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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58 views

Why was the $Z$-boson first theorized? What problem did it solve?

I have looked around, but I can't find a single (or simple-ish) explanation as to why the $Z$-boson was first dreamed up by theorists, years before it was discovered.
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Does the Kalb-Ramond field lead to electroweak force?

String theory predicts the following massless fields: $G_{\mu\nu}(X)$, $B_{\mu\nu}(X)$ and $\Phi(X)$. I understand that when one reduces to $4$-D then the $G_{\mu\nu}(X)$ is the spin-$2$ field of the ...
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Do the strong and weak nuclear forces also travel at the speed of light?

Among the four fundamental forces, it is now pretty well-known that the electromagnetic and gravitational ones travel at the speed of light. How about the other two (strong and weak nuclear forces)? ...
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51 views

Meaning of “unification of interactions”

What do we exactly mean when we speak about "unification of two interactions" or say "the electromagnetic and weak interactions are unified"? Wikipedia states that: the ...
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Feynman diagram of Higgs production by $gg$-Fusion

I am slowly going to develop intuition for dealing with Feynman diagrams but have a couple of problems understanding the following Feynman diagrams representing the Higgs production via gluon-gluon ...
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What is the value of electromagnetic coupling at the energy where it merges into electroweak couplings?

It is known that its zero-energy value is the fine-structure constant α, about 1/137.036. Various sources state that the running value is in the 1/129-1/127 range at the Z-boson energy (91 GeV). ...
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62 views

Can we infer from weak isospin symmetry the existence of sub-quark particles?

In the old theory of the strong force, where the strong force was thought to be conveyed by massive mesons (pions), as one can read here: The discovery of the neutron in 1932 revealed that atomic ...
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Magnetic Monopoles and the Inflationary Epoch

What leads to magnetic monopoles existing before the Inflationary Epoch and becoming infinitely diluted during inflation (if indeed that is the explanation to their absence), but the electric ...
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46 views

$U(1)_Y$ coupling costant and hypercharge arbitrariness in Electroweak unification

When trying to unificate $SU(2)_L$ and $U(1)_{em}$ one introduces and extended Gauge group with the direct product $SU(2)_L \times U(1)_Y$, where are introduced the concepts of hypercharge $Y(\psi)$, ...
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What would happen to the physical photon if the electroweak symmetry were to be restored?

Suppose the Higgs field goes back to its initial unstable state, as it was before electroweak symmetry breaking. Or, in other words, suppose the electroweak symmetry is restored. Since, the physical ...
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What is the usual method by which the 'freeze-out' temperature of the early universe is calculated?

I am trying to work through a derivation (for part of my thesis) to calculate the thermodynamically 'expected' baryon-to-antibaryon ratio ($\sim 10^{-19}$) that is often referenced in cosmology talks, ...
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Other type of “hadronization” if the electroweak force would be stronger?

Let's suppose that we have no symmetry breaking and the electroweak bosons remain massless (the W, Z and the photon). Let's also suppose that the coupling constants of SU(2) and U(1) are of the order ...
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Why are electric monopoles not interpreted as topological defects but magnetic monopoles are?

What explains this asymmetry between the electric and magnetic fields if both electric and magnetic monopoles exist? Can't Maxwell's equations be formulated to be symmetric between the two in the ...
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Fermion masses and $SU(2)$ symmetry

Why is the standard mass (Dirac) not compatible with $SU(2)$ symmetry? I consider the standard mass this $$ m\bar{e}e = m(\bar{e}_Le_R+ \bar{e}_Re_L)$$
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Are weak force particle transformations continuous or instantaneous?

The weak force transforms particles from one type to another. What can we say about the transition? Take this as an example: In the discrete view: Before junction A there are 2 up quarks and one ...
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Does Goldstone-boson absorption by $W$ and $Z$ bosons mean that their masses are stochastic?

I have heard it explained that a complex doublet scalar field produces the Higgs boson, and also three Goldstone bosons which are absorbed by $W$ and $Z$ bosons, giving them mass. Does this mean that ...
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Why should the electroweak Lagrangian have an $\rm SU(2)$ invariance?

The QED Lagrangian has a $\rm U(1)$ invariance so as to preserve electric charge, which has been empirically demonstrated to be conserved. The QCD Lagrangian has a $\rm SU(3)$ invariance so as to ...
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Electroweak Unification and Electroweak scale

We said that the EM and weak interactions are unified as Electroweak Unification. However, for usual Grand Unification, it requires that the gauge group G is simple Lie group -- which means the G has ...
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Mistakes in the Wikipedia figure on elementary particle interactions

There are some mistakes I think in the figure of Wikipedia on particle interactions in standard model: https://en.wikipedia.org/wiki/Mathematical_formulation_of_the_Standard_Model#...
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What is the relative strength of the weak force?

When comparing the weak gauge coupling to the electromagnetic gauge coupling (fine structure constant alpha) textbooks give the value ("relative strength") 10^-5 or the value 10^-13. Why are ...
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Why is gravitational wave production in early Universe disfavoured for 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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129 views

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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133 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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41 views

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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1answer
96 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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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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1answer
84 views

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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1answer
79 views

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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1answer
39 views

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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