New growth bounds for set products in the Heisenberg and affine groups over prime fields, plus an application to Freiman's isomorphism in nonabelian groups.
Stronger sum-product inequalities for small sets
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abstract
Let $F$ be a field and a finite $A\subset F$ be sufficiently small in terms of the characteristic $p$ of $F$ if $p>0$. We strengthen the "threshold" sum-product inequality $$|AA|^3 |A\pm A|^2 \gg |A|^6\,,\;\;\;\;\mbox{hence} \;\; \;\;|AA|+|A+A|\gg |A|^{1+\frac{1}{5}},$$ due to Roche-Newton, Rudnev and Shkredov, to $$|AA|^5 |A\pm A|^4 \gg |A|^{11-o(1)}\,,\;\;\;\;\mbox{hence} \;\; \;\;|AA|+|A\pm A|\gg |A|^{1+\frac{2}{9}-o(1)},$$ as well as $$ |AA|^{36}|A-A|^{24} \gg |A|^{73-o(1)}. $$ The latter inequality is "threshold-breaking", for it shows for $\epsilon>0$, one has $$|AA| \le |A|^{1+\epsilon}\;\;\;\Rightarrow\;\;\; |A-A|\gg |A|^{\frac{3}{2}+c(\epsilon)},$$ with $c(\epsilon)>0$ if $\epsilon$ is sufficiently small. This implies that regardless of $\epsilon$, $$|AA-AA|\gg |A|^{\frac{3}{2}+\frac{1}{56}-o(1)}\,.$$
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math.CO 1years
2019 1verdicts
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Some remarks on products of sets in the Heisenberg group and in the affine group
New growth bounds for set products in the Heisenberg and affine groups over prime fields, plus an application to Freiman's isomorphism in nonabelian groups.