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A. Vartanian

Publications and source records attributed to A. Vartanian.

7 recordsLinked to original sources
arXiv2026

The Degenerate Third Painleve' Equation: Complete Asymptotic Classification of Solutions in the Neighbourhood of the Regular Singular Point

We give a classification for the small-$τ$ asymptotic behaviours of solutions to the degenerate third Painlevé equation, $u^{''}(τ) = \frac{(u^{\prime}(τ))^{2}}{u(τ)} - \frac{u^{\prime}(τ)}τ + \frac{1}τ\left(-8 \varepsilon (u(τ))^{2} + 2ab \right) + \frac{b^{2}}{u(τ)}, \quad\varepsilon=\pm1,\quad\varepsilon b>0, \quad a\in\mathbb{C}\setminus i\mathbb{Z}$, in terms of the monodromy data of a $2\times2$ matrix linear ODE whose isomonodromy deformations they describe. We also study the complete asymptotic expansions of the solutions.

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arXiv2025

Trans-Series Asymptotics of Solutions to the Degenerate Painlevé III Equation: A Case Study

A one-parameter family of trans-series asymptotics of solutions to the Degenerate Painlevé III Equation (DP3E) are parametrised in terms of the monodromy data of an associated two-by-two linear auxiliary problem via the isomonodromy deformation approach: trans-series asymptotics for the associated Hamiltonian and principal auxiliary functions and the solution of one of the sigma-forms of the DP3E are also obtained. The actions of Lie-point symmetries for the DP3E are derived.

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arXiv2023

One-Parameter Meromorphic Solution of the Degenerate Third Painlevé Equation with Formal Monodromy Parameter $a=\pm i/2$ Vanishing at the Origin

We prove that there exists a one-parameter meromorphic solution $u(τ)$ vanishing at $τ=0$ of the degenerate third Painlevé equation, \begin{equation*} u^{\prime \prime}(τ) \! = \! \frac{(u^{\prime}(τ))^{2}}{u(τ)} \! - \! \frac{u^{\prime}(τ)}τ \! + \! \frac{1}τ \! \left(-8 \varepsilon (u(τ))^{2} \! + \! 2ab \right) \! + \! \frac{b^{2}}{u(τ)},\qquad \varepsilon=\pm1,\quad\varepsilon b>0, \end{equation*} for formal monodromy parameter $a=\pm i/2$. We study number-theoretic properties of the coefficients of the Taylor-series expansion of $u(τ)$ at $τ=0$ and its asymptotic behaviour as $τ\to+\infty$. These asymptotics are visualized for generic initial data.

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arXiv2023

Algebroid Solutions of the Degenerate Third Painlevé Equation for Vanishing Formal Monodromy Parameter

Various properties of algebroid solutions of the degenerate third Painlevé equation, \begin{equation*} u^{\prime \prime}(τ) \! = \! \frac{(u^{\prime}(τ))^{2}}{u(τ)} \! - \! \frac{u^{\prime}(τ)}τ \! + \! \frac{1}τ \! \left(-8 \varepsilon (u(τ))^{2} \! + \! 2ab \right) \! + \! \frac{b^{2}}{u(τ)},\qquad \varepsilon=\pm1,\quad\varepsilon b>0, \end{equation*} for the monodromy parameter $a=0$ are studied. The paper contains connection results for asymptotics as $τ\to+0$ and as $τ\to+\infty$ for $a\in\mathbb{C}$. Using these results, the simplest algebroid solution with asymptotics $u(τ)\to cτ^{1/3}$ as $τ\to0$, where $c\in\mathbb{C}\setminus\{0\}$, together with its associated integral $\int_0^τ{(u(t))^{-1}\,d t}$, are considered in detail, and their basic asymptotic behaviours are visualized.

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arXiv2019

Riemann-Hilbert Characterisation of Rational Functions with a General Distribution of Poles on the Extended Real Line Orthogonal with Respect to Varying Exponential Weights: Multi-Point Padé Approximants and Asymptotics

Given $K$ arbitrary poles, which are neither necessarily distinct nor bounded, on the extended real line, a corresponding ordered base of rational functions orthogonal with respect to varying exponential weights is constructed: this gives rise to a $K$-fold family of orthogonal rational functions (ORFs). The ORF problem is characterised as a family of $K$ matrix Riemann-Hilbert problems (RHPs) on the extended real line, and a corresponding family of $K$ energy minimisation (variational) problems containing external fields with singular points is formulated, and the existence, uniqueness, and regularity properties of the associated family of equilibrium measures is established. The family of $K$ equilibrium measures is used to derive a family of $K$ model matrix RHPs on the extended real line that are amenable to asymptotic analysis via the Deift-Zhou non-linear steepest-descent method: this is used to derive uniform asymptotics, in a certain double-scaling limit, of the ORFs and their leading coefficients, as well as related, important objects, in the entire complex plane. A family of $K$ multi-point Padé approximants (MPAs) for the Markov-Stieltjes transform is also presented, and uniform asymptotics, in a certain double-scaling limit, are obtained for the corresponding MPAs and their associated errors in approximation (MPA error terms) in the entire complex plane.

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arXiv2010

Connection Formulae for Asymptotics of Solutions of the Degenerate Third Painleve' Equation: II

The degenerate third Painleve' equation, $u"(t)=(u'(t))^2/u(t)-u'(t)/t+1/t(-8c u^2(t)+2ab)+b^2/u(t)$, where $c=+/-1$, $b>0$, and $a$ is a complex parameter, is studied via the Isomonodromy Deformation Method. Asymptotics of general regular and singular solutions $u(t)$ as $t -> +/-\infty$ and $t -> +/-i\infty$ are derived and parametrized in terms of the monodromy data of the associated 2X2 linear auxiliary problem introduced in the first part of this work [1]. Using these results, three-real-parameter families of solutions that have infinite sequences of zeroes and poles that are asymptotically located along the real and imaginary axes are distinguished: asymptotics of these zeroes and poles are also obtained.

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