arXiv subjects

Gregory Natanson

Publications and source records attributed to Gregory Natanson.

8 recordsLinked to original sources

arXiv2021

Quantization of rationally deformed Morse potentials by Wronskian transforms of Romanovski-Bessel polynomials

The paper advances the suggestion by Odake and Sasaki to re-write eigenfunctions of rationally deformed Morse potentials in terms of Wronskians of Laguerre polynomials in the reciprocal argument. It is shown that the constructed quasi-rational seed solutions of the Schrodinger equation with the Morse potential are formed by generalized Bessel polynomials with degree-independent indexes. As a new achievement we can point to the construction of the Darboux-Crum net of isospectral rational potentials using Wronskians of generalized Bessel polynomials with no positive zeros. It was then proved that any solvable rational Darboux-Crum transform of the Morse potential can be re-expressed in terms of Wronskians of the latter polynomials accompanied by juxtaposed pairs of Romanovski-Bessel polynomials.

math-ph↗

arXiv2018

Biorthogonal Polynomial System Composed of X-Jacobi Polynomials from Different Sequences

The paper examines rational Darboux transformations (RDTs) of the Jacobi equation written in the canonical form, with emphasis on the Sturm-Liouville problems (SLPs) solved under the Dirichlet boundary conditions (DBCs) at the ends of the infinite interval [1, inf). To be able to extend the analysis to the Darboux-Crum net of rational SL equations (SLEs) solved under the cited DBCs in terms of multi-indexed orthogonal exceptional Romanovski-Jacobi (XR-Jacobi) polynomials, we consider only seed functions which represent principal Frobenius solutions (PFSs) near one of the singular endpoints. . There are three distinct types of such solutions with no zeros inside the selected interval: two infinite sequences formed by the PFSs near the lower endpoint and one finite sequence formed by the PFSs near infinity. It is shown that use of classical Jacobi polynomials as seed functions results in the double-indexed manifold composed of orthogonal X_m-Jacobi polynomials in the reversed argument. As a result polynomials from this manifold obey the cross-orthogonality relation when integrated from +1 to inf. As a corollary we assert that each X_m-Jacobi polynomial of degree m + n has exactly m exceptional zeros between -inf and -1 as far as its indexes are restricted by the derived constraints on indexes of XR-Jacobi polynomials.

math.CA↗

arXiv2016

Survey of Nodeless Regular Almost-Everywhere Holomorphic Solutions for Exactly Solvable Gauss-Reference Liouville Potentials on the Line I.Subsets of Nodeless Jacobi-Seed Solutions Co-Existent with Discrete Energy Spectrum

The paper collates a complete list of nodeless regular almost-everywhere holomorphic (AEH) solutions for a subset of rational canonical Sturm-Liouville equations (RCSLEs) exactly quantized on a finite interval by classical Jacobi polynomials. The subset was constrained by the requirement that the appropriate Liouville transformation results in the Schrodinger equation on the line. The common remarkable feature of the selected nodeless solutions co-existent with the discrete energy spectrum is that they can be used as seed functions for multi-step 'canonical Liouville-Darboux transformations' (CLDTs) to convert the Gauss-Reference (GRef) potential (appearing in the resultant Schrodinger equation) into its isospectral rational SUSY partners conditionally exactly quantized by the so-called 'Jacobi-Seed' Heine polynomials.

math-ph↗

arXiv2015

Single-Source Nets of Algebraically-Quantized Reflective Liouville Potentials on the Line I. Almost-Everywhere Holomorphic Solutions of Rational Canonical Sturm-Liouville Equations with Second-Order Poles

The paper presents the unified technique for constructing SUSY ladders of rational Liouville potentials (RLPs) starting from the so-called "Gauss-reference" (GRef) potentials exactly quantized on the line via classical Jacobi, classical (generalized) Laguerre, or Romanovski-Routh polynomials with energy-dependent indexes. Each RLP is obtained by means of the Liouville transformation (LT) of the appropriate rational canonical Sturm-Liouville equation (RCSLE) with second-order poles. The presented analysis takes advantage of the generic factorization of canonical Sturm-Liouville equations (CSLEs) in terms of intertwining "generalized" Darboux operators. We refer to the latter operators as the canonical Liouville-Darboux transformations (CLDTs) to stress that they are equivalent to three-step operations: i) the LT from the CSLE to the Schrodinger equation; ii) the Darboux transformation (DT) of the appropriate LP; and iii) the inverse LT from the Schrodinger equation to the new CSLE. It is proven that the CLDT preserves the rational form of the RCSLE if its factorization function (FF) is an almost-everywhere holomorphic (AEH) solution of the RCSLE (or, in other words, a solution with a rational logarithmic derivative). As explained in the paper there are up to four gauge transformations which convert each RCSLE of our interest into the second-order differential equations with energy-dependent polynomial coefficients. The most important result of the paper is that polynomial solutions of these equations belong to sequences of Heine polynomials obtained by varying free terms at fixed values of singular points and the appropriate characteristic exponents. This allows us to construct networks of polynomial solutions -- the so-called "r-, c-, or i-Gauss-seed" (r-, c-, or i-GS) Heine polynomials -- starting from Jacobi, (generalized) Laguerre or Routh polynomials, respectively.

