<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" article-type="research-article" dtd-version="1.2" xml:lang="ru"><front><journal-meta><journal-id journal-id-type="publisher-id">Journal of Experimental and Theoretical Physics</journal-id><journal-title-group><journal-title>Journal of Experimental and Theoretical Physics</journal-title></journal-title-group><issn publication-format="print">0044-4510</issn><issn publication-format="electronic">3034-641X</issn><publisher><publisher-name>Russian Academy of Science</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.31857/S0044451023050127</article-id><title-group><article-title>Evolution of Nonlinear Wave Pulses in the sine-Gordon Equation Theory</article-title><trans-title-group xml:lang="ru"><trans-title>Эволюция нелинейных волновых импульсов в теории уравнения синус-Гордон</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author"><contrib-id contrib-id-type="orcid"></contrib-id><name-alternatives><name xml:lang="en"><surname>Kamchatnov</surname><given-names>A. M</given-names></name><name xml:lang="ru"><surname>Камчатнов</surname><given-names>А. М </given-names></name></name-alternatives><email>kamch@isan.troitsk.ru</email><xref ref-type="aff" rid="aff-1"></xref><xref ref-type="aff" rid="aff-2"></xref></contrib></contrib-group><aff-alternatives id="aff-1"><aff><institution xml:lang="ru">Институт спектроскопии Российской академии наук</institution><institution xml:lang="en">Institute of Spectroscopy, Russian Academy of Sciences</institution></aff></aff-alternatives><aff-alternatives id="aff-2"><aff><institution xml:lang="ru"></institution><institution xml:lang="en"></institution></aff></aff-alternatives><pub-date date-type="pub" iso-8601-date="2023-05-01" publication-format="electronic"><day>01</day><month>05</month><year>2023</year></pub-date><volume>163</volume><issue>5</issue><fpage>734</fpage><lpage>743</lpage><abstract xml:lang="en"><p>The solution to the Whitham modulation equations for envelopes of one-phase periodic waves evolving according to the sine-Gordon equation is obtained. Using the hodograph method, these equations are reduced to a linear partial differential equation, and the class of solutions to this equation with separation of variables is described. The theory is illustrated by an example in which a complete analytic solution is obtained for the problem of nonlinear wave packet evolution accompanied with self-contraction and a decrease in the number of oscillations in the Whitham nonlinear region.</p></abstract><trans-abstract xml:lang="ru"><p>Дано решение модуляционных уравнений Уизема, описывающих эволюцию огибающих однофазных периодических волн, подчиняющихся уравнению синус-Гордон. Методом годографа задача сведена к линейному уравнению в частных производных и описан класс решений этого уравнения с разделяющимися переменными. 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