Small Coupling Constant Research Articles

On the interference of J(HH) modulation in HSQMBC‐IPAP and HMBC‐IPAP experiments

The effects of phase modulation due to homonuclear proton-proton coupling constants in HSQMBC-IPAP and HMBC-IPAP experiments are experimentally evaluated. We show that accurate values of small proton-carbon coupling constants, (n)J(CH), can be extracted even for phase-distorted cross-peaks obtained from a selHSQMBC experiment applied simultaneously on two mutually J-coupled protons. On the other hand, an assessment of the reliability of (n)J(CH) measurement from distorted cross-peaks obtained in broadband IPAP versions of equivalent HMBC and HSQMBC experiments is also presented. Finally, we show that HMBC-COSY experiments could be an excellent complement to HMBC for the measurement of small (n)J(CH) values.

On the detectability of57Fe axion-photon mode conversion in the Sun

The purpose of this paper is to assess the feasibility of axion detection by X-ray spectroscopy of the sun. We review the theory of axion-photon mode conversion with special attention to axions emitted in the 14.4 keV M1 decay of 57Fe at the solar center. These then mode convert to photons in the outer layers of the solar envelope, and may in principle be detected subsequently as X-rays. For axion masses above about 10^-4 eV, resonant mode conversion at a layer where the axion mass matches the local electron plasma frequency is necessary. For axion masses above about 10^-2 eV, this mode conversion occurs too deep in the solar atmosphere for the resulting photon to escape the solar surface and be detected before Compton scattering obscures the line. At the (detectable) axion masses below this, the flux of mode converted photons predicted by axion models appears to be too low for detection to be feasible with current instrumentation. Nonresonant mode conversion for axion masses below 10^-4 eV is also plausible, but with still lower predicted fluxes, since the axion coupling constant is related to it mass. Prospects for meaningful constraints on massive axion parameters from X-ray observations of this transition from the Sun do not appear to be promising. However parameters for massless counterparts (e.g. the "arion") may still result from such observations. It may mode convert in the outer layers of the solar atmosphere, but is not restricted by this to have a small coupling constant.

Classically scale-invariant B-L model and dilaton gravity

We consider a coupling of dilaton gravity to the classically scale-invariant B-L extended standard model, which has been recently proposed as a phenomenologically viable model realizing the Coleman-Weinberg mechanism of breakdown of the electroweak symmetry. It is shown in the present model that without recourse to the Coleman-Weinberg mechanism, the B-L gauge symmetry is broken in the process of spontaneous symmetry breakdown of scale invariance at the tree level, and as a result the B-L gauge field becomes massive via the Higgs mechanism. Since the dimensionful parameter is only the Planck mass in our model, one is forced to pick up very small coupling constants if one wishes to realize the breaking of the B-L symmetry at the TeV scale.

Detection of protonated vinyl cyanide, CH2CHCNH+, a prototypical branched nitrile cation

The rotational spectrum of protonated vinyl cyanide, CH2CHCNH(+), a prototypical branched nitrile species and likely intermediate in astronomical sources and in the planetary atmosphere of Titan, has been detected in a pulsed-discharge supersonic molecular beam by means of Fourier transform microwave spectroscopy. Fifteen lines arising from 11 a-type rotational transitions have been observed between 9 and 46 GHz, several with partially resolved nitrogen hyperfine structure. From this data set, the leading spectroscopic constants, including all three rotational constants, have been determined to high accuracy. The agreement between experimental rotational constants and those calculated at the CCSD(T) level of theory is of order 0.1%. An even better estimate was obtained through empirical scaling using calculated and experimental rotational constants of isoelectronic vinyl acetylene. Measurement of a small nitrogen quadrupole coupling constant in protonated vinyl cyanide is consistent with a quadruply bound nitrogen atom and a H(+)-N≡C-R type structure. Because vinyl cyanide is abundant in molecule-rich astronomical sources and possesses a high proton affinity, and because protonated vinyl cyanide is unreactive with hydrogen and other well-known interstellar species, this cation is an excellent candidate for astronomical detection. The present work suggests that other organic molecules containing the nitrile group and closely related species such as protonated vinyl acetylene can probably be detected with the same instrumentation.

Minimization of the energy of the nonrelativistic one-electron Pauli-Fierz model over quasifree states

In this article the existence of a minimizer for the energy for the nonrelativistic one-electron Pauli-Fierz model within the class of quasifree states is established. To this end it is shown that the minimum of the energy on quasifree states coincides with the minimum of the energy on pure quasifree states, where existence and uniqueness of a minimizer holds. Infrared and ultraviolet cutoffs are assumed, along with sufficiently small coupling constant and momentum of the dressed electron. A perturbative expression of the minimum of the energy on quasifree states for a small momentum of the dressed electron and small coupling constant is given. We also express the Lagrange equation for the minimizer in terms of the generalized one particle density matrix of the pure quasifree state.

