  A model of spin relaxation in Kondo lattices is proposed to explain the
presence of an electron spin resonance (ESR) signal in the heavy fermion
compounds YbRh2Si2 and YbIr2Si2. Coupled equations for dynamical
susceptibilities of Kondo ions and conduction electrons are derived by means of
the functional derivative method. The perturbational scaling approach reveals
the collective spin motion of Yb ions with conduction electrons in the
bottleneck regime. A common energy scale due to the Kondo effect regulates the
temperature dependence of the different kinetic coefficients and results in a
mutual cancelation of all divergent parts in a collective spin mode. The
angular dependence of the ESR linewidth is shown to be in a qualitative
agreement with experimental data on YbRh2Si2 and YbIr2Si2. Linewidth
contributions other than the Kondo interaction are also discussed.
