Quote from propseeker:
costless? nothing is free. doesn't matter if you're db, ubs, bcly's, or a retail trader in his undies, you're going to be financing your trades one way or the other. arb is no different.
also, if i may be as pretentious as a previous poster... the 'risk-free' definition is 'so abused'. you always have risk. the purer the arb, the more your risk moves away from structural (mispricing model), to mechanics (IT, feeds, middleware, etc.). risk doesn't go away, it just gets transferred.
in reality, arbitrage, is simply capturing 'near' risk-less alpha from diverging relative valuations. these can be as linear as same issue inter-market valuations, to loose synthetic basket vs index valuations. the looser the coupling: the greater the alpha, the greater the risk; the tighter the coupling: the smaller the alpha, the lower the risk. pick your poison.