Back to search
2204.06209

An analogue of the Blaschke-Santaló inequality for billiard dynamics

Daniel Tsodikovich

correcthigh confidence
Category
math.DS
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper defines the billiard product β(K) = inf_z α(K) α(K^z) and proves the sharp bound β(K) ≤ 16 in all dimensions, with β(B) = 16 for balls, and in the plane it identifies the equality case with constant width bodies via the identity β(K) = 8 α(K)/diam(K) and a pair of elementary lemmas relating segments and slabs (Lemma 3.2) and the planar lower/upper bounds on α(K^z) (eq. (4.1)) . By contrast, the model’s proof hinges on the blanket claim α(K) = 2·w_min(K) for every convex body, which is false in general (the paper only uses α(K) ≤ 2·w(K) and α(K) ≤ 2·diam(K) and shows equality only in special cases) . The model also misapplies the Bezdek–Bezdek non-translatability criterion to arbitrary billiard trajectories, whereas that criterion characterizes minimizers in a specific variational set (Eq. (2.1)) rather than all trajectories . Although the model arrives at the correct numerical bound 16, its core step is invalid, so the argument is incorrect.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The paper formulates a natural billiard-theoretic analogue of the Blaschke–Santaló product and proves sharp bounds with clear equality characterizations. Proofs are elementary yet insightful, relying on segment–slab duality and careful planar analysis. The exposition is generally good; minor clarifications would make the flow even smoother.