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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Physicality of electroweak bosons

The energies achieved at modern particle accelerators are much higher than the all scales relevant to the electroweak unification. I was therefore wondering why what is measured at scattering ...
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What happened to particles with less energy than their rest mass?

Today, particles like electrons can only be created if there is enough energy that exceed their corresponding rest-mass energy. As far as i understand, all particles were massless before the higgs ...
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Could the low Higgs mass be relevant to the unification of the (weak) nuclear force and gravity?

I found in a paragraph in a research paper (although it was talking about something else) the statement: that it is possible to unite the weak nuclear force and gravity, but that requires that: Both ...
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Why does the photon not see electroweak symmetry breaking?

So I watched this video where it mentions that in the Higgs mechanism, massless particles fluctuate in the azimuthal direction and massive particles fluctuate in the radial direction, causing them to ...
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Why are there more opposite sign events than same-sign ones in the QCD background of three-prong tau decays?

So im dealing with three-prong tau decays. Specifically, two taus are produced via the Drell-Yan process and one decays leptonicly into a muon and the other decays hadronicly into three charged pions (...
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What does $SU(2)\times U(1)$ really mean?

I know that $SU(2)\times U(1)$ is the product of each element of $SU(2)$ by an element of $U(1)$. But looking at the Lagrangian, such a product exists only in covariant derivatives of Higgs or fermion ...
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Can there be bound states of two $Z$ bosons or of a $W^+$ and a $W^-$ boson? [duplicate]

Obviously, the Z and W are extremely short-lived. But could they form bound states? Such bound states would be the weak analogon of glueballs. Have they been studied? Or is beyond-standard-model ...
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Deriving the charged pion decay matrix element

From M Schwarz's QFT (p 570), Goldstone's theorem indicates that pions are created from the vacuum by the chiral ${\rm SU}(2)$ current $J_\mu^{5a}$, $$ \langle \Omega| J_\mu^{5a}(x)|\pi^b(p) \rangle =...
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Which particles do $W$ bosons interact with to gain mass?

Which particles interact with $W$ bosons to give them mass? I am aware that Higgs particles alone are not responsible for the mass of other particles. In non-mathematical terms which particles give ...
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Evidence of neutral weak currents

Why is muonic anitneutrino, electron scattering an experimental evidence of the existence of neutral weak current? This is $\bar{\nu_{\mu}}+e^-\to \bar{\nu_{\mu}}+e^-$. And why the electron ...
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Antimuon-electron interaction

I was wondering if the following interaction is possible: $\mu^++e^-\to \bar{\nu_{\mu}}+\nu_e$ Clearly every conservation law is satisfied, including each lepton number conservation, but I can’t seem ...
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Have the $W_0$, $W_1$, $W_2$ and $B$ bosons of Electroweak fame ever been discovered experimentally?

I have read that the LHC, and perhaps other collides, have reached so-called electroweak energies, where the two forces are unified.... So how much energy, exactly, is needed to produce fields/...
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What is the effect of top quark on Flavor Changing Neutral Current (FCNC) suppression?

We know that the introduction of charm quark (GIM mechanism) suppresses Flavor Changing Neutral Current (FCNC) decays occuring via Electroweak box and penguin diagrams. But we have another doublet of ...
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Why do we need a cubic term in the Higgs potential to have a first-order electroweak phase transition?

When talking about the first-order electroweak phase transition, it is often said in the literature that we need a cubic or linear term in the scalar potential to render the transition first order. Is ...
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Hypercharge and photon definitions in $SU(5)$ GUT

So, a weak isospin and hypercharge in $SU(5)$ are defined as $$ T_3 = \frac{1}{2}diag(0,0,0,1,-1) $$ $$ Y = \sqrt{\frac{3}{5}}diag(-1/3,-1/3,-1/3,1/2,1/2) $$ The hypercharge already has the $\sqrt{3/5}...
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Chirality in muon decay

Consider the muon decay process: We assign the chirality according to the $W$ boson current: (i.e. P&S eq.(20.80)) $$J_W^{\mu+}=\frac{1}{\sqrt{2}}\bar{\nu}_{\mu L}\gamma^{\mu}\mu_L \quad J_W^{\mu-...
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What is the connection between the electroweak energy scale and the vacuum expectation value?

I am quite confused about energy scale and vacuum expectation value (VEV). For example, this wiki page says 246Gev is VEV of Higgs field. Does it mean if we go to a higher energy scale (like 24600Gev)...
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Transverse momentum of $W$ boson decay products

This paper on top-antitop events (ATLAS, 2014) states (page 11, 3rd paragraph) that Because of the $V$−$A$ structure of the $W$ boson decay, down-type jets have on average a lower $p_\mathrm{T}$ than ...
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Lagrangian formalism for boson mass

Why for charged boson, it's mass term is $m^2 W^+_{\mu}W^{-\mu}$? While for neutral boson, it's mass term is $\frac{1}{2}m^2 Z_{\mu}Z^{\mu}$. (Is their a mathematical reason that charged boson mass ...
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Do quarks oscillate via Charged Weak Interaction (CKM Matrix)?

