Bronowski's conjecture on identifiability and tangential projections

Let XPhn+h1X\subset\mathbb{P}^{hn+h-1} be an irreducible and non-degenerate variety of dimension nn. A variety is hh-identifiable when a general point in its hh-secant variety lies on a unique (h1)(h-1)-plane spanned by hh points of XX, and a general (h1)(h-1)-tangential projection is the projection from the span of the tangent spaces at h1h-1 general points.

Bronowski's conjecture. The variety XX is hh-identifiable if and only if a general (h1)(h-1)-tangential projection

τh1X:X\dasharrowPn\tau_{h-1}^X:X\dasharrow\mathbb{P}^n

is birational.

The conjecture connects identifiability with unexpected birational maps to projective space. The implication from hh-identifiability to birationality is known, and the full equivalence is known for curves, smooth surfaces, and linearly normal smooth threefolds when h=2h=2; the general case is refuted by counterexamples.

Sources & referencesView supporting material

Primary source

Alex Massarenti and Massimiliano Mella, “Bronowski's conjecture and the identifiability of projective varieties”, arXiv:2210.13524 (2024).

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