Energy densities offer a new path to resolve the Hubble tension

Researchers at the University of Waterloo have proposed a new method to measure the Hubble constant which could help resolve one of the pressing puzzles of modern cosmology: Hubble tension.

The study published in Physical examination letters aims to solve the hubble tension, a gap between the value of the hubble constant (h₀) of the local method (distance scale) and the cosmic microwave (CMB) background method.

Phys.org met with the first author of the study, Dr. Alex Krolewski, postdoctoral researcher at the University of Waterloo.

“Hubble tension between early, large -scale and local measurements, late for the universe expansion rate, has now reached the level of 5 Sigma! This is a probability of less than 0.0000003 to occur by chance,” said Dr. Kroley.

The distance scale method gives a value of 73 km / s / MPC (kilometers per second by Megaparsec), while the CMB method gives 67 km / s / MPC. This difference is significant and indicates a gap in our understanding.

The sound horizon

The distance-scale method uses nearby objects such as Variables Cepheid and Type 1a supernovas as candles, that is to say objects whose light is known to us. The distances of these objects and their red -haired offsets are measured, which can be used to calculate the Hubble constant.

On the other hand, the methods using CMB is based on Sound Horizon, a standard measurement in cosmology. It is a measure of the maximum distance traveled by sound waves in the early universe before the decoupling of light and matter.

These approaches force researchers to make hypotheses on the λCDM model, the best cosmological model in the universe today.

This has led researchers to modify early physics of the universe to reduce the sound horizon, which increases the value of the hubble constant derived from CMB data, lowering the gap. The problem here is dependence on the sound horizon and therefore the λcdm model. Dr. Krolewski and his team aimed to eliminate this problem.

“Our new method rather estimates the total energy density of the universe or of critical density, which is directly linked to the expansion rate. As John Archibald Wheeler said,” Spacetime says to matter how to move; The material said in space-time how to bend, “said Dr. Kroley.

Baryonic fraction measures

The researchers’ approach is a completely new method to measure the Hubble constant from large -scale structural observations with low shift and large -scale independent of the sound horizon.

Their method combines four independent measures to calculate the Hubble constant.

These are the physical density of photons from the CMB temperature, the Baryon / Photon ratio derived from the abundance of the primordial deuterium, the baron fraction of the amplitude of the acoustic baryon oscillations in the measurements of the galaxy and the geometric density from the measurements of Alcock-Paczynski.

“Our method is based on the bootstrap of well -known energy densities of photons and ordinary material to the total energy density of the universe,” said Dr. Kroley.

Innovation in their method lies in the extraction of the Baryon fraction from Galaxies clustering data, a parameter which is generally neglected in standard analyzes.

This measure indicates the report of ordinary material (or baronic) to total matter (which includes dark matter) in the universe. This parameter would be unity if the whole question in the universe was Baryonic and Zero if the whole problem was dark matter.

The approach to the sound horizon uses data on the distribution of Baryon acoustic oscillations (BAO), which are undulations in the distribution of material. On the other hand, the measurement of the baronic fraction focuses on the strength of these undulations, which makes it independent of the sound horizon.

Tightening constraints

The researchers used their approach without a sound horizon and tested it on the data of the spectroscopic study of oscillation baron oscillation of the Sloan Digital Survey (Boss Dr12).

Their method gave a constant hubble value of 67.1 km / s / MPC with an uncertainty of + 6.3 / −5.3. This value is consistent with the two measurements, and therefore does not promote any of the two sides of the tension.

“We tested our method on Mock Galaxy surveys with different cosmological models and found that we were always able to recover the correct value of the expansion rate. Overall, our method is very robust to systematic uncertainty,” noted Dr. Krolewski.

Although their results do not definitively solve the hubble tension, future surveys such as black energy spectroscopic instrument (DESI) and Euclid satellite should improve constraints.

“Desi and Euclid will measure the BAO characteristic in the distribution of the galaxy to the precision of under-cent.

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