  The dielectric spectra of the twist bend nematic phase of the bent shaped
achiral liquid crystal dimer are studied for the determination of the different
relaxation modes. The two molecular processes were assigned one to the
precessional rotation of the longitudinal components of the cyanobiphenyl
groups and the second to the spinning rotation of the transverse component of
the dimer. The low frequency peak shows a peculiar temperature behavior at the
twist bend nematic to nematic transition. This peak can be assigned to a
collective fluctuation of the tilt angle of the coarse grained director N with
respect the pseudo layer normal. This corresponds well with the electro clinic
effect observed as a response to an electric field in electro optic
experiments. The low frequency relaxation process can be identified as a
Goldstone mode, related to long-scale fluctuation of the cone phase. The
birefringence data in the presence of strong bias fields in the temperature
range where the twist bend nematic phase is formed is interpreted as unwinding
of a helix and an indication of the formation of a field induced nematic splay
bend phase.
