@article{ISI:000355101300021,
 abstract = {Experiments find coherent information transfer through biological groups
on length and time scales distinctly below those on which asymptotically
correct hydrodynamic theories apply. We present here a new continuum
theory of collective motion coupling the velocity and density fields of
Toner and Tu to the inertial spin field recently introduced to describe
information propagation in natural flocks of birds. The long-wavelength
limit of the new equations reproduces the Toner-Tu theory, while at
shorter wavelengths (or, equivalently, smaller damping), spin
fluctuations dominate over density fluctuations, and second-sound
propagation of the kind observed in real flocks emerges. We study the
dispersion relation of the new theory and find that when the speed of
second sound is large, a gap in momentum space sharply separates
first-from second-sound modes. This gap implies the existence of silent
flocks, namely, of medium-sized systems across which information cannot
propagate in a linear and underdamped way, either under the form of
orientational fluctuations or under that of density fluctuations, making
it hard for the group to achieve coordination.},
 article-number = {218101},
 author = {Cavagna, Andrea and Giardina, Irene and Grigera, Tomas S. and Jelic,
Asja and Levine, Dov and Ramaswamy, Sriram and Viale, Massimiliano},
 doi = {10.1103/PhysRevLett.114.218101},
 eissn = {1079-7114},
 issn = {0031-9007},
 journal = {PHYSICAL REVIEW LETTERS},
 month = {MAY 27},
 number = {21},
 orcid-numbers = {cavagna, andrea/0000-0003-2057-5971
Giardina, Irene/0000-0001-6900-1739
Viale, Massimiliano/0000-0003-4808-4103
Grigera, Tomas/0000-0002-3165-4838},
 researcherid-numbers = {cavagna, andrea/B-6400-2008
Giardina, Irene/O-4211-2015
},
 title = {Silent Flocks: Constraints on Signal Propagation Across Biological
Groups},
 unique-id = {ISI:000355101300021},
 volume = {114},
 year = {2015}
}