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Questions tagged [electroweak]

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 and SU(2) flavor symmetry in weak forces.

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Regarding vanishing of a triangle diagram

Furry's theorem ($C$ symmetry) is very important in calculations in QCD, Electroweak theory. Primarily it says everything about QED (three photon triangle diagram), but can be extended to QCD, and ($Z$...
Tanmoy Pati's user avatar
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Renormalization in Background field gauge

The purpose of this question is not very straightforward to explain. So, I just state the question. If we use Background field gauge for renormalization, due to the QED-like Ward identities, the ...
Tanmoy Pati's user avatar
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How does the CDF II $W$ boson mass measurement position itself relative to previous measurements?

The paper High-precision measurement of the W boson mass with the CDF II detector compares their results to the results of previous measurements in Fig. 5. While they show this visual comparison, ...
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$W$ and $B$ bosons when choosing a different minimum of the Higgs doublet

When comparing the experimental phenomenology with the standard model, one usually takes a combination of the $W^a_\mu$ and $B_\mu$ gauge bosons to obtain the physically observable ones ${W^+}_\mu$, ${...
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Gauge boson interacting with derivative of the Higgs field

Consider the $\mathrm{SU}(2)\times \mathrm U(1)_Y$ Lagrangian $$ \mathcal L=-\frac{1}{4} (W^a_{\mu\nu})^2 -\frac{1}{4} B_{\mu\nu}^2 + (D_\mu H)^\dagger (D^\mu H) +m^2 H^\dagger H -\lambda (H^\...
Liu Zhiyu's user avatar
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Why did Peter Higgs, et al. suspect that the $W$ boson(s) had mass? All the way back in 1963, '64?

I cannot understand why so many people (the PRL Symmetry authors) were so sure that the weak interaction particles had mass. The gluon, for instance, and its attendant strong force are also very short ...
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Different representations of the Yukawa interaction

during studying Yukawa sector of the SM, I got confused with different reps of the Yukawa interaction. First, this is what I am familiar with(let me show only electron mass term): $$y_e \bar{L}_e H ...
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Is it possible for electroweak monopoles to catalyze electroweak burning?

Given that both electroweak monopoles and the Sphaleron process involve the non-trivial aspects of electroweak interactions, I am curious about whether there is theoretical or experimental evidence to ...
Stardust Somnium's user avatar
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Can $W^\pm$ bosons act by changing the weak isospin state of particles?

From what I understand, the weak isospin part of the symmetry-unbroken electroweak interaction consists of the $\mathfrak{su}(2)$ valued gauge field $\hat W_\mu = \sum_i^3W^i_\mu \hat T^i$, where $\{\...
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Furry's theorem in Electroweak and strong interactions

We can think of Furry's theorem as the consequence of $CP$ invariance of $QED$. For parity, the vector bilinear changes sign, hence, under charge conjugation, it should. The vacuum is $C$-invariant, ...
Tanmoy Pati's user avatar
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Why are $W$ and $Z$ bosons called 'intermediate' vector bosons?

What does the 'intermediate' part mean? Somehow, I thought an answer would be easy to come across, but I have yet to find one.
Kurt Hikes's user avatar
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How was the tau lepton predicted?

I know the tau lepton has been predicted before it was discovered – unlike the muon. But how does our theory (SM/electroweak theory) predict the existence of a third lepton generation?
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Can $\gamma^5$ matrices be ignored in $q\bar{q}\to ZZ$ processes?

In the $q\bar{q}\to ZZ$ process, the following Feynman diagram in LO appears: This means for each vertex, the Feynman amplitude contains a term proportional to $(g_V-g_A\gamma^5)$, which makes $D$-...
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Is there an experimental set up that would produce a "macroscopic" a weak or strong nuclear force fields?

I was wondering if there is an experimental set up that would produce something equivalent to a classical electromagnetic field for the weak and strong nuclear forces. I know that the those forces are ...
Bryan D's user avatar
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$W$ vs $Z$ Boson Interaction

My apologies for the simplicity of this question, but I am learning how to analyze basic particle interactions. My rationale is the following: The output and the input are both leptons, which means ...
Dr. Ernesto Chinchilla's user avatar
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Is the weak quark mixing a consequence of electroweak symmetry breaking?

Because of the CKM matrix, the quark doublets that are changed by $W^{+}$ and $W^{-}$ include a linear combination of quark flavours, instead of the pure quark flavours. I was wondering if, before ...
TrentKent6's user avatar
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What does it mean to probe a certain energy scale?

