Model Of Weak Interactions Research Articles

Limiting absorption principle at low energies for a mathematical model of weak interaction: The decay of a boson

We study the spectral properties of a Hamiltonian describing the weak decay of spin 1 massive bosons into the full family of leptons. We prove that the considered Hamiltonian is self-adjoint, with a unique ground state and we derive a Mourre estimate and a limiting absorption principle above the ground state energy and below the first threshold, for a sufficiently small coupling constant. As a corollary, we prove absence of eigenvalues and absolute continuity of the energy spectrum in the same spectral interval. To cite this article: J.-M. Barbaroux, J.-C. Guillot, C. R. Acad. Sci. Paris, Ser. I 347 (2009).

Mott-Schwinger scattering of polarized low energy neutrons up to thermal energies

The availability of new, high-intensity, cold and thermal neutron sources has opened the possibility of performing high-precision fundamental neutron physics experiments, including measurements that study the hadronic weak interaction and standard model test measurements, using neutron $\ensuremath{\beta}$ decay. The observables in these experiments are usually correlated with the direction of neutron polarization and are often very small $({10}^{\ensuremath{-}8}\ensuremath{\rightarrow}{10}^{\ensuremath{-}6})$. Mott-Schwinger scattering of polarized neutrons can produce spin-dependent shifts in beam centroids, which has the potential to produce significant systematic effects for these types of experiments. An accurate calculation of this process for neutral atoms and basic molecules has not been carried out for low neutron energies. In this work, we derive a general expression for the electromagnetic (Mott-Schwinger) contributions to the analyzing power for low-energy neutron scattering. We obtain numerical results for 11 nuclei in the range of $A=1$ to $A=208$ and provide a series of graphs for easy reference and interpolation between $A$ values. We also estimate the contribution of spin-dependent nucleon-nucleon forces and apply our results to determine the analyzing power of parahydrogen. Numerical calculations are performed to determine the analyzing power for the parahydrogen molecule and are compared to results obtained using analytical expressions.

Weak Attractive Ligand–Polymer and Related Interactions in Catalysis and Reactivity: Impact, Applications, and Modeling

The notion of weak attractive ligand-polymer interactions is introduced, and its potential application, importance, and conceptual links with "cooperative" ligand-substrate interactions are discussed. Synthetic models of weak attractive ligand-polymer interactions are described, in which intramolecular weak C-H...F-C interactions (the existence of which remains contentious) have been detected by NMR spectroscopy and neutron and X-ray diffraction experiments. These C-H...F-C interactions carry important implications for the design of catalysts for olefin polymerization, because they provide support for the practical feasibility of ortho-F...H(beta) ligand-polymer contacts proposed for living Group 4 fluorinated phenoxyimine catalysts. The notion of weak attractive noncovalent interactions between an "active" ligand and the growing polymer chain is a novel concept in polyolefin catalysis.

Large negative magnetoresistance and strong localization in highly disordered electrospun pregraphitic carbon nanofiber

A highly disordered pregraphitic carbon nanofiber with the product of its quasi-Fermi wave vector and mean free path close to 1 was fabricated using electrospinning technique. Strong localization made the conductivity vary with temperature as lnσ∝T−1∕2 from 300to5K, suggesting variable range hopping as the conductivity mechanism, and resulted in a large negative magnetoresistance from 300K down to 1.9K that can still be quantitatively described using weak localization and electron interaction models.

Alpha particles accompanying the weak decay of Λ 10 Be and Λ 10 B hypernuclei

The possibility of a detailed investigation of weak ΛN interaction in the Λ10Be and Λ/10B hypernuclei, which stand out owing to their ααNΛ cluster structure, is discussed. The detection of a few groups of correlated αα pairs will furnish information about decays to specific states of product nuclei (8Be*, 8Li, 8B), thereby paving the way to a phenomenological analysis of the weak decays of p-shell hypernuclei. The ratios of the intensities of individual alpha-particle groups to be measured in experiments at the nuclotron of the Joint Institute for Nuclear Research (JINR, Dubna) will provide a useful criterion for choosing an appropriate model of weak ΛN interaction. The current state of hypernuclear physics is briefly reviewed.

