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.

Filter by
Sorted by
Tagged with
1 vote
1 answer
82 views

How do massless particles have the same chirality and helicity when they are different properties?

I read this article about chirality and helicity. At some point it says For massless particles, chirality is the same as helicity. But as far as I know, helicity takes form in numbers, $(-1/2, +1/2)...
user avatar
1 vote
2 answers
66 views

Is there a law stating why a quark never decays weakly into a quark of the same weak-isospin ($T_3$)?

So I read multiple articles on weak isospin and one of them stated that "a quark never decays weakly into a quark of the same $T_3$". If this is true, can someone please explain what law ...
user avatar
0 votes
0 answers
41 views

Where does the Energy for $W$ and $Z$ Boson Emission come from?

I understand that the Weak interaction is mediated by the $W$ and $Z$ bosons, and that their huge masses are the reason for the Weak interaction's short range. However, I cannot find an explanation ...
user avatar
  • 329
2 votes
0 answers
36 views

What is the lagrangian interaction term of a charged current weak interaction?

For example, if you have an electron coupling to a $W^{-}$ and producing an electron neutrino $e\rightarrow \nu_{e}W^{-}$. Is something like $$\frac{-g_{w}}{2\sqrt{2}}\bar{\nu}_{e}\gamma^{\mu}W^{-}_{\...
user avatar
2 votes
0 answers
43 views

Resource of worked out examples of scattering amplitudes at one-loop for electroweak processes

Please suggest a book, notes, videos, etc where a few scattering amplitudes are worked out in (understandable) detail at one-loop in the standard electroweak theory. Feel free to recommend more than ...
0 votes
1 answer
41 views

In the unified electroweak theory, do the gauge bosons couple to right handed states?

In the weak interaction the gauge bosons couple to left handed chiral states only. When the two interactions are unified do the bosons couple to both left and right handed chiral states?
user avatar
0 votes
1 answer
72 views

Charged current $e^-e^+$ weak interaction Feynman diagram

I am new to the weak interactions and in particular to the interactions given by charged current interaction lagrangian $$ \mathcal{L}_{int}^{CC} = \frac{g}{2\sqrt{2}}\left[J^{\mu}W^{+}_{\mu}+J^{\mu \...
user avatar
0 votes
0 answers
37 views

Standard Model $\rho$ parameter with changing Electroweak gauge symmetry

In Standard Model Electroweak Theory (Governed by $SU(2)_L$ gauge symmetry), $\rho$ parameter is defined as $\frac{M_W^2}{M^2_{Z^0}\cos^2{\theta_w}}=1$. Where $M_W$ and $M_{Z^0}$ are the SM $W$ and $Z^...
user avatar
2 votes
0 answers
138 views

Does the theoretical prediction of the $W$ boson mass rely on the mass of the $Z$ boson?

Regarding the recent problem of discrepancy between theoretical and experimental value of $W$ boson mass: I do remember that standard model gives only a relation between $W$ and $Z$ mass and not a ...
user avatar
0 votes
1 answer
158 views

How could negative $W$ "eat" the positive Goldstone bosons $\phi_1$ and $\phi_2$?

In the Standard Model, the Higgs field is $\Phi=\left(\begin{array}{c}\phi^+\\\phi^0\\\end{array}\right)=\frac{1}{\sqrt{2}}\left(\begin{array}{c}\phi_1+i\phi_2\\\phi_3+i\phi_4\\\end{array}\right)$. ...
user avatar
2 votes
0 answers
67 views

Electroweak theory Landau pole

It is known that non-asymptotically free theories like Quantum Electrodynamics or Scalar field with quartic interactions ($\phi^4$) have a landau pole which mainly investigated through lattice ...
user avatar
  • 165
1 vote
1 answer
54 views

Are fields $B_{\mu}$, $W_{\mu}$ only before electroweak symmetry breaking (EWSB), and $\gamma$, $Z$, $W^{\pm}$ after it?

