On the behavior at infinity of an integrable function

International audienceWe prove that, in a weak sense, any integrable function on the real line tends to zero at infinity : if f is an integrable function on R, then for almost all real number x, the sequence (f(nx)) tends to zero when n goes to infinity. Using Khinchin's metric theorem on Diophantine approximation, we establish that this convergence to zero can be arbitrarily slow