An eigenvalue interlacing approach to Garland's method
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866911119183970304 |
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| author | Lew, Alan |
| author_facet | Lew, Alan |
| contents | Let $X$ be a pure $d$-dimensional simplicial complex. For $0\le k\le d$, let $X(k)$ be the set of $k$-dimensional faces of $X$, let $\tilde{L}_k(X)$ be the $k$-dimensional weighted total Laplacian operator on $X$, and let $\tilde{H}_k(X;\mathbb{R})$ be its $k$-dimensional reduced homology group with real coefficients. For $σ\in X$, let $\text{lk}(X,σ)$ be the link of $σ$ in $X$. For a matrix $M$, we denote by $\text{Spec}(M)$ the multi-set containing all the eigenvalues of $M$. We show that, for every $0\le \ell<k \le d$, \[
\text{dim}(\tilde{H}_k(X;\mathbb{R}))\le \sum_{η\in X(\ell)}\left| \left\{ λ\in \text{Spec}(\tilde{L}_{k-\ell-1}(\text{lk}(X,η))) :\, λ\le \frac{(\ell+1)(d-k)}{k+1}\right\}\right|. \] This extends the classical vanishing theorem of Garland, corresponding to the special case when the right hand side of the inequality is equal to zero, and a more recent result by Hino and Kanazawa, corresponding to the case $\ell=k-1$. A main new ingredient in our proof is an abstract version of Garland's local to global principle, which follows as a simple consequence of the eigenvalue interlacing theorem, and may be of independent interest. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_17279 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An eigenvalue interlacing approach to Garland's method Lew, Alan Combinatorics Let $X$ be a pure $d$-dimensional simplicial complex. For $0\le k\le d$, let $X(k)$ be the set of $k$-dimensional faces of $X$, let $\tilde{L}_k(X)$ be the $k$-dimensional weighted total Laplacian operator on $X$, and let $\tilde{H}_k(X;\mathbb{R})$ be its $k$-dimensional reduced homology group with real coefficients. For $σ\in X$, let $\text{lk}(X,σ)$ be the link of $σ$ in $X$. For a matrix $M$, we denote by $\text{Spec}(M)$ the multi-set containing all the eigenvalues of $M$. We show that, for every $0\le \ell<k \le d$, \[ \text{dim}(\tilde{H}_k(X;\mathbb{R}))\le \sum_{η\in X(\ell)}\left| \left\{ λ\in \text{Spec}(\tilde{L}_{k-\ell-1}(\text{lk}(X,η))) :\, λ\le \frac{(\ell+1)(d-k)}{k+1}\right\}\right|. \] This extends the classical vanishing theorem of Garland, corresponding to the special case when the right hand side of the inequality is equal to zero, and a more recent result by Hino and Kanazawa, corresponding to the case $\ell=k-1$. A main new ingredient in our proof is an abstract version of Garland's local to global principle, which follows as a simple consequence of the eigenvalue interlacing theorem, and may be of independent interest. |
| title | An eigenvalue interlacing approach to Garland's method |
| topic | Combinatorics |
| url | https://arxiv.org/abs/2508.17279 |