For example, what does it mean that the LHC probe the electroweak scale, $M_{EW} \sim 10^3 GeV$? Also why is this energy called the electroweak scale?
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Derivation of hypercharge neglecting squared amplitude for WZ helicities in paper

I am trying to get from equations (20) and (21) in this paper to equations (13) in this one. I will start with my attempt at deriving this for the LL case. (With $F$ from equation (4), $g_2-g_1$ from (...
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Can not follow derivation of $WZ(0, 0)$ amplitude in paper

i am re-reading this paper and trying to follow the derivation of equation (21) from equation (15). Maybe someone can tell me where i am going wrong. So the original equation 15 is: $$M(0,0) = F\frac{\...
J.N.'s user avatar
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Gauge Boson Self-Interactions with covariant derivative

Self-Interactions of the unphysical gauge bosons $W_1, W_2, W_3$ are written within the gauge term $L_\mathrm{Gauge}=-\frac{1}{4} W_{\mu \nu} W^{\mu \nu}$ with $W_{\mu \nu}= \partial_\mu W_\nu - \...
Jan's user avatar
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Inverse muon decay on Mandl shaw- Help on $W$ boson propagator

Hello, I cannot understand why here the other term of the propagator of $W$ boson $k^{\alpha} k^{\beta}/m_{W}^{2}$ is not present, and how/if this absence is linked to the fact that we neglect terms ...
A22MS's user avatar
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Nonconservation of hypercharge in Higgs decay

From Wikipedia, Higgs boson has hypercharge of +1 and isospin of -1/2. W bosons have hypercharge 0 and isospin +-1. Now Higgs boson can decay into 2 W bosons of opposite electric charge. No matter how ...
haael's user avatar
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Identification of $W$ and $Z$ mass terms in SSB and Unitary Gauge [closed]

I have two questions, both relating to the SSB of Electroweak Lagrangian. My notes say that after breaking and expanding around the VEV, the masses of $W$ and $Z$ are identified by comparing to the ...
Blazeboy01's user avatar
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Why is the fermionic sector of Standard Model the way it is? [closed]

"Because it works!" will be considered too broad an answer. I want to precisely know which experiments forced to consider the model construction the way it is. For example, I can see Wu's ...
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Can two $W$ bosons convert a proton into an antiproton by becoming two $W^+$ bosons?

Would this process have been more or less likely in the high energy conditions around the time of the big bang?
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Concluding that local $SU(2)$ symmetry implies that we have charged and uncharged fields

In Samoil Bilenky's (2nd. ed) "Introduction to the Physics of Massive and Mixed Neutrinos," he constructs the $SU(2)$ Yang-Mills model. He starts by introducing the doublet (section 3.2, ...
Fernando Garcia Cortez's user avatar
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Understanding $\mathscr{L}_Y^{\text{down} }=-\sqrt{2}\sum _{a,q}\overline{\psi }_{iL}Y^{\text{down} }_{iq}q'_RH+\text{h.c.} $

Currently reading Bilenky's "Introduction to the Physics of Massive and Mixed Neutrinos." (2nd ed.) On page 56 (Section 3.4 on the Standard model) elaborates "Let us assume that in the ...
Fernando Garcia Cortez's user avatar
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Electroweak Interaction and SSB

I read that above unification energy, on the order of 100 GeV, electromagnetic force and weak force would merge into a single electroweak force. I do not really understand how and when exactly two ...
Alex's user avatar
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Why are there no diccussions of hypercharge conservation or Dirac hypercharge monopoles?

The Maxwell equations can be derived from an equation for a spin 1 field with $U(1)$ symmetry. From this field equation is possible to postulate Dirac monopoles by simply roting the real and complex ...
yeaton's user avatar
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3 votes
1 answer
96 views

Flavor changing neutral current with photon

I'm trying to understand why the penguin diagram for photons takes its form. $I$ here is the integral and some CKM elements. The author (Ch1.6.1) says that for $b\rightarrow s\gamma$, we get a factor ...
Mohamed Ahmed's user avatar
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1 answer
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How do we prove that hypercharge is different for singlets and doublets?

I am trying to teach myself about the standard model and I am stumped by this point. I understand that: When picking an U(1) generator for SU(2)xU(1), any multiple of the identity will do ($YI_n$) ...
SgtJohn74's user avatar
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144 views

Dirac adjoint of $SU(2)$ lepton doublet

The leptonic $SU(2)$ left-handed doublet is $$L_L = \begin{pmatrix}\nu_L\\ e_L\end{pmatrix}.$$ Both $\nu_L$ and $e_L$ are Dirac spinors so both are 4-spinors. The dirac adjoint on 4-spinors is the ...
Mohamed Ahmed's user avatar
1 vote
1 answer
76 views

Charged and neutral currents in electroweak theory

We describe electroweak theory by $SU(2)_L\times U(1)_Y$. This group has four generators which will be the W's, Z and $\gamma$ and we get 4 associated currents. We complexify the first 2 generators of ...
Mohamed Ahmed's user avatar
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51 views

Maximum energy of neutrino from decay of $W$ boson

Figure 2 of this paper suggests that neutrinos from the decay of on shell W bosons can have an energy as high as the W boson mass. However, in the $W^{-} \rightarrow e^{-} + \bar{\nu}_{e}$ process, ...
Nownuri's user avatar
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What would an inertial observer see watching a particle as the local temperature drops below the electroweak unification temperature?

