## Center for Astrophysics Research and Technologies Seminar Series

### The Problem with Late-time Solutions to the Hubble Tension

#### Presented by Kylar Greene (UNM)

The current values of the Hubble constant (H_0) inferred from the local distance ladder (74.22 +- 1.82 km/s/Mpc) and from the cosmic microwave background (67.4 +- 0.5 km/s/Mpc) are at a 4.4-sigma tension with each other. Ubiquitously, studies that propose solutions to alleviate the Hubble tension by modifying the physics of dark energy at late times assume a simple Gaussian prior distribution on H_0. The H_0 value used in these analyses is inferred from the local distance ladder by first measuring the peak absolute supernova magnitude, and then using this value to determine the distance to faraway supernovae. This methodology falters when considering models which change the cosmological evolution at redshifts comparable to those found in the Pantheon supernova data set, z < 2, because a Gaussian prior on H_0 cannot capture the resulting change to the inferred luminosity distance to Pantheon supernovae. In this talk, a brief history of measurements of H_0 will be given and the local distance ladder reviewed. After, solutions that propose changes to late time cosmology will be reviewed. As a case example, we then consider a dynamical late-time dark energy model which modifies the cosmological dynamics at low redshifts. We demonstrate using a new numerical package that incorporates a likelihood approach to the local distance ladder that these dynamical dark energy models are misleading and do not actually solve the Hubble tension. Finally, we discuss the future implications of an updated prior on H_0 and its necessity established.

**2:00 pm, Thursday, April 22, 2021
Zoom,
**

Individuals with disabilities who need an auxiliary aid or service to attend or participate in P&A events should contact Sandra Ortiz (phone: 505-277-5900, email: sportiz@unm.edu) well in advance to ensure your needs are accomodated. Event handouts can be provided in alternative accessible formats upon request. Please contact Mrs. Ortiz if you need written information in an alternative format.

*A schedule of talks within the Department of Physics and Astronomy is available on the P&A web site at http://physics.unm.edu/pandaweb/events/index.php*