Multi-site breathers in Klein–Gordon lattices: stability, resonances and bifurcations

We prove a general criterion of spectral stability of multi-site breathers in the discrete Klein–Gordon equation with a small coupling constant. In the anti-continuum limit, multi-site breathers represent excited oscillations at different sites of the lattice separated by a number of ‘holes’ (sites at rest). The criterion describes how the stability or instability of a multi-site breather depends on the phase difference and distance between the excited oscillators. Previously, only multi-site breathers with adjacent excited sites were considered within the first-order perturbation theory. We show that the stability of multi-site breathers with one-site holes changes for large-amplitude oscillations in soft nonlinear potentials. We also discover and study a symmetry-breaking (pitchfork) bifurcation of one-site and multi-site breathers in soft quartic potentials near the points of 1 : 3 resonance.

A solid-state NMR investigation of the colossal expansion material, Ag3Co(CN)6

Presented here is a solid-state NMR investigation of the so-called “colossal expansion” material, Ag3Co(CN)6, a compound that exhibits some of the largest positive and negative thermal expansion properties reported. This study explores the 13C, 15N, and 59Co NMR properties of this material at room temperature and at variable temperatures with the goal of probing the effects of this colossal expansion behaviour on these properties. We found that the flexible nature of the crystal framework leads to a distribution of electric field gradients, and that, oddly enough, no strong correlation is observed between the NMR parameters of Ag3Co(CN)6 and its colossal expansion nature. The 59Co isotropic chemical shift increased and the 59Co nuclear quadrupolar coupling constant decreased with increasing temperature, but neither of these relationships were extraordinary when compared to other octahedral Co(III) complexes. The link between the colossal expansion and the NMR properties of Ag3Co(CN)6 may be the distribution of lattice parameters and hence unusually broad features in the 59Co NMR spectra. The high order of symmetry at the cobalt site resulted in a small quadrupolar coupling constant less than 1 MHz in magnitude. We also observed a |1J(107/109Ag,15N)| value of 96 Hz, the largest 107/109Ag–15N coupling constant reported to date.

The quasi-magnetic-hysteresis behavior of polydisperse ferrofluids with small coupling constant

The magnetization behaviors of ferrofluids based on γ-Fe 2 O 3 /Ni 2 O 3 composite nanoparticles of size about 11 nm have been investigated. The dipole coupling constant λ of these particles is so small (0.43) that they cannot form aggregates through magnetic interaction alone. Experimental results have shown that for a polydisperse ferrofluid with a particle volume fraction of ϕ V =2.4%, the magnetization curve exhibits quasi-magnetic-hysteresis behavior, i.e., the demagnetization curve lies above the magnetization curve in a high field. However, for a more dilute γ-Fe 2 O 3 /Ni 2 O 3 ferrofluid with ϕ V =0.94%, the magnetization curve does not show such behavior. According to the bidisperse model for polydisperse ferrofluids, these magnetization behaviors may be attributed to field-induced effects of self-assembled pre-existing chain-like aggregates. For such pre-existing chain-like aggregates, the orientation of the moments inside the particles is not co-linear, so that during the magnetization and demagnetization processes, their apparent magnetizations at the high-field limit are different. As a consequence, the magnetization curve of the ferrofluid with ϕ V =2.4% displays quasi-magnetic-hysteresis.

A Non-Karplus Effect: Evidence from Phosphorus Heterocycles and DFT Calculations of the Dependence of Vicinal Phosphorus–Hydrogen NMR Coupling Constants on Lone-Pair Conformation

In contrast to literature reports of a Karplus-type curve that correlates (3)J(PH) with phosphorus-hydrogen dihedral angle, a recently reported glycine-derived 1,3,2-oxazaphospholidine (7c) has two hydrogen atoms on the ring with identical PNCH dihedral angles but measured coupling constants of ∼6 and 1.5 Hz. DFT calculations were in accord with these values and suggested that the smaller coupling constant is negative. Experimental evidence of the opposite signs of these coupling constants was obtained by analysis of the ABX NMR spectrum of the new glycine-derived N-p-toluenesulfonyl phosphorus heterocycle 6c. DFT calculations on 6c and on Me(2)NPCl(2) and t-BuPCl(2) were also in accord with NMR data and allowed confirmation of unusual features including a lone pair effect on (3)J(PH), the negative coupling constant, temperature-dependent chemical shifts due to rotation about the sulfonamide S-N bond, and vicinal phosphorus-hydrogen coupling constants over 40 Hz. Calculation of phosphorus-hydrogen coupling constants both as a function of PYCH dihedral angle θ (Y = O, N, C) and lone pair-PYC dihedral angle ω shows similar θ,ω surfaces for (3)J(PH) with a range of (3)J(PH) from -4.4 to +51 Hz and demonstrates the large non-Karplus effect of lone-pair conformation on vicinal phosphorus-hydrogen coupling constants.

