  We study the low energy behavior of the one dimensional Hubbard model across
the Mott metal-insulator phase transition in an external magnetic field. In
particular we calculate elements of the dressed charge matrix at the critical
point of the Mott transition for arbitrary Hubbard repulsion and magnetization
numerically and, in certain limiting cases, analytically. These results are
combined with a non-perturbative effective field theory approach to reveal how
the breaking of time reversal symmetry influences the Mott transition.
