Occurring in theories with massless particles, for 10 points, identify this phenomenon in which QED integrals diverge as the particle momentum goes to zero, as opposed to infinity.
An early solution to the problem of these phenomena was provided by a 1937 paper by Bloch and Nordsieck. Lee and Nauenberg have shown that these phenomena can be eliminated by summing over both acceptable final states and the correct distribution of initial states. In the Drell-Yan process, these phenomena emerge as a consequence of the presence of gluon fields, and if those fields couple to other massless fields, the collinear variety of these phenomena occur. These phenomena occur during processes like "soft" bremmstrahlung and are usually resolved by imposing a low-energy cutoff below which the photon energy is not measurable, and including photons below that energy in the emission calculation. Occurring in theories with massless particles, for 10 points, identify this phenomenon in which QED integrals diverge as the particle momentum goes to zero, as opposed to infinity.
An early solution to the problem of these phenomena was provided by a 1937 paper by Bloch and Nordsieck.
infrared divergence or catastrophe or singularity [prompt on "singularity", do not accept "ultraviolet" singularity]