We present analytic results for the finite-frequency current noise and the
nonequilibrium ac conductance for a Kondo quantum dot in presence of a magnetic
field. Using the real-time renormalization group method, we determine the line
shape close to resonances and show that while all resonances in the ac
conductance are broadened by the transverse spin relaxation rate, the noise at
finite field additionally involves the longitudinal rate as well as sharp kinks
resulting in singular derivatives. Our results provide a consistent theoretical
description of recent experimental data for the emission noise at zero magnetic
field, and we propose the extension to finite field for which we present a
detailed prediction.Comment: 21 pages, 13 figure
