arXiv subjects

Domenico P. L. Castrigiano

Publications and source records attributed to Domenico P. L. Castrigiano.

12 recordsLinked to original sources

arXiv2026

Representation of the causal logic for the Dirac system and the electron

We construct a covariant representation of the causal logic for the Dirac system and the electron, based on the conserved Dirac probability current and a general current-to-localization procedure for achronal regions. A polynomial decay estimate, derived by a non-stationary phase argument, verifies the conditions required to define covariant achronal localization for the full Dirac system. Extending this localization to complete spacetime regions yields the corresponding causal-logic representation; restriction to the positive-energy invariant subspace gives the analogous construction for the electron. We establish several structural properties. On Euclidean space, Dirac localization agrees with canonical projection-valued localization, while its position operator differs from the Newton--Wigner operator by an explicitly determined bounded self-adjoint correction. Full Dirac achronal localization is projection valued and represents achronal separateness by orthogonality, thus satisfying microscopic causality. After compression to the electron subspace, it becomes positive-operator valued while preserving causality. We further extend known results from spatial to general achronal regions, prove separation and norm-one criteria, and analyze the high-boost limit, obtaining Lorentz contraction in a precise probabilistic sense. Finally, we discuss the electron--positron decomposition and the state transformation induced by position measurements, showing that measurement-induced positron production is universal and independent of the specific measuring device.

math-ph↗

arXiv2026

Achronal localization and representation of the causal logic from a conserved current, application to the massive scalar boson

Only recently the concept of achronal localization has been developed as the adequate frame for the description of the localizability of a relativistic quantum mechanical system. Here covariant achronal localizations are gained out of covariant conserved currents computing their flux passing through achronal surfaces. This general method is applied to the probability density currents with causal kernel regarding the massive scalar boson. As (covariant) achronal localizations correspond one-to-one to (covariant) representations of the causal logic, thus, apparently for the first time, a covariant representation of the causal logic for an elementary relativistic quantum mechanical system has been achieved. Similarly a covariant family of representations of the causal logic is derived from the stress-energy tensor of the massive scalar boson. The construction of an achronal localization from a conserved current relies on a version of the divergence theorem for open sets with almost Lipschitz boundary. This result is stated and proved in this work.

math-ph↗

arXiv2025

Localization of the massive scalar boson on achronal hyperplanes, derivation of Lorentz contraction

It is shown that the causal localizations of the massive scalar boson on spacelike hyperplanes extend uniquely to all achronal hyperplanes. The extension occurs by means of the high boost limit in a covariant manner. Towards a localization in maximal achronal surfaces a simple but emblematic case shows that normalization, demanded by causality, is preserved. Moreover the existence of the high boost limit, as a consequence of causality, implies the phenomenon of Lorentz contraction discussed in detail. In conclusion, these considerations constitute a clear plea for the concept of achronal localization.

math-ph↗

arXiv2025

Achronal Localization, Representations of the Causal Logic for massive systems

On plain physical grounds localization of relativistic quantum particles is extended to the achronal regions of Minkowski spacetime. Achronal localization fulfills automatically the requirements of causality. It constitutes the frame which complies most completely with the principle of causality for quantum mechanical systems. Achronal localization is equivalent to the localization in the regions of the causal logic. Representations of the causal logic are constructed for the systems with mass spectrum of positive Lebesgue measure and every definite spin. Apparently no representation of the causal logic for a real mass system has been achieved in the past.

math-ph↗

arXiv2024

Dirac and Weyl Fermions -- the Only Causal Systems

Causal systems describe the localizability of relativistic quantum systems complying with the principles of special relativity and elementary causality. At their classification we restrict ourselves to real mass and finite spinor systems. It follows that (up to certain not yet discarded unitarily related systems) the only irreducible causal systems are the Dirac and the Weyl fermions. Their wave-equations are established as a mere consequence of causal localization. - The bounded localized Dirac and Weyl wavefunctions are studied in detail. One finds that, at the speed of light, the carriers shrink in the past and expand in the future. For every direction in space there is a definite time at which the change from shrinking to expanding occurs. A late changing time characterizes those states, which shrink to a delta-strip if boosted in the opposite direction. Using a density result for these late-change states one shows that all Dirac and Weyl wave-functions are subjected to Lorentz contraction. The latter is discussed in some detail. - We tackle the question whether a causal system induces a representation of a causal logic and thus provides a localization in proper space-time regions rather than on spacelike hyperplanes. The causal logic generated by the spacelike relation is shown to do not admit representations at all. But the logic generated by the non-timelike relation in general does, and the necessary condition is derived that there is a projection valued measure on every non-timelike non-spacelike hyperplane being the high boost limit of the localization on the spacelike hyperplanes. Dirac and Weyl systems are shown to satisfy this condition and thus to extend to all non-timelike hyperplanes, which implies more profound properties of the causal systems. The bounded localized eigenstates of the projections to non-spacelike flat strips are late-change states.

