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S. Scherer

Publications and source records attributed to S. Scherer.

At least 19 recordsLinked to original sources
arXiv2021

Quark-mass and $1/N_c$ corrections to the vector-meson pseudoscalar-meson photon ($VP\gamma$) interaction

We analyze quark-mass and $1/N_c$ corrections to all of the radiative transitions between the vector-meson nonet and the pseudoscalar-meson nonet within a chiral effective Lagrangian approach. We perform fits of the available coupling constants to experimental data and discuss the corresponding approximations. In terms of five (six) coupling constants, we obtain a reasonably good description of the 12 experimental decay rates.

hep-ph↗
arXiv2021

Axial-vector nucleon-to-delta transition form factors using the complex-mass renormalization scheme

We investigate the axial-vector nucleon-to-delta transition form factors in the framework of relativistic baryon chiral perturbation theory at the one-loop order using the complex-mass renormalization scheme. We determine the available six free parameters by fitting to an empirical parametrization of the form factors obtained from the BNL neutrino bubble chamber experiments. A unique feature of our calculation is the prediction of a non-vanishing form factor $C_3^A(Q^2)$. Moreover, our results show a surprising sensitivity to the coupling constant $\texttt{g}_1$ of the leading-order Lagrangian ${\cal L}^{(1)}_{\pi \Delta}$.

hep-ph↗
arXiv2018

Contribution of the $a_1$ meson to the axial nucleon-to-$\Delta$ transition form factors

We analyze the low-$Q^2$ behavior of the axial form factor $G_A(Q^2)$, the induced pseudoscalar form factor $G_P(Q^2)$, and the axial nucleon-to-$\Delta$ transition form factors $C^A_5(Q^2)$ and $C^A_6(Q^2)$. Building on the results of chiral perturbation theory, we first discuss $G_A(Q^2)$ in a chiral effective-Lagrangian model including the $a_1$ meson and determine the relevant coupling parameters from a fit to experimental data. With this information, the form factor $G_P(Q^2)$ can be predicted. For the determination of the transition form factor $C^A_5(Q^2)$ we make use of an SU(6) spin-flavor quark-model relation to fix two coupling constants such that only one free parameter is left. Finally, the transition form factor $C^A_6(Q^2)$ can be predicted in terms of $G_P(Q^2)$, the mean-square axial radius $\langle r^2_A\rangle$, and the mean-square axial nucleon-to-$\Delta$ transition radius $\langle r^2_{AN\Delta}\rangle$.

hep-ph↗
arXiv2016

Mass and width of the $\Delta(1232)$ resonance using complex-mass renormalization

We discuss the pole mass and the width of the $\Delta(1232)$ resonance to third order in chiral effective field theory. In our calculation we choose the complex-mass renormalization scheme (CMS) and show that the CMS provides a consistent power-counting scheme. In terms of the pion-mass dependence, we compare the convergence behavior of the CMS with the small-scale expansion (SSE).

nucl-th↗
arXiv2016

$\eta$-$\eta'$ Mixing in Large-$N_c$ Chiral Perturbation Theory

We present a calculation of the $\eta$-$\eta'$ mixing in the framework of large-$N_c$ chiral perturbation theory. A general expression for the $\eta$-$\eta'$ mixing at next-to-next-to-leading order (NNLO) is derived, including higher-derivative terms up to fourth order in the four momentum, kinetic and mass terms. In addition, the axial-vector decay constants of the $\eta$-$\eta'$ system are determined at NNLO. The numerical analysis of the results is performed successively at LO, NLO, and NNLO. We investigate the influence of one-loop corrections, OZI-rule-violating parameters, and $\mathcal{O}(N_c p^6)$ contact terms.

hep-ph↗
arXiv2015

Pion Photo- and Electroproduction and the Chiral MAID Interface

We discuss the extended on-mass-shell scheme for manifestly Lorentz-invariant baryon chiral perturbation theory. We present a calculation of pion photo- and electroproduction up to and including order $q^4$. The low-energy constants have been fixed by fitting experimental data in all available reaction channels. Our results can be accessed via a web interface, the so-called chiral MAID (http://www.kph.uni-mainz.de/MAID/chiralmaid/).

nucl-th↗
arXiv2015

Interaction of the vector-meson octet with the baryon octet in effective field theory

We analyze the constraint structure of the interaction of vector mesons with baryons using the classical Dirac constraint analysis. We show that the standard interaction in terms of two independent SU(3) structures is consistent at the classical level. We then require the self-consistency condition of the interacting system in terms of perturbative renormalizability to obtain relations for the renormalized coupling constants at the one-loop level. As a result we find a universal interaction with one coupling constant which is the same as in the massive Yang-Mills Lagrangian of the vector-meson sector.

