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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What determines the Lifetime of $Z$-Boson?

What determines the lifetime of the Z Boson? Is it it's mass? What else is involved? Is the coupling to Higgs involved?
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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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How are length and time scales for the different kinds of interactions (strong, weak, electroweak) determined?

I was recently asked what the length scale of the strong interaction is and found my self a bit lost at the question. A quick Google search revealed a result of $10^{-15}\,\text{m}\approx 1\,\text{GeV}...
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References for Glashow-Weinberg-Salam model

I am looking for reference recommendations on the Glashow-Weinberg-Salam theory of electroweak symmetry breaking. In particular, I am looking for a discussion of the $SU(2)\times U(1)$ gauge symmetry "...
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Below which energy would the weak interaction become confining?

Claudson et al considered an alternative formulation of the standard model where the SU(2) interaction was strengthened to become confining below ≈ 300 GeV, above the electroweak scale. Consider if ...
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What processes conserve (and don't conserve) GUT $X$-charge?

I've been Wikipedia-ing the weak interaction and GUTs and I came across 2 seemingly conflicting pieces of information. In the page for Weak Hypercharge it says this: one of the interactions is with ...
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Why is the term $\bar{L}\phi R$ invariant under $SU(2)_L \times U(1)_Y$ where $\phi$ is the Higgs field?

In the explanation for the fermion masses, the term $$\bar{L}\phi R$$ is added to the Lagrangian where $L$ is a left-handed $SU(2)$ doublet, $\phi$ is the Higgs left-handed $SU(2)$ doublet and $R$ is ...
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How $W^{\pm}$ bosons get their electric charge $\pm 1$ as opposed to $Z_0$ that have neutral electric charge?

In the 'Standard Model' book by Y. Grossman and Y. Nir, in chapter 7 (the leptonic standard model) on page 93 after defining the charge of the broken symmetry generator, i.e $Q=T_3+Y$ they say that ...
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How do we know that the $W$ and $Z$ bosons aren't composite?

Background to my reasoning: When the strong force was first discovered, it was considered to be the force that interacts between nucleons to keep the nucleus together and that the mediator bosons of ...
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In what sense $Z_\mu^0$ is orthogonal to $A_\mu$?

I am reading Standard model. Please explain in what sense the $Z$-boson $$Z_\mu^0=(g^2+g^{\prime 2})^{-1/2}(g A^3_\mu-g^\prime B_\mu)$$ is an orthogonal linear combination of the photon $$A_\mu=(g^2+...
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Neutral kaon semileptonic decays, why is $\overline{K^0}\rightarrow l^+\nu\pi^-$ not allowed?

On several texts it is stated that the semileptonic decays are different for the $K^0$ and $\overline{K^0}$, and each only gives leptons of particular charges (see www.hep.ph.ic.ac.uk/~dauncey/will/...
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Why is the relation $M_W=M_Z\cos\theta_W$ true only at tree-level?

In Glashow-Weinberg-Salam electroweak theory, the relation $$M_W=M_Z\cos\theta_W\tag{1}$$ is said to be remain true only at the tree-level; it receives corrections from the loop diagrams. See here. ...
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Why can't we have a massive photon in the Standard Model of Particle Physics

I've heard that in the Standard Model of Particle Physics you can´t have a massive photon whatever you do but I'm having a few problems showing that. I understand that the trick to make this work is ...
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Detecting the electroweak unification in data of quark gluon plasma

Electroweak unification is discussed in the Big Bang model and variant proposals, and there is a transition at energies of 100 GeV where the EW symmetry is unbroken and a quark gluon plasma phase ...
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What accelerator energies and types would be needed to explore electroweak unification, and if accessible, what would be the likely observables?

Question originally referred to electrostrong, but I actually meant to ask about electroweak. Edited to fix, but this is why there's an answer referencing ES not EW - that's my bad. Broadly as the ...
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Gauge group of Electroweak theory

I am doing a question that asks me to identify the gauge groups of a Lagrangian with the field strength tensors $$\bf{F}_{\mu \nu} = \partial_{\mu}\bf{W}_{\nu} - \partial_{\nu} \bf{W}_{\mu} - g\bf{...
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Z and $\gamma$ bosons as mixtures of W and B: Part II

When it is said that the photon is ["a mixture of W and B"][1] ($B$ being a gauge field associated with the $U(1)$ hypercharge) I have one question on this: Why there isn't a boson directly ...
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Z and $\gamma$ bosons as mixtures of W and B: Part I

When it is said that the photon is "a mixture of W and B" ($B$ being a gauge field associated with the $U(1)$ hypercharge) I have a question on this: When speaking of "mixtures", this is meant as ...
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Why do we require gauge symmetries to commute?