math-ph↗

arXiv2024

Causal Localizations of the Massive Scalar Boson

The positive operator valued localizations (POL) of a massive scalar boson are constructed and a characterization and structural analyses of their kernels are obtained. In the focus of this article are the causal features of the POL. There is the well-known causal time evolution (CT). Recently a POL by Terno and Moretti, which is a kinematical deformation of the Newton-Wigner localization (NWL) and belongs to the here fully analyzed class of finite POL, is shown by V.Moretti to comply with CT. A further POL with CT treated here, which is in the same class, is the only one being the trace of a projection valued localization (like NWL) with CT. - Causality imposes a condition CC, which implies CT but is more restrictive than CT. Extending Moretti's method it is shown rigorously that the POL of the class introduced by Petzold et al. satisfy CC. Their kernels are called causal kernels, of which a rather detailed description is achieved. One the way there the case of one spatial dimension is solved completely. This case is instructive. In particular it directed Petzold et al. and subsequently Henning, Wolf to find their basic one-parameter family $K_r$ of causal kernels. The causal kernels are, up to a fixed energy factor, normalized positive definite Lorentz invariant kernels. A full characterization of the latter is attained due to their close relation to the zonal spherical functions on the Lorentz group. Finally these considerations discharge into the main result that $K_{3/2}$ is the absolute maximum, viz. $|K|\le K_{3/2}$ for all causal kernels $K$.

math-ph↗

arXiv2021

Unbounded Toeplitz Operators with Rational Symbols

Unbounded (and bounded) Toeplitz operators (TO) with rational symbols are analysed in detail showing that they are densely defined closed and have finite dimensional kernels and deficiency spaces. The latter spaces as well as the domains, ranges, spectral and Fredholm points are determined. In particular, in the symmetric case, i.e., for a real rational symbol the deficiency spaces and indices are explicitly available. The concluding section gives a brief overview on the research on unbounded TO in order to locate the present contribution. Regarding properties of unbounded TO in general, it furnishes some new results recalling the close relationship to Wiener-Hopf operators and, in case of semiboundedness, to singular operators of Hilbert transformation type. Specific symbols considered in the literature admit further analysis. Some conclusions are drawn for semibounded integrable and real square-integrable symbols. There is an approach to semibounded TO, which starts from closable semibounded forms related to a Toeplitz matrix. The Friedrichs extension of the TO associated with such a form is studied. Finally, analytic TO and Toeplitz-like operators are briefly examined, which in general differ from the TO treated here.

math.FA↗

arXiv2020

Unbounded Wiener-Hopf Operators and Isomorphic Singular Integral Operators

Some preliminaries and basic facts regarding unbounded Wiener-Hopf operators (WH) are provided. WH with rational symbols are studied in detail showing that they are densely defined closed and have finite dimensional kernels and deficiency spaces. The latter spaces as well as the domains and ranges are explicitly determined. A further topic concerns semibounded WH. Expressing a semibounded WH by a product of a closable operator and its adjoint this representation allows for a natural self-adjoint extension. It is shown that it coincides with the Friedrichs extension. Polar decomposition gives rise to a Hilbert space isomorphism relating semibounded WH to singular integral operators of a well-studied type based on the Hilbert transformation.

math.FA↗

arXiv2020

Rebound Motion of Localized Dirac Wavefunctions

It is shown that the carrier of a bounded localized free Dirac wavefunction shrinks from infinity and subsequently expands to infinity again. The motion occurs isotropicly at the speed of light. In between there is the phase of rebound, which is limited in time and space in the order of the diameter of the carrier at its minimal extension. This motion proceeds anisotropicly and abruptly as for every direction in space there is a specific time, at which the change from shrinking to expanding happens instantaneously. Asymptotically, regarding the past and the future as well, the probability of position concentrates up to 1 within any spherical shell whose outer radius increases at light speed.

math-ph↗

arXiv2020

Spectral Representations of the Wiener-Hopf Operator for the sinc Kernel and some Related Operators

The spectral representation of the Wiener-Hopf operator K with kernel $1/π$ sinc is given determining explicitly the Hilbert space isomorphism, which transforms K into the multiplication operator by the identity on $L^2(0,1)$. Several related integral operators are studied. A close relationship of K to the finite Hilbert transformation is revealed yielding the spectral representation of the latter. This is of particular interest as it concerns a general feature of self-adjoint Wiener-Hopf operators [15].

math.FA↗

arXiv2013

Cyclicity for Unbounded Multiplication Operators in Lp- and C0-Spaces

For every, possibly unbounded, multiplication operator in $L^p$-space, $p\in ]0,\infty[$, on finite separable measure space we show that multicyclicity, multi-*-cyclicity, and multiplicity coincide. This result includes and generalizes Bram's much cited theorem from 1955 on bounded *-cyclic normal operators. It also includes as a core result cyclicity of the multiplication operator $M_z$ by the complex variable $z$ in $L^p(μ)$ for every Borel measure $μ$ on $\C$. The concise proof is based in part on the result that the function $e^{-|z|^2}$ is a *-cyclic vector for $M_z$ in $C_0(\C)$ and further in $L^p(μ)$. We characterize topologically those locally compact sets $X\subset \C$, for which $M_z$ in $C_0(X)$ is cyclic.

math.FA↗

arXiv2000

Orbits of Lie Group Actions are Weakly Embedded

In this note we prove that whenever a Lie group $G$ acts on a manifold $X$, then the orbit $Gx$ through any point $x$ of $X$ is a weakly embedded submanifold of $X$. The investigation of this problem was inspired by an application to Cat astrophe Theory.

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