In the Standard Model, with the introduction of the CKM matrix, we have that quark mixing between different generations is possible via a charged current (W boson). My question is if this also implies ...
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Theory of weak interactions

Why don't we have a theory solely of weak interaction, like QED or QCD? I.e $SU(2)$ gauge theory describing neutrinos and massive $W^{+-}$ bosons. But instead we have a unified electroweak theory ...
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Why are these loop diagrams involving Goldstone bosons cancelling one another in the zero-momentum limit?

I have been working with one-loop corrections to certain processes. Let's say, corrections to the $Z\bar{f}f$ vertex. Of, course I need to consider the following diagrams: Here $\phi^{\pm}$ is the ...
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Weinberg mixing angle matrix for photon and $Z$ bosons

I'm currently studying the GWS-model and am a bit confused with the matrix (def. via the Weinberg mixing angle) "mixing" photon and $Z$ boson mass eigenstates. It is defined as $$ \begin{...
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Is there a probability that a neutrino and anti-neutrino transform into two photons?

A neutrinos and an anti-neutrino can meet, form a virtual $Z^0$, which subsequently can create a new pair of leptons. Now, an electron-anti-electron pair can do the same, but they can create two ...
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What are the differences between electroweak interactions before and after unification?

I am very confused by this point, although its mathematical description is not hard. I still cannot see how these two theories are "unified", which term in lagrangian indicates this ...
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how can the virtual fermionic lines be vertical in kaon mixing feynman diagram?

how can the virtual fermionic lines be vertical in kaon mixing Feynman box diagram (or in general)? Wuouldn't this mean that they travel a distance $\neq 0$ in 0 time?
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Color confinement vs. Weak charge confinement

Sometimes, color confinement is explained loosely by stating that the gauge group of QCD, namely SU(3), is non-abelian gauge group and, therefore, tends to form narrow "flux tubes" through ...
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Mathematically, why does spontaneous symmetry breaking occur?

I think that: the Higgs potential is a function $$V: \mathbb{C}^2 \times (0, \infty) \longrightarrow \mathbb{R},$$ where the parameters $(0, \infty)$ are the energy scales. Then, for each $E \in (0, \...
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Is it true that even-spin bosons give rise only to attractive forces? [duplicate]

In the standard model, electroweak and chromodynamic interactions are modelled as Yang-Mills fields. It also happens that the electroweak field is mediated by spin 1 vector bosons, and this leads to ...
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$Z$-boson discovery by observing a peak in the $e^+e^-\to\mu^+\mu^-$ amplitude at $s=M_Z^2$ when the Z-boson is virtual?

Apologies if this question sounds dumb. The contribution to the amplitude of $$e^+(k_1)e^-(k_2)\to\mu^+(p_1)\mu^-(p_2)$$ scattering, mediated by the virtual $Z$ boson, is proportional to the quantity $...
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Can we derive the formula $Q=I_3+\frac{1}{2}(B+S)$ instead of accepting it as an empirical relation?

The electric charge of a quark or lepton, $Q$, is related to the third component of the weak Isospin $T_3$ and weak hypercharge $Y$ according to the formula $$Q=T_3+\frac{Y_W}{2}.\tag{1}$$ This, in a ...
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Was combing gauge fields into photon and $Z$ boson already considered before incorportating Higgs mechanism in Standard Model?

Before physicists had the idea to incorporate the Higgs mechanism in the Standard Model, was there already the idea to combine the gauge fields $B_{\mu}$, $W_{\mu}^1$, $W_{\mu}^2$, $W_{\mu}^3$ into $$...
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How is it possible for $W$-boson to be so heavy when neutron and proton have similar mass? [duplicate]

I know that in a beta decay a neutron turns into a proton and a $W$-boson. I know that a $W$-boson is very heavy, so I intuitively expect the proton to by much lighter than neutron — I would expect ...
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How (if) are the Higgs scalar and the $W/Z$ vectors related (apart from interaction)?

An idea popped up in my mind. There are three vector bosons, the two charged $W$-particles, and the $Z$-particle, all three with spin 1. Is the Higgs particle, having spin 0, related to them, apart ...
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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, $(-1/2, +1/2)...
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Is there a law stating why a quark never decays weakly into a quark of the same weak-isospin ($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 ...
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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 ...
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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^{-}_{\...
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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 ...
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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?
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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 \...
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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^...
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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 ...
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How could negative $W$ "eat" the positive Goldstone bosons $\phi_1$ and $\phi_2$?

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