Halo structure and lensing signatures of a polytropic dark matter fluid

This research explores how a minimal effective pressure in dark matter can alter nonlinear halo structure while maintaining the successful large-scale predictions of the Lambda cold dark matter (CDM) model. By considering a barotropic relation, the study finds that dark matter develops a finite effective sound speed inside collapsed halos, leading to density profiles with quadratic central flattening. The model predicts a moderate suppression of central lensing amplitude compared to Navarro-Frenk-White halos, with modifications to the convergence power spectrum only at high multipoles.