THE DARK MATTER SERIES
EP-3 What Could be Dark Matter?
In the last episode, we covered some of the candidates which we could safely discard, from being candidates of Dark Matter. Now, we will look at some of the candidates that have a shot at being called possible candidates of Dark Matter.
When searching for particle candidates of Dark Matter, there are two lines of thought:
They are particles in the Standard Model itself but they are behaving differently.
They are some exotic particles for which, there arises a need to extend the standard model.
The first candidate which was thought could be a Dark Matter (DM) candidate was a neutrino. Yes, a neutrino, and why not ….they were thought to be massless, and they also interact very weakly with matter. So, far so good ….did we solve the dilemma ….well not yet. So, there were some profound reasons to debunk the neutrino as a candidate of DM.
From the Cosmic Microwave Background (CMB), it was observed that in the early universe, according to the patterns formed from the CMB scientists were able to conclude that the DM we are looking for should be Cold Dark Matter(CDM).
Cold here means that they have less kinetic energy and in turn less speed. Hot refers to particles that have more kinetic energy and higher speed.
So, the neutrinos we found to be hot, meaning they had more kinetic energy and hence could not be a possible candidate for DM.
The next particle we will consider is the AXION. Axion is a hypothetical particle that would be detected in a magnetic field. They were also thought to be a possible candidate for DM. But the Axion Dark Matter Experiment which was conducted in the 2000s and again in the 2010s didn’t give any concrete proof of axions and hence they were scrapped from the race.
Another possible candidate is the WIMPs, the acronym standing for Weakly Interacting Massive Particles. As the name suggests, WIMPs are a class of particles that interact weakly with other particles and this class is a promising class for being a candidate of DM.
Finally, another line of thought is that there is no new particle but it is gravity that is behaving differently. Gravity behaves differently on the galactic scale from the behavior which it shows on the solar system scale. We will discuss these gravitational theories in detail in the next episode. Till then, stay tuned for the next episode!
