Anisotropic Lifshitz holography in Einstein–Proca theory with stable negative mass spectrum Roberto Cartas-Fuentevilla, Alfredo Herrera-Aguilar, V. Matlalcuatzi-Zamora, Uriel Noriega and Juan M. Romero Eur. Phys. J. Plus, 135 2 (2020) 155 Published online: 28 January 2020 DOI: 10.1140/epjp/s13360-019-00091-2