<p>This paper investigates the zero distribution of the expression <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\( F = f^n P(z,f) - a \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>F</mi> <mo>=</mo> <msup> <mi>f</mi> <mi>n</mi> </msup> <mi>P</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <mi>f</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mi>a</mi> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\( f \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>f</mi> </math></EquationSource> </InlineEquation> is a transcendental meromorphic function of hyper-order less than one, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\( a \not \equiv 0 \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo>≢</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation> is a small function with respect to <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\( f \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>f</mi> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\( P(z,f) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <mi>f</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a non-vanishing delay-differential polynomial with small coefficients. We introduce the notions of sum-degree and sum-weight of <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\( P(z,f) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <mi>f</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, and use them to formulate conditions under which <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\( F \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>F</mi> </math></EquationSource> </InlineEquation> has sufficiently many zeros. We also study paired delay-differential expressions of the form <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\( F_1 = f_1^{n_1} P_1(z, f_2) - a \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>F</mi> <mn>1</mn> </msub> <mo>=</mo> <msubsup> <mi>f</mi> <mn>1</mn> <msub> <mi>n</mi> <mn>1</mn> </msub> </msubsup> <msub> <mi>P</mi> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mi>a</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\( F_2 = f_2^{n_2} P_2(z, f_1) - a \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>F</mi> <mn>2</mn> </msub> <mo>=</mo> <msubsup> <mi>f</mi> <mn>2</mn> <msub> <mi>n</mi> <mn>2</mn> </msub> </msubsup> <msub> <mi>P</mi> <mn>2</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mi>a</mi> </mrow> </math></EquationSource> </InlineEquation>, and establish conditions on <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(P_1 (z,f_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>P</mi> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(P_2 (z,f_1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>P</mi> <mn>2</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo>,</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> to ensure that at least one of the functions <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\( F_1 \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>F</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> or <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\( F_2 \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>F</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation> has infinitely many zeros.</p>

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Zero distribution of delay-differential polynomials

  • Zinelaabidine Latreuch,
  • Ilpo Laine

摘要

This paper investigates the zero distribution of the expression \( F = f^n P(z,f) - a \) F = f n P ( z , f ) - a , where \( f \) f is a transcendental meromorphic function of hyper-order less than one, \( a \not \equiv 0 \) a 0 is a small function with respect to \( f \) f , and \( P(z,f) \) P ( z , f ) is a non-vanishing delay-differential polynomial with small coefficients. We introduce the notions of sum-degree and sum-weight of \( P(z,f) \) P ( z , f ) , and use them to formulate conditions under which \( F \) F has sufficiently many zeros. We also study paired delay-differential expressions of the form \( F_1 = f_1^{n_1} P_1(z, f_2) - a \) F 1 = f 1 n 1 P 1 ( z , f 2 ) - a and \( F_2 = f_2^{n_2} P_2(z, f_1) - a \) F 2 = f 2 n 2 P 2 ( z , f 1 ) - a , and establish conditions on \(P_1 (z,f_2)\) P 1 ( z , f 2 ) and \(P_2 (z,f_1)\) P 2 ( z , f 1 ) to ensure that at least one of the functions \( F_1 \) F 1 or \( F_2 \) F 2 has infinitely many zeros.