The hypervalent PF 4H species dimer: A system with double blue-shifted P–H⋯F hydrogen bonding?

The hypervalent PF 4H species dimer has been studied using second-order perturbation theory and coupled-cluster methods with augmented correlation-consistent basis sets up to truncated quadruple-zeta. The dimer involving two P–H⋯F contacts serves a model of weak interaction between PF 4H molecules in the crystal. We found dimer structures of C 1 and C i symmetry with interaction energy of the order of −2.5 kcal/mol. SAPT (symmetry-adapted perturbation theory) energy decomposition scheme reveals major electrostatic, polarization and dispersion stabilizing contributions. We are not conclusive as to the presence of improper H-bonding in this complex.

Bound-state β decay of a neutron in a strong magnetic field

The \ensuremath{\beta} decay of a neutron into a bound $({\mathit{pe}}^{\ensuremath{-}})$ state and an antineutrino in the presence of a strong uniform magnetic field ($B\ensuremath{\gtrsim}{10}^{13}$ G) is considered. The \ensuremath{\beta} decay process is treated within the framework of the standard model of weak interactions. A Bethe-Salpeter formalism is employed for description of the bound $({\mathit{pe}}^{\ensuremath{-}})$ system in a strong magnetic field. For the field strengths ${10}^{13}\ensuremath{\lesssim}B\ensuremath{\lesssim}{10}^{18}$ G the estimate for the ratio of the bound-state decay rate ${w}_{b}$ and the usual (continuum-state) decay rate ${w}_{c}$ is derived. It is found that in such strong magnetic fields ${w}_{b}/{w}_{c}~0.1\text{\ensuremath{-}}0.4$. This is in contrast to the field-free case, where ${w}_{b}/{w}_{c}\ensuremath{\simeq}4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ [J. N. Bahcall, Phys. Rev. 124, 495 (1961); L. L. Nemenov, Sov. J. Nucl. Phys. 15, 582 (1972); X. Song, J. Phys. G: Nucl. Phys. 13, 1023 (1987)]. The dependence of the ratio ${w}_{b}/{w}_{c}$ on the magnetic field strength B exhibits a logarithmiclike behavior. The obtained results can be important for applications in astrophysics and cosmology.

Publisher's Note: Measurement of theWboson polarization in top decay at CDF ats=1∶8 TeV[Phys. Rev. D71, 031101 (2005)

The polarization of the $W$ boson in $t \to W b$ decay is unambiguously predicted by the Standard Model of weak interactions and is a powerful test of our understanding of the $tbW$ vertex. The subsequent $W \to l \nu$ decay serves as a polarimeter for the $W$, and the invariant mass of the lepton and $b$ quark in top decay provides a measurement of the $W$ decay angle. In this paper we present a measurement of the decay rate of the W produced from the decay of the top quark in the hypothesis of V+A structure of the tWb vertex. We find no evidence for the non-standard V+A vertex and set a limit on $f_{V+A}$ $<$ 0.80 @ 95% confidence level. By combining this result with a complementary observable in the same data, we assign a limit of $f_{V+A}$ $<$ 0.61 @ 95% CL.

The van der Waals Energy of an Atom near a Carbon Nanotube

Using a unified macroscopic QED formalism, an integral equation for the van der Waals energy of a two-level atomic system near a carbon nanotube is derived. The equation is valid for both strong and weak atom-vacuum field coupling. By solving it numerically, the inapplicability of weak coupling-based van der Waals interaction models in the close vicinity of the nanotube surface is demonstrated. It is also shown that encapsulation of doped atoms into the nanotube is energetically more favorable than their outside adsorption by the nanotube surface.

