Electroweak stands for the unification of the electromagnetism and the weak force. The unification energy scale is around 100~200 GeV, the mass scale of the Higgs boson. It is widely accepted to be formulated as a quantum field theory with gauge symmetries of U(1) symmetry in electromagnet forces ...

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289 views

'Validity' of QED/QCD/Electroweak interaction

I am currently attending a course on Quantum Field Theory and I got into thinking how valid these theories are. As the theory attempts to describe reality only far above the Planck (length) scale, ...
2
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1answer
39 views

Is the mass of the Z due to mixing with the photon “precursor” B or to interaction with the Higgs?

I want to get something clear that I do not seem to understand. I used to read that the photon A and the Z boson are (different) linear combinations between the W^0 (neutral weak boson before SU(2) ...
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1answer
38 views

2x2 Representation for triplet Higgs

I am perplexed by the $2\times2$ representation of the Higgs that one finds in Higgs triplet models and Left-Right symmetric models. If $\vec{\phi}=(\phi^{++},\phi^{+},\phi^{0})\in(3,0)$ is the ...
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1answer
74 views

Why only left-handed neutrinos have been observed yet?

This is what I understood (it may be wrong, so please correct me): since every particle is "divided" into a lefthand and a righthand partner, which is what guarantees the particles to have mass, and ...
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20 views

Semileptonic decay of neutral D meson: branching ratios?

I am looking for the branching ratio of the semileptonic decay of the neutral $D^0$ meson: BR($D^0 \to \pi^+e^-\bar\nu_e$) = ? According to the PDG book the branching ratio for $D^0 \to \pi^-e^+\...
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44 views

phase transition and effect on leptogenesis

What is the effect on leptogenesis in the standard model if the electroweak phase transition is (i) first order and (ii) second order?
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149 views

Invariance under charge conjugation… Or not?

I have read some paper which says that the electroweak Lagrangian includes these terms like $\bar{\psi} \gamma_a\gamma_5\psi$ and $\bar{\psi} \gamma_a \psi$. They violate charge conjugation symmetry. ...
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130 views

Is the search for a Simple-group-based Electro-Weak theory over?

Just wondering: We know that, in its current form of the $SU(2)_L\times U(1)$, the electroweak theroy rides a wave of huge success. However, is it not possible that the correct simple group ...
6
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187 views

What is the rate of B violation expected in the standard model during high energy collisions?

In a recent question Can colliders detect B violation? I asked about detecting B violation in collisions. Here I am interested in the theory aspect. (I asked both questions originally in the same ...
6
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88 views

$WW\to t\bar{t}$ growth

I was told recently that "it is well known that processes like $WW\to t\bar{t}$ ($t$ being a top, or any massive fermion) grows linearly with the energy in the absence of an Higgs boson." Does anyone ...
5
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167 views

If weak isospin is not conserved in time, what does the Noether theorem tell us?

As far as I understand weak isospin is only conserved in interactions but not as time evolves. Nevertheless, we get from Noethers theorem, because of global $SU(2)$ invariance a conserved quantity ...
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42 views

$ZZ^{(*)}$ decaying to leptons mass spectrum

I was looking the mass spectrum of the $ZZ^{(*)}$: and I was wondering why the shape is the way it is. The peak around 90 GeV is the single Z resonant, what is reason behind the slight peak in the ...
3
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71 views

Is the right-handed antineutrino the CPT conjugate of the left-handed neutrino?

I am working from the book Massive Neutrinos in Physics and Astrophysics by Mohapatra and Pal (which is available here). On page 66, the authors claim that $\psi_{L}$ is the $\mathcal{CPT}$ conjugate ...
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40 views

Massless excitations without SSB

Is there possible the situation when there are massless excitations in spectrum of states in a theory with phase transition but without spontaneous symmetry breaking? The motivation for this question ...
2
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146 views

Feynman amplitude for electron-positron annihilation and $W^{\pm}$ production

I'm working with this interaction Hamiltonian density $$ H_{int}(x) = ig\bar{\Psi}_{\nu_e}(x)\gamma^\rho P_L \Psi_e(x)V_\rho(x) + igV^\dagger_\rho(x)\bar{\Psi}_e(x)\gamma^\rho P_L \Psi_{\nu_e} $$ ...
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34 views

Topological susceptibility of electroweak theta-term

Suppose EW theory generating functional: $$ Z[\text{sources}] = \int D(A,\psi,\bar{\psi}, H,H^{\dagger})\text{exp}\bigg[i\int d^{4}x\bigg(-\frac{1}{4g_{EW}^2}F_{EW}^2 + \bar{\psi}(D - m)\psi + DH^{\...
2
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235 views

Can the mass of longitudinal and transverse W bosons be measured separately?

