<p>For each <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(0&lt;\alpha &lt;\frac{1}{2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0</mn> <mo>&lt;</mo> <mi>α</mi> <mo>&lt;</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </math></EquationSource> </InlineEquation>, there exists a Bayer–Lahoz–Macrì–Stellari inducing Bridgeland stability condition <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\sigma (\alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> on a Kuznetsov component <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\textrm{Ku}(Q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Ku</mtext> <mo stretchy="false">(</mo> <mi>Q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> of the smooth quadric threefold <i>Q</i>. We obtain the non-emptiness of the moduli space <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>M</mi> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">[</mo> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo stretchy="false">]</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\sigma (\alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-semistable objects in <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\textrm{Ku}(Q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Ku</mtext> <mo stretchy="false">(</mo> <mi>Q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> with the numerical class <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\([{\mathcal {P}}_{x}]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">[</mo> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\({\mathcal {P}}_{x}\in \textrm{Ku}(Q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo>∈</mo> <mtext>Ku</mtext> <mrow> <mo stretchy="false">(</mo> <mi>Q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is the projection sheaf of the skyscraper sheaf at a closed point <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(x\in Q\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>x</mi> <mo>∈</mo> <mi>Q</mi> </mrow> </math></EquationSource> </InlineEquation>. We show that the moduli space <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\({\overline{M}}_{Q}({\textbf{v}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mover> <mi>M</mi> <mo>¯</mo> </mover> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="bold">v</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of Gieseker semistable sheaves with Chern character <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\({\textbf{v}}=\textrm{ch}({\mathcal {P}}_{x})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="bold">v</mi> <mo>=</mo> <mtext>ch</mtext> <mo stretchy="false">(</mo> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is smooth and irreducible of dimension four, and prove that the moduli space <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>M</mi> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">[</mo> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo stretchy="false">]</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is isomorphic to <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\({\overline{M}}_{Q}({\textbf{v}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mover> <mi>M</mi> <mo>¯</mo> </mover> <mi>Q</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="bold">v</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. As an application, we show that the quadric threefold <i>Q</i> can be reinterpreted as a Brill–Noether locus in the Bridgeland moduli space <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>M</mi> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">[</mo> <msub> <mi mathvariant="script">P</mi> <mi>x</mi> </msub> <mo stretchy="false">]</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In the appendices, we show that the moduli space <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(M_{\sigma (\alpha )}([S])\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>M</mi> <mrow> <mi>σ</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">[</mo> <mi>S</mi> <mo stretchy="false">]</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> contains only one single point corresponding to the spinor bundle <i>S</i> and give a Bridgeland moduli interpretation for the Hilbert scheme of lines in <i>Q</i>.</p>

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Moduli of stable sheaves on quadric threefold

  • Song Yang

摘要

For each \(0<\alpha <\frac{1}{2}\) 0 < α < 1 2 , there exists a Bayer–Lahoz–Macrì–Stellari inducing Bridgeland stability condition \(\sigma (\alpha )\) σ ( α ) on a Kuznetsov component \(\textrm{Ku}(Q)\) Ku ( Q ) of the smooth quadric threefold Q. We obtain the non-emptiness of the moduli space \(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\) M σ ( α ) ( [ P x ] ) of \(\sigma (\alpha )\) σ ( α ) -semistable objects in \(\textrm{Ku}(Q)\) Ku ( Q ) with the numerical class \([{\mathcal {P}}_{x}]\) [ P x ] , where \({\mathcal {P}}_{x}\in \textrm{Ku}(Q)\) P x Ku ( Q ) is the projection sheaf of the skyscraper sheaf at a closed point \(x\in Q\) x Q . We show that the moduli space \({\overline{M}}_{Q}({\textbf{v}})\) M ¯ Q ( v ) of Gieseker semistable sheaves with Chern character \({\textbf{v}}=\textrm{ch}({\mathcal {P}}_{x})\) v = ch ( P x ) is smooth and irreducible of dimension four, and prove that the moduli space \(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\) M σ ( α ) ( [ P x ] ) is isomorphic to \({\overline{M}}_{Q}({\textbf{v}})\) M ¯ Q ( v ) . As an application, we show that the quadric threefold Q can be reinterpreted as a Brill–Noether locus in the Bridgeland moduli space \(M_{\sigma (\alpha )}([{\mathcal {P}}_{x}])\) M σ ( α ) ( [ P x ] ) . In the appendices, we show that the moduli space \(M_{\sigma (\alpha )}([S])\) M σ ( α ) ( [ S ] ) contains only one single point corresponding to the spinor bundle S and give a Bridgeland moduli interpretation for the Hilbert scheme of lines in Q.