A Perspective on the Solar Modulation of Cosmic Anti-Matter

Abstract

Global modulation studies with comprehensive numerical models contribute meaningfully to the refinement of very local interstellar spectra (VLISs) for cosmic rays. Modulation of positrons and anti-protons are investigated to establish how the ratio of their intensity, and with respect to electrons and protons, are changing with solar activity. This includes the polarity reversal of the solar magnetic field which creates a 22-year modulation cycle. Modeling illustrates how they are modulated over time and the particle drift they experience which is significant at lower kinetic energy. The VLIS for anti-protons has a peculiar spectral shape in contrast to protons so that the total modulation of anti-protons is awkwardly different to that for protons. We find that the proton-to-anti-proton ratio between 1–2 GeV may change by a factor of 1.5 over a solar cycle and that the intensity for anti-protons may decrease by a factor of ~2 at 100 MeV during this cycle. A composition is presented of VLIS for protons, deuteron, helium isotopes, electrons, and particularly for positrons and anti-protons. Gaining knowledge of their respective 11 and 22 year modulation is useful to interpret observations of low-energy anti-nuclei at the Earth as tests of dark matter annihilation.

Time Dependence of 50–250 MeV Galactic Cosmic-Ray Protons between Solar Cycles 24 and 25, Measured by the High-energy Particle Detector on board the CSES-01 Satellite

“…It is important to note that to successfully model GCR spectra, assumptions about the LIS, shape of the heliosphere, HMF and its polarity, solar wind velocity, HCS tilt angle, and elements of the diffusion and drift tensor must be specified beforehand in the model. In our 3D model, the expressions for the diffusion and drift coefficients used for the computations, as well as other relevant heliospheric parameters and proxies, are described in detail in Ngobeni et al (2020), Aslam et al (2021), andPotgieter et al (2021). Figure 6 depicts the computed proton spectra overlaid on the corresponding observed HEPD-01 spectra for CR 2207 and CR 2252.…”

Unfolding Drift Effects for Cosmic Rays over the Period of the Sun’s Magnetic Field Reversal

“…They compared the modeling results to the PAMELA positron-to-electron flux ratio reported by Adriani et al (2016a) and AMS positron and electron fluxes reported by Aguilar et al (2018b). In a similar way, Potgieter et al (2021) illustrated from a modeling perspective how the antiproton-to-proton flux ratio varied over the Sun's recent magnetic polarity reversal.…”

“…The vLISs used for this numerical study are shown in Figure 2 as a differential intensity per gigaelectronvolt (left panel) and as a differential intensity per gigavolt (right panel), as a function of kinetic energy and rigidity, respectively, for GCR protons, shown in both panels, from ; for antiprotons, shown in both panels, from Potgieter et al (2021); for GCR electrons, shown in left panel, from Potgieter et al (2015); and for positrons, shown in left panel, from Aslam et al (2019). These vLISs are validated by utilizing PAMELA observations (Adriani et al 2013a(Adriani et al , 2013b(Adriani et al , 2015Munini 2015;Adriani et al 2016b) and AMS observations at the Earth (Aguilar et al 2018a(Aguilar et al , 2018b at high kinetic energy/rigidity, as indicated, and Voyager 1 and 2 observations (Cummings et al 2016;Stone et al 2019) at the HP at lower energies, as indicated.…”

Towards Understanding the Time Variations of Proton to Helium Ratios in the Heliosphere: Implication for the Time Dependence of the Elements of the Diffusion Tensor

“…The solar modulation of GCRs changes significantly with their energy (rigidity), is highly spatial dependent and their intensity varies with different time scales, periodically usually on the longer time scales and non-periodically on a variety of shorter time scales (e.g., Modzelewska et al, 2020;Krainev et al, 2021, Stozhkov, Makhmutov, and Svirzhevsky, 2022, Koldobskiy et al, 2022. In the context of describing observational features and the theoretical foundation, see reviews by Quenby (1984); Heber (2013), Kóta (2013); Potgieter (2013), Potgieter et al (2021) and a comprehensive observational review by Rankin et al (2022, and references there-in) and a comprehensive overview of the theory as applicable to the heliosphere by Engelbrecht et al (2022, and references there-in).…”

“…Model computations/simulations are compared with the corresponding observed time 3 He2/ 4 He2 and p/He ratios. The objective is to demonstrate that this model reproduces both PAMELA and AMS observational features well over a wide rigidity range and that the modeling assumptions about the global heliosphere as well as all the modulation parameters, including diffusion and drift coefficients, were tested and vindicated (Ngobeni et al, 2022(Ngobeni et al, , 2020Potgieter et al, 2021;Aslam et al 2023). The model is then applied to investigate quantitatively the relative importance of the role of the parallel, radial perpendicular and polar perpendicular diffusion coefficients, as the essential elements of the modulation process, on the time dependences of p/He and 3 He2/ 4 He2 below 3 GV from 2006 to 2017.…”