Some higgsless unified models of particle physics predict that the mass of longitudinally polarized W bosons and the mass of transversely polarized W bosons are different. In those models, a ...
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142 views

About generator of $SU(2)$ flavor symmetry group

I am reading the textbook, "weak interactions" by Howard Georgi which can be founded in his homepage. Here i am trying to solve the problem 1b-2. The problem is given as follows. Consider the ...
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30 views

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants?

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants? If any, which (types of) ones? For the ones that do, what are the relations ...
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65 views

Mass generation for Z' and W' bosons

I read that some Beyond the Standard Model theories require the existence of additional gauge bosons such as $Z'$ and $W'$. As far as I understood, an extension of the $SU(2)_L$ symmetry is required, ...
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52 views

About Paschos-Wolfenstein relation (Weinberg angle measuring)

There is Paschos-Wolfenstein relation: $$ \tag 1 \frac{\sigma^{NC}_{\nu_{\mu}} - \sigma^{NC}_{\bar{\nu}_{\mu}}}{\sigma^{CC}_{\nu_{\mu}} - \sigma^{CC}_{\bar{\nu}_{\mu}}} = \frac{1}{2} - \sin^{2}(\...
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0answers
108 views

What's the most precise test of electroweak unification in the standard model?

As I understood, there is a coincidence of the weak coupling constant $g$ calculated in two different ways: 1) The muon lifetime $\tau_{\mu}$ is related to $g$ by the formula $(m_{\mu} c^2)^5 \tau_{\...
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27 views

Hamiltonian of the charged current in SM (related to the lorentz invariance)

recently when I was studying the scatterings which involves a vector boson (like W boson) as an intermediate particle, I saw that the propagator is not Lorentz invariant, I read that there is another ...
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166 views

Why does the electron energy distribution from muon decay peak near the kinematic maximum?

I'm trying to understand why when you have a muon decay event, the energy of the electron peaks near the maximum kinematically allowed value. Is there an intuitive explanation for why this is the case ...
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352 views

How to show the oblique parameters S, T, and U are coefficients of d=6 operators

In Morii, Lim, Mukherjee, The Physics of the Standard Model and Beyond. 2004, ch. 8, they claim that the Peskin–Takeuchi oblique parameters S, T and U are in fact Wilson coefficients of certain ...
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12 views

Selection Rules in FCNC mediated diagrams

I am studying the flavour changing processes mediated by flavor changing neutral current (FCNC). Are there any selection rules involved in assigning the flavor to the outgoing quark? Can the ...
0
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0answers
30 views

Electroweak phase transition

Is it true that when the temperature of the universe was greater than ~200GeV the Higgs did not have any nonzero vacuum expectation value, hence all the particles were massless? So if one calculates ...
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0answers
36 views

Why can an electric chargeless Z-particle decay in three photons?

The Z-particle that is supposed to convey the weak force has no electrical charge. So how is it possible the particle can decay in three photons. Because the weak and e.m. force are more or less ...
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18 views

Neutral pion mass correction from electroweak instantons

It is stated that the virtual process $$ \pi^{0}\to 2W \to \pi^{0}, $$ where $\pi^{0}$ is neutral pion and $W$ denotes $W-$boson, generates the small correction to the pion mass, namely $$ \delta m_{\...
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33 views

Electroweak instanton calculations

Consider an electroweak instanton in a model beyond the Standard Model with explicit baryon plus lepton number ($B+L$) violation. This instanton decays into nine quarks $q$ and three leptons $l$, ...
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28 views

Electroweak symmetry breaking with additional gauge group(s)

Is it possible that rather than the electroweak splitting into SU(2)xU(1), that there could instead of another gauge group in the dark sector? Suppose SU(2)xU(1)xSU(N)_d. Is that ruled out by the full ...
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76 views

Understanding $ee\to h \to ff$ process

can anyone tell me where to find a good reference that talks about $$e^+ e^-\rightarrow H \rightarrow f\bar{f}$$ where this describes an electron-positron annihilation into a Higgs that in term ...
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77 views

How to theoretically determine electric charges of $W^{\pm}$ bosons?

I just realised that I don't remember how to conclude theoretically that $W^{\pm}$ bosons have electric charges of $\pm 1$. After some searching I'm quite surprise that I couldn't find a satisfying ...
0
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213 views

Off-shell corrections to massive vector boson propagator in polarization form

As an exercise for myself, I have been working on rewriting the massive vector boson propagator (unitary gauge). I have run into a problem interpreting some of the terms that stick around when the ...