<p>We describe all schematic limits of families of divisors associated to a given family of rank-<i>r</i> linear series on a one-dimensional family of projective varieties degenerating to a connected, reduced projective scheme <i>X</i> defined over any field, under the assumption that the total space of the family is regular along <i>X</i>. More precisely, the degenerating family gives rise to a special quiver <i>Q</i>, called a <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathbb {Z}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">Z</mi> </mrow> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation><i>-quiver</i>, where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(n+1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> is the number of irreducible components of <i>X</i>, a special representation <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\mathfrak {L}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">L</mi> </math></EquationSource> </InlineEquation> of <i>Q</i> in the category of line bundles over <i>X</i>, called a <i>maximal exact linked net</i>, and a special subrepresentation <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\mathfrak {V}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">V</mi> </math></EquationSource> </InlineEquation> of the representation <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(H^0(X,{\mathfrak {L}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>H</mi> <mn>0</mn> </msup> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>,</mo> <mi mathvariant="fraktur">L</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> induced from <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\({\mathfrak {L}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">L</mi> </math></EquationSource> </InlineEquation> by taking global sections, called a <i>pure exact finitely generated linked net</i> of dimension <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(r+1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo>+</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. Given <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\({\mathfrak {g}}=(Q,{\mathfrak {L}},{\mathfrak {V}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">g</mi> <mo>=</mo> <mo stretchy="false">(</mo> <mi>Q</mi> <mo>,</mo> <mi mathvariant="fraktur">L</mi> <mo>,</mo> <mi mathvariant="fraktur">V</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> satisfying these properties, we prove that the quiver Grassmanian <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\mathbb{L}\mathbb{P}(\mathfrak {V})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">L</mi> <mi mathvariant="double-struck">P</mi> <mo stretchy="false">(</mo> <mi mathvariant="fraktur">V</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of subrepresentations of <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\mathfrak {V}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">V</mi> </math></EquationSource> </InlineEquation> of pure dimension 1, called a <i>linked projective space</i>, is local complete intersection, reduced and of pure dimension <i>r</i>. Furthermore, we prove that there is a morphism <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\mathbb{L}\mathbb{P}(\mathfrak {V})\rightarrow \text {Hilb}_X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">L</mi> <mi mathvariant="double-struck">P</mi> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="fraktur">V</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">→</mo> <msub> <mtext>Hilb</mtext> <mi>X</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>, and that its image parameterizes all schematic limits of divisors along the degenerating family of linear series if <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\({\mathfrak {g}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">g</mi> </math></EquationSource> </InlineEquation> arises from one.</p>

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Quiver Representations Arising from Degenerations of Linear Series, II

  • Eduardo Esteves,
  • Renan Santos,
  • Eduardo Vital

摘要

We describe all schematic limits of families of divisors associated to a given family of rank-r linear series on a one-dimensional family of projective varieties degenerating to a connected, reduced projective scheme X defined over any field, under the assumption that the total space of the family is regular along X. More precisely, the degenerating family gives rise to a special quiver Q, called a \(\mathbb {Z}^n\) Z n -quiver, where \(n+1\) n + 1 is the number of irreducible components of X, a special representation \({\mathfrak {L}}\) L of Q in the category of line bundles over X, called a maximal exact linked net, and a special subrepresentation \({\mathfrak {V}}\) V of the representation \(H^0(X,{\mathfrak {L}})\) H 0 ( X , L ) induced from \({\mathfrak {L}}\) L by taking global sections, called a pure exact finitely generated linked net of dimension \(r+1\) r + 1 . Given \({\mathfrak {g}}=(Q,{\mathfrak {L}},{\mathfrak {V}})\) g = ( Q , L , V ) satisfying these properties, we prove that the quiver Grassmanian \(\mathbb{L}\mathbb{P}(\mathfrak {V})\) L P ( V ) of subrepresentations of \(\mathfrak {V}\) V of pure dimension 1, called a linked projective space, is local complete intersection, reduced and of pure dimension r. Furthermore, we prove that there is a morphism \(\mathbb{L}\mathbb{P}(\mathfrak {V})\rightarrow \text {Hilb}_X\) L P ( V ) Hilb X , and that its image parameterizes all schematic limits of divisors along the degenerating family of linear series if \({\mathfrak {g}}\) g arises from one.