Long-Range Nematic Order in Two-Dimensional Active Matter

Working in two space dimensions, we show that the orientational order emerging from self-propelled polar particles aligning nematically is quasi-long-ranged beyond $\ell_{\rm r}$, scale associated to induced velocity reversals, which typically extremely large and often cannot even be measured. Below nematic long-range. We construct study a hydrodynamic theory for this de facto phase its structure symmetries differ conventional descriptions of active nematics. check numerically our theoretical predictions, particular presence $\pi$-symmetric propagative sound modes, provide estimates all scaling exponents governing long-range space-time correlations.