QCD vacuum contribution to W/Z masses

In summary, the QCD vacuum condensate breaks both chiral symmetry in QCD and the SU(2) electroweak gauge symmetry. This is because the operator that obtains a vacuum expectation value is not SU(2) invariant due to being made of left and right-handed quarks in different representations. This contributes approximately 100 MeV to the W and Z masses, but is not considered in EWPT because it is assumed that the condensate is the same for both up and down quarks. However, it does contribute to the S parameter, though it is smaller than estimated at around 10-20 MeV. This effect is negligible in comparison to the Higgs mechanism in precision EWK calculations.
  • #1
ofirg
129
13
The QCD vacuum condensate which breaks chiral symmetry in qcd, also break the SU(2) electoweak gauge symmtery, right?
The operator which gets a vacuum expectation value isn't SU(2) invariant since it is built out of left handed quarks and right handed quarks which are in different representations of SU(2).
This should contribute about ~100MeV the W and Z masses. Why is this never taken into account in EWPT? because the condensate should be the same for up and down type quarks, I would think it woudn't contibute to the T parameter (isospin symmetry), But it should contribute to the S parameter.
Is this simply negligible, or I've got it all wrong?
 
Physics news on Phys.org
  • #2
It is a real effect, although it's smaller than what you estimate: more like 10 or 20 MeV. It acts in quadrature with the Higgs mechanism, so the numeric effect on precision EWK is negligible.
 

1. What is the QCD vacuum contribution to W/Z masses?

The QCD vacuum contribution to W/Z masses refers to the effect of the quantum chromodynamics (QCD) force on the masses of the W and Z bosons. This contribution arises from the interactions between the W and Z bosons and the gluons, which are the particles responsible for the strong force in QCD.

2. How does the QCD vacuum contribution affect the masses of the W and Z bosons?

The QCD vacuum contribution has a small but significant effect on the masses of the W and Z bosons. It is responsible for about 15% of the mass of the W boson and about 5% of the mass of the Z boson. This contribution is necessary to account for the experimental measurements of the masses of these particles.

3. How is the QCD vacuum contribution calculated?

The QCD vacuum contribution is calculated using a mathematical framework called perturbative quantum chromodynamics (pQCD). This involves breaking down the complex interactions between the W and Z bosons and the gluons into simpler equations that can be solved using computational methods.

4. Is the QCD vacuum contribution the only factor affecting the masses of the W and Z bosons?

No, the QCD vacuum contribution is not the only factor affecting the masses of the W and Z bosons. There are also contributions from other fundamental forces, such as the weak force and the Higgs field. Together, these contributions make up the total mass of the W and Z bosons.

5. Why is studying the QCD vacuum contribution important?

Studying the QCD vacuum contribution is important because it helps us understand the fundamental forces and particles that make up our universe. It also plays a crucial role in the precision of experimental measurements and theoretical predictions in particle physics. Additionally, understanding the QCD vacuum contribution can provide insights into the behavior of particles at high energies, such as those found in particle colliders.

Similar threads

A What New Experiments, If Any, Would Help Determine Light Quark Masses?
    • High Energy, Nuclear, Particle Physics
2
Replies
46
Views
4K
I Spontaneous symmetry breaking of chiral symmetry
    • High Energy, Nuclear, Particle Physics
Replies
9
Views
2K
Puzzling Chiral Symmetry Breaking
    • High Energy, Nuclear, Particle Physics
Replies
16
Views
3K
A New model of high-spin Baryons
    • High Energy, Nuclear, Particle Physics
Replies
3
Views
3K
I How do the collider experiments measure the mass of the W boson?
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
2K
I Imagining a Higgsless Universe
    • High Energy, Nuclear, Particle Physics
2
Replies
35
Views
7K
I Are Light Quark Pole Masses Below 1 GeV Meaningful or Non-Physical?
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
1K
New ansatz for low-energy QCD
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
2K
Questions about chiral symmetry breaking
    • High Energy, Nuclear, Particle Physics
Replies
5
Views
3K
Is it possible there are many mass parameters for different type of forces ?
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top