{"title":"A generalized Sylvester equation and discrete Ablowitz–Kaup–Newell–Segur type equations","authors":"Ya-Nan Hu, Shou-feng Shen, Song-lin Zhao","doi":"10.1134/S004057792505006X","DOIUrl":"10.1134/S004057792505006X","url":null,"abstract":"<p> A generalized Sylvester equation is introduced to revisit the Cauchy matrix schemes of the discrete negative-order Ablowitz–Kaup–Newell–Segur (AKNS) equation and the discrete third-order AKNS equation. Starting from the generalized Sylvester equation, we introduce a master function <span>(boldsymbol{S}^{(i,j)})</span> that admits a recurrence relation under a constraint relation. By imposing the shifts on matrices <span>(boldsymbol{r})</span> and <span>(,^mathrm{t}! {boldsymbol{s}})</span>, the shifts of the master function <span>(boldsymbol{S}^{(i,j)})</span> are derived. By introducing the dependent variables, the above two discrete AKNS equations are constructed as closed forms. For two different choices of the coefficient matrices in the Sylvester equation that preserve the constraint condition, exact solutions in asymmetric and symmetric cases are presented, with one-soliton, two-soliton, and the simplest Jordan-block solutions given explicitly. Continuum limits to the semidiscrete and continuous AKNS-type equations as well as the corresponding exact solutions are also discussed. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"782 - 809"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Integration of equations of acoustics of inhomogeneous media","authors":"O. V. Kaptsov","doi":"10.1134/S0040577925050058","DOIUrl":"10.1134/S0040577925050058","url":null,"abstract":"<p> We propose two approaches to integrating linear acoustic equations in inhomogeneous media. The first is based on the Laplace cascade method. For one-dimensional nonstationary equations, new solutions are obtained that depend on two arbitrary functions. These solutions are generalizations of relatively undistorted waves. In the two-dimensional case, conformal maps are used that allow reducing some equations with variable coefficients to equations with constant coefficients. Special three-dimensional equations can also be transformed to a wave equation. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"770 - 781"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Butterfly velocity and chaos suppression in de Sitter space","authors":"D. S. Ageev","doi":"10.1134/S0040577925050101","DOIUrl":"10.1134/S0040577925050101","url":null,"abstract":"<p> We study the holographic CFT in the de Sitter static patch at a finite temperature <span>(T)</span> and chemical potential. We find that the butterfly velocity <span>(v_B)</span> in such a field theory degenerates for all values of the Hubble parameter <span>(H)</span> and <span>(T)</span>. We interpret this as a chaos disruption caused by the interplay between the expansion of chaotic correlations constrained by <span>(v_B)</span> and effects caused by the de Sitter curvature. The chemical potential restores healthy butterfly velocity for some range of temperatures. Also, we provide some analogy of this chaos suppression with the Schwinger effect in the de Sitter space and black hole formation from shock wave collisions. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"863 - 871"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Dimensional reduction of nonlinear differential equations on homogeneous spaces","authors":"O. L. Kurnyavko, I. V. Shirokov","doi":"10.1134/S0040577925050046","DOIUrl":"10.1134/S0040577925050046","url":null,"abstract":"<p> We consider the problem of dimensional reduction of nonlinear differential equations on homogeneous spaces that have no symmetries in general. The proposed method allows passing to a differential equation with fewer independent variables and, in particular, to ordinary differential equations. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"755 - 769"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. V. Val’kov, A. S. Martynov, D. M. Dzebisashvili
{"title":"Néel temperature of a quasi-two-dimensional triangular-lattice antiferromagnet","authors":"V. V. Val’kov, A. S. Martynov, D. M. Dzebisashvili","doi":"10.1134/S0040577925050083","DOIUrl":"10.1134/S0040577925050083","url":null,"abstract":"<p> Based on the atomic representation for spin operators in the case of an arbitrary value of the spin <span>(S)</span>, we study the influence of quantum fluctuations on spin-wave renormalizations of the Néel temperature <span>(T_mathrm{N})</span> and on the magnetization of quasi-two-dimensional triangular-lattice antiferromagnet sublattices. The application of combined Green’s functions constructed using spin operators and their partial components allows easily obtaining a closed system of equations determining not only all branches of the spectrum of collective excitations but also the occupation numbers of states of an atom with different values of the spin projection. We show that the renormalization of <span>(T_mathrm{N})</span> is expressed in terms of the generalized Watson integral. Its nontrivial dependence on the degree of quasi-two-dimensionality and on the dynamical properties of three spectral branches determines the behavior of the critical temperature in the cases of different relations between the parameters of the quasi-two-dimensional antiferromagnet. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"826 - 838"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Integrable Hamiltonians related to the (mathfrak{e}(3)), (mathfrak{so}(4)), and (mathfrak{so}(3,1)) Poisson brackets","authors":"V. V. Sokolov","doi":"10.1134/S0040577925050034","DOIUrl":"10.1134/S0040577925050034","url":null,"abstract":"<p> We present a brief overview of our results on new integrable cases in Hamiltonian mechanics. The paper is devoted to a description of quadratic Hamiltonians that have an additional integral of motion in the cases of linear Poisson brackets <span>(mathfrak{e}(3))</span>, <span>(mathfrak{so}(4))</span> and <span>(mathfrak{so}(3,1))</span>. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"742 - 754"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the (k)th higher Nash blow-up derivation Lie algebras of isolated hypersurface singularities","authors":"N. Hussain, S. S.-T. Yau, Huaiqing Zuo","doi":"10.1134/S0040577925050022","DOIUrl":"10.1134/S0040577925050022","url":null,"abstract":"<p> Many physical questions such as <span>(4d)</span> <span>(N=2)</span> superconformal field theories, the Coulomb branch spectrum, and the Seiberg–Witten solutions are related to singularities. In this paper, we introduce some new invariants <span>(mathcal L^k_n(V))</span>, <span>(rho_n^k)</span>, and <span>(d_n^k(V))</span> of isolated hypersurface singularities <span>((V,0))</span>. We give a new conjecture for the characterization of simple curve singularities using the <span>(k)</span>th higher Nash blow-up derivation Lie algebra <span>(mathcal L^k_n(V))</span>. This conjecture is verified for small <span>(n)</span> and <span>(k)</span>. A inequality conjecture for <span>(rho_n^k)</span> and <span>(d_n^k(V))</span> is proposed. These two conjectures are verified for binomial singularities. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"705 - 741"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Pseudosolution of an integral convolution equation of the first kind","authors":"N. B. Yengibaryan","doi":"10.1134/S0040577925050113","DOIUrl":"10.1134/S0040577925050113","url":null,"abstract":"<p> We consider the equation <span>(int_{0}^{r}T(|x-t|)f(t),dt =g(x))</span>, where <span>(r<infty)</span> and the functions <span>(T)</span> and <span>(g)</span> and their first derivatives are absolutely continuous on <span>([0,r])</span> and <span>(T'(0)ne 0)</span>. An arbitrary term <span>(ax+b)</span> is added to the right-hand side of the equation. The obtained family of equations is reduced by double differentiation to an equation of the second kind. In the case of its unique solvability in <span>(L_{1}(0,r))</span>, the solution <span>(tilde{f})</span> is called a <span>(D^{2})</span>-pseudosolution of the original equation. We introduce the partial regularization of the equation and present some cases of the existence of a <span>(D^{2})</span>-pseudosolution. We propose a criterion for the suitability of <span>(tilde{f})</span> as an approximate solution. The problem of constructing a pseudosolution of an equation on the half-line is discussed. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"872 - 877"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Debye mass in the accelerating frame","authors":"D. V. Diakonov, K. V. Bazarov","doi":"10.1134/S0040577925050095","DOIUrl":"10.1134/S0040577925050095","url":null,"abstract":"<p> We consider a conformal scalar field theory with the <span>(lambda phi^4)</span> self-coupling in Rindler and Minkowski coordinates at a finite-temperature with the Planckian distribution for exact modes. The solution of the one-loop Dyson–Schwinger equation is found through the order <span>(lambda^{3/2})</span>. The appearance of a thermal (Debye) mass is shown. Unlike the physical mass, the thermal mass gives a gap in the energy spectrum in the quantization in the Rindler coordinates. The difference between such calculations in Minkowski and Rindler coordinates for exact modes is discussed. It is also shown that states with a temperature lower than the Unruh temperature are unstable. It is proved that for the canonical Unruh temperature, the thermal mass is equal to zero. The contribution to the quantum average of the stress–energy tensor is also calculated, it remains traceless even in the presence of the thermal mass. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"839 - 862"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Quantifying measurement incompatibility via measurement disturbance","authors":"Yi Guo, Shunlong Luo","doi":"10.1134/S0040577925050071","DOIUrl":"10.1134/S0040577925050071","url":null,"abstract":"<p> The incompatibility between quantum measurements (as mathematically represented by positive operator-valued measures, i.e., POVMs) is a key feature of quantum mechanics and is intrinsically related to the noncommutativity of operators. For both theoretical and practical considerations, it is desirable to quantify the degree of incompatibility between quantum measurements, and considerable effort has been devoted to this issue. In this paper, we provide a novel approach to measurement incompatibility by exploiting the Lüders channels derived from POVMs and employing the measurement disturbance to quantify incompatibility. This is achieved by constructing an approximately joint measurement for a pair of POVMs, which is an enlarged POVM with the correct marginal property for one of the two POVMs but not necessarily for the other. The degree of failure of the marginal property for the other POVM is a kind of measurement disturbance and can be naturally interpreted as a quantifier of the incompatibility between the two POVMs. We reveal basic properties of this quantifier of measurement incompatibility, identify its maximal value in some cases, compare it with several popular measures in the literature, and illustrate it with some typical examples. Some related open issues are also discussed. </p>","PeriodicalId":797,"journal":{"name":"Theoretical and Mathematical Physics","volume":"223 2","pages":"810 - 825"},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}