Next step in the universe simulation

Computer simulations have struggled to capture the impact of elusive particles called neutrinos on the formation and growth of the large-scale structure of the universe. But now, a research team from Japan has developed a method that overcomes this obstacle.

In a study published this month on Astrophysical Journal, researchers led by Tsukuba University present simulations that accurately describe the role of neutrinos in the evolution of the universe.

Why are these simulations important? One of the main reasons is that they can set constraints on a currently unknown quantity: the mass of the neutrino. If this quantity is set to a particular value in simulations and the simulation results differ from observations, that value can be excluded. However, the constraints can only be trusted if the simulations are accurate, which was not guaranteed in the previous work. The team behind this latest research aimed to address this limitation.

“Previous simulations used some approximations that may not be valid,” says study lecturer lead author Kohji Yoshikawa. ‘In our work, we have avoided these approximations by employing a technique that accurately represents the neutrino velocity distribution function and follows its time evolution.’

To do this, the research team directly solved a system of equations known as the Vlasov-Poisson equations, which describe how particles move around the universe. They then ran simulations for different neutrino mass values ​​and systematically examined the effects of neutrinos on the large-scale structure of the universe.

The simulation results show, for example, that neutrinos suppress the cluster of dark matter – the “missing” mass in the universe – and in turn the galaxies. They also show that neutrino-rich regions are strongly correlated with massive clusters of galaxies and that the effective temperature of neutrinos varies substantially with neutrino mass.

“Overall, our results suggest that neutrinos greatly influence large-scale structure formation and that our simulations provide an accurate account of the important effect of neutrinos,” explains professor Yoshikawa. “It is also reassuring that our new results are consistent with those of completely different simulation approaches.”

This work represents a milestone in the simulation of the universe and paves the way for further exploration of how neutrinos affect the formation and growth of the large-scale structure. For example, the new simulation approach could be used to study the dynamics of neutrinos and unconventional types of dark matter. Eventually, it could lead to a determination of the neutrino mass.