  We provide a detailed analysis on the acoustic radiation force and torque
exerted on a homogeneous viscoelastic particle in the long-wave limit (the
particle radius is much smaller than the incident wavelength) by an arbitrary
wave. We assume that the particle behaves as a linear viscoelastic solid, which
obeys the fractional Kelvin-Voigt model. Simple analytical expressions for the
radiation force and torque are obtained considering the low- and high-frequency
approximation in the viscoelastic model. The developed theory is used to
describe the interaction of acoustic waves (traveling and standing plane waves,
and zero- and first-order Bessel beams) with a low- and high-density
polyethylene particle chosen as examples. Negative axial radiation force and
torque are predicted when the ratio of the longitudinal to shear relaxation
times is smaller than a constant that depends on the speed of sound in the
particle. In addition, a full 3D tractor Bessel vortex beam acting on the
high-density polyethylene is depicted. These predictions may enable new
possibilities of particle handling in acoustophoretic techniques.
