Search results for "Vertex function"
showing 10 items of 21 documents
On-shell two-loop three-gluon vertex
1998
The two-loop three-gluon vertex is calculated in an arbitrary covariant gauge, in the limit when two of the gluons are on the mass shell. The corresponding two-loop results for the ghost-gluon vertex are also obtained. It is shown that the results are consistent with the Ward-Slavnov-Taylor identities.
Decay of vector-vector resonances into $\gamma$ and a pseudoscalar meson
2010
We study the decay of dynamically generated resonances from the interaction of two vectors into a $\ensuremath{\gamma}$ and a pseudoscalar meson. The dynamics requires anomalous terms involving vertices with two vectors and a pseudoscalar, which renders it special. We compare our result with data on ${K}_{2}^{*+}(1430)\ensuremath{\rightarrow}{K}^{+}\ensuremath{\gamma}$ and ${K}_{2}^{*0}(1430)\ensuremath{\rightarrow}{K}^{0}\ensuremath{\gamma}$ and find a good agreement with the data for the ${K}_{2}^{*+}(1430)$ case and a width considerably smaller than the upper bound measured for the ${K}_{2}^{*0}(1430)$ meson. We also investigate the decay into ${\ensuremath{\pi}}^{+}\ensuremath{\gamma}$ …
Anomalous magnetic moment of the muon in a dispersive approach
2014
We present a new general dispersive formalism for evaluating the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. In the suggested approach, this correction is related to the imaginary part of the muon's electromagnetic vertex function. The latter may be directly related to measurable hadronic processes by means of unitarity and analyticity. As a test we apply the introduced formalism to the case of meson pole exchanges and find agreement with the direct two-loop calculation.
Weak-interaction and nuclear-structure aspects of nuclear double beta decay
1998
Abstract Weak-interaction and nuclear-structure aspects of double beta decay are reviewed. Starting from effective electroweak lagrangians, decay rates for the two-neutrino and neutrinoless modes of the nuclear double beta decay transitions are defined and second-order perturbative expressions for the nuclear decay amplitudes are given. Nuclear matrix elements of the relevant operators are presented, as extracted from data and from shell-model and QRPA calculations as well as from other theoretical approximations. The analysis is performed both for the two-neutrino and neutrinoless modes of the decay. The expressions for ground-state-to-ground-state and ground-state-to-excited-state transit…
Dynamically screened vertex correction to $GW$
2020
Diagrammatic perturbation theory is a powerful tool for the investigation of interacting many-body systems, the self-energy operator $\mathrm{\ensuremath{\Sigma}}$ encoding all the variety of scattering processes. In the simplest scenario of correlated electrons described by the $GW$ approximation for the electron self-energy, a particle transfers a part of its energy to neutral excitations. Higher-order (in screened Coulomb interaction $W$) self-energy diagrams lead to improved electron spectral functions (SFs) by taking more complicated scattering channels into account and by adding corrections to lower order self-energy terms. However, they also may lead to unphysical negative spectral f…
Generalized Nutbrown representation of the vector vertex function and the magnetic moment of the chargedρmeson
1975
A former representation of the vector vertex function, due to Nutbrown, is generalized. It is shown how this resolves an apparent contradiction between the effective-Lagrangian and hard-meson techniques. Further possible applications are discussed. (AIP)
Two-loop Anomalous Dimensions of Heavy Baryon Currents in Heavy Quark Effective Theory
1996
We present results on the two-loop anomalous dimensions of the heavy baryon HQET currents $J=(q^TC\Gamma\tau q)\Gamma'Q$ with arbitrary Dirac matrices $\Gamma$ and $\Gamma'$. From our general result we obtain the two-loop anomalous dimensions for currents with quantum numbers of the ground state heavy baryons $\Lambda_Q$, $\Sigma_Q$ and $\Sigma_Q^*$. As a by-product of our calculation and as an additional check we rederive the known two-loop anomalous dimensions of mesonic scalar, pseudoscalar, vector, axial vector and tensor currents $(J=\bar q\Gamma q)$ in massless QCD as well as in HQET.
Scalar diagrammatic rules for Born amplitudes in QCD
2005
We show that all Born amplitudes in QCD can be calculated from scalar propagators and a set of three- and four-valent vertices. In particular, our approach includes amplitudes with any number of quark pairs. The quarks may be massless or massive. The proof of the formalism is given entirely within quantum field theory.
Semileptonic decays of double heavy baryons in a relativistic constituent three-quark model
2009
We study the semileptonic decays of double heavy baryons using a manifestly Lorentz covariant constituent three-quark model. We present complete results on transition form factors between double-heavy baryons for finite values of the heavy quark/baryon masses and in the heavy quark symmetry limit which is valid at and close to zero recoil. Decay rates are calculated and compared to each other in the full theory, keeping masses finite, and also in the heavy quark limit.
Two-loop tensor integrals in quantum field theory
2004
A comprehensive study is performed of general massive, tensor, two-loop Feynman diagrams with two and three external legs. Reduction to generalized scalar functions is discussed. Integral representations, supporting the same class of smoothness algorithms already employed for the numerical evaluation of ordinary scalar functions, are introduced for each family of diagrams.