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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Why is there no theta-angle (topological term) for the weak interactions?

Why is there no analog for $\Theta_\text{QCD}$ for the weak interaction? Is this topological term generated? If not, why not? Is this related to the fact that $SU(2)_L$ is broken?
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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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What happens to matter in a standard model with zero Higgs VEV?

Suppose you reset the parameters of the standard model so that the Higgs field average value is zero in the vacuum, what would happen to standard matter? If the fundamental fermions go from a finite ...
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Why is the Symmetry Group for the Electroweak force $SU(2) \times U(1)$ and not $U(2)$?

Let me first say that I'm a layman who's trying to understand group theory and gauge theory, so excuse me if my question doesn't make sense. Before symmetry breaking, the Electroweak force has 4 ...
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Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism?

A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four ...
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Hypercharge for $U(1)$ in $SU(2)\times U(1)$ model

I understand that the fundamental representation of $U(1)$ amounts to a multiplication by a phase factor, e.g. EM. I thought that when it is extended to higher dimensional representations, it would ...
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Phase factors under rotations of strong and weak isospin

The strong isospin raising operator changes a $d$ quark into a $u$: $$ \tau_+ \big|d\big> = \big|u\big> $$ However, for antiquarks, there is an additional phase factor: $$ \tau_+ \big|\bar u\big&...
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Are there really left-chiral particles?

A chiral eigenstate is always a linear combination of a particle and an antiparticle state and a particle or antiparticle state is always a linear combination of chiral eigenstates. Now, how can we ...
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How do we know we've unified two interactions?

What is the precise definition of unification of fields (in classical and quantum mechanics)? In general, does unification of a field mean that we can write both of them at both sides of an equation (...
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How many kinds of “weak charges” exist?

For electricity, we have one charge, for the strong force three. How many are there connected to the weak force? Three, because of the W- and Z-particles? For the weak force, there is the isospin, ...
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Are all fermions massless at high temperatures?

According to the standard model, the electroweak symmetry is unbroken at high temperatures, and therefore all gauge bosons are massless then. But since fermions are said to acquire mass by a different ...
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What did electroweak symmetry breaking actually look like?

Approximately one picosecond after the Big Bang, the universe cooled down enough to pass through the electroweak phase transition. At this point the Higgs mechanism kicked in, the weak force became ...
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temperature of electroweak phase transition

How does one estimate the temperature at which electroweak phase transition (EWPT) occurred? Somewhere I have read it is around 100GeV but the reason was not explained.
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Is there a “difference” between photons that act as virtual particles and photons that act as the quanta of EM radiation?

I) I know that virtual-photons are known to be the force-carriers for the Electromagnetic force, and that they are called "virtual" because the Energy-Time-inequality version of the Heisenberg ...
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How was the electroweak force operating/acting in the early universe?

In the early universe the temperature was high enough for the electromagnetic force and weak force to act as one. My question is how exactly does that work, because the weak force uses the W and Z ...
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Coupling constant in electroweak theory

Electroweak theory has two coupling constants before and after Spontaneous Symmetry Breaking (SSB) each one for $SU(2)_L$ and $U(1)_Y$, though they are connected by Weinberg angle after SSB. My ...
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No monopoles in the Weinberg-Salam model

I'm reading Chapter 10.4 on the 't Hooft-Polyakov monopoles in Ryder's Quantum Field Theory. On page 412 he explains why magnetic monopoles cannot appear in the Weinberg-Salam model. I'm I right by ...
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What's the isospin of photons?

What's the isospin of photons? Why PDG book says $0, 1(1^{--})$ for its $I(J^{PC})$? What does $0, 1$ mean here? Is it that the isospins aren't determined and can be 0 or 1?
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Very short decay: A bare quark?

I keep reading the same phrase about the very short life time of the top quark: Because the t-quark decays on a shorter than the characteristic QCD interaction-time it cannot hadronize. ...
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CP violation from the Electroweak SU(2)$_{weak,flavor}$ by $\int \theta F \wedge F $

Question: Why there is NO Charge-Parity (CP) violation from a potential Theta term in the electroweak SU(2)$_{weak,flavor}$ sector by $\theta_{electroweak} \int F \wedge F$? (ps. an explicit ...
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What is the rate of B violation expected in the standard model during high energy collisions?

In a recent question Can colliders detect B violation? I asked about detecting B violation in collisions. Here I am interested in the theory aspect. (I asked both questions originally in the same ...
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Georgi-Glashow model and the VEV of the scalar field

Consider the Georgi-Glashow model, an $SU(2)$ gauge theory with a real scalar in the adjoint (thus a 3-vector in the colour space) $\phi$. The Lagrangian is $$ L = -\frac{1}{4g^2} F_{\mu \nu}^{\, a} ...
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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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Changing the hypercharge of the Higgs field

I'm trying to solve a question about the Higgs mechanism: If the hypercharge of the Higgs were to be $Y=1$ (Changing from $Y=1/2$ ), what would be the photon of this world? Meaning, how can I ...
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Unification of Weak and Electromagnetic forces

I'm curious how the weak and em forces relate to one another. My knowledge in this area is weak (ha) but I am interested in an explanation for how these two forces relate to one another, and how / why ...
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Jarlskog Invariant and its mathematical origin

