<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article  PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "http://dtd.nlm.nih.gov/publishing/3.0/journalpublishing3.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="3.0" xml:lang="en" article-type="research article"><front><journal-meta><journal-id journal-id-type="publisher-id">APM</journal-id><journal-title-group><journal-title>Advances in Pure Mathematics</journal-title></journal-title-group><issn pub-type="epub">2160-0368</issn><publisher><publisher-name>Scientific Research Publishing</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.4236/apm.2012.26063</article-id><article-id pub-id-type="publisher-id">APM-24668</article-id><article-categories><subj-group subj-group-type="heading"><subject>Articles</subject></subj-group><subj-group subj-group-type="Discipline-v2"><subject>Physics&amp;Mathematics</subject></subj-group></article-categories><title-group><article-title>
 
 
  Some Classes of Operators Related to &lt;i&gt;p&lt;/i&gt;-Hyponormal Operator
 
</article-title></title-group><contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>d.</surname><given-names>Ilyas</given-names></name><xref ref-type="aff" rid="aff1"><sup>1</sup></xref><xref ref-type="corresp" rid="cor1"><sup>*</sup></xref></contrib><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Reyaz</surname><given-names>Ahmad</given-names></name><xref ref-type="aff" rid="aff2"><sup>2</sup></xref></contrib></contrib-group><aff id="aff1"><addr-line>Department of Mathematics, Gaya College, Gaya, Bihar, India</addr-line></aff><aff id="aff2"><addr-line>Al-Ain University of Science and Technology, Al Ain &amp;amp; Abu Dhabi, UAE</addr-line></aff><author-notes><corresp id="cor1">* E-mail:<email>reyaz56@hotmail.com(DI)</email>;</corresp></author-notes><pub-date pub-type="epub"><day>09</day><month>11</month><year>2012</year></pub-date><volume>02</volume><issue>06</issue><fpage>419</fpage><lpage>422</lpage><history><date date-type="received"><day>August</day>	<month>11,</month>	<year>2012</year></date><date date-type="rev-recd"><day>September</day>	<month>16,</month>	<year>2012</year>	</date><date date-type="accepted"><day>September</day>	<month>28,</month>	<year>2012</year></date></history><permissions><copyright-statement>&#169; Copyright  2014 by authors and Scientific Research Publishing Inc. </copyright-statement><copyright-year>2014</copyright-year><license><license-p>This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/</license-p></license></permissions><abstract><p>
 
 
  We introduce a new family of classes of operators termed as *
  p-paranormal operator, classes *A(p,p); 
  p &gt; 0 and *A(p,q); 
  p, 
  q &gt; 0, parallel to 
  p-paranormal operator and classes A(p,p); 
  p&gt; 0 and A(p,q); 
  p, 
  q &gt; 0 introduced by M. Fujii, D. Jung, S. H. Lee, M. Y. Lee and R. Nakamoto [1]. We present a necessary and sufficient condition for 
  p-hyponormal operator T∈B（H）to be *
  p-paranormal and the monotonicity of *A(p,q). We also present an alternative proof of a result of M. Fujii, 
  et al. [1, Theorem 3.4].
