Half-order Fine-Tuning for Diffusion Model: A Recursive Likelihood Ratio Optimizer - Ren, Tao; Zhang, Zishi; Jiang, Jinyang; Li, Zehao; Qin, Shentao; Zheng, Yi; Li, Guanghao; Sun, Qianyou; Li, Yan; Liang, Jiafeng; Li, Xinping; Peng, Yijie (International Conference on Learning Representations, 2026)