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Lower bounds on degree for locally unbalanced HDX

Investigate whether every infinite family of bounded-degree high dimensional expanders that are either λ-Trickling-Down or η-spectrally independent must have super-exponential degree as a function of the dimension; namely, ascertain whether deg(X_n) exp(ω(d)) for sufficiently large members X_n of the family.

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Background

The paper proves super-exponential degree lower bounds for certain hyper-regular HDX and highlights a threshold phenomenon at the TD barrier. Extending these lower bounds to complexes with highly unbalanced links (e.g., Ramanujan-type constructions) would settle whether degree blow-up is inevitable.

This question captures a central limitation in using HDX as gadgets in complexity-theoretic applications, where degree controls the overhead.

References

Question [Lower Bounds for Locally Unbalanced HDX] Let ${X_n}$ be an infinite family of bounded-degree HDX that are either $\lambda$-TD or $\eta$-SI. Is the degree of every (sufficiently large) $X_n$ super-exponential:

\text{deg}(X_n) \exp(\omega(d))?

Chernoff Bounds and Reverse Hypercontractivity on HDX (2404.10961 - Dikstein et al., 17 Apr 2024) in Section: Degree Lower Bounds, Question [Lower Bounds for Locally Unbalanced HDX]