<p>A radially weighted Besov space <i>H</i> is a space of holomorphic functions on the unit ball <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathbb {B}_d \subseteq \mathbb {C}^d\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="double-struck">B</mi> <mi>d</mi> </msub> <mo>⊆</mo> <msup> <mrow> <mi mathvariant="double-struck">C</mi> </mrow> <mi>d</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> whose <i>N</i>-th radial derivative is square integrable with respect to a given admissible radial measure. We write <i>Mult</i>(<i>H</i>) for its multiplier algebra. The cyclic vectors in <i>H</i> are those functions <i>f</i> whose multiplier multiples are dense in <i>H</i>. We call a multiplier <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(f \in Mult(H)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>∈</mo> <mi>M</mi> <mi>u</mi> <mi>l</mi> <mi>t</mi> <mo stretchy="false">(</mo> <mi>H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> <i>weak</i><sup>*</sup> <i>sequentially cyclic</i> if its multiplier multiples are weak<sup>*</sup> sequentially dense in <i>Mult</i>(<i>H</i>). It is immediate that every weak<sup>*</sup> sequentially cyclic multiplier is cyclic, and it turns out that the two notions coincide whenever <i>H</i> has the complete Pick property. However, in more general radially weighted Besov spaces there may be multipliers that are cyclic, but not weak<sup>*</sup> sequentially cyclic. For bounded holomorphic functions <i>f</i> with no zeros in <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathbb {B}_d\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">B</mi> <mi>d</mi> </msub> </math></EquationSource> </InlineEquation>, we obtain a condition on <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\log f\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>log</mo> <mi>f</mi> </mrow> </math></EquationSource> </InlineEquation> that implies the cyclicity of <i>f</i> in <i>H</i> and yields invertibility properties for 1/<i>f</i> within an associated Smirnov-type class. This condition is formulated in terms of weak<sup>*</sup> sequentially cyclic multipliers and can often be verified using a comparison principle: if <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(f, g \in Mult(H)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>,</mo> <mi>g</mi> <mo>∈</mo> <mi>M</mi> <mi>u</mi> <mi>l</mi> <mi>t</mi> <mo stretchy="false">(</mo> <mi>H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> satisfy <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(|f| \le |g|\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>f</mi> <mo stretchy="false">|</mo> <mo>≤</mo> <mo stretchy="false">|</mo> <mi>g</mi> <mo stretchy="false">|</mo> </mrow> </math></EquationSource> </InlineEquation> and if <i>f</i> is weak<sup>*</sup> sequentially cyclic, then <i>g</i> is also weak<sup>*</sup> sequentially cyclic. These results provide new insights into cyclicity phenomena in radially weighted Besov spaces in settings where <i>H</i> fails to be a complete Pick space.</p>

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Cyclicity via weak* Sequential Cyclicity in Radially Weighted Besov Spaces

  • Anusrika Datta,
  • Stefan Richter

摘要

A radially weighted Besov space H is a space of holomorphic functions on the unit ball \(\mathbb {B}_d \subseteq \mathbb {C}^d\) B d C d whose N-th radial derivative is square integrable with respect to a given admissible radial measure. We write Mult(H) for its multiplier algebra. The cyclic vectors in H are those functions f whose multiplier multiples are dense in H. We call a multiplier \(f \in Mult(H)\) f M u l t ( H ) weak* sequentially cyclic if its multiplier multiples are weak* sequentially dense in Mult(H). It is immediate that every weak* sequentially cyclic multiplier is cyclic, and it turns out that the two notions coincide whenever H has the complete Pick property. However, in more general radially weighted Besov spaces there may be multipliers that are cyclic, but not weak* sequentially cyclic. For bounded holomorphic functions f with no zeros in \(\mathbb {B}_d\) B d , we obtain a condition on \(\log f\) log f that implies the cyclicity of f in H and yields invertibility properties for 1/f within an associated Smirnov-type class. This condition is formulated in terms of weak* sequentially cyclic multipliers and can often be verified using a comparison principle: if \(f, g \in Mult(H)\) f , g M u l t ( H ) satisfy \(|f| \le |g|\) | f | | g | and if f is weak* sequentially cyclic, then g is also weak* sequentially cyclic. These results provide new insights into cyclicity phenomena in radially weighted Besov spaces in settings where H fails to be a complete Pick space.