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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Why is gravitational wave production in early Universe disfavoured for smooth crossovers?

Production of gravitational waves in the early Universe (for example, in the electroweak phase transition) is favoured only if the Universe undergoes a first-order phase transition but not favoured if ...
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What is the lifetime of the deuteron with respect to sphaleron-induced decay

As far as I've understood, instantons like the sphaleron can give rise to processes that violate $B+L$ but conserve $B-L$, where the baryon and lepton number can only change by a multiple of three. ...
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Fundamental invariants of the electroweak sector?

In a previous question, I asked what the matrix representation of the electroweak fields is, and I was told they are identical to the Faraday tensors, but come in a set of three ($W_i, i\in \{1,2,3\}$)...
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How does the motion of a charged particle in a magnetic field with the right-hand rule obey mirror symmetry?

In The New Cosmic Onion, I read the following: If mirror symmetry were an exact property of Nature, it would be impossible to tell whether a film of an experiment has been made directly or by filming ...
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Fermion couplings

We know that the absolute sign of Axial and Vector couplings of fermions cannot be measured. Could anyone help me understand which symmetry does this condition arise from?
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What is the sign of Weinberg angle?

One has $\cos{\theta_W}=m_W/m_Z$, and $\sin^2{\theta_W}=1-(m_W/m_Z)^2$ Is the sign of the Weinberg angle defined or an important quantity? If yes, are there constraints?
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How to represent graphically the relationship of $Z$ and $\gamma$ to $W_3$ and $B^0$?

How to represent graphically the relationship of $Z$ and $\gamma$ to $W_3$ and $B^0$ ? I made these two schematics below, but I'm not sure which one is correct, nor if we we should put $W_3$ or $B^0$ ...
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What is the value of electroweak scale? Depends on literature?

Depending on the literature, we see for the electroweak scale the following typical values : 100 GeV, 125 GeV (Higgs mass), 246 GeV (vev), 1 TeV So what is really the value of electroweak scale?
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Electroweak field-strength tensors

The Lagrangian density for the interaction term of the bosons $W_1,W_2,W_3,B$ in the electroweak theory is $$ \mathcal{L}_g=-\frac{1}{4}\operatorname{Tr}(W^{\mu\nu}_aW_{\mu\nu}^a)-\frac{1}{4}B^{\mu\...
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Ward identity in the electroweak theory

I'm studying Peskin & Schroeder's An Introduction to Quantum Field Theory, specifically the section about the quantization of the Glashow-Weinberg-Salam model of the electroweak gauge theory where ...
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118 views

$Q=I_3 + Y/2$. How can this be true when Charge does not commute with Weak Hypercharge or Weak Isospin?

About the familiar formula $Q=I_3 + Y/2$. As an example, the left-handed electron has charge $Q=-1$, weak isospin $I_3 = -1/2$, and weak hypercharge $Y=-1$. The electron is represented in the Dirac ...
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Top quark decay rate calculation $\Gamma(t\rightarrow W^+b)$

I'm trying to calculate the disintegration rate $\Gamma(t\rightarrow W^+b)$ from the Fermi Diagram: I know the lagrangian for the interaction would be: $$ -iF = \bar{u_b}\gamma^\mu P_Li\frac{g}{\...
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Non-quadratic terms in Higgs Lagrangian after the expansion about the minimum

Let's consider the Higgs Lagrangian \begin{equation} \mathcal{L}= -(\partial^\mu\phi+B^\mu\phi)^\dagger(\partial_\mu\phi+B_\mu\phi)-V(\phi^\dagger\phi) \end{equation} where $B^\mu$ is the $\mu$ ...
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How does the unitary gauge make Goldstone modes disappear?

I know that, in the Glashow-Weinberg-Salam model of electroweak theory, small oscillations of the Higgs field about the minimum \begin{equation} \phi_0= \begin{pmatrix} 0\\ a \end{pmatrix} \end{...
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81 views

Where does the Goldstone couplings go in the unitary gauge?

Imagine that you have some model with an enlarged scalar potential, such that there is, for instance, a quartic coupling $\kappa$ between the Higgs charged component and three other scalars, which do ...
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The Unusual Mass of the $W$ Bosons

A quick look on wikipedia (https://en.wikipedia.org/wiki/W_and_Z_bosons) will tell me that the rest mass of a $W$ boson is 2 orders of magnitude higher than that of a proton. It seems weird that a ...
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Was photon *defined* according to Standard Model *before* electroweak symmetry breaking ? Or were there only $W_3$ and $B$?

