arXiv subjects

H. Neufeld

Publications and source records attributed to H. Neufeld.

31 records · Page 2Linked to original sources

arXiv1999

Chiral Perturbation Theory with Virtual Photons and Leptons

We construct a low-energy effective field theory which allows the full treatment of isospin-breaking effects in semileptonic weak interactions. To this end, we enlarge the particle spectrum of chiral perturbation theory with virtual photons by including also the light leptons as dynamical degrees of freedom. Using super-heat-kernel techniques, we determine the additional one-loop divergences generated by the presence of virtual leptons and give the full list of associated local counterterms. We illustrate the use of our effective theory by applying it to the decays pi -> l nu_{l} and K -> l nu_{l}.

hep-ph↗

arXiv1999

eta -> pi^+ pi^- pi^0 gamma in Chiral Perturbation Theory

We analyse the radiative decay $η\to π^+π^- π^0γ$ in the low--energy expansion of the Standard Model. We employ the notion of ``generalized bremsstrahlung'' to take full advantage of the theoretical and experimental information on the corresponding non-radiative $η\to 3 π$ decay. The direct emission amplitude of ${\cal O}(p^4)$ is due to one-loop diagrams with intermediate pions (isospin violating) and kaons (isospin conserving). The isospin conserving contributions to direct emission, including vector meson exchange appearing at ${\cal O}(p^6)$, are suppressed.

hep-ph↗

arXiv1998

The Super-Heat-Kernel Expansion and the Renormalization of the Pion-Nucleon Interaction

A recently proposed super-heat-kernel technique is applied to heavy baryon chiral perturbation theory with two flavours. A previous result for the one-loop divergences of the pion-nucleon system is confirmed, giving at the same time an impressive demonstration of the efficiency of the new method. The cumbersome and tedious calculations of the conventional approach are now reduced to a few simple algebraic manipulations. The present computational scheme is not restricted to chiral perturbation theory, but can easily be applied or extended to any (in general non-renormalizable) theory with boson-fermion interactions.

hep-ph↗

arXiv1998

The one-loop functional as a Berezinian

We employ notions familiar from supersymmetry for constructing the one-loop functional of general quantum field theories with bosons and fermions (spin < 1). To demonstrate the advantages of such an approach for calculating one-loop divergences, we analyse a simple Yukawa theory with two different versions of a super-heat-kernel expansion. These methods also simplify the calculation of one-loop divergences for non-renormalizable meson--baryon Lagrangians occurring in chiral perturbation theory.

hep-ph↗

arXiv1996

K -> pi pi pi gamma in chiral perturbation theory

We present a complete analysis of K -> 3 pi gamma decays to O(p^4) in the low-energy expansion of the Standard Model. We employ the notion of "generalized bremsstrahlung" to take full advantage of experimental information on the corresponding non-radiative K -> 3 pi decays.

hep-ph↗

arXiv1996

Radiative Four--Meson Amplitudes in Chiral Perturbation Theory

We present a general discussion of radiative four--meson processes to $O(p^4)$ in chiral perturbation theory. We propose a definition of ``generalized bremsstrahlung'' that takes full advantage of experimental information on the corresponding non--radiative process. We also derive general formulae for one--loop amplitudes which can be applied, for instance, to $η\ra 3πγ$, $ππ\ra ππγ$ and $K \ra 3πγ$.

hep-ph↗

arXiv1995

The Electromagnetic Interaction in Chiral Perturbation Theory

We investigate electromagnetic effects in the framework of chiral perturbation theory. Using a completely independent method, we confirm Urech's results for the divergences of the one--loop functional in the electromagnetic sector. We perform a one--loop analysis of all $P_{\ell 2}$ ($P = π, K, η$) and the $K_{\ell 3}$ form factors $f_+^{K^+π^0}(0)$, $f_+^{K^0π^-}(0)$, including a systematic treatment of the $\cO(e^2p^2)$ contributions in the mesonic part. We illustrate our results by several numerical estimates.

hep-ph↗

arXiv1995

The decay $ρ^0 \to π^+ π^- γ$ and the chiral invariant interactions of vector mesons

Using the close relationship between the low--energy constants of chiral perturbation theory and the chiral invariant interactions of the vector meson resonances with the pseudoscalar mesons, we investigate the process $ρ^0 \ra π^+ π^- γ$. Compared with the contribution from the pure bremsstrahlung mechanism, we find an enhancement of the decay rate near the endpoint of the photon energy spectrum. Such a particular shape of the differential decay rate has indeed been observed experimentally and turns out to be an important confirmation of the theoretical concept of chiral vector meson dominance.

hep-ph↗

arXiv1994

Isospin Violation in Chiral Perturbation Theory and the Decays $η\ra π\ell ν$ and $τ\ra ηπν$

I discuss isospin breaking effects within the standard model. Chiral perturbation theory presents the appropriate theoretical framework for such an investigation in the low--energy range. Recent results on the electromagnetic contributions to the masses of the pseudoscalar mesons and the $K_{\ell 3}$ amplitudes are reported. Using the one--loop formulae for the $η_{\ell 3}$ form factors, rather precise predictions for the decay rates of $η\rightarrow π\ell ν$ can be obtained. Finally, I present an estimate of the $τ\ra ηπν$ branching ratio derived from the dominant meson resonance contributions to this decay.

hep-ph↗

arXiv1994

Radiative Non-Leptonic Kaon Decays

We investigate to what extent DA$Φ$NE will be able to test the Standard Model in the confinement regime with radiative kaon decays. We concentrate on processes which can be detected at DA$Φ$NE and we review briefly those decays where only upper limits can be expected. The Standard Model predictions for these decays are analyzed in the framework of chiral perturbation theory.

hep-ph↗

arXiv1994

Neutrinos interacting with Polarizable Media

We study Cherenkov and transition radiation of neutral spin 1/2 particles which carry magnetic moments or electric dipole moments. In particular, we estimate the radiation caused by the solar neutrino flux in dielectric media.

hep-ph↗

arXiv1994

Transition Radiation of Ultrarelativistic Neutral Particles

We perform a quantum theoretical calculation of transition radiation by neutral particles with spin 1/2 equipped with magnetic moments and/or electric dipole moments. The limit of vanishing masses is treated exactly for arbitrary refraction index. Finally we apply our result to the solar neutrino flux.

hep-ph↗

arXiv1993

Non-Leptonic Kaon Decays and the Chiral Anomaly

An investigation is performed of all non-leptonic kaon decays sensitive to the chiral anomaly. Within the framework of chiral perturbation theory, there are two classes of anomalous amplitudes at $O(p^4)$: reducible and direct contributions. Only radiative transitions are affected by the anomaly. The phenomenology of the decays $K_L \to π^+ π^- γ$ and $K^+ \to π^+ π^0 γ$ is studied in detail. Including the dominant contributions of $O(p^6)$, the experimentally observed dependence of the direct emission amplitude for $K_L \to π^+ π^- γ$ on the photon energy can be understood. A survey is made of the rare ``anomalous'' decays $K \to ππγγ$ and $K \to 3 πγ(γ)$, including some numerical estimates.

hep-ph↗