On the beaming of gluonic fields at strong coupling

Radiation and a dynamical UV/IR connection in AdS/CFT

“…A concrete example is the interesting proposal put forth by Hubeny [10] to provide a gravity-side explanation of the beaming of gluonic radiation, by approximating the string as a collection of point sources that set up gravitational shock waves. This approximation is valid as long as certain conditions are met [10,11], which in general happens only beyond some radial distance z m away from the AdS boundary (where the value of z m depends on the behavior of the quark). 2 Again, by the standard UV/IR reasoning, we would expect the missing near-boundary information not to matter if we retreat to distances R z m away from the quark.…”

Branes from light: embeddings and energetics for symmetric k-quarks in N = 4 $$ \mathcal{N}=4 $$ SYM

“…Physically, the implication is that these four vectors define a nonrotating reference frame. It is easy to check that (37) and (38) hold in the rest frame, and they then follow in general from the fact that the angular derivatives commute both with the boost (35) and with the transport (36). Finally, it follows from the definition (36) of Fermi-Walker transport that ∂ tr n I · n J = 0 = ∂ tr v · ∂ tr n I ,…”

“…4 The fact that, unlike in classical electromagnetism, the gluonic field is a nonlinear medium that can rescatter signals is accounted for in the dual gravity description by the fact that fields at the AdS boundary receive contributions from each and every point along the string [17,18]. Even so, 1-point functions of gluonic field observables turn out to have some surprising features, such as beaming [19,37,38], lack of radial/temporal broadening [39,20,18] and a 'near'-field tail reaching out to infinity [21,4].…”

“…Another interesting use of light rays in the holographic description of quarks appeared in the beaming proposal of[37] to determine the gravitational backreaction of the string (see also[38]). A relation between light rays and the string worldsheet was also postulated in[46] in the finite temperature context, but it was not shown whether the ansatz in question satisfies the equation of motion.…”

QCD, with strings attached

“…In the case of an accelerating quark, one can study the propagation of disturbances of the gluonic field [111,113], encountering the 1/| x| 2 falloff characteristic of radiation [114,115], and making interesting inferences about the angular and temporal distribution. In spite of the strong coupling, beams of radiation can remain collimated instead of rapidly spreading out [116,117,118]. And even though the nonlinear character of the gluonic medium implies that signals are reradiated from all possible scales [111], the net disturbance is found not to broaden in the radial/temporal direction [119,120,121,122].…”