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Title: Do two-dimensional dry active nematics keep quasi-long-range order
Plain: Active nematics are layers of elongated self-driven units that line up without a preferred head or tail. Whether such a layer stays orientationally ordered over large distances, or activity always creates enough defects to destroy the order, is disputed.
Precise: In $2\mathrm{D}$ dry active nematics (no momentum conservation, e.g. Chate-Ginelli-Montagne-type particle models), determine whether the ordered phase has quasi-long-range orientational order with algebraically decaying correlations, or whether activity unbinds $+1/2$ and $-1/2$ disclinations at any finite activity so that order is lost beyond a finite length. An answer gives the asymptotic form of the orientational correlation function and the defect density versus system size.
Settled by: Simulations over several decades of system size measuring orientational correlations and defect density, together with a renormalization-group treatment including defects.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: (empty)