Time dependence of the p/He ratio in cosmic rays according to the force-field approximation

TL;DR

This paper investigates how the p/He ratio in cosmic rays varies over time using the force-field approximation, highlighting the influence of interstellar spectrum shape and A/Z ratio on solar cycle correlations.

Contribution

It provides a detailed analysis of the time dependence of the p/He ratio considering the LIS shape and A/Z ratio, explaining recent AMS-02 observations.

Findings

p/He ratio variation correlates or anti-correlates with solar cycle phase depending on spectral index.

A/Z dependence explains the recent decrease in p/He ratio observed by AMS-02 after 2015.

The shape of the local interstellar spectrum significantly influences p/He time variation.

Abstract

We study the predictions for the p/He ratio in galactic cosmic rays according to the force-field approximation. The dependence of the time variation of p/He on the local interstellar spectrum (LIS) shape and on the mass-to-charge ratio, A/Z, is analyzed in detail. We find that, depending on the rigidity range and the sign of the spectral index of the p/He LIS ratio, the p/He time variation can be correlated or anti-correlated with the phase of the solar cycle. We show that the A/Z dependence is the most probable cause for the p/He decrease recently observed by AMS-02 after 2015 between 2 and 3 GV.