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. See also the [Wiki page](http://en.wikipedia.org/wiki/Electroweak_interaction).

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Hypercharge of the Higgs field

I am puzzled by the hypercharge of the Higgs field. Under the entry "Higgs Mechanism" in Wikipedia, it is written: Its (weak hypercharge) U(1) charge is 1 However, under the entry "Higgs Boson" ...
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Interaction terms in the Standard model which cause Higgs decay to electroweak bosons

The coupling of the Higgs boson to the electroweak gauge bosons in the Standard model is given by $$\mathcal{L}_{\text{H-g}} = - \left( \frac{H}{v} + \frac{H^{2}}{2v^{2}} \right) \left(2M_{W}^{2}W_{\...
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What is Weak isospin in Laymans terms?

What is Weak isospin in Laymans terms? I apologise if this is a bit of a basic question but I have read the Wikipedia page and all it says is that it is quantum number relating to weak interaction. I'...
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What is the weak isospin of hadrons?

What are the weak isospins (T3 values) of various hadrons, including the proton, neutron, mesons, hyperons and other hadrons? How is the weak isospin calculated for any hadron? Published sources ...
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Electroweak Theory: Charge definition and Weinberg angle

Given the gauge fields $B$ (generator Y) for weak hypercharge and $W_3$ (generator $I_3$) for isospin, we combine the generators as $$Q=I_3+Y/2\tag{1}$$ to represent electric charge. Why does this not ...
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What electric charges do the $SU(2)$ weak isospin bosons carry?

The $SU(2)$ weak isospin group has three bosons, before symmetry breaking: The $W^1$, $W^2$, and $W^3$ weak isospin bosons. The $W^1$ and $W^2$ mix to form the $W^+$ and $W^-$ bosons with electric ...
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Standard Model without Electroweak Unification

From what I have read it seems that the Electroweak Unification $$SU(2)×U(1)$$ was developed because the Weak Interaction by itself is non-renormalizable and combining it with the Electromagnetic ...
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If weak force causes decay of a single particle, why is it called a force between two particles?

Weak force acts at very short distances (10^-16 to 10^-17 m), but what is this distance ? Is this the distance between two particles that can experience this force ?...
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How to calculate the charges of W and Z bosons?

In the Standard Model, electroweak unification is based on the symmetry breaking of $ \text{SU(2)}\times \text{U(1)}_Y \rightarrow \text{U(1)}_{EM}$ by the VEV of a complex doublet $H$ with ...
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What happens to the Weak Interaction after Electroweak Symmetry Breaking?

As far as I know the electroweak theory only holds for some energy scale (probably the one we use at the LHC). For that scale there is a gauge theory for the electroweak interaction. Under this scale ...
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Weak isospin in electroweak theory

I have seen this confusion surface in multiple questions, but neither contained the answer I was seeking. I hope you can help me understand where I'm going wrong. Assume the electroweak symmetry is ...
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Are quarks in a doublet weak analogues to strong color states?

Quarks and gluons interact so frequently that it makes little sense to regard each color state as a unique fundamental particle. These interactions also do not change any of the quarks' other ...
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Why are the Higgs field and the electroweak field so closely related?

To my understanding, the Higgs field condensed at the same time as the electroweak symmetry was broken. The fields' doublet components merged, while the singlet components became the Higgs boson and ...
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How was the electroweak force operating/acting in the early universe?

In the early universe the temperature was high enough for the electromagnetic force and weak force to act as one. My question is how exactly does that work, because the weak force uses the W and Z ...
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Is it interesting to ask why the Higgs vacuum expectation has its particular value?

By interesting, I mean more interesting than asking why any of the free parameters of the SM (electron mass, CP-violating phase, etc) have their particular values. The vacuum expectation value $\nu \...
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How were Electromagnetism and Weak interaction unified and proven?

How did the electroweak interaction come into fruition?
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Estimating Feynman diagrams for $B_s \rightarrow \mu \mu$ decays

Is there a straightforward way to infer the relative contributions of each diagram depicted (from this blog) to the $B^0_S \rightarrow \mu^+ \mu^- $ branching fraction? Naively, as they each have 4 ...
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What's the difference between the gauge bosons $W^+$ and $W^-$?

If someone would ask me this question I'd say: "Nothing but their charges. The thing is so because we don't know what exactly happens in the virtual part of the process (say a scattering). Physicists ...
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How do the right-handed fermions acquire mass?

I am constructing a presentation on how elementary particles acquire mass via interaction with Higgs field. I asked this question previously in a different form and received the usual clap trap, so I ...
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Representation in $SU(2)_{L}\times U(1)_{Y}$

I'm reading the book "Massive neutrinos in physics and astrophysics" by R. N. Mohapatra and P. B. Pal, and have a question about its notation. The Equation 2.10, it says: $$ q_{L}=\binom{u_{L}}{d_{L}}...
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Generators of $SU(2)\times U(1)$

I'm currently reading about spontanous symmetry breaking. In particular about a Lagrangian that is invariant under $SU(2)\times U(1)$, in other words pretty standard QFT stuff. I know that the ...
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How it is possible to mediate a weak interactions by very heavy particle such as Boson?

