# Even sets of nodes on sextic surfaces

Fabrizio Catanese; Fabio Tonoli

Journal of the European Mathematical Society (2007)

- Volume: 009, Issue: 4, page 705-737
- ISSN: 1435-9855

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topCatanese, Fabrizio, and Tonoli, Fabio. "Even sets of nodes on sextic surfaces." Journal of the European Mathematical Society 009.4 (2007): 705-737. <http://eudml.org/doc/277671>.

@article{Catanese2007,

abstract = {We determine the possible even sets of nodes on sextic surfaces in $\mathbb \{P\}^3$, showing in particular that their cardinalities are exactly the numbers in the set $\lbrace 24,32,40,56\rbrace $. We also show that all the possible cases admit an explicit description. The methods that we use are an interplay of coding theory and projective geometry on one hand, and of homological and computer algebra on
the other.
We give a detailed geometric construction for the new case of an even set of 56 nodes, but the ultimate verification of existence relies on computer calculations. Moreover, computer calculations have been used more than once in our research in order to get good guesses.
The construction gives a maximal family, unirational and of dimension 27, of nodal sextics with an even set of 56 nodes.
As in [Ca-Ca] (where other cases were described), each such nodal surface $F$ is given as the determinant of a symmetric map $\varphi :\mathcal \{E\}^\vee \rightarrow \mathcal \{E\}$, for an appropriate vector bundle $\mathcal \{E\}$ depending on $F$. The first difficulty here is to show the existence of such vector bundles. This leads us to
the investigation of a hitherto unknown moduli space of rank 6 vector bundles which we show elsewhere to be birational to a moduli space of plane representations of cubic surfaces in P3. The
resulting picture shows a very rich and interesting geometry. The main difficulty is to show the existence of “good” maps $\varphi $, and the interesting phenomenon which shows up is the following: the “moduli space” of such pairs $(\mathcal \{E\},\varphi )$ is (against our initial hope) reducible, and for a general choice of $\mathcal \{E\}$ the determinant of $\varphi $ is the double of a cubic surface $G$. Only when the vector bundle $\mathcal \{E\}$ corresponds to a reducible cubic surface, we get an extra component of the space of such pairs $(\mathcal \{E\},\varphi )$, and a general choice in this component yields one of our desired nodal sextic surfaces.},

author = {Catanese, Fabrizio, Tonoli, Fabio},

journal = {Journal of the European Mathematical Society},

keywords = {nodes on surfaces; coding theory; even sets of nodes; nodes on surfaces; coding theory; even sets of nodes},

language = {eng},

number = {4},

pages = {705-737},

publisher = {European Mathematical Society Publishing House},

title = {Even sets of nodes on sextic surfaces},

url = {http://eudml.org/doc/277671},

volume = {009},

year = {2007},

}

TY - JOUR

AU - Catanese, Fabrizio

AU - Tonoli, Fabio

TI - Even sets of nodes on sextic surfaces

JO - Journal of the European Mathematical Society

PY - 2007

PB - European Mathematical Society Publishing House

VL - 009

IS - 4

SP - 705

EP - 737

AB - We determine the possible even sets of nodes on sextic surfaces in $\mathbb {P}^3$, showing in particular that their cardinalities are exactly the numbers in the set $\lbrace 24,32,40,56\rbrace $. We also show that all the possible cases admit an explicit description. The methods that we use are an interplay of coding theory and projective geometry on one hand, and of homological and computer algebra on
the other.
We give a detailed geometric construction for the new case of an even set of 56 nodes, but the ultimate verification of existence relies on computer calculations. Moreover, computer calculations have been used more than once in our research in order to get good guesses.
The construction gives a maximal family, unirational and of dimension 27, of nodal sextics with an even set of 56 nodes.
As in [Ca-Ca] (where other cases were described), each such nodal surface $F$ is given as the determinant of a symmetric map $\varphi :\mathcal {E}^\vee \rightarrow \mathcal {E}$, for an appropriate vector bundle $\mathcal {E}$ depending on $F$. The first difficulty here is to show the existence of such vector bundles. This leads us to
the investigation of a hitherto unknown moduli space of rank 6 vector bundles which we show elsewhere to be birational to a moduli space of plane representations of cubic surfaces in P3. The
resulting picture shows a very rich and interesting geometry. The main difficulty is to show the existence of “good” maps $\varphi $, and the interesting phenomenon which shows up is the following: the “moduli space” of such pairs $(\mathcal {E},\varphi )$ is (against our initial hope) reducible, and for a general choice of $\mathcal {E}$ the determinant of $\varphi $ is the double of a cubic surface $G$. Only when the vector bundle $\mathcal {E}$ corresponds to a reducible cubic surface, we get an extra component of the space of such pairs $(\mathcal {E},\varphi )$, and a general choice in this component yields one of our desired nodal sextic surfaces.

LA - eng

KW - nodes on surfaces; coding theory; even sets of nodes; nodes on surfaces; coding theory; even sets of nodes

UR - http://eudml.org/doc/277671

ER -

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