math-ph↗

arXiv2015

Exact quantization of the Milson potential via Romanovski-Routh polynomials

The paper re-examines Milson's analysis of the rational Sturm-Liouville (RSL) problem with two complex conjugated regular singular points -i and +i by taking advantage of Stevenson's complex linear-fraction transformation S(y) of the variable y restricted to the real axis. It was explicitly demonstrated that Stevenson's hypergeometric polynomials in a complex argument S are nothing but Romanovsky polynomials converted from y to S. The use of Stevenson's mathematical arguments unambiguously confirmed 'exact solvability' of the Milson potential. It was revealed that the Milson potential has two branches referred to as 'inside' and 'outside' depending on positions of zeros of the so-called 'tangent polynomial' (TP) relative to the unit circle. The two intersect along the shape-invariant Gendenshtein (Scarf II) potential. The remarkable feature of the RCSLE associated with the inner branch of the Milson potential (as well as its shape-invariant limit) is that it has two sequences of nodeless almost-everywhere holomorphic (AEH) solutions which can be used as factorization functions (FFs) for constructing new quantized-by-polynomials potentials. In case of the Gendenshtein potential complex-conjugated characteristic exponents (ChExps) at finite singular points of the given RCSLE become energy independent so that each polynomial sequence turns into a finite set of orthogonal polynomials. This confirms Quesne's conjecture [J. Math. Phys. 54 122103 (2013)] that the 'Case III' polynomials discovered by her can be used for constructing orthogonal polynomials of novel type.

math-ph↗

arXiv2014

Heun-Polynomial Representation of Regular-at-Infinity Solutions for the Basic SUSY Ladder of Hyperbolic Pöschl-Teller Potentials Starting from the Reflectionless Symmetric Potential Well

It is shown that the regular-at-infinity solution of the 1D Schrodinger equation with the hyperbolic Poschl-Teller (h-PT) potential with integer parameters is expressible in terms of a n-order Heun polynomial in y=thr at an arbitrary negative energy. It was proven that the Heun polynomials in question form a subset of generally complex Lambe-Ward polynomials corresponding to zero value of the accessory parameter. Since the mentioned solution expressed in the new variable y has an almost-everywhere holomorphic (AEH) form it can be used as the factorization function (FF) for canonical Liouville-Darboux transformations (CLDTs) to construct a continuous family of shape-invariant rational potentials exactly-solvable by the Hp-seed (HpS) Heine polynomials. There are also two sequences of infinitely many rational potentials generated using CLDTs with nodeless regular-at-origin AEH FFs.

math-ph↗

arXiv2014

Breakup of SUSY Quantum Mechanics in the Limit-Circle Region of the Reflective Kratzer Oscillator

The paper studies violation of conventional rules of SUSY quantum mechanics for the centrifugal potential V(r) within the limit-circle (LC) range. A special attention is given to transformation properties of the Titchmarsh-Weyl m-function under Darboux deformations of the reflective Kratzer oscillator: centrifugal Kepler-Coulomb (KC) potential plus a Taylor series in r. Since our analysis is based on Fulton's representation of a regular-at-infinity solution [Math. Nachr. 281, 1418 (2008)] as a superposition of two Frobenius solutions at the origin, we refer to the appropriate expressions as the Titchmarsh-Weyl-Fulton (TWF) functions. Explicit transformation relations are derived for partner TWF functions associated with SUSY pairs of centrifugal potentials. It is shown that these relations have a completely different form for Darboux transformations (DTs) keeping the potential within the LC range. As an illustration, we use regular nodeless Frobenius solutions to construct SUSY partners of the radial r- and c-Gauss-reference (GRef) potentials solvable via hypergeometric and confluent hypergeometric functions, respectively. We explicitly demonstrate existence of non-isospectral partners of both radial potentials in the LC region and obtain their discrete energy spectra using the derived closed-form expressions for the TWF functions. The general transformation relations for the TWF function have been verified taking advantage of form-invariance of the radial GRef potentials under double-step DTs with the so-called 'basic' seed solutions (SSs). Similarly we directly ratify that TWF functions for three shape-invariant reflective potentials on the half-line -- hyperbolic Poschl-Teller (h-PT), Eckart/Manning-Rosen (E/MR), and centrifugal KC potentials - do retain their form under basic DTs.

physics.gen-ph↗

arXiv2013

Gauss-Seed Nets of Sturm-Liouville Problems With Energy-Independent Characteristic Exponents and Related Sequences of Exceptional Orthogonal Polynomials I. Canonical Darboux Transformations Using AEH Functions

The paper applies the so-called 'Canonical-Darboux-Transformation' (CDT) method to reproduce general expressions for rational potentials (RPs) quantized in terms of exceptional orthogonal polynomial systems (X-OPSs). The benchmark of the new method recently developed by the author for implicit potentials solvable via hypergeometric functions is that rationally-extended SUSY partners of the original potential are quantized in terms of sequences of the so-called 'Gauss-seed' (GS) Heine polynomials starting from a polynomial of non-zero order. The common mark of the Darboux-Poschl-Teller (DPT) potential and isotonic oscillator discussed in this paper is that the appropriate rational Sturm-Liouville (RSL) equations have energy-independent characteristic exponents at both singular end points and as a result the appropriate sequences of GS Heine polynomials turn into X-OPSs with infinitely many members.

math-ph↗