@article{ISI:000529832400002,
 abstract = {As the constituent particles of a flock are polar and in a driven state,
their interactions must, in general, be fore-aft asymmetric and
nonreciprocal. Within a model that explicitly retains the classical spin
angular momentum field of the particles we show that the resulting
asymmetric contribution to interparticle torques, if large enough, leads
to a buckling instability of the flock. More precisely, this asymmetry
also yields a natural mechanism for a difference between the speed of
advection of polarization information along the flock and the speed of
the flock itself, concretely establishing that the absence of detailed
balance, and not merely the breaking of Galilean invariance, is crucial
for this distinction. To highlight this we construct a model of
asymmetrically interacting spins fixed to lattice points and demonstrate
that the speed of advection of polarization remains nonzero. We
delineate the conditions on parameters and wave number for the existence
of the buckling instability. Our theory should be consequential for
interpreting the behavior of real animal groups as well as experimental
studies of artificial flocks composed of polar motile rods on
substrates.},
 article-number = {052601},
 author = {Dadhichi, Lokrshi Prawar and Kethapelli, Jitendra and Chajwa, Rahul and
Ramaswamy, Sriram and Maitra, Ananyo},
 doi = {10.1103/PhysRevE.101.052601},
 eissn = {2470-0053},
 issn = {2470-0045},
 journal = {PHYSICAL REVIEW E},
 month = {MAY 1},
 number = {5},
 orcid-numbers = {Chajwa, Rahul/0000-0002-6488-1834
Dadhichi, Lokrshi Prawar/0000-0002-7883-131X
Maitra, Ananyo/0000-0003-3701-6981},
 times-cited = {0},
 title = {Nonmutual torques and the unimportance of motility for long-range order
in two-dimensional flocks},
 unique-id = {ISI:000529832400002},
 volume = {101},
 year = {2020}
}