In the context of Lagrangian of Standard Model of particle physics, is the usage of the notation with $B_{\mu}$ and $W_{\mu}$ before electroweak symmetry breaking (EWSB), and the notation with $\gamma$...
user avatar
9 votes
2 answers
709 views

Why is the electron massless before interaction with the Higgs field?

Can't the electron have a mass before electroweak symmetry breaking, which is then just modified by its interaction with the Higgs field, instead of gaining all its mass this way? Apparently other ...
user avatar
  • 428
1 vote
2 answers
74 views

Why is the Fermi Constant sometimes listed in units of 'joule metre$^3$'? How is that related to its normal units of GeV$^{-2}$ or J$^{-2}$?

Normally, the Fermi Constant is valued as $1.1663787\times10^{-5}$ GeV$^{-2}$ or its equivalent in Joules. But on Rampfesthudson and Oxford Reference, it says, $1.435\times10^{-36}$ joule metre$^3$ I ...
user avatar
  • 3,441
2 votes
1 answer
90 views

Physical interpretation of changing phase around the Higgs potential

Disclaimer: I don't know much detail about the Higgs except for a few basic points. The field can be written as $$\phi(x) = \Phi e^{i\Theta(x)}$$ Which I took from the Wiki. I think I can see how the ...
user avatar
  • 1,412
1 vote
0 answers
78 views

Does the photon propagator see the $Z$ boson propagator pole?

As I understand, the $Z$ boson (as it decays) has a pole in its propagator that is somewhere in the complex plane, shifted off the real line. Now, suppose that I look at the full (interacting) photon ...
user avatar
  • 5,694
3 votes
2 answers
180 views

What does the "weak scale" mean?

In dark matter research, one of the properties of WIMPs is that "Interactions only through the weak nuclear force and gravity, or possibly other interactions with cross-sections no higher than ...
user avatar
0 votes
0 answers
47 views

Why do Higgs phase particles transform nontrivially under the gauge group?

In the electroweak theory, $SU(2)\times U(1)$ is Higgsed down to one of its $U(1)$ subgroups. The resulting theory consists of particles which have $U(1)$ charges. My understanding of gauge symmetry ...
user avatar
  • 3,294
2 votes
3 answers
233 views

Silly question on electromagnetism and electroweak interaction

Introduction So, consider the Maxwell action: $$S_{\text{Electromagnetism}} = -\frac{1}{4\pi}\int F_{\mu\nu}F^{\mu\nu}dx^4.$$ Then, consider the Electroweak action$[1]$: $$S_{\text{Electroweak}} = ...
user avatar
  • 2,679
0 votes
1 answer
39 views

How to convert a singlet current in electroweak theory to a doublet current?

I am referring to an aspect of Glashow-Salam-Weinberg theory of leptons. More specifically a step in the book 'Gauge Theory of Weak Interactions' by Walter Greiner page 147. We can write the ...
user avatar
0 votes
1 answer
33 views

Does stimulated emission also occur under the weak force?

Q: is stimulated emission only relevant for electromagnetic interactions through photons, or is it also valid for beta-decay? Example: Imagine an amount of tritium decaying in a strong beam of anti-...
user avatar
  • 213
0 votes
0 answers
34 views

How do you get the squared amplitude for the decay of the Higg's boson to W+ W- bosons from the matrix element?

I have the matrix element from the Feynman rules, but can't work out how to get to the squared amplitude summed over final spin states. Online sources seem to use some identities but never specify ...
user avatar
3 votes
0 answers
55 views

Homotopy group of $[SU(2) \times U(1)] / U(1)$ dependent on embedding of $U(1)$?

I have read, that the topology and thus the homotopy groups of $[SU(2) \times U(1)] / U(1)$ depend upon the embedding of $U(1)$ into $SU(2) \times U(1)$. For the Electroweak theory inside the standard ...
user avatar
1 vote
0 answers
33 views

Goldstone and longitudinal polarization equivalence between off-shell $W$s

If I understand correctly, the couplings of the longitudinal component of the $W$ and $Z$ bosons should be "equivalent" to the Goldstone bosons they ate after SSB. In practice, this makes ...
user avatar
0 votes
0 answers
64 views

When Higgs mechanism occurred ? Or it occurs everytime?

