  Cs2CoBr4 is a triangular-lattice antiferromagnet which can be viewed as
weakly interacting spin chains due to spatially anisotropic frustrating
exchange couplings. The spin-orbit interaction in Co(2+) spin-3/2 ions leads to
a strong easy-plane single-ion anisotropy which allows to consider the
low-energy spin dynamics of this system using an anisotropic pseudospin-1/2
model. By means of the electron spin resonance (ESR) technique, we study the
spin dynamics of Cs2CoBr4 in magnetic field in a spin-liquid regime, i.e.,
above the N'eel temperature of 1.3 K but below the temperature of the crossover
to in-chain correlations of pseudospins (6 K). Our experiments reveal two
bright branches of excitations which strongly differ both from excitations in
the low-temperature ordered phases and from high-temperature paramagnetic
resonance of uncorrelated pseudospins and spins. These two branches are
interpreted as excitations with zero momentum of an anisotropic spin-1/2 chain.
Besides, we observe several weak modes of unknown origin which arise mostly as
satellites of one of the bright modes.
