Radiative Corrections to K^0_{l3} Decays

We calculate the long-distance radiative corrections \delta^e_{LD} and \delta^{\mu}_{LD} to the K^0 -> \pi^- e^+ \nu_e and the K^0 -> pi^- \mu^+ \nu_{\mu} decay rates. This analysis includes contributions to the long-distance radiative corrections from outside the kinematically-allowed three-body Dalitz region and tests the sensitivity of the radiative corrections to the hadronic K-pi form factors. A program, KLOR, was written to numerically evaluate the radiative corrections and to generate Monte Carlo events for experimental acceptance studies. The K^0_{e3} and the K^0_{\mu 3} long-distance radiative correction parameters are determined to be (1.3 +/- 0.3)% and (1.9 +/- 0.3)%, respectively. We also present predictions for the fraction of radiative K^0_{l3} events satisfying various requirements on final-state photon kinematics.Comment: Accepted in Annals of Physics; 16 pages, 8 figures; v3 contains minor text change

Comments on two papers by Kapusta and Wong

We critically examine recently published results on the thermal production of massive vector bosons in a quark-gluon plasma. We claim the production rate is a collinear safe observable.Comment: 6 pages LATEX documen

Infrared Behavior of High-Temperature QCD

The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft momentum p is calculated in the context of next-to-leading-order hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained in an expansion to second order in p. The first coefficient is recovered but that of order p^2 is found divergent in the infrared. Divergences from light-like momenta do also occur but are circumvented. Our result and method are critically discussed, particularly regarding a Ward identity obtained in the literature. When enforcing the equality between \gamma_t(0) and \gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a similar calculation in the context of scalar quantum electrodynamics shows that the early ultrasoft-momentum expansion we make has little to do with the infrared sensitivity of the result.Comment: REVTEX4, 55 page

Isospin Breaking in Kℓ4K_{\ell 4} Decays of the Neutral Kaon

In the presence of photons, the neutral $K_{\ell 4}$ decay, $K^0\to\pi^0\pi^-\ell^+\nu_\ell$, can be parameterized in terms of three vectorial, one anomalous, and one tensorial form factors. We present here analytic expressions of two vectorial form factors, $f$ and $g$, calculated at one-loop level in the framework of chiral perturbation theory based on the effective Lagrangian including mesons, photons, and leptons. These expressions may then be used to disentangle the Isospin breaking part from the measured form factors and hence improve the accuracy in the determination of $\pi\pi$ scattering parameters from $K_{\ell 4}$ experiments.Comment: 62 pages, LaTeX, 5 postscript figures, 1 tabl

Analyse du processus n + n → n + n + π entre 1 et 3 gev

The reaction N + N → N + N + π has been studied in a peripheral-isobaric model where the resonance N*33 has been treated as an elementary particle of spin 3/2. Introducing a form factor with one single arbitrary parameter for the exchanged pion, we have fitted a great number of experimental curves : i. e. energy distributions of outgoing neutrons and protons (results of Barnes et al.) and momentum distributions of outgoing protons at fixed angle (results of Chadwick et al.) for the reactions p + p → p + n + π+ and p + p → p + p + πo at various incident kinetic energies between 1 and 3 GeV.La réaction N + N → N + N + π a été étudiée dans un modèle périphériqueisobarique où la résonance N* 33 est traitée comme une particule élémentaire de spin 3/2. En introduisant un facteur de forme à un seul paramètre arbitraire pour le pion virtuel échangé, on a obtenu un ajustement satisfaisant avec les résultats expérimentaux de Barnes et al. (mesures de distribution en énergie des neutrons et protons sortants) et Chadwick et al. (mesures de la distribution en impulsion des protons sortants, à angle fixe) pour les réactions p + p → p + n + π+ et p + p → p + p + π° à diverses énergies comprises entre 1 et 3 GeV