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CONTRADICTIONS IN SCATTERING THEORY

Vladimir K. Ignatovich

Published Jan 1, 2004• 2 citations
OpenAlex

Abstract

The standard scattering theory (SST) in non relativistic quantum mechanics (QM) is analyzed. Self-contradictions of SST are demonstrated. A direct way to calculate scatter-ing probability without introduction of a finite volume is dis-cussed. Substantiation of SST in textbooks with the help of wave packets is shown to be incomplete. A complete theory of wave packets scattering on a fixed center is presented, and its similarity to the plane wave scattering is demonstrated. The neutron scattering on a monatomic gas is investigated, and several problems are pointed out. A catastrophic ambi-guity of the cross section is revealed, and a way to resolve this ambiguity is discussed.

Related papers

Contradictions of the quantum scattering theory

V. K. Ignatovich

The standard scattering theory (SST) in non relativistic quantum mechanics (QM) is analyzed. Self-contradictions of SST are deconstructed. A direct way to calculate scattering probability without introduction of a finite volume is discussed. Substantiation of SST in textbooks with the help of wave packets is shown to be incomplete. A complete theory of wave packets scattering on a fixed center is presented, and its similarity to the plane wave scattering is demonstrated. The neutron scattering on a monatomic gas is investigated, and several problems are pointed out. A catastrophic ambiguity of the cross section is revealed, and a way to resolve this ambiguity is discussed.

arXiv:quant-ph/0403067•Mar 9, 2004•0 citations

Wave packets in the quantum theory of collisions

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Two methodological difficulties of the quantum theory of collisions are considered. The first is the undesirable interference of the incident and scattered waves in the stationary approach to scattering. The second concerns the nonstationary approach to the theory of collisions of the type a + b → c + d. In order to calculate the cross section one uses the matrix element 〈cd|S|ab〉 of the S-matrix. The element is proportional to δ-function expressing the energy conservation. The corresponding probability |〈cd|S|ab〉|2 contains δ2, which is mathematically meaningless. The known regular way to overcome the difficulty seems to be unsatisfactory. In this paper, both the problems are resolved using wave packets of incident particles.

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Abstract In quantum mechanics textbooks, a single-particle scattering theory is introduced. In the present work, a generalized scattering theory is presented, which can be in principle applied to the scattering problems of arbitrary number of particle. In laboratory frame, a generalized Lippmann-Schwinger scattering equation is derived. We emphasized that the derivation is rigorous, even for treating infinitesimals. No manual operation such as analytical continuation is allowed. In the case that before scattering N particles are plane waves and after the scattering they are new plane waves, the transition amplitude and transition probability are given and the generalized S matrix is presented. It is proved that the transition probability from a set of plane waves to a new set of plane waves of the N particles equal to that of the reciprocal process. The generalized theory is applied to the cases of one- and two-particle scattering as two examples. When applied to single-particle scattering problems, our generalized formalism degrades to that usually seen in the literature. When our generalized theory is applied to two-particle scattering problems, the formula of the transition probability of two-particle collision is given. It is shown that the transition probability of the scattering of two free particles is identical to that of the reciprocal process. This transition probability and the identity are needed in deriving Boltzmann transport equation in statistical mechanics. The case of identical particles is also discussed.

arXiv:2307.01235•Journal of Physics Communications•Jun 13, 2023•5 citations

Quantum mechanics illustrated with neutrons

Vladimir K. Ignatovich

The book contains four chapters. The first one deals with elementary problems of one dimensional quantum mechanics of scalar particles, and their solution is given by much more simpler method than in standard textbooks. Attention should be paid to problems with periodic potentials. In the second chapter methods of one-dimensional quantum mechanics are applied to three-dimensional scattering problems. Here a new approach to the dynamic diffraction theory based on multiple wave scattering method is proposed. Diffraction on a crystalline plane is solved exactly, and is shown to vanish in contradiction with experimental observations. In the third chapter, all the problems of the first one are generalized to spinor particles. The most interesting questions are related to polarization of particles and rotation of polarization by means of radio-frequency fields, which create superpositions of states with different energies and speeds. The fourth chapter is devoted to fundamental questions of quantum mechanics. The theory of weak measurements is criticized. Some experiments related to wave packets and to determination of quantization axis of non polarized neutron beams are proposed.

