With Samuel Eto'o arriving at Chelsea and Fernando Torres' contract being basically not being transferable, Demba Ba is almost certainly surplus toStamford Bridge's requirements. One might guess that Chelsea would be unwilling to sell him to a direct rival, but France Football believes that they're currently in negotiations with Arsenal to loan the Senegalese striker.
Chelsea have done this before with the loan of Yossi Benayoun to Arsenal for the 2011-12 season. Arsenal would likely pay a significant loan fee and almost certainly pay all of Ba's wages if the deal were to go through.
Arsenal seem confident that Olivier Giroud is good enough to be their starting center forward, but they could definitely use some depth up top. Lukas Podolski and Theo Walcott are competent center forwards, but both are probably better as wide players.
Ba would give Arsenal a big and athletic option at striker at a discount price and for no risk. Because of that , it's an easy move for Arsene Wenger to make if Chelsea are interested.