提出可分解归一化流,高效建模参数依赖的分布变化。
Factorizable Normalizing Flows for parameter-dependent density morphing

- 将参数依赖密度分解为参考流与参数多项式变换的组合。
- 单参数变化时独立学习,多参数响应通过求和恢复。
- 线性扩展、可解释,适合高能物理无束定率拟合。
归一化流擅长建模单一固定分布,但许多科学问题(如高能物理)需要建模分布如何随连续参数变化——例如物理效应强度或系统误差源。为每个参数配置训练独立流会因组合爆炸而不可行。本文提出可分解归一化流(FNF),将参数依赖分布表示为固定高保真参考流与在参数上多项式且可分解的可学习变换之组合。该结构使每个参数的影响可独立学习,仅需在该参数单独变化时采样数据。多参数联合响应在推理时通过求和获得,无需采样组合爆炸的联合空间。在一个双参数可控变形任务中,模型准确复现真实变形并达到最优似然;可选交互项可捕捉强同时变化下的残余相关性。该模型兼具可解释性、线性扩展性和可计算似然,适用于任意需连续密度变形的推断流程,直接支持下一代无束定率拟合在高能物理中的应用。
原文摘要 · Abstract (English)
Normalizing Flows excel at modeling a single fixed density, yet many problems across the sciences, such as high energy physics, instead require modeling how that density deforms as a function of continuous parameters: the strength of a physical effect, a calibration constant, or a source of systematic uncertainty. Learning a separate flow for every parameter configuration quickly becomes intractable, since the number of joint settings grows exponentially with the number of parameters. We introduce Factorizable Normalizing Flows (FNFs), which represent the parameter-dependent density as a fixed, high-fidelity flow for a reference configuration composed with a learnable transformation that is polynomial in the parameters and factorized over them. This structure has a practical consequence: each parameter's effect is learned in isolation, from samples in which that parameter alone is varied. The combined response of many parameters is then recovered by summation at inference, without ever sampling their combinatorially large joint space. On a controlled problem with two interpretable deformations applied jointly to the data, the learned transformation reproduces the true deformations and matches the optimal likelihood, while optional interaction terms capture residual correlations when several parameters vary strongly at once. The resulting model is interpretable, scales linearly with the number of parameters, and keeps the likelihood tractable. This provides a general tool for any inference workflow requiring continuous density morphing, and directly enables the next generation of unbinned likelihood fits in high energy physics.
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