Comment on "Quantum theory of collective strong coupling of molecular vibrations with a microcavity mode"
We have found missing terms and incorrect signs in the secular master equations reported by Del Pino et. al., New J. Phys., 17 (2015), 053040 for vibrational polariton relaxation. Inclusion of these terms and signs are essential to yield correct (vanishing) pure dephasing rates between polariton states, as well as coherence transfer pathways between polaritons and dark states. We provide corrected expressions for the master equations as well as comparisons with the results reported by the authors. Even though the main conclusions of the article are not significantly altered, the corrections are important to provide a proper description of all possible polariton relaxation mechanisms within the invoked approximations, especially when applying the theory to model nonlinear spectroscopy of vibrational polaritons.