<p>Constant cycle curves on a K3 surface <i>X</i> over <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathbb C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">C</mi> </math></EquationSource> </InlineEquation> are curves whose points all define the same class in the Chow group. In this paper we study correspondences <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(Z \subseteq X\times X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Z</mi> <mo>⊆</mo> <mi>X</mi> <mo>×</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> over <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\mathbb C}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">C</mi> </math></EquationSource> </InlineEquation> acting on the group <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({{\,\textrm{ccc}\,}}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mspace width="0.166667em" /> <mtext>ccc</mtext> <mspace width="0.166667em" /> </mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of cycles generated by irreducible constant cycle curves. We construct for any <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(n\ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> and any very ample line bundle <i>L</i> a locus <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(Z_n(L)\subseteq X\times X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Z</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>L</mi> <mo stretchy="false">)</mo> </mrow> <mo>⊆</mo> <mi>X</mi> <mo>×</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> which is expected to have dimension 2 and which yields a correspondence that acts on <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\({{\,\textrm{ccc}\,}}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mspace width="0.166667em" /> <mtext>ccc</mtext> <mspace width="0.166667em" /> </mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, when it has dimension 2. We provide examples of <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(Z_n(L)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Z</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>L</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for low <i>n</i> and exhibit one correspondence different from <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(Z_n(L)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>Z</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>L</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> acting on <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\({{\,\textrm{ccc}\,}}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mspace width="0.166667em" /> <mtext>ccc</mtext> <mspace width="0.166667em" /> </mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Correspondences acting on constant cycle curves on K3 surfaces

  • Sara Torelli

摘要

Constant cycle curves on a K3 surface X over \({\mathbb C}\) C are curves whose points all define the same class in the Chow group. In this paper we study correspondences \(Z \subseteq X\times X\) Z X × X over \({\mathbb C}\) C acting on the group \({{\,\textrm{ccc}\,}}(X)\) ccc ( X ) of cycles generated by irreducible constant cycle curves. We construct for any \(n\ge 2\) n 2 and any very ample line bundle L a locus \(Z_n(L)\subseteq X\times X\) Z n ( L ) X × X which is expected to have dimension 2 and which yields a correspondence that acts on \({{\,\textrm{ccc}\,}}(X)\) ccc ( X ) , when it has dimension 2. We provide examples of \(Z_n(L)\) Z n ( L ) for low n and exhibit one correspondence different from \(Z_n(L)\) Z n ( L ) acting on \({{\,\textrm{ccc}\,}}(X)\) ccc ( X ) .