Above about $10^{15} K$ (the electroweak unification temperature), the Higgs field doesn't interact with elementary particles to grant them masses. Above this temperature, they are all massless. This ...
Logan J. Fisher's user avatar
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1 answer
102 views

Massless electrons pre electroweak symmetry breaking observation

I recently heard that electrons are massless at energies above electroweak symmetry breaking, has this ever been observed experimentally? I looked for it but couldn’t find anything
Simon's user avatar
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1 answer
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Is the electroweak gauge group a semidirect product?

In the typical treatment of electroweak theory, the gauge group is $G = \mathrm{SU}(2)_I \times \mathrm{U}(1)_Y$. This group is broken by the Higgs mechanism, while the combination of generators $Q = ...
w123's user avatar
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Has it been verified experimentally that the $Z$ boson interact with gravity?

Does the $Z$ boson interact with gravity? I understand it has a measurable mass. I'm instead looking for an experiment that says, unequivocally, it interacts with gravity (as opposed to, e.g., having ...
Feynmanfan85's user avatar
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73 views

How can we talk about the mass of $W^\pm$ bosons when they don't diagonalise the mass matrix?

In the electroweak lagrangian, after symmetry breaking we get $W^1_\mu,W^2\mu,W^3\mu$ and $B_\mu$ bosons. These fields don't however diagonalise the mass matrix $\frac{\partial^2V}{\partial\phi_i\...
acernine's user avatar
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Is there an operator to measure pre-SSB boson states?

A common statement is that post-SSB electroweak gauge bosons are linear combinations of pre-SSB gauge bosons. It is also usually stated that pre-SSB bosons can also be thought of as linear ...
Vitaly Korzhik's user avatar
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1 answer
124 views

Is it possible to construct a realistic $SU(2)$ model for the weak interaction despite the failure to introduce full weak isospin symmetry?

In his chapter on the electroweak unification, Griffiths introduces the weak hypercharge explaining that his attempt at introducing full weak isospin symmetry with the Pauli spin matrices failed ...
Hrach's user avatar
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Is there an explanation for why electric charge, or hypercharge, are rational multiples of each other? [duplicate]

Electromagnetic charges are obviously quantized - I suppose the lowest charge being the $d$ charge of $e/3$. Every other charged particle has a multiple of that charge (actually all stable free ...
AXensen's user avatar
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Why were weak neutral currents considered evidence for electroweak theory?

For example, Wikipedia says: The existence of the electroweak interactions was experimentally established in two stages, the first being the discovery of neutral currents in neutrino scattering by ...
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Is there any something something force other than the electro magnetic force?

Far as I can tell, the force generated by electromagnetic field can be seen as an electrical force or as a magnetic force depending on the observer, i.e., these forces are actually the same phenomenon ...
João Mendes's user avatar
1 vote
1 answer
211 views

Is weak hypercharge carried by $Z$ boson?

In the PBS spacetime video about charge (https://www.youtube.com/watch?v=esayi49OAk4), at 10:55 he said that weak hypercharge is carried by the $Z$ boson. Is this accurate?
Crinoid's user avatar
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What is a CP number? In terms of CP-Symmetry and CP-Violation?

When researching the origins of CP-symmetry and CP-violation, and the Fitch-Cronin experiment demonstrating 'indirect' CP-violation, I came across these statements: https://www2.lbl.gov/abc/wallchart/...
Kurt Hikes's user avatar
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How is the $SU(2)_L$ conjugation applied?

I'm reading a paper where they introduce the lepton doublets $L$ and "their $SU(2)_L$ conjugations" $\tilde{L}$, which I'm guessing means $$ \tilde{L} = i\sigma_2L^*. $$ After $\textit{vev}$,...
Depenau's user avatar
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1 answer
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What is a fermion doublet exactly?

I am trying to prove that the Weinberg operator is the only dimension-5 operator that can be constructed out of Standard Model fields. To that end, I've tried to write up all the dimension-5 operators ...
Depenau's user avatar
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Can the weak isospin of elementary particles be measured experimentally or is it penciled into the Standard Model?

The chart below from Wikipedia lists the weak isospins of all elementary particles. It states that right-handed matter particles and left-handed anti-matter particles have a weak isospin of 0. Is ...
NonPartisanObservor's user avatar
2 votes
3 answers
834 views

Why are interactions mediated by the $W$ bosons and the $Z$ bosons classified as a single type of force when they are so different?

We always hear of 4 Forces or interactions, i.e. the Strong Force, Electromagnetic Force, Weak Force and Gravity. Each force has its mediating Bosons, i.e. gluons for Strong Force, photons for ...
Suneet's user avatar
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