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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 ...

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Hydrogen and the neutron

I have a question about Hydrogen and the neutron. So a neutral hydrogen atom has structure ${}^1H\equiv[p^+ e^-]$, a bound proton and electron. From a quantum theoretical viewpoint, one would write ...
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1answer
112 views

Is the right-handed electron really an $SU(2)$ singlet?

In the Standard Model, neutrinos are assumed to be massless, and the right-handed neutrinos thus do not exit. Is this the reason that the right-handed electron is regarded as an $SU(2)$ singlet? ...
2
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1answer
93 views

Why do we regard ($e^{-}, \nu_{e}$) as a doublet?

To my understanding, particles in a multiplet have similar properties (similar masses and so on) and slight or symmetric differences (in mass, electric charge, spin, and so on). They can be regarded ...
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49 views

How could particles with electric charge be massless before the electroweak symmetry breaking?

How could particles with electric charge be massless before the electroweak symmetry breaking? Wouldn't the energy stored in the electric field contribute to the mass of the particle?
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62 views

Relation between electroweak force and gravity? [closed]

I'm really stuck on the following idea. For gravity to in any way be 'unified' with the electroweak interaction wouldn't it need to include a model whereby the electron somehow tunnels to within the ...
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1answer
68 views

Equality of positron and proton charge problem statement

When I hear that the equality of positron and proton charge is an unsolved problem I assume that we are putting the electric charge by hand in the electroweak section of the SM Lagrangian. Is this ...
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20 views

Electroweak Force Capabilities

I understand that Electroweak force is the unification of Weak force and electromagnetism, but that are the actual effects or capabilities of this fundamental force? or at the very lease, what are the ...
2
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1answer
62 views

What happens when a neutron star loses enough mass to go under Chandrasekhar limit?

Say if a blackhole passes very close by a neutron star at high speed fly-by and eats half of the neutron star. What happens to the other half? Does it blow up in size as the electroweak force pushes ...
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66 views

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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88 views

Does the LHC see electro-weak symmetry breaking? [duplicate]

The energy scale of electro-weak processes is around $160$ GeV. But the LHC has a centre of mass energy of $7$ TeV... so do they see processes involving the $W^1, W^2, W^3$ and $B$ fields, before ...
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22 views

How would you explain the Higgs Mechanism to a kid? [duplicate]

I am currently studying the Electroweak Symmetry breaking and the Higgs Mechanism and I am wondering how could I explain it to a kid or my grandpa. How would you describe the mechanism and its ...
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39 views

Self-coupling Higgs boson and composite Higgs models

I'm currently doing my Bachelor Thesis about the Higgs boson and I've read that there are new models which describe the Electroweak Symmetry Breaking considering the Higgs boson as a composite ...
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0answers
29 views

First order phase transitions in cosmology

I am reading about Electroweak phase transitions in presence of singlet(under SU(2)$_L$) scalar particle. For this model, effective potential at finite temperature turns out to be $$ V(\phi,T)=D(T^2-...
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1answer
36 views

Elastic scattering of neutrinos on atomic electrons

In the elastic scattering of neutrinos on atomic electrons, why can tau and muon neutrinos only interact via weak neutral currents but electron neutrinos can interact with W or Z bosons?
2
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1answer
62 views

How do you know $W$ and $Z$ bosons are really bosons and not fermions?

It has been always said that $W$ an $Z$ bosons are bosons and not fermions but is there any experimental trial that prove that? Has anyone put two of them in the same quantum state or studies have ...
2
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1answer
69 views

$\tau \rightarrow \rho \nu $ relation with $ \rho \rightarrow e^+ e^-$

I'm reading "Okun, Leptons and quarks.", specifically subsection 13.3 "Semihadronic decays. General remarks." Okun says "The amplitude of the $\tau \rightarrow \rho \nu $ decay is related directly to ...
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1answer
74 views

ElectroWeak symmetry breaking and the early universe

I'm trying to piece together a coherent understanding of the EW symmetry breaking and its effect on early cosmology, from a number of somewhat incomplete sources. Any corrections to the following ...
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0answers
30 views

Fermionic CW potential unbounded below for large background?

I'm studying the Coleman Weinberg potential in presence of the background Higgs h. It seems to be well known that the CW potential goes like $(-1)^F m^4 \log(m^2)$, where $m^2$ is the background-...
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19 views

Monopoles from hypothetical Weinberg-Salam model with massless Z boson

We know that no monopoles exist in the Weinberg-Salam model (a good explanation is provided in the answer to this previous question). Now let us assume that the initial $SU(2)\times U(1)$ gauge ...
4
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1answer
122 views

Calculating $W$ - $Z$ bosons mass difference

Naively one might expect the W weak vector bosons to have slightly higher mass than the Z due to EM self-energy, while the opposite is true (80 vs. 91 Gev). Presumably due to the strong interactions ...
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2answers
151 views

Which $W$ boson is involved in electron capture?

I am learning about Electron Capture. $$p+e\to n+\nu_e$$ My question is whether the $W^+$ boson or the $W^-$ boson is involved in this transfer. I can consider this two ways: 1) Since the electron ...
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1answer
99 views

In electron-positron annihilation, why is photon exchange dominant at energies below the Z-resonance?

In a plot of the Z resonance from e+ e- collisions, why is photon exchange dominant below the center of mass energy below the Z peak?
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1answer
60 views

Weak hypercharge assignments in the Standard Model

While refreshing my memory on details of the Standard Model, I ran into a muddle. I might not exist to ask bizarre questions if the neutron, neutrino, and hydrogen atom were not electrically neutral. ...
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1answer
42 views

Weak isospin current

I cannot understand the product of a Dirac gamma matrix and a Pauli matrix in this formula of the weak isospin current: $$J_α^i(x)=\frac12\bar \psi_L(x)\gamma_\alpha\tau^i\psi_L(x),$$ where $γ_α$ is ...
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1answer
71 views

What Makes a $W$-Boson a Gauge Boson?

