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Salerno, Italy

Lambiase G.,University of Salerno | Lambiase G.,National Institute of Nuclear Physics, Italy | Lambiase G.,International Institute for Advanced Scientific Studies | Sakellariadou M.,Kings College London | And 2 more authors.
Journal of Cosmology and Astroparticle Physics | Year: 2013

Noncommutative spectral geometry offers a purely geometric explanation for the standard model of strong and electroweak interactions, including a geometric explanation for the origin of the Higgs field. Within this framework, the gravitational, the electroweak and the strong forces are all described as purely gravitational forces on a unified noncommutative space-time. In this study, we infer a constraint on one of the three free parameters of the model, namely the one characterising the coupling constants at unification, by linearising the field equations in the limit of weak gravitational fields generated by a rotating gravitational source, and by making use of recent experimental data. In particular, using data obtained by Gravity Probe B, we set a lower bound on the Weyl term appearing in the noncommutative spectral action, namely β10 -6m-1. This constraint becomes stronger once we use results from torsion balance experiments, leading to β104m -1. The latter is much stronger than any constraint imposed so far to curvature squared terms. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

Papini G.,University of Regina | Papini G.,International Institute for Advanced Scientific Studies
Modern Physics Letters A | Year: 2014

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. © 2014 World Scientific Publishing Company.

Papini G.,University of Regina | Papini G.,International Institute for Advanced Scientific Studies
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

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. © 2012 Elsevier B.V. All rights reserved.

Papini G.,University of Regina | Papini G.,International Institute for Advanced Scientific Studies
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Kinematically forbidden processes may be allowed in the presence of external gravitational fields. These can 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. © 2010 The American Physical Society.

Papini G.,University of Regina | Papini G.,International Institute for Advanced Scientific Studies
Modern Physics Letters A | Year: 2013

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, resulting in an increased production of matter over antimatter. © 2013 World Scientific Publishing Company.

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