Screened fifth forces lower the TRGB-calibrated Hubble constant too
  The local distance ladder measurement of the Hubble constant requires a
connection between geometric distances at low redshift and Type Ia supernovae
in the Hubble flow, which may be achieved through either the Cepheid
period--luminosity relation or the luminosity of the Tip of the Red Giant
Branch (TRGB) feature of the Hertzsprung--Russell diagram. Any potential
solution to the Hubble tension that works by altering the distance ladder must
produce consistency of both the Cepheid and TRGB $H_0$ calibrations with the
CMB. In this paper we extend our models of screened fifth forces (Desmond et al
2019) to cover the TRGB framework. A fifth force lowers TRGB luminosity, so a
reduction in inferred $H_0$ requires that the stars that calibrate the
luminosity---currently in the LMC---are on average less screened than those
that calibrate the supernova magnitude. We show that even under pessimistic
assumptions for the extinction to the LMC, full consistency with Planck can be
achieved for a fifth force strength in unscreened RGB stars $\sim$0.2 that of
Newtonian gravity. This is allowed by the comparison of Cepheid and TRGB
distance measurements to nearby galaxies. Our results indicate that the
framework of Desmond et al (2019) is more versatile than initially
demonstrated, capable of ameliorating the Hubble tension on a second front.
