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

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Vector-like Representation of fermions

In the literature, they often extend the Standard Model by adding a so-called vector-like fermion which is a multiplet invariant under $SU(2)_L\times U(1)$. The left- and right-handed components of ...
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Why doesn't observing a photon collapse it's wave function into a B or W3 boson?

According to electroweak theory, the photon ($\gamma^0$) and weak bosons ($W^+, W^-, Z^0$) are all linear combinations or superpositions of the weak hypercharge boson ($B$) and the weak isospin bosons ...
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How do Fermions with $0$ weak hyper charge couple to electro-weak force?

If you have two fermions (with spin $\pm \frac{1}{2}$) that form a weak-isospin doublet and their respective right-handed fermions which are weak-isospin singlets, what would it imply if the doublet ...
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What was the prediction of the standard electroweak theory about the $W$ and $Z$ boson masses?

The standard electroweak theory has two coupling constants $g$ and $g^\prime$. In this theory, the $W$ mass and $Z$ mass are given by $$M_W=\frac{1}{2}gv,~M_Z=\frac{1}{2}(g^2+g^{\prime 2})^{1/2}v$$ ...
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What would a universe with a long range weak force look like?

If the W's and Z bosons were massless at low energies (i.e. no Higgs interaction), what would the universe look like? Would there be "weak bound states" ? How would electromagnetic theory differ with ...
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Can the EM field self-interact in the Standard Model?

Since the EM field is a linear combination of the electroweak $U(1)$ gauge field and one of the $SU(2)$ gauge fields, does this mean that it has self-interaction terms carried over from the ...
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Leptons during Electroweak Epoch

Prior to the electroweak force splitting, did charged leptons still carry a charge of $e$? I was under the impression that, since electromagnetism didn't exist in its current state prior to ...
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Is this feynman diagram possible? $e^- + e^+ \to \nu_\mu + \bar{\nu}_\mu$

I am starting to learn about Feynman diagrams and I have been told that flavour has to be conserved at vertices in the case that the exchange particle was neutral. Since here the exchange particle is ...
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$SU(2)$ Invariant Lagrangian

Consider two arbitrary scalar multiplets $\Phi$ and $\Psi$ invariant under $SU(2)\times U(1)$. When writing the potential for this model, in addition to usual terms like $\Phi^\dagger \Phi + (\Phi^\...
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Electroweak to Electro/Weak Bosons?

I apologise in advance, this is something I just can't seem to get my head around. So it's my understanding that before the electroweak force split, there were four bosons - $W1$, $W2$, $W3$ and $B$ - ...
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Half-life of $W$ and $Z$ bosons

$W$ and $Z$ bosons should decay through weak interaction. But their half-life is around $\tau = 10^{-25} s$ which is a typical value for particles decaying through strong force (instead of a $10^{-12}-...
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CERN and electroweak interaction

I know that the EM and the weak force were described in the same mathematical formalization by GSW and that it was predicted that they would appear as one at energies of 200 GeV. I know that the $W^+$,...
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About the electroweak force

So, I'm struggling to understand how the electromagnetic and the weak force were connected. Separately, I know pretty much how the two forces work and interact with the environment. I read a few about,...
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Hydrogen and the neutron

I have a question about Hydrogen and the neutron. So a neutral hydrogen atom has structure ${}^1H\equiv[p^+ e^-]$, a bound proton and electron. From a quantum theoretical viewpoint, one would write ...
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Is the right-handed electron really an $SU(2)$ singlet?

In the Standard Model, neutrinos are assumed to be massless, and the right-handed neutrinos thus do not exit. Is this the reason that the right-handed electron is regarded as an $SU(2)$ singlet? ...
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Why do we regard ($e^{-}, \nu_{e}$) as a doublet?

To my understanding, particles in a multiplet have similar properties (similar masses and so on) and slight or symmetric differences (in mass, electric charge, spin, and so on). They can be regarded ...
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How could particles with electric charge be massless before the electroweak symmetry breaking?

