Questions regarding "Thermal History of the Early Universe"

[Buzz Bloom]

I do not have any education in particle physics, and I am trying to read the paper
http://www.helsinki.fi/~hkurkisu/cosmology/Cosmo6.pdf .
I would much appreciate some help regarding the specific questions below.

The following is from the first page of the article.

I gather that g is a count of the different varieties of particles of different types. There are some oddities in the table I can't figure out, and I hope someone will be able to explain them to me.

1. Under Quarks, g = 2⋅2⋅3. I get that one "2" is for the particle and its antiparticle, and the "3"is for 3 colors. What is the other "2"? Is it +1/2 and -1/2 spin values?
2. For each of τ, μ, and e, g = 2⋅2=4, making 12 altogether. One "2" corresponds to the particle and antiparticle. What is the other "2" Is it +1/2 and -1/2 spin values?
3. For Electroweak gauge bosons, g=3. Is this because there are 3 spin values: +1, 0, and -1?
4. Under Electroweak gauge bosons, there is a single line for γ, the photon. Why is g = 2 for the photon?
5. Also, what is the photon mass value in parentheses, "< 6×10^-17 eV"?
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Regards,
Buzz

 

[Orodruin]

1. Under Quarks, g = 2⋅2⋅3. I get that one "2" is for the particle and its antiparticle, and the "3"is for 3 colors. What is the other "2"? Is it + and - spin values?
2. For each of τ, μ, and e, g = 2⋅2=4, making 12 altogether. One "2" corresponds to the particle and antiparticle. What is the other "2" Is it + and - spin values?

The thing you are missing in both your first questions is polarisation. Both particle and anti-particle come with two spin possibilities.

3. Under Electroweak gauge bosons, there is a single line for γ, the photon. Why is g = 2 for the photon?

Same as for the quarks and leptons. It is the two polarisation directions.

4. Also, what is the photon mass value in parentheses, "< 6×10-17 eV"?

Most likely because it is zero according to theory and that is the upper bound.

 

[Buzz Bloom]

Hi Orodruin:

Thanks a lot for your prompt and useful answers.

I have been updating the post, and I think I added a question after your answer post. Please look at the revised questions #3.

Regards,
Buzz

 

[mfb]

It is from 2006, so the experimental upper limit on the photon mass is a bit outdated. See the current status. Most of those values are a bit model-dependent, but they are all extremely tiny.