I Axion Mass Acquisition: Do Axions Acquire Mass?

[Ranku]

Do axions acquire mass the same way as other particles, through the Higgs mechanism?

 

[ohwilleke]

Given that we don't even know if axions exist, this question is up for grabs and highly axion-model dependent.

In light of the fact that axions and axion-like particles are typically hypothesized to have masses close to or many orders of magnitude smaller than neutrinos, and that the compatibility of neutrino mass with the Higgs mechanism is problematic, probably not (although in the case of neutrinos, one of the big issues is the lack of right handed neutrinos and left handed anti-neutrinos, an issue not shared with axions).

The canonical view for QCD axions is that they acquire mass not through the Higgs mechanism but as a consequence of the fact that they are pseudo-Goldstone bosons. It is a mechanism more similar to how hadrons acquire most of their mass in QCD than it is to how fundamental SM particles acquire mass through the Higgs mechanism.

 

[malawi_glenn]

You can read about axions in the PDG book: https://pdg.lbl.gov/2017/reviews/rpp2017-rev-axions.pdf

 

[Orodruin]

right handed anti-neutrinos

Left-handed anti-neutrinos
There are plenty of right-handed anti-neutrinos around. (Although to be fair, in the field we typically just say ”right-handed neutrinos” with the anti-part impliciy.)

Just adding RHN to the model works though, but let’s not change the subject to neutrino mass generation because that can be discussed for a long long time

 

[ohwilleke]

Left-handed anti-neutrinos
There are plenty of right-handed anti-neutrinos around. (Although to be fair, in the field we typically just say ”right-handed neutrinos” with the anti-part impliciy.)

Just adding RHN to the model works though, but let’s not change the subject to neutrino mass generation because that can be discussed for a long long time

Oops! Yeah, that was just an unintended goof due to poor proofreading which I've now corrected in my post.

But in many contexts it is important to say left handed neutrinos and right handed anti-neutrinos, to avoid confusion, since there are many BSM theories that hypothesize right handed neutrinos and left handed anti-neutrinos.

 

[Orodruin]

But in many contexts it is important to say left handed neutrinos and right handed anti-neutrinos, to avoid confusion, since there are many BSM theories that hypothesize right handed neutrinos and left handed anti-neutrinos.

What I am saying is that people working with neutrino mass models generally just specify right-handed neutrino and leave the anti-neutrino part implicit. It is also a question of convention of what is called ”anti-neutrino”. Adding additional singlet Weyl fermions to the Standard Model, you add a left and a right handed state per fermion. After that it is a question of lepton number assignment/convention (if any) what you call what.

 

[ohwilleke]

After that it is a question of lepton number assignment/convention (if any) what you call what.

But, once you choose a convention regarding the lepton number of the electron, the assignment of left handed neutrinos as matter and right handed neutrinos as antimatter is required by physical reality. W bosons decay into electrons and right handed neutrinos, or positrons and left handed neutrinos.

 

[Orodruin]

But, once you choose a convention regarding the lepton number of the electron, the assignment of left handed neutrinos as matter and right handed neutrinos as antimatter is required by physical reality. W bosons decay into electrons and right handed neutrinos, or positrons and left handed neutrinos.

I was referring to the sterile states. Those do not have any lepton number fixed by the choice for the electron as they are singlet states.