  This work presents a lattice quantum chromodynamics (QCD) calculation of the
nonperturbative Collins-Soper kernel, which describes the rapidity evolution of
quark transverse-momentum-dependent parton distribution functions. The kernel
is extracted at transverse momentum scales in the range 400 MeV $< q_T < 1.7$
GeV in a calculation with dynamical fermions and quark masses corresponding to
a larger-than-physical pion mass, $m_\pi=538(1)$ MeV. It is found that
different approaches to extract the Collins-Soper kernel from the same
underlying lattice QCD matrix elements yield significantly different results
and uncertainty estimates, revealing that power corrections, such as those
associated with higher-twist effects, and perturbative matching between quasi
and light-cone beam functions, cannot be neglected.
