  The splitting of the Kondo resonance in the density of states of an Anderson
impurity in finite magnetic field is calculated from the exact Bethe-ansatz
solution. The result gives an estimate of the electron spectral function for
nonzero magnetic field and Kondo temperature, with consequences for transport
experiments on quantum dots in the Kondo regime. The strong correlations of the
Kondo ground state cause a significant low-temperature reduction of the peak
splitting. Explicit formulae are found for the shift and broadening of the
Kondo peaks. A likely cause of the problems of large-N approaches to spin-1/2
impurities at finite magnetic field is suggested.
