The Lifted Free Score: Norm, Weak Identity and the Second-Moment Identity
lemmaAnalysisProbabilitylem:free-score-lift-2026aFor a square-integrable random variable whose law has finite free Fisher information, the lifted free score has squared norm equal to the free Fisher information and pairs with the lifted derivative of a test function to the integral of the difference quotient against the product measure; and the free score of any law with finite free Fisher information pairs with the identity map to one, so the lifted free score pairs with the random variable itself to one.
In the setting of Square-Integrable Vector Fields Against a Probability Measure on Euclidean Space, and Test Functions: Standing Notation, in dimension , with the real line identified with and as in One-Dimensional Test Functions: Scalars, Derivatives, and the Difference Quotient of the Derivative. Let and let be its law, which belongs to by The Space of Square-Integrable Random Vectors is a Real Hilbert Space; Its Laws Have Finite Second Moment; Constants and Translations §law. Let be the identity map of , an element of for every by Basic Properties of the Tangent Space: Closed Subspace, the Identity Map Belongs to It, Second-Moment Limits, and Representation of Bounded Functionals on Gradients §identity; for let be the composition; for let be its derivative and the difference quotient of its derivative; and let finite free Fisher information, the set , the free score and the free Fisher information of a be as defined there.
1. (The lifted free score)¶ If , then and, for every ,
2. (Second-moment identity)¶ For every , whether or not it is the law of an element of , . In particular, if , then
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