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Giorgio Papini

Publications and source records attributed to Giorgio Papini.

At least 19 recordsLinked to original sources
arXiv2019

Condensation phenomena in gravity

Gravity can play a role in critical phenomena. Topological singularities induce ground state degeneracy and break the continuum symmetry of the vacuum. They also generate momenta oscillations about an average momentum and a positive gravitational susceptibility. Gravitational analogues of the laws of Curie and Bloch have been found for a one-dimensional model. The critical temperature for a change in phase from unbound to isolated vortices has also been calculated in a $XY$-model.

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arXiv2019

Gravitational qubits

We report on the behaviour of two-level quantum systems, or qubits, in the background of rotating and non-rotating metrics and provide a method to derive the related spin currents and motions. The calculations are performed in the external field approximation.

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arXiv2019

Long range order in gravity

Gravity induced condensation takes the form of momentum alignment in an ensemble of identical particles. Use is made of a one-dimensional Ising model to calculate the alignment per particle and the correlation length as a function of the temperature. These parameters indicate that momentum alignment is possible in the proximity of some astrophysical objects and in earth, or near earth laboratories. Momenta oscillations behave as known spin oscillations and obey identical dispersion relations.

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arXiv2018

Structured objects in quantum gravity. The external field approximation

In the external field approximation (EFA) gravity and inertia are represented by a two-point vector that is the byproduct of symmetry breaking. The vector is accompanied by the appearance of classical, vortical structures. Its interaction range is, in general, that of the metric tensor, but, in the context of a simple symmetry breaking model, the range can be made finite by the presence of massive scalar particles. Vortices can then be produced that conceal matter making it effectively "dark". In EFA fermion relativistic vortices can be induced, in particular, by rotation.

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arXiv2017

Spin and maximal acceleration

We study the spin current tensor of a Dirac particle at accelerations close to the upper limit introduced by Caianiello. Continual interchange between particle spin and angular momentum is possible only when the acceleration is time-dependent. This represents a stringent limit on the effect that maximal acceleration may have on spin physics in astrophysical applications. We also investigate some dynamical consequences of maximal acceleration.

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arXiv2017

Classical and Quantum Aspects of Particle Propagation in External Gravitational Fields

In the study of covariant wave equations, linear gravity manifests itself through the metric deviation $γ_{μν}$ and a two-point vector potential $K_λ$ itself constructed from $γ_{μν}$ and its derivatives. The simultaneous presence of the two gravitational potentials is non contradictory. Particles also assume the character of quasiparticles and $K_λ$ carries information about the matter with which it interacts. We consider the influence of $K_λ$ on the dispersion relations of the particles involved, the particles' motion, quantum tunneling through a horizon, radiation, energy-momentum dissipation and flux quantization. % No {\it REVTEX} limit to number of lines.

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arXiv2015

Maximal acceleration and radiative processes

We derive the radiation characteristics of an accelerated, charged particle in a model due to Caianiello in which the proper acceleration of a particle of mass $m$ has the upper limit $\mathcal{A}_m=2mc^3/\hbar$. We find two power laws, one applicable to lower accelerations, the other more suitable for accelerations closer to $\mathcal{A}_m$ and to the related physical singularity in the Ricci scalar. Geometrical constraints and power spectra are also discussed. By comparing the power laws due to the maximal acceleration with that for particles in gravitational fields, we find that the model of Caianiello allows, in principle, the use of charged particles as tools to distinguish inertial from gravitational fields locally.

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arXiv2015

Perspectives on gravity-induced radiative processes in astrophysics

Single-vertex Feynman diagrams represent the dominant contribution to physical processes, but are frequently forbidden kinematically. This is changed when the particles involved propagate in a gravitational background and acquire an effective mass. Procedures are introduced that allow the calculation of lowest order diagrams, their corresponding transition probabilities, emission powers and spectra to all orders in the metric deviation, for particles of any spin propagating in gravitational fields described by any metric. Physical properties of the "space-time medium" are also discussed. It is shown in particular that a small dissipation term in the particle wave equations can trigger a strong back-reaction that introduces resonances in the radiative process and affects the resulting gravitational background.