Physics and present status of the WITCH experiment

The WITCH experiment (Weak Interaction Trap for CHarged particles) is starting measurements at the ISOLDE facility at CERN at present. It has been set up to measure the energy spectrum of the recoiling daughter ions after nuclear beta decay for precision tests of the Standard Model of weak interactions. However, many other topics of interest are accessible. In this article, the possibilities of recoil spectroscopy with the WITCH experiment are discussed, as well as the principle of the setup and its present situation.

BV photometry of five shell galaxies

AbstractCurrent views consider shell structures as bona fide signatures of a recent minor/major merging event though also weak interaction models (WIM) could produce long lasting shells on host galaxies possessing a stellar thick disc.We present a B V band photometric study of a sample of 5 shell galaxies belonging to the Malin &amp; Carter (1983) compilation. The structural properties and colors of the galaxies, as well as the colors of their shells are examined in detail.We did not find signatures of the presence of double nuclei. NGC 7585 is the only E galaxy in the sample and has a moderately boxy structure. The other galaxies have either a discy structure or are mixed E/S0 type galaxies. NGC 474 is a true lenticular. NGC 6776 shows a diffuse asymmetric outer structure and a system of tails of the the same color of the galaxy body; but not clear shells. In general, the color of the shells in our sample is similar or slightly redder than that of the host galaxy, whose color, in turn, is typical of the early‐type morphological class. One of the outer shells of NGC 474 is significantly bluer than the body of the galaxy. Since NGC 474 appears to be interacting with NGC 470, the color of this one shell could be explained as result of a recent acquisition of material through tidal interaction.The WIM hypothesis could explain both the red and the blue shells of NGC 474, this latter acquired from the fly‐by of the nearby companion NGC 470, but the lack of the constancy of shell surface brightness as a ratio of the underlying galaxy brightness argues against WIM. We speculate about evidence, which also comes from different observations, that suggests a merging/accretion origin of the shells. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Toward the Experimental Structure Determination of Larger Molecular Clusters: Application and Limitations of the Weak Interaction Model to the (C6H6)13B2u← A1g000Spectrum

The experimental B2u ← A1g00 0 spectrum of (C6H6)13 was analyzed within the weak-interaction model using minimum energy structures calculated from six different potential energy surfaces. The coexistence of two isomers—both of C3 symmetry and with nearly equal populations—is supported. Structures predicted by two of the six potential energy surfaces are strongly favored. The transition dipole of benzene moieties within the cluster has a magnitude of ∼0.23 Debye. Weak transition dipole–dipole interactions fall between −1.95 and +2.24 cm−1 and site shifts of ligand molecules range from −160.3 to −153.8 cm−1. Although the weak-interaction transition dipole–dipole model falls short of unambiguously determining isomeric structures of benzene-13, it establishes a solid foundation on which modeling can be based for determining structures of larger, high-symmetry, molecular clusters.

CPviolation in weak interactions from orbifold reduction: Possible unification structures

We present a mechanism to generate complex phases from real 4+1 dimensional couplings in a model of weak interactions through dimensional reduction of a gauge theory. The orbifolding of a 4+1 dimensional Sp(4) \times U(1) group is the minimal setup which provides both CP violation and an SU(2) \times U(1) structure. We show that grand unification requires at least SO(11).

LOCAL SYMMETRIES BEYOND THE STANDARD MODEL INDICATED BY NEUTRINO RESULTS

The present atmospheric neutrino oscillation data viewed within the context of see-saw mechanism for small neutrino masses, requires right handed neutrino masses (MR) around the conventional GUT scale i.e. 1015 to 1016 GeV. This raises a new hierarchy puzzle i.e. why MR≪Mpℓ? This can be interpreted as an indication in favor of new local symmetries around MR. In this paper, we argue that depending on the nature of neutrino mass patterns, this symmetry could either be: (i) the local B-L symmetry arising from a larger symmetry group such as in the left-right symmetric model of weak interactions, grand unified SO(10) models etc. or (ii) a local horizontal symmetry group SU(2)H operating on the fermions of the first two generations which is often invoked to understand the generation puzzles. We discuss some simple consequences of these symmetries and propose experimental for these ideas.