Was photon defined according to Standard Model theory before electroweak symmetry breaking ? Or were there only $W_3$ and $B$ ? Indeed, in Electroweak to Electro/Weak Bosons? Aman pawar answers "no" ...
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Helicity and chirality of particles in the pion decay

Let us consider the $\pi^+$ decay: $$\pi^+(q) \rightarrow \nu_\mu(p_1) + \mu^+(p_2)$$ In the Standard Model, the neutrinos are left-handed. Since they are massless, chirality corresponds to helicity. ...
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Feynman rules of electroweak interactions applied to the muon decay

We know that the muon can decay as follows: $$\mu^{-}(p){\longrightarrow}e^-(p') + \bar{\nu}_e(k')+\nu_{\mu}(k)$$ I want to write down the invariant matrix element for this process at tree level, ...
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Objects falling in a black hole [closed]

I was wondering : object approaching the event horizon of a black hole reach relative velocities ~ c ( But since the object has relative velocities of nearly c then its buildings blocks have ...
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Unpolarized muon decay rate and Feynman diagram trick

In class, while evaluating the unpolarized muon decay rate, in the Fermi theory (low energy limit) we got the result for the matrix element $$\frac{G^2_F}{2}\text{tr}\left[\gamma^\rho(1-\gamma_5)(\...
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Decay of electron? [closed]

Have we detected any decays of electrons to an electron neutrino and $W$-boson in Fermilab or in CERN? Are neutrinos the only possible stable leptons inside an electroweak field?
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Energies needed for massive particles to reach light speed, such as W/Z bosons at electroweak energy levels - limitation of special relativity?

I have learned that before 10^-32 s after the big bang, when the universe was at 10^15 degrees Kelvin, particles that carry the weak nuclear force, the W and Z bosons (which have mass), no longer ...
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Spin Four-vector of a polarized top-quark in its center-of-mass frame in a weak decay

I am very confused about how the spin-four-vector of a polarized top-quark in its center-of-mass frame should look like in a weak decay. Could you help me, please? The definition of the spin four-...
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Why do we know that the right-handed electrons exist?

I am wondering how come Weinberg and Salam put the right-handed electrons and did not put right-handed neutrinos* into the theory? In other words, are there any experimental/theoretical indications ...
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Would Majorana antinetrinos have opposite weak isospin?

There was a question about the difference between a neutrino and antineutrino, and answers suggested that weak isospin is different, as well as handedness. This would make sense if you expect pair ...
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Lower-dimensional analogues of electroweak interaction

Do there exist any models or theories of the 1+1 dimensional or 2+1 dimensional analogues of the standard 3+1 dimensional electroweak interaction theory?
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$e^{-}(p_1)+e^{+}(p_2) \longrightarrow H(k_1) + Z(k_2)$ propagator approximation

I'm considering the scattering: $$e^{-}(p_1)+e^{+}(p_2) \longrightarrow H(k_1) + Z(k_2)$$                   &...
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Why are the masses of $W^{\pm}$ and $Z^0$ different?

We know that through the Higgs phenomenon, the weak bosons become massive. In our Lagrangian the $W^\pm$ boson is usually defined as $\frac{1}{\sqrt{2}}(W^1_\mu\mp iW^2_\mu)$ and $Z^o$ is usually ...
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Glashow-Weinberg-Salam (GWS) Theory for Gauge Boson Masses

I am supposed to find the mass of the $W^\pm$ and $Z$ bosons from the following covariant derivative: $$D_\mu = \partial\mu - \frac{ig_1}{2}B^\mu -ig_2t^iW^{i\mu} $$ and from $\mathcal{L}_{kin. ...
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Choosing $Z$ particles from a simulator results

I am pretty new to particle Physics. As one of my first projects, I have run a simulation using MadGraph and Delphes. From the simulator result, I am trying to find Z particles produced in the ...
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What are the allowed $W$ bosons in Muon decay?

I am curious about the allowed Feynman diagrams in Muon decay and whether the $W$ boson can be either the $W^+$ or $W^-$. Muon decay follows the reaction: \begin{equation} \mu^-\rightarrow e^-+\...
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Why Higgs field need hypercharge to work?

I know that photon and gluon don't have any hypercharge so they can zip through higgs field at speed of light while left and right handed particles seems to communicate with these hypercharge, so then ...
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Gauge invariance for a Feynman diagram/set of diagrams in the Standard Model

As the question suggests, I am interested if there is a "rule of the thumb" (or some similar "trick") that allows one to tell which set of subgraphs in the Standard Model are gauge invariant. To be ...
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Charm prediction: Required electroweak or just weak?

Everywhere I look it up the prediction of the charm quark is predicted by the electroweak interaction, which of course recovers the weak interaction with the spontaneous symmetry break and the Brout-...
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Isovector Representation of $SU(2)$

In Electroweak Interactions by Renton (page 407) there is the calculation of matrix elements for electromagnetic interactions/weak interactions involving nuclei: A point of confusion for me is the ...
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When are W-bosons emitted?

According to this Wikipedia page W-bosons are involved in beta decay. According to Wikipedia, this occurs when a down quark turns into an up quark and also emits a W− boson. When this happens in a ...
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Self-interaction of gauge bosons in electroweak theory

As one learns in QFT, in Yang-Mills theories non-Abelian gauge transformations give rise to self-interactions of the gauge fields in the quadratic field strength term. In QCD this produces the 3- and ...
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Why does the Higgs boson have electroweak charges $~T_3~$ and $~Y_w~$ but does not have an antiparticle with opposite charges?

(Using $Q=T_3+Y_W$) The Higgs boson has weak isospin $T_3=-\cfrac12$ and weak hypercharge $Y_W=+\cfrac12$. Since every particle has all opposite charges of its antiparticle, why isn't there an anti-...
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Where does the extra mass of a $W$ boson come from in particle decay?

I’ve seen everywhere explaining that it can exist because of time/energy uncertainty. I get this. I understand that’s WHY it exists but I’ve still never gotten WHERE the extra mass comes from. Is the ...
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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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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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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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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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