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arXiv2014

Covariance and gauge invariance in relativistic theories of gravity

Any metric theory of gravity whose interaction with quantum particles is described by a covariant wave equation is equivalent to a vector theory that satisfies Maxwell-type equations identically. This result does not depend on any particular set of field equations for the metric tensor, but only on covariance. It is derived in the linear case, but can be extended to any order of approximation in the metric deviation. In this formulation of the interaction of gravity with matter, angular momentum and momentum are conserved locally.

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arXiv2013

Fermion-antifermion mixing in gravitational fields

Mixing of fermion and antifermion states occurs in gravitational interactions, leading to non-conservation of fermion number above temperatures determined by the particle masses. We study the evolution of a $f\,,\bar{f}$ system and calculate the cross sections for the reactions $f\rightleftharpoons\bar{f}$. Their values are identical in both directions. However, if $\bar{f}$ changes quickly into a lighter antiparticle, then the reaction symmetry is broken, \emph{resulting in an increased production of matter over antimatter}.

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arXiv2012

Zitterbewegung and gravitational Berry phase

Berry phases mix states of positive and negative energy in the propagation of fermions and bosons in external gravitational and electromagnetic fields and generate Zitterbewegung oscillations. The results are valid in any reference frame and to any order of approximation in the metric deviation.

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arXiv2010

Radiative processes in external gravitational fields

Kinematically forbidden processes may be allowed in the presence of external gravitational fields. These ca be taken into account by introducing generalized particle momenta. The corresponding transition probabilities can then be calculated to all orders in the metric deviation from the field-free expressions by simply replacing the particle momenta with their generalized counterparts. The procedure applies to particles of any spin and to any gravitational fields. transition probabilities, emission power, and spectra are, to leading order, linear in the metric deviation. It is also shown how a small dissipation term in the particle wave equations can trigger a strong backreaction that introduces resonances in the radiative process and deeply affects the resulting gravitational background.

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arXiv2007

Spin-gravity coupling and gravity-induced quantum phases

External gravitational fields induce phase factors in the wave functions of particles. The phases are exact to first order in the background gravitational field, are manifestly covariant and gauge invariant and provide a useful tool for the study of spin-gravity coupling and of the optics of particles in gravitational or inertial fields. We discuss the role that spin-gravity coupling plays in particular problems.

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arXiv2006

Can Gravity Distinguish Between Dirac and Majorana Neutrinos?

We show that spin-gravity interaction can distinguish between Dirac and Majorana neutrino wave packets propagating in a Lense-Thirring background. Using time-independent perturbation theory and gravitational phase to generate a perturbation Hamiltonian with spin-gravity coupling, we show that the associated matrix element for the Majorana neutrino differs significantly from its Dirac counterpart. This difference can be demonstrated through significant gravitational corrections to the neutrino oscillation length for a two-flavour system, as shown explicitly for SN1987A.

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arXiv2006

The Distinction Between Dirac and Majorana Neutrino Wave Packets Due to Gravity and Its Impact on Neutrino Oscillations

We present the possibility that Dirac and Majorana neutrino wave packets can be distinguished when subject to spin-gravity interaction while propagating through vacuum described by the Lense-Thirring metric. By adopting the techniques of gravitational phase and time-independent perturbation theory following the Brillouin-Wigner method, we generate spin-gravity matrix elements from a perturbation Hamiltonian and show that this distinction is easily reflected in well-defined gravitational corrections to the neutrino oscillation length for a two-flavour system. Explicit examples are presented using the Sun and SN1987A as the gravitational sources for the Lense-Thirring metric. This approach offers the possibility to determine the absolute neutrino masses by this method and identify a theoretical upper bound for the absolute neutrino mass difference, where the distinctions between the Dirac and Majorana cases are evident. We discuss the relevance of this analysis to the upcoming attempts to measure the properties of low-energy neutrinos by SNO and other solar neutrino observatories.

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arXiv2005

Neutrino Wave Packet Propagation in Gravitational Fields

We discuss the propagation of neutrino wave packets in a Lense-Thirring space-time using a gravitational phase approach. We show that the neutrino oscillation length is altered by gravitational corrections and that neutrinos are subject to helicity flip induced by stellar rotation. For the case of a rapidly rotating neutron star, we show that absolute neutrino masses can be derived, in principle, from rotational contributions to the mass-induced energy shift, without recourse to mass generation models presently discussed in the literature.

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