  We study electron transport through a serial double quantum dot with Rashba
spin-orbit interaction (SOI) and Zeeman field of amplitude B in presence of
local Coulomb repulsion. The linear conductance as a function of a gate voltage
Vg equally shifting the levels on both dots shows two B=0 Kondo ridges which
are robust against SOI as time-reversal symmetry is preserved. Resulting from
the crossing of a spin-up and a spin-down level at vanishing SOI two additional
Kondo plateaus appear at finite B. They are not protected by symmetry and
rapidly vanish if the SOI is turned on. Left-right asymmetric level-lead
couplings and detuned on-site energies lead to a simultaneous breaking of
left-right and bonding-anti-bonding state symmetry. In this case the finite-B
Kondo ridges in the Vg-B plane are bent with respect to the Vg-axis. For the
Kondo ridge to develop different level renormalizations must be compensated by
adjusting B.
