Questions tagged [standard-model]

A model of the basic particles and forces featuring six quarks, three charged leptons, three massless neutral leptons and four fundamental force carrying bosons. The twelve fermions are arranged into three generations, while the bosons serve to explain the electromagnetic interaction plus the strong and weak nuclear forces (and the Higgs mechanism). Do NOT use this tag for the standard model of cosmology, etc..

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81 views

Why are semileptonic decays of the $\Lambda$ baryon so suppressed?

Looking at the Particle Data Group tables of the $\Lambda$ baryon, I find that the rate of the hadronic decay $\Lambda \to p \pi^-$ is 64% while the semileptonic decay $\Lambda \to p e^-\nu_e$ has the ...
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Why are the lifetimes of the neutral and charged $\Xi$ hyperons so different?

According to the Particle Data Group, the lifetimes of the neutral and charged $\Xi$ baryons differ significantly: $\tau(\Xi^-) = (1.639 \pm 0.015) \times 10^{-10}$ s, while $\tau(\Xi^0) = (2.90 \pm 0....
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What is the sign of Weinberg angle?

One has $\cos{\theta_W}=m_W/m_Z$, and $\sin^2{\theta_W}=1-(m_W/m_Z)^2$ Is the sign of the Weinberg angle defined or an important quantity? If yes, are there constraints?
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Do fermions have groups like how gauge bosons have gauge groups?

As I understand it, the Lie groups $U(1)$, $SU(2)$, and $SU(3)$ correspond to the electromagnetic, weak, and strong forces respectively (ignoring electroweak mixing) and the generators of their ...
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How to represent graphically the relationship of $Z$ and $\gamma$ to $W_3$ and $B^0$?

How to represent graphically the relationship of $Z$ and $\gamma$ to $W_3$ and $B^0$ ? I made these two schematics below, but I'm not sure which one is correct, nor if we we should put $W_3$ or $B^0$ ...
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The charge of an electron is a constant. In any case? [closed]

Since Millikan it is obvious that the charge of the electron can be measured as a result of the force exerted by an external electric field. What we get in detail is the charge from the excess of ...
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What is the value of electroweak scale? Depends on literature?

Depending on the literature, we see for the electroweak scale the following typical values : 100 GeV, 125 GeV (Higgs mass), 246 GeV (vev), 1 TeV So what is really the value of electroweak scale?
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How many elementary particles are predicted by Wigner's classification?

My understanding is that when it comes to the correspondence between representation theory and particle physics, every irreducible representation of the Poincare group has a corresponding fundamental ...
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37 views

Conservation of left-handed quark current

I'm reading about the Operator Product Expansion in Gelis's A Stroll Through Quantum Fields section 7.4.2. As an example, he's using the product of currents $$A_1^\mu = \overline{d}_L\gamma^\mu u_L$, ...
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Is the analytical dependence of the theoretical Higgs potential with temperature known?

At the very beginning of the unvierse, the Higgs potential had a paraboloid shape. After the electroweak Symmetry Breaking, it took the mexican hat shape. Is the analytical dependence of Higgs ...
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Is it possible to falsify the $SU(2)_{lepton, left}*SU(2)_{quark, left}*U(1)$ symmetry group as an alternative candidate for GSW Model?

We know that the current symmetry of GSW is $SU(2)_{fermions, left}*U(1)$, and the correct representation of the $SU(2)_{fermions, left}$ is the $2+2$ representation. I want to know what is the reason ...
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Electroweak field-strength tensors

The Lagrangian density for the interaction term of the bosons $W_1,W_2,W_3,B$ in the electroweak theory is $$ \mathcal{L}_g=-\frac{1}{4}\operatorname{Tr}(W^{uv}_aW_{uv}^a)-\frac{1}{4}B^{uv}B_{uv} $$ ...
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Why do theories of nature prefer to be renormalizable and not super-renormalizable?

It seems to me (correct me if I am wrong) that all theories in the Standard Model are exactly renormalizable, as opposed to non-renormalizable or super-renormalizable. In a sense, we could say that ...
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Decay of the Phi Meson: Error in Question?

