Weak Coupling Constants Research Articles

Radiative Neutron β-Decay in Effective Field Theory.

We consider radiative β-decay of the neutron in heavy baryon chiral perturbation theory. Nucleon-structure effects not encoded in the weak coupling constants gA and gV are determined at next-to-leading order in the chiral expansion, and enter at the -level, making a sensitive test of the Dirac structure of the weak currents possible.

A method for an improved measurement of the electron–antineutrino correlation in free neutron beta decay

The angular correlation between the beta electron and antineutrino in nuclear beta decay is characterized by the dimensionless parameter a . The value of a for free neutron decay, when combined with other neutron decay parameters, can be used to determine the weak vector and axial vector coupling constants g V and g A and test the validity and self-consistency of the Electroweak Standard Model. Previous experiments that measured a in neutron decay relied on precise proton spectroscopy and were limited by systematic effects at about the 5% level. We present a new approach to measuring a for which systematic uncertainties promise to be much smaller.

Parity-nonconserving observables in thermal neutron capture on a proton

We calculate parity nonconserving observables in the processes where a neutron is captured on a proton at the threshold energy radiating a photon. Various potential models such as Paris, Bonn and Argonne $v18$ are used for the strong interactions, and the meson-exchange description is employed for the weak interactions between hadrons. The photon polarization $P_\gamma$ in the unpolarized neutron capture process and photon asymmetry $A_\gamma$ in the polarized neutron capture process are obtained in terms of the weak meson-nucleon coupling constants. $A_\gamma$ turns out to be basically insensitive to the employed strong interaction models and thus can be uniquely determined in terms of the weak coupling constants, but $P_\gamma$ depends significantly on the strong interaction models.

Intra and intermodular exchange interactions in bis(α-aminoisobutyrato)oxalamidodicopper(Aib-COCO-Aib)Cu 2

Magnetic susceptibility and electron paramagnetic resonance (EPR) spectra of exquisite two-dimensional supramolecular assembly of [bis(α-aminoisobutyrato)oxalamidodicopper](Aib-COCO-Aib)Cu 2 were studied. The temperature dependent magnetic susceptibility studies reveal temperature dependency of the exchange coupling constant. Single crystal EPR studies both at X- and Q-bands show the two-dimensional nature of magnetic lattice and yield the weak intermodular exchange coupling constant in presence of strong intramodular exchange. The intermodular coupling is about five orders of magnitude smaller than the intramodular coupling but it produces a broadening and coalescence of the EPR lines. The temperature dependence of exchange coupling constant reflects dynamical properties of the crystal lattice.

Half-life and [formula omitted] value for the bare triton

Experimental and theoretical data on the atomic effects accompanying triton beta decay have been used to derive the bare triton half-life both for the case where only electrons of the continuous spectrum are formed and for the case where decay to bound states in the 3He+ ion is taken into account, and to calculate the comparative half-life which proved to be fT1/2=1129.6±3.0 s. Estimate of the ratio of axial-vector-to-vector weak coupling constants for the triton beta decay (GA/GV)t=−1.2646±0.0035 has been obtained from the relation connecting GA/GV and fT1/2.

Strangeness-conserving effective weak chiral Lagrangian

We consider the strangeness-conserving effective weak chiral Lagrangian based on the nonlocal chiral quark model from the instanton vacuum. We incorporate the effect of the strong interaction by the gluon into the effective Lagrangian. The effect of the Wilson coefficients on the weak pion-nucleon coupling constant is discussed briefly.

Parity violation in nuclear systems

Experimental measurements of Parity Non-Conserving (PNC) asymmetries in simple nuclear systems represent always a key-tool for the study of the weak nucleon-nucleon interaction and consequently an accurate experimental method for the determination of the meson-nucleon weak coupling constants of the underlying theory. Recent theoretical analysis on the deuteron photodisintegration with polarized photons, a few MeV above threshold, have drastically improved previous theoretical estimates. Based on that, the feasibility of measuring the photon asymmetry A γ in the reaction \( \bar \gamma + d \to n + p \) with the 10-MeV CW Linac at the Institute of Accelerating Systems and Applications (IASA) is considered here. A brief review on previous experimental results obtained in the deuteron photodisintegration and in the thermal-neutron radiative capture on protons (inverse reaction) is given. The most important parameters in the design of a nuclear parity experiment are presented and the crucial factors, such as beam intensity, beam polarization and neutron detection techniques with the required high accuracy are outlined.