My question arises after reading the 87th page of Elementary particle physics in a nutshell by Tully: which is also given by the following link: https://books.google.se/books?id=vLy2YlkXZuEC&pg=...
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Motivation for Weinberg angle in electroweak gauge interaction?

Suppose I have the following lagrangian If we only focus on the neutral current in the lagrangian: Where $L$ is defined as: And $Y_L$,$Y_{R}^{\nu}$,$Y_{R}^{e}$, are the hypercharge values of the ...
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B violation and electric charge

Within SM you can prove that despite we have baryon number conservation respect to Noether theorem, at quantum level baryon (and lepton) number is violated as $$ \Delta B = 3·\Delta n_{CS}, \quad n_{...
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Weak hypercharge physical existence

How do we know that electrons are chiral? Even if left-handed electron carries weak hypercharge, it's only for an infinitesimally small time or is it predicted by QFT?
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Embedding of $SU(2)_L \times U(1)_Y$ into $SU(2)_L \times SU(2)_R$ in electroweak chiral effective theories

In the context of chiral effective theories we usually deal with the pion field \begin{equation} U= ie^{\frac{\pi^a \sigma^a}{2f}} \end{equation} where $\pi^a=\big(\pi^1, \pi^2, \pi^3\big)$ are the ...
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Could electroweak interactions derive from higgsing of gauged chiral symmetry?

A recent question discussed the practice of introducing electroweak interactions into chiral perturbation theory by gauging part of the chiral symmetry. Gauging chiral symmetry is normally regarded as ...
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Fierz identities and Weinberg operator

I've been told that $$ (\bar{L_i^c}\widetilde{\phi}^{\ *})(\widetilde{\phi}^\dagger L_k) = -\frac{1}{2}(\bar{\widetilde{L}}_i \vec{\sigma}L_k)(\widetilde{\phi}^\dagger \vec{\sigma} \phi) \tag1 $$ by ...
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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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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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Is there a weak hypercharge : spin-3/2 analogy?

So I was not trained as a particle physicist, but I left a table of particles on a post on Hacker News based on what little I do understand about the conservation of weak hypercharge and weak isospin. ...
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Same $U(1)$ charge for the $SU(2)$ doublet

Consider the symmetry $SU_L(2)\times U_Y(1)$. The entries of $SU_L(2)$ doublet will have same $U(1)$-charge. How can this be shown mathematically?
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What is (meant by) a non-compact $U(1)$ Lie group?

In John Preskill's review of monopoles he states on p. 471 Nowadays, we have another way of understanding why electric charge is quantized. Charge is quantized if the electromagnetic $U(l)_{\rm em}$...
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Cross section for 2 particles that decay independently

This maybe is a naive basic question but I want to be sure. If I want to calculate the cross section of the process $$p\bar{p} \rightarrow W^+HX \rightarrow e^+\nu_e b\bar{b} X$$ ($H$ is a Higgs ...
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EW theory vertices

I'm trying to undertand the following vertex: Initial state of up and anti-down quarks with finalk state made of $W^+$ boson. Does it go with left or right projector? I think that from Lagrangian it ...
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Detection of W and Z bosons

What specific behaviour confirmed the existence of the W and Z bosons at the UA1 and UA2 experiments?
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mechanism of annihilation

Can the annihilation of matter and antimatter be explained by the electro-weak interaction? Can pair-production be explained in the same way?
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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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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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Global $U(1)$ Symmetry in GSW Model

Consider the theory of a single generation of $e, \nu_L$ matter content. The initial lagrangian is $$ \mathcal{L} = i\bar{\ell}\not \partial\ell + i\bar{e}_R\not \partial e_R \tag{1} $$ where $$ ...
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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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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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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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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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$SU(2)$ 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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Calculation of Wilson Coefficients

In Flavour physics, amplitude of decay processes is generally expressed in terms of effective operators (reference). In the framework of effective field theory amplitude $\propto C_iO_i$, where $O_i$ ...
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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^...