I'm trying to draw Feynman diagrams for the decay of the pseudoscalar meson $\phi = |s \bar{s}\rangle $ into two pions
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Fujikawa Jacobian for Baryon number anomaly

Reviewing the anomalies of the standard model, one knows that the Baryon number is not conserved because of an anomaly associated to the global $U(1)$ symmetry that quarks have. That is the current $$...
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Decay of particle question

How would you draw the diagram for the $D$ meson decay mode: $$ D^- \rightarrow K^+ + \pi^- + \pi^- $$
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$Q=I_3 + Y/2$. How can this be true when Charge does not commute with Weak Hypercharge or Weak Isospin?

About the familiar formula $Q=I_3 + Y/2$. As an example, the left-handed electron has charge $Q=-1$, weak isospin $I_3 = -1/2$, and weak hypercharge $Y=-1$. The electron is represented in the Dirac ...
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Charged Higgs Decay Width

How can we calculate Charged Higgs Boson DEcay width into the fermionic channel? and Other Channels? Actually I am reviewing paper entitled "Probing charged Higgs boson couplings at FCC-hh" https://...
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1answer
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Scattering $u\bar{d} - c\bar{b}$

I'm trying to define if the scattering $u\bar{d} \rightarrow c\bar{b}$ is possible in any of the fundamental interactions, I know that in QCD (channel t) is allowed because of the charge conservation, ...
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63 views

Why do we need two gluons for the decay $ϕ \to 2K$?

The Feynman diagram for the decay $\phi \to K^+K^-$ usually depicts two gluons. (This can be seen e.g. on Wikipedia). Why do we need two gluons, instead of just one?
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Higgs boson positive parity, and zero spin

Can we predict the positive parity, and zero spin of the Higgs boson from the decay mode: 𝐻 → 𝛾𝛾
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Dark Matter Abundance and Being a Cold Relic

I was reading Longair its stated that, "An important conclusion was that, if dark matter particles were as common as neutrinos and photons,their rest mass energies could not be much greater than $...
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Outgoing $Z$-bosons in $s$-channel

I'm working on the process $e^-+e^+\rightarrow ZZ$, taking into account Yukawa interactions, at tree level. Below is the diagram I got for the interaction with the Higgs. I want to write its ...
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Top quark decay rate calculation $\Gamma(t\rightarrow W^+b)$

I'm trying to calculate the disintegration rate $\Gamma(t\rightarrow W^+b)$ from the Fermi Diagram: I know the lagrangian for the interaction would be: $$ -iF = \bar{u_b}\gamma^\mu P_Li\frac{g}{\...
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$u$-channel in Feynman diagrams

I have two questions regarding the $u$-channel in Feynman diagrams. $\textbf{Question 1:}$ Suppose I have a $\gamma\gamma\to\bar{\nu}_{\mu}\nu_{\mu}.$ One of the diagrams will look as one of the ...
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A particle without gauge interactions

Please, Can anyone helps me to understand What does it mean a particle with no gauge interactions?
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$W^+/W^-$ bosons ratio in proton-proton collision

I'm studying my first-year physics in college, and I'm having to write a report of some proton-proton collisions that were registered in the LHC of CERN years ago. The main goal is to identify ...
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What would happen if the Higgs boson and the $Z$ boson collided?

I am thinking the $z$ boson would remain with the combined mass of both the $Z$ boson and the Higgs boson. This is because the Higgs boson is a spin-0 boson and the $Z$ boson is a spin-1 boson.
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Higgs Field and its application [duplicate]

Today I was wondering about how elementary particle gets the mass. Well, you know that's the Higgs Field and we all know a lot about it. It is well known that more a elementary particle interacts ...
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Can an electron and an electron antineutrino annihilate? [closed]

Is the annihilation between an electron and an electron antineutrino possible. How much energy is needed for the annihilations. Could the annihilations be mutual and could this result in a pion if ...
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1answer
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$SU(2) \to I$ symmetry breaking

In "Cosmic strings and other topological defects" by A. Vilenkin and E. P. S. Shellard, section 2.1.3, they detail some examples of spontaneous symmetry breaking. In the first example, they discuss ...
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Does knowing the Yang-Mills field give us the principal bundle structure

Although the principal bundle view of Yang-Mills theory is very satisfactory geometrically, I find it hard to relate with the experience of actually computing potentials as we do in physics. Say ...
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Why is $W$ boson decay more favorable for strange quark than $Z$ decay?

