  We show that a strained wire of a Weyl semimetal supports a new type of
gapless excitation, the chiral sound wave (CSW). It is a longitudinal charge
density wave analog to the chiral magnetic wave predicted in the quark-gluon
plasma but driven by an elastic axial pseudo-magnetic field. It involves the
axial-axial-axial contribution to the chiral anomaly which couples the chiral
charge density to the elastic axial gauge field. The chiral sound is
unidirectional: it propagates along the elastic magnetic field and not in the
opposite direction. The CSW may propagate for long distances as it does not
couple directly to quickly dissipating electromagnetic plasmons, while its
damping is controlled by the slow chirality flip rate. We propose an
experimental setup to directly detect the chiral sound, which is excited by
mechanical vibrations of the crystal lattice in the GHz frequency range. Our
findings contribute to a new trend, the chiral acoustics, in strained Weyl
semimetals.