How could particles with electric charge be massless before the electroweak symmetry breaking? Wouldn't the energy stored in the electric field contribute to the mass of the particle?
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Relation between electroweak force and gravity? [closed]

I'm really stuck on the following idea. For gravity to in any way be 'unified' with the electroweak interaction wouldn't it need to include a model whereby the electron somehow tunnels to within the ...
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Equality of positron and proton charge problem statement

When I hear that the equality of positron and proton charge is an unsolved problem I assume that we are putting the electric charge by hand in the electroweak section of the SM Lagrangian. Is this ...
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Electroweak Force Capabilities

I understand that Electroweak force is the unification of Weak force and electromagnetism, but that are the actual effects or capabilities of this fundamental force? or at the very lease, what are the ...
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What happens when a neutron star loses enough mass to go under Chandrasekhar limit?

Say if a blackhole passes very close by a neutron star at high speed fly-by and eats half of the neutron star. What happens to the other half? Does it blow up in size as the electroweak force pushes ...
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Why did physicists in the 1950s and 1960s suspect the weak and EM interactions were at some level the same interaction?

Around the 1950s and 1960s there was a lot of work in particle physics motivated by two issues - finding a workable quantum field model for the weak interaction, and finding a model that unified the ...
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Does the LHC see electro-weak symmetry breaking? [duplicate]

The energy scale of electro-weak processes is around $160$ GeV. But the LHC has a centre of mass energy of $7$ TeV... so do they see processes involving the $W^1, W^2, W^3$ and $B$ fields, before ...
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How would you explain the Higgs Mechanism to a kid? [duplicate]

I am currently studying the Electroweak Symmetry breaking and the Higgs Mechanism and I am wondering how could I explain it to a kid or my grandpa. How would you describe the mechanism and its ...
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Self-coupling Higgs boson and composite Higgs models

I'm currently doing my Bachelor Thesis about the Higgs boson and I've read that there are new models which describe the Electroweak Symmetry Breaking considering the Higgs boson as a composite ...
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First order phase transitions in cosmology

I am reading about Electroweak phase transitions in presence of singlet(under SU(2)$_L$) scalar particle. For this model, effective potential at finite temperature turns out to be $$ V(\phi,T)=D(T^2-...
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Elastic scattering of neutrinos on atomic electrons

In the elastic scattering of neutrinos on atomic electrons, why can tau and muon neutrinos only interact via weak neutral currents but electron neutrinos can interact with W or Z bosons?
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How do you know $W$ and $Z$ bosons are really bosons and not fermions?

It has been always said that $W$ an $Z$ bosons are bosons and not fermions but is there any experimental trial that prove that? Has anyone put two of them in the same quantum state or studies have ...
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$\tau \rightarrow \rho \nu $ relation with $ \rho \rightarrow e^+ e^-$

I'm reading "Okun, Leptons and quarks.", specifically subsection 13.3 "Semihadronic decays. General remarks." Okun says "The amplitude of the $\tau \rightarrow \rho \nu $ decay is related directly to ...
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ElectroWeak symmetry breaking and the early universe

I'm trying to piece together a coherent understanding of the EW symmetry breaking and its effect on early cosmology, from a number of somewhat incomplete sources. Any corrections to the following ...
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Fermionic CW potential unbounded below for large background?

I'm studying the Coleman Weinberg potential in presence of the background Higgs h. It seems to be well known that the CW potential goes like $(-1)^F m^4 \log(m^2)$, where $m^2$ is the background-...
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Monopoles from hypothetical Weinberg-Salam model with massless Z boson

We know that no monopoles exist in the Weinberg-Salam model (a good explanation is provided in the answer to this previous question). Now let us assume that the initial $SU(2)\times U(1)$ gauge ...
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Calculating $W$ - $Z$ bosons mass difference

Naively one might expect the W weak vector bosons to have slightly higher mass than the Z due to EM self-energy, while the opposite is true (80 vs. 91 Gev). Presumably due to the strong interactions ...
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Which $W$ boson is involved in electron capture?

I am learning about Electron Capture. $$p+e\to n+\nu_e$$ My question is whether the $W^+$ boson or the $W^-$ boson is involved in this transfer. I can consider this two ways: 1) Since the electron ...
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In electron-positron annihilation, why is photon exchange dominant at energies below the Z-resonance?

