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Energetic particles of galactic and solar origin charge the metal free-falling test masses (TMs) of the interferometers for gravitational wave detection in space. The deposited charge couples with stray electric fields thus generating spurious Coulomb forces between the TMs and the electrode housing that limit the interferometer sensitivity. Long-term and short-term galactic cosmic-ray variations are strongly energy-dependent and the TM charging varies with particle energy distribution. We propose three different approaches involving Monte Carlo simulations and machine learning models in comparison to particle transport with the Parker equation to study the recurrent modulation of energy spectra of galactic particles ascribable to the passage of high-speed solar wind streams. The transit of interplanetary counterparts of coronal mass ejections modifies the effects of high-speed streams. This work aims at better understanding the energy-dependence of galactic cosmic-ray short-term variations for the Laser Interferometer Space Antenna (LISA), the first interferometer for gravitational wave detection in space, starting from lessons learned with LISA Pathfinder. The outcomes of our models will be used to assess the TM charging during the time LISA will remain in orbit around the Sun. [ABSTRACT FROM AUTHOR]

The European Space Agency Laser Interferometer Space Antenna (LISA) will be the first mission dedicated to the detection of low-frequency gravitational waves in space. Particles of galactic and solar origin above tens of MeV will penetrate the spacecraft and charge the metal free-falling test masses (TMs) playing the role of mirrors of the interferometer. The poissonian fluctuations of the charging process and associated spurious Coulomb forces acting on the TMs limit the sensitivity of LISA mainly below 1 mHz. Moreover, galactic cosmic-ray (GCR) flux short-term variations will modulate differently the TM charging on the three satellites of the LISA constellation. Without a proper GCR flux monitoring, the LISA TM charging estimates will be carried out on the basis of the long-term solar modulation only. In this work we report about models of galactic cosmic-ray short-term variations to investigate to which extent the galactic cosmic-ray depressions can be also used as a proxy of the increase of interplanetary magnetic field and solar wind speed observed at the passage of high-speed solar wind streams and interplanetary coronal mass ejections. Our final aim is to study the optimum characteristics of particle detectors for both TM charging estimate and interplanetary medium monitoring for LISA. [ABSTRACT FROM AUTHOR]