of SMSI. For the model of WMSI, the authors found that in their system the interaction of a supported Ni with the approaching H atom induces the rupture of the Ni-substrate bond and the formation of a Ni-H molecule which easily desorbs from the surface.« less