 
</p></abstract><kwd-group><kwd>&lt;i&gt;p&lt;/i&gt;-Hyponormal Operator; Monotonicity; Class of Operators *A(p</kwd><kwd>q); *Paranormal Operator; *&lt;i&gt;p&lt;/i&gt;-Paranormal Operator</kwd></kwd-group></article-meta></front><body><sec id="s1"><title>1. Introduction</title><p>Let <img src="11-5300265\06337834-4999-48e2-99d2-2a4f19659ee5.jpg" /> denote the algebra of bounded liner operators on a Hilbert space H. An operator <img src="11-5300265\8b43dd95-3f0f-45f3-a3ed-d4d568a2118b.jpg" /> is positive if <img src="11-5300265\024aac90-453a-4822-a09f-4b1a58b6235c.jpg" /> for all<img src="11-5300265\8e587cdb-4d5b-4537-b83b-7d062ea45079.jpg" />. An operator <img src="11-5300265\0e7ec623-8819-403a-b219-01e8097fb93b.jpg" /> is hyponormal if <img src="11-5300265\8a54846d-74a9-4ca2-89da-f6ea7e093e28.jpg" /> and p-hyponormal if <img src="11-5300265\1c665bb8-3dd5-4612-a4a4-ed5bb7193fb8.jpg" /> for p &gt; 0. By the well known Lowner-Heinz theorem “<img src="11-5300265\92b687d7-c9c8-4ff0-9b8d-0af351b63439.jpg" />ensures <img src="11-5300265\18ab2d21-b4b8-452d-a195-84bcae6ab13d.jpg" /> for<img src="11-5300265\ccd8e689-89d2-4560-9ad6-c0f264c97196.jpg" />”, every p-hyponormal operator is q-hyponormal for<img src="11-5300265\c8035226-ab19-4da3-8b5e-d78d08539760.jpg" />. The Furuta’s inequalities [<xref ref-type="bibr" rid="scirp.24668-ref2">2</xref>] are as follows:</p><p>If <img src="11-5300265\d25f4ce9-22e3-4da9-af51-49afdca459c6.jpg" />then for each<img src="11-5300265\0a91c41e-52e8-4b86-a40c-47a58ce9a57f.jpg" />&#160;</p><disp-formula id="scirp.24668-formula23861"><label>(1.1)</label><graphic position="anchor" xlink:href="11-5300265\ba667237-6ca4-4363-a029-6856d8598777.jpg"  xlink:type="simple"/></disp-formula><disp-formula id="scirp.24668-formula23862"><label>(1.2)</label><graphic position="anchor" xlink:href="11-5300265\9ca9c3d2-f6f5-4c9a-b743-961f706363a1.jpg"  xlink:type="simple"/></disp-formula><p>hold for p<sub>0</sub> ≥ 0 and q<sub>0</sub> ≥ 1 with<img src="11-5300265\2fadd5a0-4810-4d1c-a7cf-8e9c0e1b11ed.jpg" />.</p><p>An operator <img src="11-5300265\bc586f97-2042-480e-ae5c-53dcc58df85b.jpg" /> is 1) paranormal if <img src="11-5300265\cd2fc950-7194-4e96-946a-0a4ce995bddf.jpg" /> for all<img src="11-5300265\5ae30ed1-a2ae-4b55-92c9-c1466b0aefdd.jpg" />;</p><p>2) <sup>*</sup>paranormal if <img src="11-5300265\b1644a3a-83a3-45ef-8a31-267ec7b45e84.jpg" /> for all<img src="11-5300265\5ec85bbc-5da4-4340-8915-7498f820e925.jpg" />.</p></sec><sec id="s2"><title>2. Preliminaries and Background</title><p>M. Fujii, D. Jung, S. H. Lee, M. Y. Lee and R. Nakamoto [<xref ref-type="bibr" rid="scirp.24668-ref1">1</xref>] introduced the following classes of operators:</p><p>An operator <img src="11-5300265\4674eaad-1631-4fc5-b13d-6389b1707c8d.jpg" /> is p-paranormal for p &gt; 0, if</p><disp-formula id="scirp.24668-formula23863"><label>(2.1)</label><graphic position="anchor" xlink:href="11-5300265\69d91e2e-1df1-4f1f-80af-ae9e340df2d2.jpg"  xlink:type="simple"/></disp-formula><p>holds for all<img src="11-5300265\181e9437-45fa-4a49-a249-229028b9501a.jpg" />, where U is the partial isometry appearing in the polar decomposition <img src="11-5300265\64278f30-0c09-4f86-9a90-bd70a5478c77.jpg" /> of T with<img src="11-5300265\bb1c0fee-bbd1-49cc-bdbe-06ca4e8bc1bd.jpg" />.