Joint continuity of the local times of fractional brownian sheets
Let BH={BH(t), t∈ℝ+N} be an (N, d)-fractional brownian sheet with index H=(H1, …, HN)∈(0, 1)N defined by BH(t)=(BH1(t), …, BHd(t)) (t∈ℝ+N), where BH1, …, BHd are independent copies of a real-valued fractional brownian sheet B0H. We prove that if d<∑ℓ=1NHℓ−1, then the local times of BH are jointly continuous. This verifies a conjecture of Xiao and Zhang (Probab. Theory Related Fields124 (2002)). We also establish sharp local and global Hölder conditions for the local times of BH. These results...