Projective monomial curves associated to numerical semigroups with multiplicity $e$, width $e-1$, and embedding dimension $e-2$
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| Format: | Preprint |
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2025
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| _version_ | 1866912696245420032 |
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| author | Bhardwaj, Om Prakash Chau, Trung Javadekar, Omkar |
| author_facet | Bhardwaj, Om Prakash Chau, Trung Javadekar, Omkar |
| contents | Numerical semigroups with multiplicity $e$, width $e-1$, and embedding dimension $e-2$ are of the form
$$S(e,m,n) = \langle \{e, e+1, \ldots, 2e-1\} \setminus \{e+m, e+n\} \rangle,$$ for some $1 \leq m < n \leq e-2$. Inspired by the work of Sally, Herzog and Stamate studied the special case $S(e,2,3)$, which they called the ``Sally numerical semigroups''. Recently, Dubey et. al. computed a minimal generating set of the defining ideal of the numerical semigroups $S(e,m,n)$ for $m \geq 2$. In this article, we first obtain an analog for the numerical semigroups $S(e,1,n)$, and then shift our focus to the projective monomial curves in $\mathbb{P}^{e-2}$ defined by the semigroups $S(e,m,n)$. We obtain a Gröbner basis for the defining ideal of the projective monomial curves associated to the semigroups $S(e,m,n)$. Moreover, we provide characterizations of Cohen--Macaulay and Gorenstein properties of these curves. Specifically, we prove that these are Cohen--Macaulay if and only if $(m,n) \neq (e-4,e-3)$, and Gorenstein if and only if $(e,m,n)\in \{ (4,1,2), (5,2,3)\}$. Furthermore, when these curves are Cohen--Macaulay, we compute the Castelnuovo--Mumford regularity of their coordinate ring. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_06482 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Projective monomial curves associated to numerical semigroups with multiplicity $e$, width $e-1$, and embedding dimension $e-2$ Bhardwaj, Om Prakash Chau, Trung Javadekar, Omkar Commutative Algebra 13P10, 13F55, 13D02, 20M14 Numerical semigroups with multiplicity $e$, width $e-1$, and embedding dimension $e-2$ are of the form $$S(e,m,n) = \langle \{e, e+1, \ldots, 2e-1\} \setminus \{e+m, e+n\} \rangle,$$ for some $1 \leq m < n \leq e-2$. Inspired by the work of Sally, Herzog and Stamate studied the special case $S(e,2,3)$, which they called the ``Sally numerical semigroups''. Recently, Dubey et. al. computed a minimal generating set of the defining ideal of the numerical semigroups $S(e,m,n)$ for $m \geq 2$. In this article, we first obtain an analog for the numerical semigroups $S(e,1,n)$, and then shift our focus to the projective monomial curves in $\mathbb{P}^{e-2}$ defined by the semigroups $S(e,m,n)$. We obtain a Gröbner basis for the defining ideal of the projective monomial curves associated to the semigroups $S(e,m,n)$. Moreover, we provide characterizations of Cohen--Macaulay and Gorenstein properties of these curves. Specifically, we prove that these are Cohen--Macaulay if and only if $(m,n) \neq (e-4,e-3)$, and Gorenstein if and only if $(e,m,n)\in \{ (4,1,2), (5,2,3)\}$. Furthermore, when these curves are Cohen--Macaulay, we compute the Castelnuovo--Mumford regularity of their coordinate ring. |
| title | Projective monomial curves associated to numerical semigroups with multiplicity $e$, width $e-1$, and embedding dimension $e-2$ |
| topic | Commutative Algebra 13P10, 13F55, 13D02, 20M14 |
| url | https://arxiv.org/abs/2511.06482 |