</p><p>For p &gt; 0, an operator <img src="11-5300265\67d47e5f-64e3-40bb-8ad0-ed321e63b71f.jpg" /> is of class <img src="11-5300265\61b16bc7-c001-4900-bed6-889d3bfd47a0.jpg" /> if it satisfies an operator inequality</p><disp-formula id="scirp.24668-formula23864"><label>(2.2)</label><graphic position="anchor" xlink:href="11-5300265\e30cb6c6-3f3c-4ffe-8ee0-5ca4fa713747.jpg"  xlink:type="simple"/></disp-formula><p>For p, q &gt; 0, an operator <img src="11-5300265\10ff9348-e682-403e-86c0-79b6669fea1b.jpg" /> is of class <img src="11-5300265\391f4853-63b2-4a29-a792-32b028cf8943.jpg" /> if it satisfies an operator inequality</p><disp-formula id="scirp.24668-formula23865"><label>(2.3)</label><graphic position="anchor" xlink:href="11-5300265\3c24a9d8-f19b-4b33-8e5a-a4064292eb84.jpg"  xlink:type="simple"/></disp-formula><p>In this sequel we introduce <sup>*</sup>p-paranormal operator, classes of operators <img src="11-5300265\196475ff-7346-4589-8e95-622b96bea226.jpg" /> for p &gt; 0 and <img src="11-5300265\657e4077-e85c-427f-be7e-2022a1684e7b.jpg" /> for p, q &gt; 0 as follows:</p><p>A p-hyponormal operator is <sup>*</sup>p-paranormal if</p><disp-formula id="scirp.24668-formula23866"><label>(2.4)</label><graphic position="anchor" xlink:href="11-5300265\7f861153-5e4b-4d19-bd21-41eaf599470c.jpg"  xlink:type="simple"/></disp-formula><p>For p &gt; 0 a p-hyponormal operator <img src="11-5300265\454a20fb-4ad4-4c46-9cdd-e592d2340ae6.jpg" /> if it satisfies an operator inequality</p><disp-formula id="scirp.24668-formula23867"><label>(2.5)</label><graphic position="anchor" xlink:href="11-5300265\c5f26d61-e386-4b27-9a63-812f5f734393.jpg"  xlink:type="simple"/></disp-formula><p>More generally, we define the class <img src="11-5300265\e3d544f0-2a1f-4226-922d-b6e9cff397a8.jpg" /> for p, q &gt; 0 by an operator inequality</p><disp-formula id="scirp.24668-formula23868"><label>(2.6)</label><graphic position="anchor" xlink:href="11-5300265\27368fe1-419d-42a0-923d-6f59f5195adc.jpg"  xlink:type="simple"/></disp-formula><p>Remark (2.1). If T is p-hyponormal then using Furuta inequality (1.1) (&#167;1) it can be proved easily that <img src="11-5300265\05e87c7d-d3d5-407a-9ebd-6cefb4b7e66a.jpg" />.</p><p>Remark (2.2). By inequality (2.6) we have</p><p><img src="11-5300265\024c6d46-ab50-4418-b01b-353db1286446.jpg" /></p><p>The well known theorem of T. Ando [<xref ref-type="bibr" rid="scirp.24668-ref3">3</xref>] for paranormal operator is required in the proof of our main result.</p><p>Theorem (2.3). (Ando’s Theorem): An operator T is paranormal if and only if</p><disp-formula id="scirp.24668-formula23869"><label>(2.7)</label><graphic position="anchor" xlink:href="11-5300265\88504aa1-6973-4b59-8804-e55831113b2e.jpg"  xlink:type="simple"/></disp-formula><p>for all real k.</p></sec><sec id="s3"><title>3. Main Results</title><p>M. Fujii, et al. [<xref ref-type="bibr" rid="scirp.24668-ref1">1</xref>] proved the following theorem [1; Theorem 3.4].</p><p>Theorem (3.1). If <img src="11-5300265\dcda11e3-2d92-4bab-b794-071828686b65.jpg" /> for p &gt; 0 then T is p-paranormal.</p><p>In the following first we present an alternative way in which Theo (3.1) is proved in [<xref ref-type="bibr" rid="scirp.24668-ref1">1</xref>]. For this we have considered a quadratic form analogous to inequation (2.7) (&#167;2). We also present a necessary and sufficient condition for a p-hyponormal operator T to be a <sup>*</sup>p-paranormal operator and the monotonicity of class<img src="11-5300265\728d5917-f0a9-4b4e-b508-a4f6e69bbd30.jpg" />.