Magnetic Properties and Electronic Structure of Ni81Fe19/Zr Multilayer Films

Magnetic properties of NiFe/Zr multilayer films, prepared by DC magnetron sputtering, have been studied by vibrating sample magnetometer and ferromagnetic resonance (FMR). Spin-wave resonances were observed in Ni81Fe19/Zr multilayer films in FMR experiments, and the spin wave was found to be sustained by both the whole films. Estimated small interlayer coupling constant shows weak exchange coupling effect between NiFe layers across Zr spacers. The FMR linewidth, in parallel geometry, of the uniform mode was found to increase with decreasing NiFe thickness (20 A ≤ \(t_{\mathrm{NiFe}}\) ≤ 120 A) indicating that it corresponds to an interfacial effect. In addition, electronic and magnetic properties of multilayers are investigated by self-consistent ab initio calculations based on Korringa–Kohn–Rostocker (KKR). Spin polarized within the framework of the Coherent Potential Approximation (CPA) is considered for calculations.

Multifractal dimensions for all moments for certain critical random-matrix ensembles in the strong multifractality regime

We construct perturbation series for the qth moment of eigenfunctions of various critical random-matrix ensembles in the strong multifractality regime close to localization. Contrary to previous investigations, our results are valid in the region q<1/2. Our findings allow one to verify, at first leading orders in the strong multifractality limit, the symmetry relation for anomalous fractal dimensions Δ(q)=Δ(1-q), recently conjectured for critical models where an analog of the metal-insulator transition takes place. It is known that this relation is verified at leading order in the weak multifractality regime. Our results thus indicate that this symmetry holds in both limits of small and large coupling constant. For general values of the coupling constant we present careful numerical verifications of this symmetry relation for different critical random-matrix ensembles. We also present an example of a system closely related to one of these critical ensembles, but where the symmetry relation, at least numerically, is not fulfilled.

A Definitive NMR Solution for a Simple and Accurate Measurement of the Magnitude and the Sign of Small Heteronuclear Coupling Constants on Protonated and Non‐Protonated Carbon Atoms

Simply successful: a proton-selective HSQMBC-TOCSY experiment can be used to measure small proton-carbon ((n)J(CH); n>1) coupling constants on both protonated and non-protonated carbon atoms. The method combines in a single pulse scheme all the benefits of the widely used HSQMBC and HSQC-TOCSY experiments. The magnitude and the sign of (n)J(CH) can be determined simply with excellent accuracy.

A Definitive NMR Solution for a Simple and Accurate Measurement of the Magnitude and the Sign of Small Heteronuclear Coupling Constants on Protonated and Non‐Protonated Carbon Atoms

Einfach erfolgreich: Mit einem protonenselektiven HSQMBC-TOCSY-Experiment wurden kleine Kopplungskonstanten zwischen Protonen und Kohlenstoffatomen (nJCH; n>1) an protonierten und nichtprotonierten Kohlenstoffatomen ermittelt (siehe Spektrum). Die Methode verbindet in einem Pulsschema die Vorzüge von HSQMBC- und HSQC-TOCSY-Experiment. Die Größe und das Vorzeichen von nJCH konnten sehr genau bestimmt werden.

Orbital fluctuation theory in iron-based superconductors: [formula omitted]-wave superconductivity, structure transition, and impurity-induced nematic order

The main features in iron-based superconductors would be (i) the orthorhombic transition accompanied by remarkable softening of shear modulus, (ii) high-Tc superconductivity close to the orthorhombic phase, and (iii) nematic transition in the tetragonal phase. In this paper, we present a unified explanation for them, based on the orbital fluctuation theory, considering both the e-ph and the Coulomb interaction. It is found that a small e-phonon coupling constant (λ∼0.2) is enough to produce large orbital (= charge quadrupole Oxz/yz) fluctuations, which causes the s-wave superconductivity without sign reversal (s++-wave state). The derived orbital fluctuations also cause the instability toward the structure transition due to the bound state formation of two orbitons with opposite momenta, which is called the “two-orbiton process”. Moreover, impurity-induced non-local orbital order with C2-symmetry is obtained when the orbital fluctuations are strong. This “impurity-induced nematic state” explains the in-plane anisotropy of resistivity in detwinned samples. We stress that (i)–(iii) are reproducible only when orbital fluctuations with respect to Oxz and Oyz charge quadrupoles are the most divergent. This fact ensures the reliability of the present model Hamiltonian and calculation.