Observation of Intramolecular CH⋅⋅⋅FC Contacts in Non‐Metallocene Polyolefin Catalysts: Model for Weak Attractive Interactions between Polymer Chain and Noninnocent Ligand

Ein ungewöhnliches Konzept: Dass bei einer Olefinpolymerisation anziehende Wechselwirkungen zwischen einem funktionalisierten Hilfsliganden und einer wachsende Alkylkette bestehen, ist eine vollkommen neue Vorstellung. Solche Wechselwirkungen dürfen nur sehr schwach sein, damit der Kettenfortpflanzungsschritt nicht behindert wird; H-Brücken mit stark dispersivem Charakter wie CH⋅⋅⋅FC-Brücken sollten für diese Rolle also bestens geeignet sein (siehe Schema).

Observation of intramolecular C-H..F-C contacts in non-metallocene polyolefin catalysts: model for weak attractive interactions between polymer chain and noninnocent ligand.

Observation of intramolecular C-H..F-C contacts in non-metallocene polyolefin catalysts: model for weak attractive interactions between polymer chain and noninnocent ligand.

Electroweak jet cascading in the decay of superheavy particles.

We study decays of superheavy particles X into leptons. We show that they initiate cascades similar to QCD parton jets, if m(X) greater or similar 10(6) GeV. Electroweak cascading is studied and the energy spectra of the produced leptons are calculated in the framework of a broken SU(2) model of weak interactions. As application, important for the Z-burst model for ultrahigh energy cosmic rays, we consider decays of superheavy particles coupled on tree level only to neutrinos and derive a stringent limit for these decays from the observed diffuse extragalactic gamma-ray flux.

0422-476: a shell galaxy with azimuthally distributed shells

A morphological and two-colour CCD photometry study of the shellgalaxy 0422-476,one of the richest known azimuthally distributed shell galaxies, is presented. Takingthis galaxy as a prototype, a general method for reducing observational data of theseobjects is defined and quantitative parameters for use in furthertheoretical studiesare derived.According to some recent models (e.g., Thomson & Wright, 1990), the shells insuch a galaxy could be density waves induced in a thick disk population of dynamicallycold stars by a weak interaction with another galaxy. In 0422-476 there is no evidenceof either a conventional exponential disk or a thick disk. Although itis not possible torule out the weak interaction model, the observations continue to favour the mergermodel (e.g., Quinn, 1984)

Hydrogen bond energetics from topological analysis of experimental electron densities: Recognising the importance of the promolecule

In a recent paper [E. Espinosa, E. Molins, C. Lecomte, Chem. Phys. Lett. 285 (1998) 170] the kinetic energy density G( r c) and potential energy density V( r c) at the bond critical point r c in X–H⋯O hydrogen bonds were deduced from topological analyses of experimental electron distributions extracted from accurate X-ray diffraction experiments. We show that the promolecule, a model of non-interacting overlapping spherical atomic electron densities, can explain many of the observed results as well as the exponential dependence on the H⋯O distance. This raises the question of whether present experimental results differ from a simple reference model for weak interactions.

The weak decays of light hypernuclei

There has been recent progress on both theoretical and experimental frontiers to constrain models of weak interactions between baryons. The status of the analysis of Λ 4,5 He decay rates is discussed, comparing new results with other recent and old measurements. In addition to total decay widths, kinetic energy distributions and some preliminary coincidence spectra are presented. These coincidences have proven to be essential to the interpretation of the weak-decay processes. In light of these new results, there is now consensus that complementary measurement of the decays of Λ 4H is essential to address some basic questions, such as the validity of the ΔI=1/2 rule for nucleon-stimulated weak decay [1–5]. Prospects for such a measurement are also discussed.