Infrared-suppressed QCD coupling and the hadronic contribution to muon g-2

A variant of QCD with the coupling suppressed in the infrared (IR) regime, as suggested by large-volume lattice calculations of the Landau-gauge gluon and ghost dressing functions, is considered. The coupling is further restricted by the condition of approximate coincidence with perturbative QCD in the high momentum regime, and by the $\tau$-lepton semihadronic decay rate in the intermediate momentum regime, the rate which is evaluated by a renormalon-motivated resummation method. The obtained coupling turns out to be free of Landau singularities. The $D=4,6$ condensate values of the Adler function are then extracted by application of the Borel sum rules to the OPAL and ALEPH (V+A)-channel data of $\tau$-decay, and the corresponding V-channel condensate values are deduced as well. We then show that the correct value of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment, $a_{\mu}^{\rm had(1)}$, is reproduced by regularizing the $D=4,6$ OPE terms in the V-channel Adler function with IR-regularization masses ${\cal M}_{D/2} \lesssim 1 \ {\rm GeV}$, suggesting the internal consistency of the presented QCD framework.Comment: 14 pages, 5 Figures, published in J.Phys.

Lattice-motivated QCD coupling and hadronic contribution to muon g−2g-2

We present an updated version of a QCD coupling which fulfills various physically motivated conditions: at high momenta it practically coincides with the perturbative QCD (pQCD) coupling; at intermediate momenta it reproduces correctly the physics of the semihadronic tau decay; and at very low momenta it is suppressed as suggested by large-volume lattice calculations. An earlier presented analysis is updated here in the sense that the Adler function, in the regime $|Q^2| \lesssim 1 \ {\rm GeV}^2$, is evaluated by a renormalon-motivated resummation method. This Adler function is then used here in the evaluation of the quantities related with the semihadronic (strangeless) $\tau$-decay spectral functions, including Borel-Laplace sum rules in the (V+A)-channel. The analysis is then extended to the evaluation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment, $a_{\mu}^{\rm had(1)}$, where we include in the Adler function the V-channel higher-twist OPE terms which are regulated in the infrared (IR) by mass parameters which are expected to be $\lesssim 1$ GeV. The correct value of $a_{\mu}^{\rm had(1)}$ can be reproduced with the mentioned IR-regulating mass parameters if the value of the condensate $\langle O_4 \rangle_{\rm V+A}$ is positive (and thus the gluon condensate value is positive). This restriction and the requirement of the acceptable quality of the fits to the various mentioned sum rules then lead us to the restriction $0.1171 < \alpha_s(M_Z^2;{\overline{MS}}) < 0.1180$.Comment: 33 pages, 10 figures; v4: minor corrections in the references; version to appear in J.Phys.

Semiconductor Halogenation in Molecular Highly-Oriented Layered p–n (n–p) Junctions

Organic p–n junctions attract widespread interest in the field of molecular electronics because of their unique optoelectronic singularities. Importantly, the molecular donor/acceptor character is strongly correlated to the degree of substitution, e.g., the introduction of electron-withdrawing groups. Herein, by gradually increasing the degree of peripheral fluorination on planar, D4h−symmetric iron(II) phthalocyanato (FePc) complexes, the energy level alignment and molecular order is defined in a metal-supported bilayered Pc-based junction using photoemission orbital tomography. This non-destructive method selectively allows identifying molecular levels of the hetero-architectures. It demonstrates that, while the symmetric fluorination of FePc does not disrupt the long-range order and degree of metal-to-molecule charge transfer in the first molecular layer, it strongly impacts the energy alignment in both the interface and topmost layer in the bilayered structures. The p–n junction formed in the bilayer of perhydrogenated FePc and perfluorinated FeF16Pc may serve as an ideal model for understanding the basic charge-transport phenomena at the metal-supported organic–organic interfaces, with possible application in photovoltaic devices

Magnetic susceptibility and spin dynamics of a polyoxovanadate cluster: A proton NMR study of a model spin tetramer

We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate compound with formula (NHEt)3[VIV8VV4As8O40(H2O)]H2O = (V12). The magnetic properties can be described by considering only the central square of localized V4+ ions and treated by an isotropic Heisenberg Hamiltonian of four intrinsic spins 1/2 coupled by nearest-neighbor antiferromagnetic interaction with J17.6K. In this simplified description the ground state is nonmagnetic with ST = 0. The 1H NMR linewidth (full width at half maximum) data depend on both the magnetic field and temperature, and are explained by the dipolar interaction between proton nuclei and V4+ ion spins. The behavior of the nuclear spin-lattice relaxation rate T-11 in the temperature range (4.2–300 K) is similar to that of χT vs T and it does not show any peak at low temperatures contrary to previous observations in antiferromagnetic rings with larger intrinsic spins. The results are explained by using the general features of the Moriya formula and by introducing a single T-independent broadening parameter for the electronic spin system. From the exponential T dependence of T-11 at low T(2.5K < T < 4.2K) we have obtained a field dependent gap following the linear relation ΔNMR = Δ0 “ gπBH, with the gap Δ0 17.6K in agreement with the susceptibility data. Below 2.5 K the proton T-11 deviates from the exponential decrease indicating the presence of a small, almost temperature independent, but strongly field dependent, nuclear relaxation contribution, which we will investigate in detail in the near future. © 2004 American Physical Society

Electronic structure and exchange interactions in V-15 magnetic molecules: LDA+U results

Contains fulltext : 60385.pdf (publisher's version ) (Open Access)Single-molecule magnets of the type V-15(K-6[V15As6O42(H2O)].8H(2)O) have attracted a great deal of attention recently, being promising systems for studying low-temperature spin-relaxation and quantum-spin tunneling. To understand in detail the internal magnetic and electronic structure, and the intramolecular interactions responsible for the formation and low-energy excitations in V-15 molecules, we have performed electronic structure calculations using the LSDA+U approach. The calculated values of magnetic moments and charge states of vanadium ions agree well with experiments, thus confirming the V4+ state of vanadium ions with a well-defined spin 1/2. We found that the account of the on-site Coulomb repulsion is important for correct description of V-15 internal properties; in particular, for the values of the on-site repulsion parameter Usimilar to4-5 eV, we can achieve good agreement with known properties of V-15, such as the temperature dependence of susceptibility, and the energies of the low-lying eigenstates of the spin Hamiltonian

Correlation effects in the electronic structure of the Mn4 molecular magnet

Contains fulltext : 72097.pdf (publisher's version ) (Open Access)4 p

A high-nuclearity "Celtic-Ring" isopolyoxotungstate, [H12W36O120] that captures trace potassium ions

Polyoxometalates have been subjected to a vast number of studies due to their attractive electronic and molecular properties that give rise to a variety of applications, e.g., in catalysis,1 medicine,2 and materials science.3 Their versatile nature originates from the ability to polymerize metal oxide-based polyhedra to form a range of clusters from low to high nuclearities. In particular, the ability for molybdenum-based systems to form very large clusters has been demonstrated by a number of nanosized cluster systems.4 Therefore, the ability to assemble large cluster systems from smaller known building blocks in a predetermined way is a great challenge, as such routes could be a direct way to systematically control the overall cluster architecture and properties. While developing strate-gies toward this goal, we recently reported a new family of isopoly-oxomolybdates5 based on the [H2Mo16O52]10- framework, and a family of sulfite-based Dawson-type polyoxomolybdates [Mo18O54