I’m studying SSB and the Higgs mechanism, and I’m having a few doubts about when Higgs mechanism occurred. From my knowledge, all particles were created massless, and they gain mass after SSB. What I ...
user avatar
  • 87
0 votes
1 answer
346 views

What, exactly, is the Fermi Constant? What is its value? And what is the difference between $G_f$ and $G_f^0$?

There is no Wikipedia page for Fermi's Constant, and the page they DO have is confusing. From Fermi's Interaction: How can $G_f^0$ not be equal to $G_f$? What is the difference? And when they give ...
user avatar
  • 3,441
2 votes
0 answers
142 views

Electroweak contribution to the anomalous magnetic dipole moment of the muon

There are 3 diagrams that contributes to the anomalous magnetic moment of the muon (in unitary gauge): The $Z$-contribution is gauge invariant, so we can focus on diagram (i) The problem is that when ...
user avatar
1 vote
0 answers
56 views

Does the weak interaction conserve both weak hypercharge and electric charge?

And if so whats the motivation for the introduction of hypercharge?
user avatar
  • 119
1 vote
2 answers
85 views

What is the official explanation of why the spin-1 $W^{\pm}$ Bosons having a magnetic moment?

How is it possible a spin-1 particle to ever have a magnetic moment? Is there any analytical solution to this?
user avatar
  • 2,986
1 vote
2 answers
110 views

Can the weak interaction be studied without bothering the electromagnetic one?

It is well known that the electroweak interaction can be studied as a $SU(2)_L \otimes U(1)_Y$ gauge theory. It is also known that the electromagnetic interaction is a $U(1)$ gauge theory, and it ...
user avatar
1 vote
0 answers
47 views

How does one usually deal with this kind of loop processes?

Now, I ask this because of the propagator of the inner line of the lepton going through a loop. Let's assume the initial Z has a momentum $p$, and the outgoing leptons have a momentum $p_1$ (for the ...
user avatar
2 votes
0 answers
49 views

Electroweak Precision Observables

I was reading some papers on electroweak theory. There I found the term "electroweak precision observables". My questions are the following: What are the electroweak precision observables? ...
user avatar
0 votes
2 answers
86 views

Behavior of the Electroweak Bosons

In an environment with high enough energy, the electromagnetic and weak interactions merge into a single electroweak interaction with 4 massless bosons; W1, W2, W3, and B. Would the three W bosons ...
user avatar
  • 419
4 votes
1 answer
130 views

If magnetic monopoles exist would magnetic charge contribute to weak hypercharge similar to how electric charge does?

Electromagnetism and the weak force are intertwined as two parts of the electroweak force and some links still exist even at low energy levels one of the being weak hypercharge which is determined by ...
user avatar
0 votes
3 answers
91 views

Why does beta decay of a free neutron not violate conservation of energy?

I apologize for gaps in my knowledge that may make this obvious, but shouldn't the emission of a W boson from a neutron violate conservation of energy? The mass of a neutron is 939.565 MeV/$c^2$, so ...
user avatar
1 vote
1 answer
51 views

Is the electroweak force similar in behavior to electromagnetism and the weak force or is it completely different?

Does the electroweak force govern particles in a similar manner to the electromagnetic and weak forces, and is therefore just an easy label or does it do something completely different? Also since it'...
user avatar
  • 419
0 votes
1 answer
83 views

The $3×3$ representation of weak $SU(2)$

I'm reading chapter 11.2 of the Cheng and Li textbook 'Gauge theory of elementary particle physics'. It says that $T_+$, $T_-$ and $Q$ do not form a closed algebra. In order to fix this problem the ...
user avatar
4 votes
1 answer
619 views

Is the discovery of the Higgs boson tantamount to discovering the Higgs mechanism?

