We present a phenomenological discussion of spin-independent, generalized dipole polarizabilities of hadrons entering the virtual Compton scattering process γ*h⃗γh. We introduce a new method of obtaining a tensor basis with appropriate Lorentz-invariant amplitudes which are free from kinematical singularities and constraints. The result is summarized in terms of a compact effective Lagrangian. We then motivate a gauge-invariant separation into a generalized Born term containing ground-state properties only and a residual contribution describing the model-dependent internal structure. The generalized dipole polarizabilities are defined in terms of Lorentz-invariant residual amplitudes. Particular emphasis is laid on a physical interpretation of these quantities as characterizing the spatial distributions of the induced electric polarization and magnetization of hadrons. It is argued that three dipole polarizabilities—namely, the longitudinal electric αL(q2), the transverse electric αT(q2), and the magnetic β(q2) ones—are required in order to fully reconstruct local polarizations induced by soft external fields in a hadron. One of these polarizabilities, αT(q2), describes an effect of higher order in the soft final-photon momentum q′. We argue that the associated spatial distributions obtained via Fourier transforms in the Breit frame are meaningful even for such a light particle as the pion. The spatial distributions are determined at large distances r∼1/mπ for pions, kaons, and octet baryons by the use of chiral perturbation theory.

Generalized dipole polarizabilities and the spatial structure of hadrons

PASQUINI, BARBARA;
2001

Abstract

We present a phenomenological discussion of spin-independent, generalized dipole polarizabilities of hadrons entering the virtual Compton scattering process γ*h⃗γh. We introduce a new method of obtaining a tensor basis with appropriate Lorentz-invariant amplitudes which are free from kinematical singularities and constraints. The result is summarized in terms of a compact effective Lagrangian. We then motivate a gauge-invariant separation into a generalized Born term containing ground-state properties only and a residual contribution describing the model-dependent internal structure. The generalized dipole polarizabilities are defined in terms of Lorentz-invariant residual amplitudes. Particular emphasis is laid on a physical interpretation of these quantities as characterizing the spatial distributions of the induced electric polarization and magnetization of hadrons. It is argued that three dipole polarizabilities—namely, the longitudinal electric αL(q2), the transverse electric αT(q2), and the magnetic β(q2) ones—are required in order to fully reconstruct local polarizations induced by soft external fields in a hadron. One of these polarizabilities, αT(q2), describes an effect of higher order in the soft final-photon momentum q′. We argue that the associated spatial distributions obtained via Fourier transforms in the Breit frame are meaningful even for such a light particle as the pion. The spatial distributions are determined at large distances r∼1/mπ for pions, kaons, and octet baryons by the use of chiral perturbation theory.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11571/115692
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 43
  • ???jsp.display-item.citation.isi??? 40
social impact