- Mathematical Constraints on Gauge in Maxwellian Electrodynamics (2008) [Updated 5 years ago]
- The Significance of Density in the Structure of Quantum Theories (2007) [Updated 1 decade ago]
- The Yukawa Lagrangian Density is Inconsistent with the Hamiltonian (2007) [Updated 1 decade ago]
- Theoretical Errors in Contemporary Physics (2006) [Updated 1 decade ago]
- Further Difficulties with the Klein-Gordon Equation (2005) [Updated 5 years ago]
- Difficulties with the Klein-Gordon Equation (2004) [Updated 5 years ago]
- Remarks on Photon-Hadron Interactions (2003) [Updated 5 years ago]

- Mathematical Constraints on Gauge in Maxwellian Electrodynamics (2008) [Updated 5 years ago]
The structure of classical electrodynamics based on the variational principle together with causality and spacetime homogeneity is analyzed. It is proved that in this case the 4-potentials are defined uniquely. On the other hand, the approach where Maxwell equations and the Lorentz law of force are regarded as cornerstones of the theory allows gauge transformations. For this reason, the two theories are not equivalent. A simple example substantiates this conclusion. Quantum physics is linked to the variational principle and it is proved that the same result holds for it.

The compatibility of this conclusion with gauge invariance of the Lagrangian density is explained. Several alternative possibilities that may follow this work are pointed out.

- The Significance of Density in the Structure of Quantum
Theories (2007) [Updated 1 decade ago]
It is proved that density plays a crucial role in the structure of quantum field theory. The Dirac and the Klein-Gordon equations are examined. The results prove that the Dirac equation is consistent with density related requirements whereas the Klein-Gordon equation fails to do that. Experimental data support these conclusions.

- The Yukawa Lagrangian Density is Inconsistent with the Hamiltonian (2007) [Updated 1 decade ago]
It is proved that no Hamiltonian exists for the real Klein-Gordon field used in the Yukawa interaction. It is also shown that a real Klein-Gordon particle can be neither in a free isolated state nor in a bound state having an angular momentum l > 0. The experimental data support these conclusions. This outcome is in a complete agreement with Dirac's negative opinion on the Klein-Gordon equation.

- Theoretical Errors in Contemporary Physics (2006) [Updated 1 decade ago]
Errors pertaining to the following physical theories are discussed: the Dirac magnetic monopole theory; the Klein-Gordon equation; the Yukawa theory of nuclear force; the idea of Vector Meson Dominance; the Aharonov-Bohm effects; the idea of diffraction-free electromagnetic beams and Quantum Chromodynamics. Implications of the theoretical errors are discussed briefly. In particular, relations between the Dirac monopole theory, the idea of Vector Meson Dominance and Quantum Chromodynamics cast doubt on the current interpretation of strong interactions.

- Further Difficulties with the Klein-Gordon Equation (2005) [Updated 5 years ago]
Herein, the Dirac equation is compared with the Klein-Gordon equation. In contrast to the Dirac case, it is proved that the Klein-Gordon equation has di?culties with the Hamiltonian di?erential operator of relativistic quantum mechanics and with the de?nition of an inner product of wave functions, which is a requirement for a construction of a Hilbert space. An added discussion of the Pauli-Weisskopf article and that of Feshbach-Villars proves that their theories lack a self-consistent expression for the Hamiltonian. Related di?culties are pointed out.

- Difficulties with the Klein-Gordon Equation (2004) [Updated 5 years ago]
Relying on the variational principle, it is proved that new contradictions emerge from an analysis of the Lagrangian density of the Klein-Gordon field: normalization problems arise and interaction with external electromagnetic fields cannot take place. By contrast, the Dirac equation is free of these problems. Other inconsistencies arise if the Klein-Gordon field is regarded as a classical field.

- Remarks on Photon-Hadron Interactions (2003) [Updated 5 years ago]
Theoretical aspects of VMD and related approaches to real photon-hadron interaction are discussed. The work relies on special relativity, properties of linearly polarized photons, angular momentum conservation and relevant experiments. It is explained why VMD and similar approaches should not be regarded as part of a theory but, at most, as phenomenological models. A further experiment pertaining to this issue is suggested.