</p><p>Theorem (3.2). A p-hyponormal operator <img src="11-5300265\20228e65-5e4b-4caf-a823-a6c1c1edbea5.jpg" /> is p-paranormal if and only if <img src="11-5300265\46c854b7-59da-427e-8455-3aff44c38413.jpg" /> for all <img src="11-5300265\906eae22-5d9d-4d84-a748-dac2fd3162ff.jpg" /> and p &gt; 0.</p><p>Proof. Let T =<img src="11-5300265\b6efed7d-f5ff-4876-b5c5-58652f6bdb81.jpg" /> be p-hyponormal where U is partial isometry, hence</p><p><img src="11-5300265\59558766-4350-4cc7-8bf5-0b4935fccf77.jpg" />.</p><p>We have</p><p><img src="11-5300265\1a863d4c-3996-4b41-a799-e05665002d0c.jpg" /></p><p>and</p><p><img src="11-5300265\f721a1a0-2d7e-4510-821f-55afef6915fa.jpg" /></p><p>Now,</p><p><img src="11-5300265\529244a2-349d-4b9c-9756-c5f163ff2cbc.jpg" /></p><p>for all <img src="11-5300265\20ea32c0-83a8-4434-9664-0eea9732a41b.jpg" /></p><p><img src="11-5300265\8db22e65-b28a-420a-9a60-d517dfaf38dd.jpg" /></p><p>for all <img src="11-5300265\658de8f9-2ed5-4692-b5f1-08f4b673bec1.jpg" /></p><p><img src="11-5300265\47c49b1e-c89a-4385-9db1-7d18f49754dd.jpg" /></p><p>for all <img src="11-5300265\97bcd4f3-d671-45fa-8fd4-cfd3cc5053b2.jpg" /></p><p><img src="11-5300265\36114525-b8b8-49ae-b4b6-bcc5175b1baa.jpg" /></p><p>for all <img src="11-5300265\ebd3f207-8132-4cf0-b0cb-c2fa3dd4c694.jpg" /></p><p>We know that if a &gt; 0, b and c are real numbers then <img src="11-5300265\9fda1654-16bd-44f2-a15e-25cb6116cbf4.jpg" /> for every real t if and only if <img src="11-5300265\f910233e-396f-428d-bf49-93899a7ed2a7.jpg" />. Hence</p><p><img src="11-5300265\029fae1d-f049-43a6-8be9-7ceaec164c95.jpg" /></p><p>for all <img src="11-5300265\33523a55-d7e3-418d-8db2-b62d2c9b1fc1.jpg" /></p><p><img src="11-5300265\cd54e2eb-8d24-44ce-89b1-c6746c032ea6.jpg" /></p><p><img src="11-5300265\c79ddbfd-a63a-42c2-9617-8b3ab8cde1e8.jpg" /></p><p>Since T be p-hyponormal, by Remark (2.1) (&#167;2) <img src="11-5300265\9b0e8bca-b5b3-4e3e-9a9b-6ac3505651bd.jpg" />i.e.</p><p><img src="11-5300265\a6d6fd86-94f9-445d-aa84-b99ca2f40704.jpg" /></p><p>Hence</p><p><img src="11-5300265\9edaadac-3c4c-44ab-979e-ecc78829155b.jpg" /></p><p><img src="11-5300265\fc5522d5-672a-4594-8066-8e4193f39505.jpg" /></p><p>i.e. if and only if T is p-paranormal.</p><p>Remark (3.3). Theorem (3.2) is independent of <img src="11-5300265\278e48ff-c388-4302-9378-d44e2251f633.jpg" /> being taken as unit vector where as M. Fujii, et al. [<xref ref-type="bibr" rid="scirp.24668-ref1">1</xref>] have considered <img src="11-5300265\8762ba53-ea10-4ffc-adb9-e98dcdd37e9d.jpg" /> as unit vector in the result [1, Theo. 3.4].</p><p>The following result presents a necessary and sufficient condition for p-hyponormal operator T to be a <sup>*</sup>pparanormal operator.</p><p>Theorem (3.4). A p-hyponormal operator T is <sup>*</sup>pparanormal if and only if</p><p><img src="11-5300265\cc63cfd9-4b70-4e34-911e-311e07a45dde.jpg" />for all<img src="11-5300265\ee905550-1db2-43cd-93fa-fbe884231af1.jpg" />(3.1)</p><p>Proof. Let <img src="11-5300265\d332c05f-5a68-4d76-b540-87f8d2300abb.jpg" /> be p-hyponormal operator where U is a partial isometry also let <img src="11-5300265\82459455-7180-4e48-a1bc-c84ed1f2e2f2.jpg" /> so that</p><p><img src="11-5300265\e87a97b2-3ec1-4566-9b49-c0c25a0950cd.jpg" />, <img src="11-5300265\af73e18d-6b8b-43b3-90b5-f64cced7c6c3.jpg" /></p><p>and<img