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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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18 views

What does the classification of finite dimensional simple Lie algebras tell in physics? [on hold]

A simple Lie algebra is a non-abelian Lie algebra whose only ideals are zero and itself. We know finite-dimensional simple Lie algebras are classified into four families $A_n,B_n,C_n,D_n$, and five ...
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Why do this meson state (consisting with $ u,s,d$) are acceptable by nature?

I am new in Particle Physics and try to understand "Quark-Antiquark States:Meson article in Quarks & Leptons by Halzen and Martin(p=46) Why do this meson states are are acceptable by nature $$A=\...
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10 views

Measurement of spin correlation and polarization

I have a project about measurement of spin polarization and correlation of top quark pairs. I am gonna analyze real collision data from LHC. Before that I had one class about undergraduate level ...
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1answer
48 views

Is it possible for a charged particle to have no spin? [duplicate]

Can a charged point particle ever have spin zero? If not why?
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17 views

Triangle gauge anomalies

In group theory, how we call this quantity \begin{equation} A^{abc}=Tr(T_{L}^{a}\{T_{L}^{b},T_{L}^{c}\}) \end{equation}
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44 views

Why aren't Delta and Omega particles stable?

Not only are they not stable their half-life is in the nanoseconds. Why are they so different from protons?
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35 views

Why don't hadrons form from quarks of all the same charge?

Why don't Hadrons ever form from quarks of all the same charge? For instance you never see 2 or 3 up quarks together with no down quarks or vice-versa.
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47 views

Parity of neutral leptons

Why we consider Hadrons as the eigenstate of parity operator? In doing so we assign each hadron a quantum no. +1 or -1. What about the parity of leptons, and more specifically parity of neutrino? The ...
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couplings between mesons and baryons (singlet and octet)

What is the basic meaning and good reference for the deep and simple meaning(in simple language) of couplings between mesons and baryons, e.g., g1 and g8 couplings (singlet and octet) from where these ...
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Within the Standard Model, for elementary particles, is the splitting “Left/Right” directly connected to electroweak symmetry breaking?

Within the Standard Model, for elementary particles, is the splitting "Left/Right" directly connected to electroweak symmetry breaking? I mean: is the splitting Left/right of particles (charged ...
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101 views

Why is the Higgs boson chargeless

Well, I know if this question was asked about another particle the answer would be that the charge of a particle in an intrinsic property and that’s that(as far as we currently know), and that might ...
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Higgs interaction

I have a question about mass and energy and the Higgs field. My understanding is that fermions 'gain' rest mass by interacting with the Higgs field. But mass is a form of energy, so is the rest mass ...
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1answer
50 views

Anomalous magnetic moment [closed]

I have the two values of the anomalous magnetic moments: $$ a_{\mu}^{SM}=(1 165 917 760 \pm 662)\cdot 10^{-12} \\ a_{\mu}^{exp}=(1 165 920 910 \pm 630) \cdot 10^{-12} $$ Where the first is the ...
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133 views

Definition of forces

In my physics textbook, while talking about the scope of physics, it mentions the four fundamental forces of nature which are Gravitational force, Electromagnetic force, Strong Nuclear force and Weak ...
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Standard model extension

this Semester I have my first QFT class and we have a homework where I got stuck at the beginning. I have some ideas but I am not sure if they are correct, so I don't want a solution, I only want to ...
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1answer
71 views

Why is there no 4th generation of leptons in the standard model?

Why is there no 4th generation of leptons in the standard model? Is there any explanation, as to why they don't exist? More precisely, is there any theoretical restriction to having only 3 generations ...
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47 views

Highest and Lowest $SU(3)_F$ states

For the finite dimensional $(p,q)$-irreducible representation of $SU(3)_F$, we can label the states as $\mid T_3,Y\rangle$. Where $T_3$ is the third component of isospin and $Y$ is the hypercharge. ...
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1answer
118 views

Why do the $c$, $b$ & $t$ quarks have strong hypercharge?

From the $SU(3)$ flavour symmetry we have quantum numbers for the up, down and strange quark, associated with the Eigenvalues of the Gell-Mann matrices $\lambda_3$ and $\lambda_8$. Namely $\lambda_3$ ...
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279 views

When does a particle have an antiparticle?

Though an electrically charged elementary particle is necessarily accompanied by an antiparticle, a particle need not be electrically charged to have an antiparticle. The cleanest example being a ...
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1answer
40 views

Charm prediction: Required electroweak or just weak?

Everywhere I look it up the prediction of the charm quark is predicted by the electroweak interaction, which of course recovers the weak interaction with the spontaneous symmetry break and the Brout-...
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1answer
60 views

Isovector Representation of $SU(2)$

In Electroweak Interactions by Renton (page 407) there is the calculation of matrix elements for electromagnetic interactions/weak interactions involving nuclei: A point of confusion for me is the ...
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1answer
63 views

Natural unit conversions within HEP

In HEP, with the $$\hbar = c = 1 \;.$$ We have $$\hbar c = 200 \;\mathrm{MeV \cdot fm}$$ 1 second is equivalent to $10^{-25}$ GeV. How these relations are used to convert seconds to GeV, GeV to ...
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Resources to understand the Higgs boson

I have to do a presentation about the Higgs boson, covering topics such as the problems with the standard model without Higgs, particle masses not being compatible with gauge symmetry and how it is ...
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Experimental evidence of interaction out of thermal euilibrium?

