Hamming distance of repeated-root constacyclic codes of length 2p^s over F_p^m + uF_p^m

Let p be an odd prime, and δ be an arbitrary unit of the finite chain ring  (u² = 0). The Hamming distances of all δ-constacyclic codes of length 2p^s over  are completely determined. We provide some examples from which some codes have better parameters than the existing ones. As applications, we determine all MDS repeated-root δδ-constacyclic codes of length 2p^s over .