For trained wide neural networks, you can have a look at "Neural Tangent Kernel: Convergence and Generalization in Neural Networks" (https://arxiv.org/abs/1806.07572) where we explain the training of very wide ANN. This sparked a numerous amount of research and in the few last results about training wide ANN you can have a look at: https://arxiv.org/abs/1909.08156 and https://arxiv.org/abs/1904.11955