<p>In this paper, we define and study a new class of bounded linear operators which is a generalization of the class of <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq1.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">\(m-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetric operators. Let <i>m</i> be a strictly positive integer number and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="75" /> </InlineMediaObject> <EquationSource Format="TEX">\(U\in {\mathcal {B}}({\mathcal {H}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>U</mi> <mo>∈</mo> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a unitary operator, an operator <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="74" /> </InlineMediaObject> <EquationSource Format="TEX">\(T\in {\mathcal {B}}({\mathcal {H}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mo>∈</mo> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is said to be a <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="63" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry if it commutes with <i>U</i> such that <Equation ID="Equ2"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_Equ2.gif" Format="GIF" Height="49" Rendition="HTML" Resolution="72" Type="Linedraw" Width="251" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \sum _{k=0}^m (-1)^{k}\left( \begin{array}{l} m \\ k \end{array}\right) T^{*(m-k)}T^{k}U^{k}=0. \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <munderover> <mo>∑</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>m</mi> </munderover> <msup> <mrow> <mo stretchy="false">(</mo> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mi>k</mi> </msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd columnalign="left"> <mi>m</mi> </mtd> </mtr> <mtr> <mtd columnalign="left"> <mrow> <mrow /> <mi>k</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mmultiscripts> <mi>T</mi> <mrow /> <mrow> <mrow /> <mo>∗</mo> <mo stretchy="false">(</mo> <mi>m</mi> <mo>-</mo> <mi>k</mi> <mo stretchy="false">)</mo> </mrow> </mmultiscripts> <msup> <mi>T</mi> <mi>k</mi> </msup> <msup> <mi>U</mi> <mi>k</mi> </msup> <mo>=</mo> <mn>0</mn> <mo>.</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>It is shown that if <i>T</i> is a <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="63" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry, then <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq8.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\(T^{p}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>T</mi> <mi>p</mi> </msup> </math></EquationSource> </InlineEquation> is a <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="72" /> </InlineMediaObject> <EquationSource Format="TEX">\((U^{p},m)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mi>U</mi> <mi>p</mi> </msup> <mo>,</mo> <mi>m</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry. We study the product and the sum of such a class. Moreover, if <i>T</i> is a <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="63" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry and <i>m</i> is even, we obtain that <i>T</i> is a <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq11.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="92" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m-1)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry. We prove that if <i>Q</i> is a nilpotent operator of order <i>n</i> which commutes with both <i>T</i> and <i>U</i>, then <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq12.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\(T+Q\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mo>+</mo> <mi>Q</mi> </mrow> </math></EquationSource> </InlineEquation> is a <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq13.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="130" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m+2n-2)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo>+</mo> <mn>2</mn> <mi>n</mi> <mo>-</mo> <mn>2</mn> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetry. Also, we give some spectral properties of <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11565_2025_585_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="63" /> </InlineMediaObject> <EquationSource Format="TEX">\((U,m)-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>U</mi> <mo>,</mo> <mi>m</mi> <mo stretchy="false">)</mo> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>symmetric operators. Finally, we show further results concerning this class of operators on a finite dimensional Hilbert space.</p>

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A new generalization of the class of \(m-\)symmetric operators

  • Souhaib Djaballah,
  • Messaoud Guesba

摘要

In this paper, we define and study a new class of bounded linear operators which is a generalization of the class of \(m-\) m - symmetric operators. Let m be a strictly positive integer number and \(U\in {\mathcal {B}}({\mathcal {H}})\) U B ( H ) is a unitary operator, an operator \(T\in {\mathcal {B}}({\mathcal {H}})\) T B ( H ) is said to be a \((U,m)-\) ( U , m ) - symmetry if it commutes with U such that \(\begin{aligned} \sum _{k=0}^m (-1)^{k}\left( \begin{array}{l} m \\ k \end{array}\right) T^{*(m-k)}T^{k}U^{k}=0. \end{aligned}\) k = 0 m ( - 1 ) k m k T ( m - k ) T k U k = 0 . It is shown that if T is a \((U,m)-\) ( U , m ) - symmetry, then \(T^{p}\) T p is a \((U^{p},m)-\) ( U p , m ) - symmetry. We study the product and the sum of such a class. Moreover, if T is a \((U,m)-\) ( U , m ) - symmetry and m is even, we obtain that T is a \((U,m-1)-\) ( U , m - 1 ) - symmetry. We prove that if Q is a nilpotent operator of order n which commutes with both T and U, then \(T+Q\) T + Q is a \((U,m+2n-2)-\) ( U , m + 2 n - 2 ) - symmetry. Also, we give some spectral properties of \((U,m)-\) ( U , m ) - symmetric operators. Finally, we show further results concerning this class of operators on a finite dimensional Hilbert space.