I understand that in beta decay, a quark changes its flavor and emits a $W$-Boson, and this $W$ (is the W Boson virtual, by the way?) quickly decays into an electron and an electron antineutrino or ...
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1answer
81 views

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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18 views

Interaction of the leptons before the electroweak phase transition

This question is related to this one: Form of Coulomb’s law before the electroweak phase transition. Given that the electromagnetic and weak forces were united before the electroweak phase transition ...
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1answer
194 views

What is the isospin of the photon?

As already mentioned in this Phys.SE post, the PDG booklet says that the isospin of a photon is $0,1$. Is it referring to the strong or to the weak isospin of the photon? What would be the 3rd ...
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57 views

SU(2) x U(1) weak model at high T

It has been shown that at very high temperature, of the order of (10 power 15) or something, electroweak SU(2) x U(1) model remains unbroken. Can anybody please point to some work on the phenomenology ...
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1answer
71 views

Form of Coulomb’s law before the electroweak phase transition

I’ve been thinking about the electroweak phase transition in the early universe, and I have some questions about the form of Coulomb’s law during that epoch. As I understand it, before the ...
2
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1answer
104 views

Total decay width of the W boson

I read in some particle physics book how they calculate the two body decays of the W boson, and then add all of them get the total decay width. I am wondering about other contributions, say, three ...
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1answer
59 views

Why is the Fermi coupling $G_F$ is measured from muon decay?

The decay rate of all weak processes, calculated from the $V$-$A$ theory will contain a factor of $G_F$, the Fermi coupling constant. However, $G_F$ is usually measured from $\mu^-$ decay which is in ...
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2answers
253 views

Calculation of the weak coupling constant

There are two ways to calculate the coupling constant of the weak interaction $g$. 1) From the electromagnetic coupling constant and the weak mixing angle, using the relation $${\sf e} = g\sin(\...
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3answers
281 views

$SU(2)$ to $U(1)$ symmetry breaking

Why does electroweak theory have $SU(2) \times U(1)$ to $U(1)$ symmetry breaking. Is it not possible to have simply $SU(2)$ to $U(1)$ symmetry breaking?
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1answer
164 views

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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1answer
152 views

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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32 views

Renormalization scale dependence of S, T parameter of Electroweak precision test

In Peskin, Takeuchi(1992) paper(link), oblique parameters S and T, U are defined as (Eqn 3.12) $\alpha S\equiv 4e^2[\Pi'_{33}(0)-\Pi'_{3Q}(0)], \\ \alpha T\equiv \frac{e^2}{s^2c^2m_Z^2}[\Pi_{11}(0)-\...
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158 views

Are Photons Goldstone Bosons?

I'm not interested in more speculative ideas, like the one of Bjorken et. al. that photons are Goldstones of broken Lorentz symmetry. Instead, I want to understand if photons are simply the ...
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1answer
53 views

Why can increasing energy, the weak force and the EM-force become a similar force?

When the heat of the universe was much higher it seems that the weak force and the EM-force was combined into the electro weak force. For a layman the EM-force and the weak force look quite different,...
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18 views

Is it possible that new forces will arise in future due to ongoing symmetry breaking? [duplicate]

Just after the big bang all forces seem to be united. Just a fraction of a second after the big bang, the electric force and the weak force appear to be one and the same. If I'm right, that was due to ...
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30 views

Why the rate of Z boson decays produce 3 generations of matter?

I read a tons of article about Z boson, I know it is a carrier of weak force similar to photon except it is much much more massive than an electron and it is extremely short lived. Sadly almost all ...
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1answer
98 views

Is the expression for CP asymmetry wrong in Wikipedia?

In the wikipedia page about neutrino oscillation (or ate least in the current revision), the CP-asymmetry is written as $$A^{(\alpha\beta)}_{\text{CP}}=P(\nu_\alpha \rightarrow\nu_\beta)-P(\bar{\nu}_{\...
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21 views

Splitting of Forces at Low Temperatures?

Since the electroweak force split from the strong force during the electroweak epoch then the electroweak force split into the electromagnetic and weak force during the quark epoch, is this an ...
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1answer
108 views

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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3answers
530 views

Could the electroweak spontaneous symmetry breaking explain dark matter and dark energy? [closed]

Electroweak spontaneous symmetry breaking is much harder for me to understand than the gluon-quark plasma phase transition. In the latter the physical laws remain the same and gluons and quarks just ...
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1answer
73 views

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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1answer
75 views

Why are the masses $m_{W}/m_{Z}$ and the coupling constants $e/g$ related in electroweak unification?

Gottfried and Weisskopf write in their book, in the chapter on electroweak theory, that $\frac{m_W}{m_Z} + \left(\frac{e}{g}\right)^2 = 1$ In this expression, $m_W$ and $m_Z$ are the masses of the $...
5
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1answer
136 views

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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3answers
207 views

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 ...
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0answers
22 views

Is it good approximation to use the Fermi theory in terms of proton and neutron for the given processes?

Suppose the processes $$ p+\gamma \to n + \bar{l} + \nu_{l}, \quad p+\gamma \to p+\bar{\nu}_{l} + \nu_{l}, $$ where $p$ denotes a proton, $\gamma$ - a photon, $l$, $\nu_{l}$ - a lepton and ...