Is the discovery of the Higgs boson tantamount to discovering the Higgs mechanism? I mean, it's clear by now that the Higgs boson is there, but what about the Higgs mechanism? How can we ever be sure ...
user avatar
2 votes
0 answers
50 views

Why is the $Z$ resonance cross section so much larger for hadrons? [duplicate]

The image shows experimental data for the ratio of cross sections $$R=\frac{\sigma(e^+e^-\rightarrow\text{hadrons})}{\sigma(e^+e^-\rightarrow\mu^+\mu^-)}.$$ I am wondering why $R$ is so large for the $...
user avatar
  • 1,287
0 votes
1 answer
59 views

SSB In Electroweak Theory

I know that when vacuum state does not remain invariant under generators of lagrangian group symmetry, we have SSB in our theory: $$ U_{a} | 0 \rangle‎ = |0\rangle‎ \Rightarrow T_{a} | 0\rangle‎ = 0 \...
user avatar
0 votes
0 answers
53 views

Is electroweak symmetry breaking equivalent to the non-zero Higgs VEV?

In the Wikipedia article on the electroweak interaction, they show the Lagrangian before and after symmetry breaking, and to my untrained eye they look totally different, in part because the 4 gauge ...
user avatar
  • 1,383
3 votes
0 answers
52 views

The Higgs mass at the electroweak phase transition (EWPT)

I have heard that the EWPT in the Standard Model ($m_h=125$ GeV) is a cross-over transition, i.e. no discontinuity in the order parameter. However what happens to the Higgs mass at the critical ...
user avatar
4 votes
1 answer
173 views

Is it accidental or deeply meaningful that the Higgs and the left-handed lepton have the same quantum numbers?

Is it accidental or deeply meaningful that the Higgs and the left-handed lepton have the same quantum numbers? Precisely, under $SU(3) \times SU(2) \times U(1)$: the Higgs has the quantum numbers: ...
user avatar
3 votes
1 answer
61 views

Does Hawking Radiation emitted by a black hole surrounded by an electroweak plasma differ from normal Hawking Radiation?

The pdf at arxiv.org/abs/hep-ph/0104160 is about the electroweak plasma surrounding a small black hole of around 700 kg mass. A radiated electron passing through the electroweak layer surrounding the ...
user avatar
0 votes
1 answer
52 views

Are these diagrams the same?

When computing the propagator of the $Z$ boson at one-loop level in the Standard Model, should we consider both of these two diagrams (where $\varphi^\pm$ are the charged Goldstone bosons) or are they ...
user avatar
  • 143
0 votes
0 answers
45 views

Higgs U(1) charge and the isospin operators

So if the higgs field $h=(h^+,h^0)$ is at its vev (up to a gauge choice) with $\langle h\rangle =\frac{1}{\sqrt{2}}(0,v)$, then in turn you can show $$I_{1}\langle h\rangle=\frac{\sigma_1}{2}\langle h\...
user avatar
  • 459
5 votes
1 answer
357 views

A Doubt on Covariant Derivatives and Particle Physics

So, for me at least, if you understand well why a covariant derivative is defined the way it is presented to you, then $25\%$ of conceptual work is done. I mean, with covariant derivatives (in General ...
user avatar
  • 2,679
4 votes
1 answer
155 views

Standard model notation on doublets

$\require{cancel}$ I have been introduced to electroweak theory in lectures and I wanted to check I understand the notation for the doublets, triplets etc. Take the first generation lepton left handed ...
user avatar
1 vote
0 answers
45 views

What are the implications of violation of the unitarity of CKM matrix?

What are the physical implications of such observation? In other words, why is everybody concentrating on the violation of the unitarity of the CKM matrix?
user avatar
0 votes
0 answers
264 views

Obtating the Fermi Coupling Constant from expeced muon decay

I recently performed a lab where we found the expected muon lifetime as $\tau = 2.02$ microseconds. I am now supposed to use this value to obtain the Fermi Coupling Constant $G_F$, by using the ...
user avatar
  • 155

1
2 3 4 5
7