<p>In this paper, we show that for any monic nonconstant polynomial with complex coefficients <i>P</i> and any <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq1.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\varepsilon &gt;0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation> there is a monic irreducible polynomial <i>Q</i> with integer coefficients such that the modulus of the resultant of <i>P</i> and <i>Q</i> is less than <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq2.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="11" /> </InlineMediaObject> <EquationSource Format="TEX">\(\varepsilon \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ε</mi> </math></EquationSource> </InlineEquation>. In particular, for any complex number <i>z</i>, for <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="148" /> </InlineMediaObject> <EquationSource Format="TEX">\(P(x)=x-z \in {\mathbb {C}}[x]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>x</mi> <mo>-</mo> <mi>z</mi> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> <mo stretchy="false">[</mo> <mi>x</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="39" /> </InlineMediaObject> <EquationSource Format="TEX">\(\varepsilon =1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo>=</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, this implies that there exists a monic irreducible polynomial <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="66" /> </InlineMediaObject> <EquationSource Format="TEX">\(Q \in {\mathbb {Z}}[x]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Q</mi> <mo>∈</mo> <mi mathvariant="double-struck">Z</mi> <mo stretchy="false">[</mo> <mi>x</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> for which <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="TEX">\(|Q(z)|&lt;1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>Q</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> <mo stretchy="false">|</mo> <mo>&lt;</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. In this context, we are also interested in the smallest possible degree <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq7.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(D_z\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>D</mi> <mi>z</mi> </msub> </math></EquationSource> </InlineEquation> of such a polynomial <i>Q</i>. We prove that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\(D_z \le 4\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>D</mi> <mi>z</mi> </msub> <mo>≤</mo> <mn>4</mn> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq9.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(z \in {\mathbb {C}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>z</mi> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> </mrow> </math></EquationSource> </InlineEquation>, except for some quadratic algebraic numbers <i>z</i>. However, there is no universal upper bound on <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq7.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(D_z\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>D</mi> <mi>z</mi> </msub> </math></EquationSource> </InlineEquation>. We show that if <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\ell \ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ℓ</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq12.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\(k&gt;\ell ^{2m-2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>&gt;</mo> <msup> <mi>ℓ</mi> <mrow> <mn>2</mn> <mi>m</mi> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> are positive integers, then the inequality <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq13.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="61" /> </InlineMediaObject> <EquationSource Format="TEX">\(D_z &gt; m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>D</mi> <mi>z</mi> </msub> <mo>&gt;</mo> <mi>m</mi> </mrow> </math></EquationSource> </InlineEquation> holds for <i>z</i> satisfying <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="25_2025_2390_Article_IEq14.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="128" /> </InlineMediaObject> <EquationSource Format="TEX">\(z^2-\ell ^{-1}z+k=0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>z</mi> <mn>2</mn> </msup> <mo>-</mo> <msup> <mi>ℓ</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mi>z</mi> <mo>+</mo> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>.</p>

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On Monic Irreducible Integer Polynomials Close to a Complex Monic Polynomial

  • Artūras Dubickas,
  • Chris Smyth

摘要

In this paper, we show that for any monic nonconstant polynomial with complex coefficients P and any \(\varepsilon >0\) ε > 0 there is a monic irreducible polynomial Q with integer coefficients such that the modulus of the resultant of P and Q is less than \(\varepsilon \) ε . In particular, for any complex number z, for \(P(x)=x-z \in {\mathbb {C}}[x]\) P ( x ) = x - z C [ x ] and \(\varepsilon =1\) ε = 1 , this implies that there exists a monic irreducible polynomial \(Q \in {\mathbb {Z}}[x]\) Q Z [ x ] for which \(|Q(z)|<1\) | Q ( z ) | < 1 . In this context, we are also interested in the smallest possible degree \(D_z\) D z of such a polynomial Q. We prove that \(D_z \le 4\) D z 4 for all \(z \in {\mathbb {C}}\) z C , except for some quadratic algebraic numbers z. However, there is no universal upper bound on \(D_z\) D z . We show that if \(\ell \ge 2\) 2 and \(k>\ell ^{2m-2}\) k > 2 m - 2 are positive integers, then the inequality \(D_z > m\) D z > m holds for z satisfying \(z^2-\ell ^{-1}z+k=0\) z 2 - - 1 z + k = 0 .