COUPLING CONSTANT UNIFICATION IN EXTENSIONS OF STANDARD MODEL

Unification of electromagnetic, weak, and strong coupling constants is studied in the extension of Standard Model with additional fermions and scalars. It is remarkable that this unification in the supersymmetric extension of Standard Model yields a value of Weinberg angle which agrees very well with experiments. We discuss the other possibilities which can also give same result.

Radiative neutron β-decay in effective field theory

We consider radiative β-decay of the neutron in heavy baryon chiral perturbation theory, with an extension including explicit Δ degrees of freedom. We compute the photon energy spectrum as well as the photon polarization; both observables are dominated by the electron bremsstrahlung contribution. Nucleon-structure effects not encoded in the weak coupling constants gA and gV are determined at next-to-leading order in the chiral expansion, and enter at the O(0.5%)-level, making a sensitive test of the Dirac structure of the weak currents possible.

Myo1c is designed for the adaptation response in the inner ear.

The molecular motor, Myo1c, a member of the myosin family, is widely expressed in vertebrate tissues. Its presence at strategic places in the stereocilia of the hair cells in the inner ear and studies using transgenic mice expressing a mutant Myo1c that can be selectively inhibited implicate it as the mediator of slow adaptation of mechanoelectrical transduction, which is required for balance. Here, we have studied the structural, mechanical and biochemical properties of Myo1c to gain an insight into how this molecular motor works. Our results support a model in which Myo1c possesses a strain-sensing ADP-release mechanism, which allows it to adapt to mechanical load.

Synthesis and studies of a trinuclear Mn(II) carboxylate complex.

We report a carboxylate triangle consisting of three manganese(II) centres which is made from manganese(II) carbonate and pivalic acid. The magnetic exchange within the triangle is extremely weak, and antiferromagnetic. Several models have been used to fit the magnetic data, and the best fit uses two weak antiferromagnetic coupling constants of J(1)=-0.588 cm(-1) and J(2)=-0.855 cm(-1). Exchange interactions between the metal centres has been calculated using DFT adopting all the three possible Heisenberg models for a trinuclear system and the results are compared with experimental values. Spin density distribution is used to analyse the nature of the coupling between the metal centres. EPR spectroscopy has been used to explore the nature of the ground state. Recrystallisation of the trinuclear compound from MeCN gives a polymer, while oxidation in air leads to a known compound--an edge-sharing bitetrahedral (MnIII2MnII4) cage.

Parity violation in proton-proton scattering at 221 MeV

pp elastic scattering at 221.3 MeV incident proton energy. This comprehensive paper includes details of the corrections, some of magnitude comparable to Az itself, required to arrive at the final result. The largest correction was for the effects of first moments of transverse polarization. The addition of the result, Az = (0.84 ± 0.29(stat.) ± 0.17(syst.)) × 10 7 , to the ~ pp parity violation experimental data base greatly improves the experimental constraints on the weak meson-nucleon coupling constants h pp and h pp , and also has implications for the interpretation of electron parity violation experiments.

Numerical solution of the color superconductivity gap in a weak coupling constant

We present the numerical solution of the full gap equation in a weak coupling constant $g$. It is found that the standard approximations to derive the gap equation to the leading order of coupling constant are essential for a secure numerical evaluation of the logarithmic singularity with a small coupling constant. The approximate integral gap equation with a very small $g$ should be inverted to a soft integral equation to smooth the logarithmic singularity near the Fermi surface. The full gap equation is solved for a rather large coupling constant $g\ge 2.0$. The approximate and soft integral gap equations are solved for small $g$ values. When their solutions are extrapolated to larger $g$ values, they coincide the full gap equation solution near the Fermi surface. Furthermore, the analytical solution matches the numerical one up to the order one O(1). Our results confirm the previous estimates that the gap energy is of the order tens to 100 MeV for the chemical potential $\mu\le 1000$ MeV. They also support the validity of leading approximations applied to the full gap equation to derive the soft integral gap equation and its analytical solution near the Fermi surface.

