How MOND-like is Quasilinear MOND? Investigating the Vertical Acceleration Field of the Milky Way

The mass discrepancy problem is a long-standing, unresolved problem in astronomy with possible consequences in many areas of physics. The problem refers to an inconsistency between the amount of observed mass in the universe and its dynamics as predicted by our best theory of gravity, General Relativity. Two proposed solutions to this problem are the dark matter paradigm, which is standard, and MOdified Newtonian Dynamics (MOND), a modification to Newtonian gravity at low accelerations which has been less studied. Both hypotheses have multiple problems and neither has been ruled out. Notably, a direct detection of dark matter is still lacking. Therefore, there is a need to test the validity of both theories. The vertical acceleration field of disk galaxies can provide a sharp test to distinguish between MOND and Dark Matter. We propose a test of MOND vs dark matter using the vertical acceleration of the Milky Way calculated from local observables. Previous work found that MOND is disfavored relative to Dark Matter due to an overprediction of the Milky Way’s vertical acceleration compared to observations, but in this work the physically inconsistent pristine MOND was used as a proxy for all MOND-like theories. Here we explore whether the tension with Milky Way data exists with the Quasilinear MOND (QUMOND). We develop a QUMOND Poisson solver using Fourier methods, and use it to compare the vertical acceleration fields in exponential disk galaxies with the pristine MOND prediction. Our results have the potential to provide evidence for MOND in the Milky Way or against it.