As seen below, a strange quark decays into a down quark and a neutral pion. Why is the top decay more likely than the bottom decay? edit: is it because of this? https://en.wikipedia.org/wiki/Flavor-...
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Is there some quantitative measurement or concept that can distinguish between a photon and a gluon?

Considering both photons and gluons have a mass of 0, a charge of 0, and a spin of 1, what distinguishes them? I want to exclude answers such as 'they influence different forces (i.e. photons are ...
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What is the obstacle to writing down a String Theory that describes our universe?

It seems like, at this point, string theory is a reasonably well-developed mathematical framework. Tools from string theory are being used to understand things in QCD and condensed matter with no ...
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What is an effective field theory (EFT)? Is the standard model (SM) an EFT? Till which scale? How is included gravity?

What is an effective field theory (EFT)? and why all the observable interactions until one scale are only a finite number that we know? Is the standard model (SM) an EFT? till what distances? I real "...
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Difference in the Lagrangian when working with different gauges

like, I have a Standard model Lagrangian, then what will be the differences in interaction terms and in interaction vertices if we work with the Feynman gauge and unitary gauge?
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The Unusual Mass of the $W$ Bosons

A quick look on wikipedia (https://en.wikipedia.org/wiki/W_and_Z_bosons) will tell me that the rest mass of a $W$ boson is 2 orders of magnitude higher than that of a proton. It seems weird that a ...
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Why is gravity the only force not quantizable only at high energies?

There are a lot of questions on this site about the quantization of gravity. Now what I do understand is, that we can quantize gravity, but only at low energies, and this is really different from all ...
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Was photon *defined* according to Standard Model *before* electroweak symmetry breaking ? Or were there only $W_3$ and $B$?

Was photon defined according to Standard Model theory before electroweak symmetry breaking ? Or were there only $W_3$ and $B$ ? Indeed, in Electroweak to Electro/Weak Bosons? Aman pawar answers "no" ...
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How can it be demonstrated that locally $SU(3) \times SU(2) \times U(1)$ is the effective field theory till $10^{-15} m $? [closed]

How can it be demonstrated that locally $SU(3) \times SU(2) \times U(1)$ is the effective field theory till $10^{-15} m $?
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Are antileptons and antibaryons linked?

The recent news about the T2K experiment got me thinking: is there any linkage in the Standard Model between the matter and antimatter categories across the families of Standard Model particles? Are ...
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What are the necessary attributes that any elementary particle must have or have a defined value for it?

We know that each elementary particle/entity must have mass, charge and spin defined. Are there any other attributes (independent) that must be defined for every elementary particle? is there any ...
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Electrons are Leptons. Other Leptons are muons, tauons and neutrinos but where are they found in the Atom?

We all know about Electrons and we use them every day. WE SEE THEM in all the basic diagrams of ATOMS TOO - BUT where are the other LEPTONS? Are they so short-lived that they really don't play a ...
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Are there any mesons with one charm antiquark?

Is there a meson with one charm antiquark, $\bar{c}$, so that $C=-1$? Can they exist?
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$W^-$ behavior in Neutron decay

Why does $W^-$ always decay into electron and anti-neutrino in neutron decay? Why doesn't the $W^-$ particle decay into quark-antiquark pair?
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155 views

$B$-$L$ global symmetry in the grand unification theories

What are the precise $B$-$L$ (baryon - lepton) global symmetry in the standard model? Is this a $U(1)$ global symmetry or a discrete finite group $\mathbb{Z}/N$ global symmetry for the following ...
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3answers
210 views

Are standard QFT and general relativity contradictory?

My professors say it's only a matter of finding the right mathematical formalism to unite GR and QFT, and that new physics can only possibly be found on extremely high energies and small scales. they ...
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Extensions to Minimal Gauged UBLM Model

Recently I have been reading a bit about BSM physics and came across the minimal gauged $U(1)_{B - L}$ model, where the gauge group of the Standard Model is extended to a larger product with another $...
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$e^+e^- \to p^+p^-$ cross-section?

Does anyone know of a calculated or measured cross-section somewhere for $e^+e^-$ annihilation into a proton-antiproton pair, say at the LEP? Seems to me that it would be rather strongly energetically ...

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