Sakharov gave three conditions for the matter-antimatter asymmetry observed in the universe. (1) Baryon number violation: Don’t have any experimental confirmation yet. (2) C-symmetry and CP-symmetry ...
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Isospin and $\Delta$ Production

Edited to add new information I have seen the relation between cross sections postulated: \begin{align} \sigma(\nu+p\to\mu^- + \Delta^{++})=9\sigma(\nu+n\to\mu^- + \Delta^{+}) \end{align} Motivated ...
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63 views

Mixing matrix in particle physics

It is familiar for us that the diagonalization of a mixing matrix which is written in the neutral basis gives the masses of the neutral particles. If I construct a mixing matrix which is written in ...
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1answer
119 views

What if there were only 1 generation of fermions?

The number of fermion generations has many effects beyond the mere existence of "3 copies of fermions," including determining scatterings, constraining CP violation, influencing electroweak symmetry ...
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105 views

Experimental proof for isospin conservation of strong interaction

I am having a surprisingly hard time to find direct experimental results for the (approx.) conservation of isospin in strong interactions. The canonical examples seem to be $\omega \! \to 3\pi^0$ and $...
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Question about the Lie group $SU(3) \times SU(2) \times U(1)$ and the concept of manifold

I don't know if this question is a duplicate, so I'll delete if is. Well, I'm in the very beginning of the study of contemporary topics such as gauge theories, I would say that I'm in a "science ...
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117 views

According to the Standard Model, were there 4 Higgs bosons at the beginning of the universe, before the electroweak symmetry breaking?

My question is in the context of the Standard Model, not about Beyond Standard Model. At the beginning of the Universe, before electroweak symmetry breaking, we have a complex Higgs isospin doublet. ...
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2answers
71 views

Standard Model Lagrangian and Euler-Lagrange Equations

First off, note that I only know physics through quantum mechanics, so forgive me if this is a foolish question. I've seen the Standard Model's Lagrangian density written out in full. My question is, ...
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1answer
74 views

How can multiple fermions combine to form a boson? [duplicate]

I understand that composite particles with integer spin form a boson. For example a helium nucleus is a boson because it has 2 protons and 2 neutrons. If all of the components on their own are ...
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A bilinear form or a dot product $X \cdot Y$ of emission X and absorpion Y of a vector boson W in the context of transformation of quark flavors

The reason for this question is related to the fact that I think something is missing when an absorpion and emission of a (intermediate) vector boson $W$ in the context of transformation of quark ...
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Deriving hadrons by their quantum numbers

While preparing for an exam I found a problem where one has to find the composition of hadrons given their quantum numbers. $$\text{ (Charge, Baryon number, Strangeness, Charm, Bottomness)=(Q,B,s,c,b)...
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Meson decay constants from PDG

I've been looking for data for meson decay constants (pseudoscalar and vector), but in the latest release of PDG review I only find information about these parameters for charged pseudoscalar mesons. ...
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Derivation of Jacobian peak in particle physics

I am reading some papers on particle phynomenology. The mathematical derivation of Jacobian peak in some paper is wrong. However, it gives the right prediction. If you have a W boson decaying in to ...
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38 views

Vev's in Beyond the Standard Model

Recently, I read a paper, the authors have mentioned that if we have $n$ stand for VEVs which are singlets of the SM gauge group, $k$ are associated with SM doublets, and $S$ is the VEV of the SM ...
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65 views

Formation of an electron

I recently asked the question (with title "electron charge") about the negative charge of an electron and I received several answers to tell me that what I had heard about the formation of the ...
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2answers
162 views

Particle notation: What does the asterisk stand for?

For instance, what's the difference between $\Sigma^0$ particles and $\Sigma^{0*}$ particles? I know they have the same quark configuration $sdu$, so how exactly are they different? Some context: I'm ...
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1answer
34 views

Physical meaning of whole state space for spin-one

The spin-one quantum states belong to $\mathbb{C}^3$, with a set of orthonormal bases taken as the spin component along a direction, which would correspond to the direction of the magnetic fild ...
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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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Why is the smallness of Higgs mass not technically natural?

Technical naturalness The smallness of a parameter $\theta$ in the Lagrangian of a quantum field theory is said to be technically natural, if in the limit of vanishing $\theta$, the theory has some ...
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172 views

Measuring strong coupling constant

How can the strong coupling constant be measured?
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1answer
69 views

What exactly is a gluon doing when acting as an gauge boson?

The question is in the title. I know that, e.g., W bosons change the flavour in electroweak processes. What do gluons do?
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1answer
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Why is $\Delta^0$ not decaying weakly?

Given the lower decay I wonder why it happens this way. Wouldn't it be possible to decay via a weak process as well?
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1answer
39 views

Main decay of $ J / \psi $

The main decay of $ J / \psi $ is $ c \bar{c} \to ggg $. How can this reaction channel be observed? 3 gluons will hadronize immediately, or not?
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40 views

Deeply Virtual Compton Scattering

what are Transition Distribution Amplitudes respectively Deeply Virtual Compton Scatterings ? I'm so unsure about the terms I can't even distinguish (in case they are not really related to each other)....
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1answer
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How does the introduction of the charm quark suppress FCNC?

I did some reading on the GIM mechanism today, and simply fail to understand how it works. I understand how the CKM-matrix can be used to do the basic calculation of the probability of, say, observing ...
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1answer
99 views

Why is $J/\psi$ not being able to decay into $\pi^+\pi^-\pi^0$ (Ozi-rule)?

There are already (very similar) questions like What is the precise statement of the OZI Rule? and Why does charmonium (and phi mesons) not decay via quark and antiquark annihilation? but, to be ...
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Regularization methods' equivalence and the hierarchy problem

There are several questions related to this one but whose answers just raise the doubt I'm going to describe here. Some facts that are everywhere are (i) The hierarchy problem results from the fact ...