Dual Reactivity of a Stable Zwitterionic N-Heterocyclic Silylene and Its Carbene Complex Probed with Muonium

The reactivity of the multifunctional cyclic silylene 4 and its carbene complex 5 have been investigated by a combination of muon spin spectroscopy and computation. The free radicals formed by muonium (Mu) addition to 4 were identified, showing that there are two dominant sites of free radical attack: on the Si atom and on the exocyclic methylene carbon. Reaction of muonium with 5 also produced two radicals, but with markedly different hyperfine constants. For both compounds avoided level-crossing resonance spectra and calculation of hyperfine constants show that one of the radicals results from Mu addition to the methylene group, yielding radicals 4a and 5a. Each contains a muoniated methyl group, −CH2Mu, which undergoes restricted rotation with respect to the plane of the ring. For 4 the second product is readily assigned as the muoniated silyl radical 4b, on the grounds of its high muon hyperfine constant (716 MHz). The second product from 5 shows instead a very small coupling constant, 19 MHz, assigna...

Solid-state 17O NMR and computational studies of terminal transition metal oxo compounds

We report solid-state NMR characterization of the 17O (I = 5/2) chemical shift and quadrupole coupling tensors in two terminal oxo compounds, 17O≡Ti(IV)(TMP) and 17O≡Cr(IV)(TMP), in which TMP is 5,10,15,20-tetramesitylporphyrin and the oxo ligand is enriched by 17O (ca. 40%). This is the first time that 17O NMR tensors are determined for this important class of compounds. The 17O nuclei in the O≡Ti and O≡Cr triple bonds are found to exhibit very large chemical shift anisotropies but rather small 17O quadrupole coupling constants. Terminal oxo compounds represent one of the rare cases where the atomic nucleus under study simultaneously experiences a highly anisotropic magnetic shielding environment, but a highly symmetrical electric field distribution. The solid-state 17O NMR data are consistent with solid-state 13C, 15N and 31P NMR results on carbido, nitrido and phosphido compounds. The density functional theory (DFT) computations using the zeroth-order regular approximation (ZORA) to account for spin-orbital relativistic effects reproduce the experimental 17O NMR results reasonably well. DFT computations also reveal the origins at the molecular orbital level of the observed 17O NMR properties for terminal oxo compounds.

D=(2+1)O(N)Wess-Zumino model in a large-Nlimit

Using the superfield formalism, the effective K\"ahlerian superpotential of the massless $\mathcal{N}=1$ $O(N)$ Wess-Zumino model is computed in the limit of large $N$, in three spacetime dimensions. The effective K\"ahlerian superpotential is evaluated at the subleading order in the $1/N$ expansion, which involves diagrams up to two-loop order, for a small coupling constant. We show that the $O(N)$ symmetry of the model is preserved in this approximation and that no mass is dynamically generated in the supersymmetric phase. We discuss why spontaneous $O(N)$ symmetry breaking cannot be induced by radiative corrections in such a model.

On the validity of the variational approximation in discrete nonlinear Schrödinger equations

The variational approximation is a well known tool to approximate localized states in nonlinear systems. In the context of a discrete nonlinear Schrödinger equation with a small coupling constant, we prove error estimates for the variational approximations of site-symmetric, bond-symmetric, and twisted discrete solitons. This is shown for various trial configurations, which become increasingly more accurate as more parameters are taken. It is also shown that the variational approximation yields the correct spectral stability result and controls the oscillatory dynamics of stable discrete solitons for long but finite time intervals.

QUANTUM GRAVITY IN PLEBANSKI FORMULATION

We present a theory of four-dimensional quantum gravity with massive gravitons which may be essentially renormalizable. In Plebanski formulation of general relativity in which the tetrads, the connection and the curvature are all independent variables (and the usual relations among these quantities are valid only on-shell), we consider the nonperturbative theory of gravity with a nonzero background connection. We predict a tiny value of the graviton mass: mg≈1.5×10-42 GeV and extremely small dimensionless coupling constant of the perturbative gravitational interaction: g~10-60. We put forward the idea by Isimori56 on renormalizability of quantum gravity having multi-gravitons with masses m0, m1, …, mN-1.

Accurate measurement of small heteronuclear coupling constants from pure-phase α/ β HSQMBC cross-peaks

A simple proton-selective α/ β-HSQMBC experiment is proposed for the accurate measurement of long-range proton–carbon coupling constants ( n J CH) in small molecules without need for an individualized and time-consuming post-processing fitting procedure. The method acquires two pure-phase In-phase (IP) and Anti-phase (AP) multiplets completely free of any phase distortion due to the absence of J HH evolution. Accurate n J CH values can be directly measured analyzing the relative displacement of the resulting IPAP cross-peaks. Discussion about signal intensity dependence and cross-talk is made for a range of experimental conditions. The robustness of the method is evaluated by comparing the n J CH value measured from the analysis of the three available IP, AP and IPAP multiplet patterns. Multiple-frequency and region-selective versions of the method can also be efficiently recorded provided that excited protons are not mutually coupled.