Nuclear spin-isospin correlations, parity violation, and thefπproblem

The strong interaction effects of isospin- and spin-dependent nucleon-nucleon correlations observed in many-body calculations are interpreted in terms of a one-pion exchange mechanism. Including such effects in computations of nuclear parity violating effects leads to enhancements of about 10%. A larger effect arises from the one-boson exchange nature of the parity non-conserving nucleon- nucleon interaction, which depends on both weak and strong meson-nucleon coupling constants. Using values of the latter that are constrained by nucleon-nucleon phase shifts leads to enhancements of parity violation by factors close to two. Thus much of previously noticed discrepancies between weak coupling constants extracted from different experiments can be removed.

Hexacyanometalate molecular chemistry: di-, tri-, tetra-, hexa- and heptanuclear heterobimetallic complexes; control of nuclearity and structural anisotropy.

Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.

Hexacyanometalate molecular chemistry: heptanuclear heterobimetallic complexes; control of the ground spin state.

Following a bottom-up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)(6)](3-) (M=Cr(III), Co(III)) cores to well-defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=Cr(III), d(3), S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single-crystal X-ray diffraction and by powder magnetic susceptibility measurements, [Cr(III)(CNbondM'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II), L(n)=polydentate ligand), showing spin ground states S(G)=9/2 [Cu(II)], with ferromagnetic interactions J(Cr,Cu)=+45 cm(-1), S(G)=15/2 [Ni(II)] and J(Cr,Ni)=+17.3 cm(-1), S(G)=27/2 [Mn(II)], with an antiferromagnetic interaction J(Cr,Mn)=-9 cm(-1), (interaction Hamiltonian H=-J(Cr,M) [S(Cr)Sigma(i)S(M)(i)], i=1-6). With M=Co(III), d(6), S=0, the heptanuclear analogues [Co(III)(CN-M'L(n))(6)](9+) (M'=Cu(II), Ni(II), Mn(II)) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.

Inclusive quasielastic ν reaction in 16O

We calculate the inclusive quasielastic ν μ cross sections in 16O. The calculations are done in the Local Density Approximation(LDA) and take into account Pauli blocking, Fermi motion and the effect of renormalization of weak coupling constants in the nuclear medium.

NONLEPTONIC KAON DECAYS: THEORY VS. EXPERIMENT

A review of the present experimental status of the rates and the Dalitz-plot slope parameters in CP conserving K→2π and K→3π decays is given. The corresponding isospin amplitudes have been determined by a common fit to the recent experimental data and have been used as an input to a consequent fit based on the constraints from O(p4) chiral Lagrangian. It has been found that the constraints of the chiral fit are well satisfied by the experimental data, allowing one to estimate the weak coupling constants and to predict the quadratic amplitudes in K→3π decays and the one-loop strong rescattering phases. The consistency of the obtained weak coupling constants with weak resonance models has also been considered.

Scattering of magnons by a vortex pair in a two-dimensional classicalXYmodel with an in-plane magnetic field

We consider the magnon modes of a vortex-antivortex pair in a two-dimensional classical XY ferromagnet in the presence of a magnetic field applied along one of the in-plane axes. The exact analytical expressions for magnon modes of zero frequency are derived. The magnon waveforms of the continuum states are obtained using the Born approximation. The results can also be applied to anisotropic three-dimensional systems with a weak interlayer coupling constant.

Methyl groups as local probes for polymer dynamics as investigated by [formula omitted] double-quantum magic-angle spinning NMR spectroscopy

We illustrate the application of high-resolution homonuclear 1 H double-quantum magic-angle spinning solid-state NMR recoupling experiments for an efficient measurement of segmental order parameters for polymers with methyl groups. A theoretical treatment of the spin dynamics of methyl groups during a corresponding pulse sequence including experimental imperfections is given. The applicability of the analytical result for the extraction of dipole–dipole coupling constants from experimental data is illustrated for a model substance. Experiments on entangled polymer melts indicate that double-quantum spectroscopy on methyl groups is well-suited for the extraction of very weak coupling constants, which permit the calculation of well-defined order parameters.