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arXiv2014

Vector form factor of the pion in chiral effective field theory

The vector form factor of the pion is calculated in the framework of chiral effective field theory with vector mesons included as dynamical degrees of freedom. To construct an effective field theory with a consistent power counting, the complex-mass scheme is applied.

hep-ph↗
arXiv2014

Constraint analysis for the interaction of the vector-meson octet with the baryon octet

We describe a constraint analysis for the interaction of the vector-meson octet with the baryon octet. Applying Dirac's Hamiltonian method, we verify that the standard interaction in terms of two independent SU(3) structures is consistent at the classical level. We argue how the requirement of self consistency with respect to perturbative renormalizability may lead to relations among the renormalized coupling constants of the system.

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arXiv2014

Light Meson Dynamics Workshop. Mini proceedings

The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from February 10th to 12th, 2014, are presented. The web page of the conference, which contains all talks, can be found at https://indico.cern.ch/event/287442/overview .

hep-ph↗
arXiv2014

Electromagnetic transition form factors of the Roper resonance in effective field theory

We analyze the form factors of the electromagnetic nucleon-to-Roper-resonance transition in the framework of low-energy effective field theory. A systematic power-counting procedure is generated by applying the complex-mass scheme. Within this power counting we calculate the form factors to next-to-next-to-leading order and fit the results to empirical data.

nucl-th↗
arXiv2013

Pion photo- and electroproduction with chiral MAID

We present a calculation of pion photo- and electroproduction in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order $q^4$. We fix the low-energy constants by fitting experimental data in all available reaction channels. Our results can be accessed via a web interface, the so-called chiral MAID. We explain how our program works and how it can be used for further analysis.

nucl-th↗
arXiv2013

Accurate Test of Chiral Dynamics in the \boldmath$\vecγ p \rightarrow π^0p$ Reaction

A precision measurement of the differential cross sections $dσ/dΩ$ and the linearly polarized photon asymmetry $Σ\equiv (dσ_\perp - dσ_\parallel) \slash (dσ_\perp + dσ_\parallel)$ for the $\vecγ p \rightarrow π^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4π$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment.

nucl-ex↗
arXiv2012

Complex-mass scheme and perturbative unitarity

We derive cutting rules for loop integrals containing propagators with complex masses. Using a field-theoretical model of a heavy vector boson interacting with a light fermion, we demonstrate that the complex-mass scheme respects unitarity order by order in a perturbative expansion provided that the renormalized coupling constant remains real.

hep-ph↗
arXiv2012

Electromagnetic form factors of the nucleon in effective field theory

We calculate the electromagnetic form factors of the nucleon to third chiral order in manifestly Lorentz-invariant effective field theory. The rho and omega mesons as well as the Delta(1232) resonance are included as explicit dynamical degrees of freedom. To obtain a self-consistent theory with respect to constraints we consider the proper relations among the couplings of the effective Lagrangian. For the purpose of generating a systematic power counting, the extended on-mass-shell renormalization scheme is applied in combination with the small-scale expansion. The results for the electric and magnetic Sachs form factors are analyzed in terms of experimental data and compared to previous findings in the framework of chiral perturbation theory. The pion-mass dependence of the form factors is briefly discussed.

nucl-th↗
arXiv2012

Magnetic moment of the Roper resonance

The magnetic moment of the Roper resonance is calculated in the framework of a low-energy effective field theory of the strong interactions. A systematic power-counting procedure is implemented by applying the complex-mass scheme.

hep-ph↗
arXiv2011

Complex-mass scheme and resonances in EFT

The complex-mass scheme (CMS) provides a consistent framework for dealing with unstable particles in quantum field theory and has been successfully applied to various loop calculations. As applications of the CMS in chiral effective field theory we consider the form factor of the pion in the time-like region and the magnetic moment of the Roper resonance.

nucl-th↗