2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/41574The Higgs vacuum -- with its constant background field -- is not `empty' but is a kind of medium. Any ordinary medium, viewed at sufficiently long length scales, has a hydrodynamic description and can propagate sound waves. The vacuum medium is unusual; the speed of sound is formally infinite and there is no linear sound-wave regime. Instead, long-wavelength disturbances are described by some intrinsically nonlinear hydrodynamic equations.9 pages, 1 eps figure (included)High Energy Physics - Phenomenologytext