In a plot of the Z resonance from e+ e- collisions, why is photon exchange dominant below the center of mass energy below the Z peak?
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Weak hypercharge assignments in the Standard Model

While refreshing my memory on details of the Standard Model, I ran into a muddle. I might not exist to ask bizarre questions if the neutron, neutrino, and hydrogen atom were not electrically neutral. ...
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Weak isospin current

I cannot understand the product of a Dirac gamma matrix and a Pauli matrix in this formula of the weak isospin current: $$J_α^i(x)=\frac12\bar \psi_L(x)\gamma_\alpha\tau^i\psi_L(x),$$ where $γ_α$ is ...
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What Makes a $W$-Boson a Gauge Boson?

I understand that in beta decay, a quark changes its flavor and emits a $W$-Boson, and this $W$ (is the W Boson virtual, by the way?) quickly decays into an electron and an electron antineutrino or ...
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Are both Gell-Mann Nishijima formulas true for the same reason?

The Gell-Mann Nishijima formula states that $$Q = I_3 + \frac{Y}{2}$$ where $Q$ is the electric charge, $I_3$ is the third component of isospin, and $Y$ is the hypercharge. This was an empirical fact ...
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What is the isospin of the photon?

As already mentioned in this Phys.SE post, the PDG booklet says that the isospin of a photon is $0,1$. Is it referring to the strong or to the weak isospin of the photon? What would be the 3rd ...
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SU(2) x U(1) weak model at high T

It has been shown that at very high temperature, of the order of (10 power 15) or something, electroweak SU(2) x U(1) model remains unbroken. Can anybody please point to some work on the phenomenology ...
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Form of Coulomb’s law before the electroweak phase transition

I’ve been thinking about the electroweak phase transition in the early universe, and I have some questions about the form of Coulomb’s law during that epoch. As I understand it, before the ...
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Total decay width of the W boson

I read in some particle physics book how they calculate the two body decays of the W boson, and then add all of them get the total decay width. I am wondering about other contributions, say, three ...
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Why is the Fermi coupling $G_F$ is measured from muon decay?

The decay rate of all weak processes, calculated from the $V$-$A$ theory will contain a factor of $G_F$, the Fermi coupling constant. However, $G_F$ is usually measured from $\mu^-$ decay which is in ...
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Calculation of the weak coupling constant

There are two ways to calculate the coupling constant of the weak interaction $g$. 1) From the electromagnetic coupling constant and the weak mixing angle, using the relation $${\sf e} = g\sin(\...
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$SU(2)$ to $U(1)$ symmetry breaking

Why does electroweak theory have $SU(2) \times U(1)$ to $U(1)$ symmetry breaking. Is it not possible to have simply $SU(2)$ to $U(1)$ symmetry breaking?
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How does a Higgs triplet transform under $SU(2)_L \times U(1)_Y$ when written as a $2\times 2$ matrix?

I recently learned that a Higgs triplet can be written as a $2 \times 2$ matrix: \begin{equation} \Delta=\begin{pmatrix} \frac{\Delta^{+}}{\sqrt{2}} & \Delta^{++} \\ \Delta^0 & - \frac{\Delta^...
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What crossed over at the electroweak crossover?

It's been known for quite some time now that the electroweak "transition" in the early universe is first-order for a Higgs mass of less than about 75 GeV, but for a larger Higgs mass (including the ...
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Renormalization scale dependence of S, T parameter of Electroweak precision test

In Peskin, Takeuchi(1992) paper(link), oblique parameters S and T, U are defined as (Eqn 3.12) $\alpha S\equiv 4e^2[\Pi'_{33}(0)-\Pi'_{3Q}(0)], \\ \alpha T\equiv \frac{e^2}{s^2c^2m_Z^2}[\Pi_{11}(0)-\...
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Are Photons Goldstone Bosons?

I'm not interested in more speculative ideas, like the one of Bjorken et. al. that photons are Goldstones of broken Lorentz symmetry. Instead, I want to understand if photons are simply the ...