When considering a weak decay interaction such as leptons , the weak force is mediate by huge particle such as bosons (W+ or W- ). How it is possible to have a such heavy particle within less massive ...
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Is it possible the weak force isn´t fundamental? [closed]

Once the strong force was thought to be a fundamental force mediated by the massive pion. Later colour and gluons were introduced. The old strong force was a residue force of the new fundamental force....
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How many kinds of “weak charges” exist?

For electricity, we have one charge, for the strong force three. How many are there connected to the weak force? Three, because of the W- and Z-particles? For the weak force, there is the isospin, ...
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Would life (as we know it) be possible without the weak interaction?

I understand why the strong interaction is important in everyday life (it holds nuclei together and also allows the fusion reactions that power the Sun) and also why the electromagnetic interaction is ...
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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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Difference between the CKM and the PMNS matrix

My question is very simple: is there a fundametal difference between the CKM (responsible for quark mixing) and the PMNS matrix (responsible for lepton mixing)? The CKM matrix allows (in charged ...
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$W^{++}$ / $W^{--}$ Bosons in theory and experiment

I wonder whether there is any theoretical interest in and/or experimental search for double charged bosons, probably to be called $W^{++}$ and $W^{--}$. The latter would obviously turn an electron ...
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Why $U(1)_Y$ hypercharge rather than $U(1)_\text{em}$ electromagnetism?

In the Standard Model we have $SU(2)_I\times U(1)_Y$, where $U(1)_Y$ is weak hypercharge and $SU(2)_I$ is the symmetry group of weak isospin. Why do we introduce $U(1)_Y$ of weak hypercharge rather ...
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Massless excitations without SSB

Is there a possible situation where there are massless excitations in spectrum of states in a theory with phase transition but without spontaneous symmetry breaking? The motivation for this question ...
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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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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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If neutrons aren't affected by electromagnetic force, what causes it to bounce off matter?

Say a neutron is heading for a mountain, what would cause it to bounce off said amalgamation of matter? Electromagnetism is ruled out, gravity is too weak, (if I'm not mistaken) nuclear strong force ...
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How is each neutrino associated with a specific charged lepton?

For instance, why is an electron neutrino called that and what is its relationship with an electron?
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Why only left-handed neutrinos have been observed yet? [duplicate]

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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Chiral symmetry breaking and confusion with terminology

I am confused about Chiral symmetry breaking and the terminology we use. First of all, I think the symmetry is started with taking quark masses zero and writing the Lagrangian as; $$ L=-\frac{1}{4}(F_{...
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Should 4 fundamental forces really be 3 because of electroweak unification?

I read @ http://www.particleadventure.org/ Physicists concluded that, in fact, the weak and electromagnetic forces have essentially equal strengths. This is because the strength of the interaction ...
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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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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^{\...
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Is the Electroweak theory chiral regardless of temperature?

Is the electroweak theory a chiral theory regardless of whether one is above the electroweak symmetry breaking temperature or not?
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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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Why we unified electromagnetic and weak force?

We have unified electromagnetic and weak force into one single force called Electroweak force. I mean we can use these different forces within their respective domains like weak interaction for short ...
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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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Georgi-Glashow model and the VEV of the scalar field

Consider the Georgi-Glashow model, an $SU(2)$ gauge theory with a real scalar in the adjoint (thus a 3-vector in the colour space) $\phi$. The Lagrangian is $$ L = -\frac{1}{4g^2} F_{\mu \nu}^{\, a} ...
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Unification of Weak and Electromagnetic forces

I'm curious how the weak and em forces relate to one another. My knowledge in this area is weak (ha) but I am interested in an explanation for how these two forces relate to one another, and how / why ...
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Why are bare mass terms for W-bosons forbidden, but coupling terms to Higgs doublets allowed?

The $W$ bosons live in the adjoint rep of $SU(2)$, which is three dimensional. The standard model Higgs lives in a $SU(2)$ doublet, i.e. the two dimensional rep. The $W$ bosons get their mass after ...
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Transformations of electroweak gauge field $W_\mu$ under $U(1)_{e.m.}$

As the vector boson field $W_\mu$ is, together with $Z^0$, the gauge field for the Standard electroweak model, I know it transforms as a connection under the $SU(2)\times U(1)_Y$ group. But, when this ...
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Why are $W$ bosons massless above electroweak scale? [duplicate]

Because of the Higgs mechanism, one must replace the Higgs field $\phi$ with $\phi_0 + \phi_1$ where $\phi_0$ is the vacuum expectation value. As far as I understand, the $\phi_0$ gives the mass term ...
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Matrix elements of four-quark operators [closed]

In weak interaction phenomenology, especially in strangeness changing processes, effective four-quark operators are used. Such as $Q_1 = (\bar{s}_\alpha \gamma_\mu (1-\gamma_5) d_\alpha) (\bar{u}_\...
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Why does the electromagnetic and weak coupling strength do not meet at the electroweak scale?

The running of the coupling strengths is usually visualized on a logarithmic scale like here What surprises me is that the weak and the electromagnetic coupling strength do not meet before the GUT ...