“…The study of such pulse propagation phenomena has been triggered by a series of papers by Sommerfeld and Brillouin [2,3] and continues to be of much interest [4,5,6,7,8,9]. It is well known that the group velocity of a light pulse can be slowed down [10,11], can become faster than its value c in vacuum, or can even become negative [12,13]. Note that superluminal light propagation with group velocity larger than c cannot transmit information faster than the vacuum speed of light [14], such that it is not at odds with causality.…”