•Jun 15, 2018•0 citations
The standard scattering theory (SST) in non relativistic quantum mechanics (QM) is analyzed. Self-contradictions of SST are demonstrated. A direct way to calculate scatter-ing probability without introduction of a finite volume is dis-cussed. Substantiation of SST in textbooks with the help of wave packets is shown to be incomplete. A complete theory of wave packets scattering on a fixed center is presented, and its similarity to the plane wave scattering is demonstrated. The neutron scattering on a monatomic gas is investigated, and several problems are pointed out. A catastrophic ambi-guity of the cross section is revealed, and a way to resolve this ambiguity is discussed.
The standard scattering theory (SST) in non relativistic quantum mechanics (QM) is analyzed. Self-contradictions of SST are deconstructed. A direct way to calculate scattering probability without introduction of a finite volume is discussed. Substantiation of SST in textbooks with the help of wave packets is shown to be incomplete. A complete theory of wave packets scattering on a fixed center is presented, and its similarity to the plane wave scattering is demonstrated. The neutron scattering on a monatomic gas is investigated, and several problems are pointed out. A catastrophic ambiguity of the cross section is revealed, and a way to resolve this ambiguity is discussed.
Two methodological difficulties of the quantum theory of collisions are considered. The first is the undesirable interference of the incident and scattered waves in the stationary approach to scattering. The second concerns the nonstationary approach to the theory of collisions of the type a + b → c + d. In order to calculate the cross section one uses the matrix element 〈cd|S|ab〉 of the S-matrix. The element is proportional to δ-function expressing the energy conservation. The corresponding probability |〈cd|S|ab〉|2 contains δ2, which is mathematically meaningless. The known regular way to overcome the difficulty seems to be unsatisfactory. In this paper, both the problems are resolved using wave packets of incident particles.
We discuss "the plane wave approximation" to quantum mechanical scattering using simple one-dimensional examples. The central points of the paper are that (a) plane waves should be thought of as infinitely wide wave packets, and (b) the calculations of reflection and transmission probabilities RRR and TTT in standard textbook presentations involve an approximation which is almost never discussed. We argue that it should be discussed explicitly, and that doing so provides a simple and intuitively revealing alternative way to derive and understand certain formulas. Using an under-appreciated exact expression for wave packet scattering probabilities, we calculate, for two standard examples, expressions for RRR and TTT for an incident Gaussian wave packet. Comparing these results to the corresponding ones calculated using the plane wave approximation helps illuminate the domain of applicability of that approximation.
Abstract In quantum mechanics textbooks, a single-particle scattering theory is introduced. In the present work, a generalized scattering theory is presented, which can be in principle applied to the scattering problems of arbitrary number of particle. In laboratory frame, a generalized Lippmann-Schwinger scattering equation is derived. We emphasized that the derivation is rigorous, even for treating infinitesimals. No manual operation such as analytical continuation is allowed. In the case that before scattering N particles are plane waves and after the scattering they are new plane waves, the transition amplitude and transition probability are given and the generalized S matrix is presented. It is proved that the transition probability from a set of plane waves to a new set of plane waves of the N particles equal to that of the reciprocal process. The generalized theory is applied to the cases of one- and two-particle scattering as two examples. When applied to single-particle scattering problems, our generalized formalism degrades to that usually seen in the literature. When our generalized theory is applied to two-particle scattering problems, the formula of the transition probability of two-particle collision is given. It is shown that the transition probability of the scattering of two free particles is identical to that of the reciprocal process. This transition probability and the identity are needed in deriving Boltzmann transport equation in statistical mechanics. The case of identical particles is also discussed.
The book contains four chapters. The first one deals with elementary problems of one dimensional quantum mechanics of scalar particles, and their solution is given by much more simpler method than in standard textbooks. Attention should be paid to problems with periodic potentials. In the second chapter methods of one-dimensional quantum mechanics are applied to three-dimensional scattering problems. Here a new approach to the dynamic diffraction theory based on multiple wave scattering method is proposed. Diffraction on a crystalline plane is solved exactly, and is shown to vanish in contradiction with experimental observations. In the third chapter, all the problems of the first one are generalized to spinor particles. The most interesting questions are related to polarization of particles and rotation of polarization by means of radio-frequency fields, which create superpositions of states with different energies and speeds. The fourth chapter is devoted to fundamental questions of quantum mechanics. The theory of weak measurements is criticized. Some experiments related to wave packets and to determination of quantization axis of non polarized neutron beams are proposed.