CP violation is present in the weak interactions if There are no degeneracies in the up-quark/down-quark matrices The Jarlskog invariant $J=Im(V_{us} V_{cb} V_{ub}^* V_{cs}^*)$ is nonvanishing ...
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2x2 Representation for triplet Higgs

I am perplexed by the $2\times2$ representation of the Higgs that one finds in Higgs triplet models and Left-Right symmetric models. If $\vec{\phi}=(\phi^{++},\phi^{+},\phi^{0})\in(3,0)$ is the ...
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Derivation of neutrino oscillation phase factor

As we know, the neutrino $\nu_{\alpha}$ with flavor $\alpha=e,\mu,\tau$ is a linear combination of mass eigenstates: $$ |\nu_{\alpha}\rangle=\sum_iU_{\alpha i}|\nu_i\rangle,\quad i=1,2,3 $$ where the ...
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Semileptonic decays of the $B_c$ meson

I am struggling with calculating the exclusive semileptonic $B_c^+\rightarrow J/\psi l^+\nu_l$ decay. I learnt that the amplitude is given by a product of the leptonic current $L^{\mu}$ and the ...
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Higgs boson mass and electroweak energy scale

Is it a coincidence that the mass of the Higgs boson is exactly half the electroweak energy scale?
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Weak isospin and types of weak charge

My understanding is that QCD has three color charges that are conserved as a result of global SU(3) invariance. What about SU(2) weak? Does it have two types of charges? What I'm getting at is: U(1) -...
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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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Would life (as we know it) be possible without the weak interaction?

I understand why the strong interaction is important in everyday life (it holds nuclei together and also allows the fusion reactions that power the Sun) and also why the electromagnetic interaction is ...
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Are electroweak particles stable?

Photons that [are associated with] the electromagnetic force are stable; while the W and Z bosons that [are associated with] the weak force are short lived. I guess that the high temperate electroweak ...
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Majorana Mass For Neutrinos In Standard Model

Neutrinos cannot have Dirac masses because there are no $SU(2)_L$ singlet right-handed neutrinos in the Standard Model (SM). But can neutrinos be given Majorana masses in the SM? I heard that Majorana ...
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If neutrons aren't affected by electromagnetic force, what causes it to bounce off matter?

Say a neutron is heading for a mountain, what would cause it to bounce off said amalgamation of matter? Electromagnetism is ruled out, gravity is too weak, (if I'm not mistaken) nuclear strong force ...
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Is Higgs mechanism necessary in QCD?

As we known, we introduce Higgs mechanism into Standard model to explain mass of Gauge boson, lepton and neutrino(maybe?). Higgs mechanism is necessary for electroweak theory because gauge symmetry ...
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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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Electroweak interaction: From $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ to $W^{\pm},Z_{\mu},A_{\mu}$

EDIT: Additional question at the end I am trying to illuminate how the "unphysical" gauge bosons $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ will be the "physical" $W^{\pm},Z_{\mu},A_{\mu}$ when ...
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QCD pion and electroweak symmetry breaking

Equation (28.33) in Matthew Schwartz's QFT text book $$ \mathcal{M}(\pi^+ \rightarrow \mu^+ \nu_\mu) = \frac{G_F}{\sqrt{2}}F_\pi p^\mu \bar{\psi}_{\nu_\mu}\gamma^\mu(1-\gamma^5)\psi_\mu \tag{28.33} $$ ...
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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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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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Higgs Mechanism

In Higgs mechanism, we take the combination of LH $SU(2)$ doublet and RH singlet along with Higgs doublet so that the overall weak hypercharge and weak isospin is zero to be $SU(2) \times U(1)$ ...
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Why are $W$ bosons massless above electroweak scale? [duplicate]

Because of the Higgs mechanism, one must replace the Higgs field $\phi$ with $\phi_0 + \phi_1$ where $\phi_0$ is the vacuum expectation value. As far as I understand, the $\phi_0$ gives the mass term ...
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If weak isospin is not conserved in time, what does the Noether theorem tell us?

As far as I understand weak isospin is only conserved in interactions but not as time evolves. Nevertheless, we get from Noethers theorem, because of global $SU(2)$ invariance a conserved quantity ...
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Is the search for a Simple-group-based Electro-Weak theory over?

Just wondering: We know that, in its current form of the $SU(2)_L\times U(1)$, the electroweak theroy rides a wave of huge success. However, is it not possible that the correct simple group ...
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How it is possible to mediate a weak interactions by very heavy particle such as Boson?

When considering a weak decay interaction such as leptons , the weak force is mediate by huge particle such as bosons (W+ or W- ). How it is possible to have a such heavy particle within less massive ...
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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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Do any good theories exist on why the weak interaction is so profoundly chiral?

I find the profound asymmetry in the sensitivity of left and right chiral particles to be one of the most remarkable analytical observations captured in the Standard Model. Yet for some, I've not ...
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Why do weak interactions exclude gluons?

Weak interactions seem the most universal after gravitation. A very few particles avoid them, only the photon and gluon, plus right leptons. The photon, however, is a part of the electroweak ...