This has become a litigated issue now in the courts, one that I have been asked about a number of times in the last few years, and have litigated. You have alternative remedies against both the other tenant, as well as the landlord. With the landlord, you need to put your complaint in writing. You have a statutory 'warranty of quiet enjoyment' of your apartment. If he fails to act, or what he does fails to resolve the harassment, you may have to take him to court. If you wish to discuss this further or seek representation, kindly contact me at the link below.