# On the diagonal ideal of $(\mathbb{C}^2)^n$ and $q,t$-Catalan numbers

Abstract : Let $I_n$ be the (big) diagonal ideal of $(\mathbb{C}^2)^n$. Haiman proved that the $q,t$-Catalan number is the Hilbert series of the graded vector space $M_n=\bigoplus_{d_1,d_2}(M_n)_{d_1,d_2}$ spanned by a minimal set of generators for $I_n$. We give simple upper bounds on $\textrm{dim} (M_n)_{d_1, d_2}$ in terms of partition numbers, and find all bi-degrees $(d_1,d_2)$ such that $\textrm{dim} (M_n)_{d_1, d_2}$ achieve the upper bounds. For such bi-degrees, we also find explicit bases for $(M_n)_{d_1, d_2}$.
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https://hal.inria.fr/hal-01186266
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Kyungyong Lee, Li Li. On the diagonal ideal of $(\mathbb{C}^2)^n$ and $q,t$-Catalan numbers. 22nd International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2010), 2010, San Francisco, United States. pp.881-888, ⟨10.46298/dmtcs.2838⟩. ⟨hal-01186266⟩

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