src="11-5300265\6303c442-0985-4ddb-9d38-032fa56b9fa6.jpg" />. Now</p><p><img src="11-5300265\1219ed8b-3cd3-4b55-ad20-a26bc7b76e87.jpg" /></p><p>for all <img src="11-5300265\53dde316-3553-491e-b61f-aae4b4d30d1f.jpg" /></p><p><img src="11-5300265\64c6ee5d-6168-464f-90c8-49ebef1120f8.jpg" /></p><p>for all <img src="11-5300265\481848e3-9e08-4095-bb65-694c2c1dc8b3.jpg" /></p><p><img src="11-5300265\e8edcbbb-b979-4d2b-ae7b-5e8dc18160b8.jpg" /></p><p>for all <img src="11-5300265\9fc9f0f1-cf0c-4213-a774-328a922b1128.jpg" /></p><p><img src="11-5300265\3a46eb88-70a2-48b2-a6d5-29af627ce4b9.jpg" /></p><p>i.e.,&#160;&#160; &#160;&#160;<img src="11-5300265\3d605b7f-c861-4989-9619-8a839e8a4ca2.jpg" />&#160;&#160;&#160;&#160; (3.2)</p><p>Since T is p-hyponormal so<img src="11-5300265\5de9c9fa-bb33-460b-9530-655f9c909543.jpg" />, i.e.</p><p><img src="11-5300265\7980e33e-7493-4df9-b511-ff50c74ec7ec.jpg" /></p><p>i.e. &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;<img src="11-5300265\88aed2ce-e34d-487d-8866-1454eda9ad9d.jpg" />&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (3.3)</p><p>From (3.2) and (3.3), we have</p><p><img src="11-5300265\39c4b95f-474e-4234-9f89-e167dd351632.jpg" /></p><p>for all <img src="11-5300265\82d75557-3d48-407d-a155-d98d598042ab.jpg" /></p><p><img src="11-5300265\c299edb4-c2e7-4424-8751-516426dcd299.jpg" /></p><p>i.e. if and only if T is <sup>*</sup>p-paranormal.</p><p>In the following we present monotonicity of<img src="11-5300265\b8446f29-63c3-4303-af4f-eedecdf40dad.jpg" />. We need Furuta inequality [2,4] to prove the following theorem, see also [5,6].</p><p>Theorem (3.5). If <img src="11-5300265\1f14ca4c-1472-4930-8a83-37bfa2f6475a.jpg" /> and 0 &lt; q then</p><p><img src="11-5300265\b12c5694-2a00-4c6c-9cc1-541cd95f8a77.jpg" />.</p><p>Proof. Let <img src="11-5300265\e74e2e5b-ff2b-4e44-8709-55496678b173.jpg" /> where <img src="11-5300265\b7f1f9cf-4dc2-4bc3-9011-207b90ad5279.jpg" /> and 0 &lt; t then by the definition of class <img src="11-5300265\5666aa74-1519-4257-8788-91396a8c89ca.jpg" /> for p, q &gt; 0.</p><p><img src="11-5300265\1b6e55e5-caaa-4788-93d8-0bbed99a71f4.jpg" /></p><p>We apply it to (1.2) (&#167;1), in the case when<img src="11-5300265\1b4bc673-1b11-401e-a82a-a260b930ecaa.jpg" />, <img src="11-5300265\cc7b2b2c-54c6-4dd3-903a-5432c950c3c2.jpg" />, <img src="11-5300265\60861660-88c9-4157-89e4-320a13cc65f0.jpg" /><img src="11-5300265\3b76fc6e-c404-4e1a-8f55-a0f61bb7af87.jpg" />We have</p><p><img src="11-5300265\0cd47f71-ed42-4243-b589-2bbd04042af8.jpg" /></p><p>and</p><p><img src="11-5300265\c8f7ac8d-5e85-4db8-930b-9c902cf0a9db.jpg" /></p><p>Hence<img src="11-5300265\97a6acc5-f630-4f11-aa41-905e0a24feeb.jpg" />, so that</p><p><img src="11-5300265\07728e8b-c396-44c0-8d0c-0c50825c045a.jpg" /></p><p>i.e. <img src="11-5300265\fd153e50-e8cd-4463-9688-9579a04fe6b8.jpg" /></p><p>i.e. <img src="11-5300265\6e71100b-1b06-4625-8178-6de6cc69b851.jpg" /></p><p>i.e.<img src="11-5300265\8d8f6de6-9ce1-493d-b9b9-0eb58be88620.jpg" />.</p><p>Hence</p><p><img src="11-5300265\85b91d67-1fed-4f10-9d4f-b76ce344247a.jpg" />.</p></sec><sec id="s4"><title>REFERENCES</title></sec></body><back><ref-list><title>References</title><ref id="scirp.24668-ref1"><label>1</label><mixed-citation publication-type="other" xlink:type="simple">M. 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