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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How do the right-handed fermions acquire mass?

I am constructing a presentation on how elementary particles acquire mass via interaction with Higgs field. I asked this question previously in a different form and received the usual clap trap, so I ...
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12 views

Selection Rules in FCNC mediated diagrams

I am studying the flavour changing processes mediated by flavor changing neutral current (FCNC). Are there any selection rules involved in assigning the flavor to the outgoing quark? Can the ...
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1answer
43 views

Representation in $SU(2)_{L}\times U(1)_{Y}$

I'm reading the book "Massive neutrinos in physics and astrophysics" by R. N. Mohapatra and P. B. Pal, and have a question about its notation. The Equation 2.10, it says: $$ q_{L}=\binom{u_{L}}{d_{L}}...
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1answer
73 views

Generators of $SU(2)\times U(1)$

I'm currently reading about spontanous symmetry breaking. In particular about a Lagrangian that is invariant under $SU(2)\times U(1)$, in other words pretty standard QFT stuff. I know that the ...
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2answers
284 views

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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214 views

Why we unified electromagnetic and weak force?

We have unified electromagnetic and weak force into one single force called Electroweak force. I mean we can use these different forces within their respective domains like weak interaction for short ...
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58 views

Is it possible the weak force isn´t fundamental? [closed]

Once the strong force was thought to be a fundamental force mediated by the massive pion. Later colour and gluons were introduced. The old strong force was a residue force of the new fundamental force....
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1k views

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?
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125 views

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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1answer
121 views

Order of Feynman diagrams for electroweak processes?

I want to compare two Feynman diagrams and be able to say which one describes a process that is more likely to happen. As far as I understand, this is done by considering the order of the diagram. ...
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1answer
43 views

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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1answer
346 views

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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1answer
66 views

Difference between the CKM and the PMNS matrix

My question is very simple: is there a fundametal difference between the CKM (responsible for quark mixing) and the PMNS matrix (responsible for lepton mixing)? The CKM matrix allows (in charged ...
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2answers
242 views

Weak interaction violate charge conjugate

How can we show that the weak interaction violates the charge conjugation symmetry?
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61 views

$W^{++}$ / $W^{--}$ Bosons in theory and experiment

I wonder whether there is any theoretical interest in and/or experimental search for double charged bosons, probably to be called $W^{++}$ and $W^{--}$. The latter would obviously turn an electron ...
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2answers
61 views

Why $U(1)_Y$ hypercharge rather than $U(1)_\text{em}$ electromagnetism?

In the Standard Model we have $SU(2)_I\times U(1)_Y$, where $U(1)_Y$ is weak hypercharge and $SU(2)_I$ is the symmetry group of weak isospin. Why do we introduce $U(1)_Y$ of weak hypercharge rather ...
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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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31 views

Electroweak phase transition

Is it true that when the temperature of the universe was greater than ~200GeV the Higgs did not have any nonzero vacuum expectation value, hence all the particles were massless? So if one calculates ...
2
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40 views

Massless excitations without SSB

Is there possible the situation when there are massless excitations in spectrum of states in a theory with phase transition but without spontaneous symmetry breaking? The motivation for this question ...
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37 views

Why can an electric chargeless Z-particle decay in three photons?

The Z-particle that is supposed to convey the weak force has no electrical charge. So how is it possible the particle can decay in three photons. Because the weak and e.m. force are more or less ...
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1answer
20 views

Semileptonic decay of neutral D meson: branching ratios?

I am looking for the branching ratio of the semileptonic decay of the neutral $D^0$ meson: BR($D^0 \to \pi^+e^-\bar\nu_e$) = ? According to the PDG book the branching ratio for $D^0 \to \pi^-e^+\...
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18 views

Neutral pion mass correction from electroweak instantons

It is stated that the virtual process $$ \pi^{0}\to 2W \to \pi^{0}, $$ where $\pi^{0}$ is neutral pion and $W$ denotes $W-$boson, generates the small correction to the pion mass, namely $$ \delta m_{\...
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33 views

Electroweak instanton calculations

Consider an electroweak instanton in a model beyond the Standard Model with explicit baryon plus lepton number ($B+L$) violation. This instanton decays into nine quarks $q$ and three leptons $l$, ...
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3answers
126 views

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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3answers
69 views

How is each neutrino associated with a specific charged lepton?

For instance, why is an electron neutrino called that and what is its relationship with an electron?
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74 views

Why only left-handed neutrinos have been observed yet?

