Down-set thresholds
Abstract
We elucidate the relationship between the threshold and the expectation-threshold of a down-set. Qualitatively, our main result demonstrates that there exist down-sets with polynomial gaps between their thresholds and expectation-thresholds; in particular, the logarithmic gap predictions of Kahn--Kalai and Talagrand (recently proved by Park--Pham and Frankston--Kahn--Narayanan--Park) about up-sets do not apply to down-sets. Quantitatively, we show that any collection $\mathcal{G}$ of graphs on $[n]$ that covers the family of all triangle-free graphs on $[n]$ satisfies the inequality $\sum_{G \in \mathcal{G}} \exp(-\delta e(G^c) / \sqrt{n}) < 1/2$ for some universal $\delta > 0$, and this is essentially best-possible.
- Publication:
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arXiv e-prints
- Pub Date:
- December 2021
- DOI:
- 10.48550/arXiv.2112.08525
- arXiv:
- arXiv:2112.08525
- Bibcode:
- 2021arXiv211208525G
- Keywords:
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- Mathematics - Combinatorics;
- Mathematics - Probability
- E-Print:
- 17 pages