Comment on ‘Do electromagnetic waves always propagate along null geodesics?’

We study the propagation of Maxwellian electromagnetic waves in curved spacetimes in terms of the appropriate geometrical optics limit, notions of signal speed, and minimal coupling prescription from Maxwellian theory in flat spacetime. In the course of this, we counter a recent major claim by Asenjo and Hojman (2017) to the effect that the geometrical optics limit is partly ill-defined in Gödel spacetime; we thereby dissolve the present tension concerning established results on wave propagation and the optical limit.

Elastic scattering of α particle at CERN-ISR energy: Three-nucleon force effect

In the framework of optical limit approximation of Glauber with inclusion of the three-nucleon force effect, we obtained a good agreement with the experimental data of [Formula: see text] elastic scattering differential cross-section at the energies [Formula: see text] and [Formula: see text][Formula: see text]GeV. The relation between the nucleon–nucleon slope parameter and the nucleon–nucleon interaction radius is discussed. In any case, the three-nucleon force is important and must be taken into account for a better agreement with the nucleus–nucleus data.

Metamaterials mimic the black holes: the effects of charge and rotation on the optical properties

Motivated by the investigation of a black hole’s properties in the lab, some interesting subjects such as analogue gravity and transformation optics are generated. In this paper, we look for analogies between the geometry of a gravitating system and the optical medium. In addition, we recognize that appropriate two-dimensional metamaterials can be used to mimic the propagation of light in the curved spacetimes and behave like black holes which are incident with light rays in the equatorial plane. The resemblance of metamaterials with Kerr and Reissner–Nordström spacetimes is studied. Finally, we compare the results of two-dimensional simulation for light propagation in the corresponding two-dimensional metamaterials with those obtained from the geometrical optical limit.

Proton-4He elastic scattering at 350–1728MeV energies: Three-body force effect

An approach for the three-body force effect is used to study p-[Formula: see text] elastic scattering at energies 350–1728[Formula: see text]MeV. The multiple scattering theory of Glauber and the optical limit approximation are used in calculations of elastic scattering differential cross-section at 350, 600, 800, 1000 and 1728[Formula: see text]MeV. The inclusion of 2[Formula: see text]-exchange three-nucleon force improves the agreement with the experimental data for both approximations. The results of optical limit approximation without three-nucleon force effect are clearly smaller than the results of multiple scattering theory for [Formula: see text] due to the absence of multiple scattering terms in the first. However, with inclusion of three-nucleon force, the results of both approximations are approximately similar.

Quantum coherence of cosmological perturbations

In this paper, the degrees of quantum coherence of cosmological perturbations of different spins are computed in the large-scale limit and compared with the standard results holding for a single mode of the electromagnetic field in an optical cavity. The degree of second-order coherence of curvature inhomogeneities (and, more generally, of the scalar modes of the geometry) reproduces faithfully the optical limit. For the vector and tensor fluctuations, the numerical values of the normalized degrees of second-order coherence in the zero time-delay limit are always larger than unity (which is the Poisson benchmark value) but differ from the corresponding expressions obtainable in the framework of the single-mode approximation. General lessons are drawn on the quantum coherence of large-scale cosmological fluctuations.