This is what I understood (it may be wrong, so please correct me): since every particle is "divided" into a lefthand and a righthand partner, which is what guarantees the particles to have mass, and ...
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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 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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74 views

Chiral symmetry breaking and confusion with terminology

I am confused about Chiral symmetry breaking and the terminology we use. First of all, I think the symmetry is started with taking quark masses zero and writing the Lagrangian as; $$ L=-\frac{1}{4}(F_{...
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449 views

Fundamental forces

I read @ http://m.particleadventure.org/electroweak.html Physicists concluded that, in fact, the weak and electromagnetic forces have essentially equal strengths. This is because the strength of the ...
2
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0answers
147 views

Feynman amplitude for electron-positron annihilation and $W^{\pm}$ production

I'm working with this interaction Hamiltonian density $$ H_{int}(x) = ig\bar{\Psi}_{\nu_e}(x)\gamma^\rho P_L \Psi_e(x)V_\rho(x) + igV^\dagger_\rho(x)\bar{\Psi}_e(x)\gamma^\rho P_L \Psi_{\nu_e} $$ ...
2
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34 views

Topological susceptibility of electroweak theta-term

Suppose EW theory generating functional: $$ Z[\text{sources}] = \int D(A,\psi,\bar{\psi}, H,H^{\dagger})\text{exp}\bigg[i\int d^{4}x\bigg(-\frac{1}{4g_{EW}^2}F_{EW}^2 + \bar{\psi}(D - m)\psi + DH^{\...
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29 views

Is the Electroweak theory chiral regardless of temperature?

Is the electroweak theory a chiral theory regardless of whether one is above the electroweak symmetry breaking temperature or not?
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475 views

Feynman rules for gauge bosons and Goldstone bosons

Does anyone know where I can find: gauge boson propagators (in an unfixed gauge) for the unphysical Electroweak gauge bosons $A^1_\mu$, $A^2_\mu$, $A^3_\mu$ and $A^4_\mu$ whose combinations give the ...
2
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1answer
135 views

CP-violation in weak and strong sectors

There is a possible CP-violating term in the strong sector of the standard model proportional to $\theta_\text{QCD}$. In the absence of this term, the strong interactions are CP-invariant. In the ...
3
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71 views

Is the right-handed antineutrino the CPT conjugate of the left-handed neutrino?

I am working from the book Massive Neutrinos in Physics and Astrophysics by Mohapatra and Pal (which is available here). On page 66, the authors claim that $\psi_{L}$ is the $\mathcal{CPT}$ conjugate ...
18
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2answers
477 views

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 ...
5
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1answer
186 views

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} ...
2
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1answer
39 views

Is the mass of the Z due to mixing with the photon “precursor” B or to interaction with the Higgs?

I want to get something clear that I do not seem to understand. I used to read that the photon A and the Z boson are (different) linear combinations between the W^0 (neutral weak boson before SU(2) ...
5
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1answer
117 views

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 ...
2
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1answer
82 views

Why are bare mass terms for W-bosons forbidden, but coupling terms to Higgs doublets allowed?

The $W$ bosons live in the adjoint rep of $SU(2)$, which is three dimensional. The standard model Higgs lives in a $SU(2)$ doublet, i.e. the two dimensional rep. The $W$ bosons get their mass ...
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1answer
49 views

Transformations of electroweak gauge field $W_\mu$ under $U(1)_{e.m.}$

As the vector boson field $W_\mu$ is, together with $Z^0$, the gauge field for the Standard electroweak model, I know it transforms as a connection under the $SU(2)\times U(1)_Y$ group. But, when this ...
5
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53 views

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 ...
3
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60 views

Matrix elements of four-quark operators [closed]

In weak interaction phenomenology, especially in strangeness changing processes, effective four-quark operators are used. Such as $Q_1 = (\bar{s}_\alpha \gamma_\mu (1-\gamma_5) d_\alpha) (\bar{u}_\...
2
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1answer
224 views

Why does the electromagnetic and weak coupling strength do not meet at the electroweak scale?

The running of the coupling strengths is usually visualized on a logarithmic scale like here What surprises me is that the weak and the electromagnetic coupling strength do not meet before the GUT ...
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50 views

Higgs mass and EW precision tests

I'm trying to understand how the Higgs mass can influence EW precision tests. In order to do that I'm using the following document (section 4.3): http://arxiv.org/pdf/0706.0684v1.pdf There are a ...
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149 views

Invariance under charge conjugation… Or not?

I have read some paper which says that the electroweak Lagrangian includes these terms like $\bar{\psi} \gamma_a\gamma_5\psi$ and $\bar{\psi} \gamma_a \psi$. They violate charge conjugation symmetry. ...
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28 views

Electroweak symmetry breaking with additional gauge group(s)

Is it possible that rather than the electroweak splitting into SU(2)xU(1), that there could instead of another gauge group in the dark sector? Suppose SU(2)xU(1)xSU(N)_d. Is that ruled out by the full ...
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142 views

About generator of $SU(2)$ flavor symmetry group

I am reading the textbook, "weak interactions" by Howard Georgi which can be founded in his homepage. Here i am trying to solve the problem 1b-2. The problem is given as follows. Consider the ...
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30 views

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants?

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants? If any, which (types of) ones? For the ones that do, what are the relations ...