Uniform upper bounds for the cyclicity of the zero solution of the Abel differential equation
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Given two polynomials <span id="mmlsi1" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si1.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=1e41c0834dc9aee569810be6faceb4e8" title="Click to view the MathML source">P,qspan><span class="mathContainer hidden"><span class="mathCode">si1.gif" overflow="scroll">P,qspan>span>span> we consider the following question: “how large can the index of the first non-zero moment <span id="mmlsi2" class="mathmlsrc">source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si2.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=4fbd410de72af33210ce95b1323cae64">ss="imgLazyJSB inlineImage" height="26" width="86" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S002203961500368X-si2.gif">script>style="vertical-align:bottom" width="86" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S002203961500368X-si2.gif">script><span class="mathContainer hidden"><span class="mathCode">si2.gif" overflow="scroll">sub>m˜ksub>=subsup>absubsup>sup>Pksup>qspan>span>span> be, assuming the sequence is not identically zero?” The answer K   to this question is known as the moment Bautin index, and we provide the first general upper bound: <span id="mmlsi3" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si3.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=59fa0200e217fff7cc3c00d58c09297c" title="Click to view the MathML source">K猢?+deg鈦+3(deg鈦&minus;1)<sup>2sup>span><span class="mathContainer hidden"><span class="mathCode">si3.gif" overflow="scroll">K猢?/mo>2+deg鈦?/mo>q+3sup>stretchy="false">(deg鈦?/mo>P&minus;1stretchy="false">)2sup>span>span>span>. The proof is based on qualitative analysis of linear ODEs, applied to Cauchy-type integrals of certain algebraic functions.

sp0020">The moment Bautin index plays an important role in the study of bifurcations of periodic solution in the polynomial Abel equation <span id="mmlsi4" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si4.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=0c708b3ff0ade5a81cdcafcf1b080410" title="Click to view the MathML source">y<sup>′sup>=py<sup>2sup>+蔚qy<sup>3sup>span><span class="mathContainer hidden"><span class="mathCode">si4.gif" overflow="scroll">sup>ysup>=psup>y2sup>+qsup>y3sup>span>span>span> for <span id="mmlsi5" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si5.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=26be93bfba7296edd5385680b567e44c" title="Click to view the MathML source">p,qspan><span class="mathContainer hidden"><span class="mathCode">si5.gif" overflow="scroll">p,qspan>span>span> polynomials and <span id="mmlsi6" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si6.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=8516f639514b58138c74c43c669dc4b3" title="Click to view the MathML source">蔚鈮?span><span class="mathContainer hidden"><span class="mathCode">si6.gif" overflow="scroll">鈮?/mo>1span>span>span>. In particular, our result implies that for p   satisfying a well-known generic condition, the number of periodic solutions near the zero solution does not exceed <span id="mmlsi7" class="mathmlsrc"><span class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S002203961500368X&_mathId=si7.gif&_user=111111111&_pii=S002203961500368X&_rdoc=1&_issn=00220396&md5=0fa1e3db2d6f0e102701ce6bc5214377" title="Click to view the MathML source">5+deg鈦+3deg<sup>2sup>鈦span><span class="mathContainer hidden"><span class="mathCode">si7.gif" overflow="scroll">5+deg鈦?/mo>q+3sup>deg2sup>鈦?/mo>pspan>span>span>. This is the first such bound depending solely on the degrees of the Abel equation.

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