In the context of brane-world extra-dimensional theories, we compute the positron production from branon dark matter annihilations and compare with the AMS-02 data. Three different scenarios have been considered; the first two assume that either pulsars or dark matter may explain separately the whole positron fraction as measured by AMS-02, whereas the third one assumes that a suitable combination of these two contributions is needed. For all of them, exclusion diagrams for the brane mass and the tension of the brane, were obtained. Our analysis has been performed for a minimal, a medium and a maximum diffusion model in one extra dimension for both pseudo-Isothermal and Navarro–Frenk–White dark matter halos. Combined with previous cosmological analyses and experimental data in colliders, constraints here enable us to set further bounds on the parameter space of branons. In particular, in the case when pulsars fit the whole AMS-02 data, we have excluded mass-tension regions for masses and tensions smaller than 60.75 TeV and 8.56 TeV respectively. With regard to the scenario in which AMS-02 data are explained by a combination of dark matter and pulsars, masses and tensions smaller than 27.32 TeV and 3.85 TeV respectively turn out to be excluded. Finally, in the scenario with no pulsar contribution, a branon with a mass <math><mn>38.1</mn><mo>±</mo><mn>0.2</mn></math> TeV and a tension <math><mn>4.99</mn><mo>±</mo><mn>0.04</mn></math> TeV can fit well the experimental data.

Spain

Jose A.R. Cembranos

South Africa

Álvaro de la Cruz-Dombriz

Peter K.S. Dunsby

Miguel Méndez-Isla

Analysis of branon dark matter and extra-dimensional models with AMS-02

It has already been shown that the gravitational waves emitted from a Schwarzschild black hole in f ( R ) gravity have no signatures of the modification of gravity from General Relativity, as the Regge–Wheeler equation remains invariant. In this paper we consider the perturbations of Ricci scalar in a vacuum Schwarzschild spacetime, which is unique to higher order theories of gravity and is absent in General Relativity. We show that the equation that governs these perturbations can be reduced to a Volterra integral equation. We explicitly calculate the reflection coefficients for the Ricci scalar perturbations, when they are scattered by the black hole potential barrier. Our analysis shows that a larger fraction of these Ricci scalar waves are reflected compared to the gravitational waves. This may provide a novel observational signature for fourth order gravity.

Dan B. Sibandze

Rituparno Goswami

Sunil D. Maharaj

Anne Marie Nzioki

Scattering of Ricci scalar perturbations from Schwarzschild black holes in modified gravity