New Insights into Galactic Rotation Curves and Gravity

A recent paper titled "Galactic rotation curves in gravity with a nondynamical scalar" by Sandipan Sengupta introduces a novel approach to understanding galactic rotation curves through a four-dimensional gravity action. The study proposes that the laws of gravitation governing galaxies and those described by Einstein's theory may represent different dynamical phases of a unified theory.

Key findings include the identification of new spacetime solutions that exhibit asymptotically flat galactic rotation curves, which are associated with anisotropic effective pressure. This could have implications for the ongoing discourse surrounding dark matter, as the model offers a geometric alternative to the conventional understanding of dark matter's role in galactic dynamics.

Additionally, the research explains the empirical correlation observed between the luminosity of galaxies and the slope of their velocity curves. An enhancement in the deflection angle of light rays passing through the galactic halo was also noted, which could serve as a practical testing ground for this model. The study indicates that for large halo radii, the leading nonbaryonic contribution to the bending angle is represented by the formula ( \frac{3\pi v^2}{2c^2} ), where ( v ) is the asymptotic rotational velocity. This value is less than what is predicted for an isothermal cold dark matter halo.

These findings may contribute to a deeper understanding of galactic structures and the fundamental nature of gravity, potentially influencing future research directions in astrophysics and cosmology. The full paper can be accessed at arXiv:2404.13118.