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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Permanence of the basic forces
I am a highly interested layperson in Germany focusing on the fundamental principles that govern our everyday reality.
I have a specific question regarding the permanence of the basic forces of ...
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Gauge dependent mass definition in perturbation theory
Let's say we describe an unstable particle using perturbation theory. Then we have a non-zero decay width, which we say $\Gamma$. Now, if we define mass to be the pole of the propagator, we get
$$
\mu^...
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Where do the charge and mass go when a gluon pops out of existence? [duplicate]
A nucleon is made up of a sea of quarks and gluons that pop in and out of existence. Color charged gluons move at $c$ and thus make up 99% of the mass of the atom. Where does this charge and kinetic ...
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Does Spacetime Curvature affect the Higgs Trilinear Self-Coupling by modifying the Vacuum Expectation Value?
I have been studying the Higgs mechanism, and most standard derivations assume flat Minkowski spacetime.However, in the early universe or near compact objects such as black holes, spacetime curvature ...
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Why a particle (specifically lepton) decays?
This is a sequel of my question. For particles with structure, it wouldn’t be strange for them to decay due to unstable structure and various reasons. But for leptons, such as the muon, it's almost ...
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Multipling a doublet by a singlet
This question is about something from page 162 of Physics from Symmetry by Schwichtenberg (second edition). The doublet is an electroweak $SU(2)$, say a left-handed neutrino and left-handed electron. ...
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Numerical results of precision tests in perturbative QFT
Where can I find a database or tables with the precisions/contributions that each Feynman diagram term adds to most common and famous numerical estimations for the standard model of particles (like $g$...
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Are positively charged hyperons (e.g., $Σ⁺$) disfavored in neutron-star matter? If so, by how much?
In cold, neutrino-free, beta-equilibrated neutron-star matter:
Is it true that positively charged hyperons (like Σ⁺) are suppressed compared to neutral/negative ones ($Σ^0$, $Σ⁻$)?
If yes, how large ...
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How can Different neutrino flavours have different masses?
I've heard about neutrino oscillation, where can neutrino can change between each flavour. I've also heard that the neutrino flavours are not guaranteed to have the same mass. If this is the case how ...
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Will a Higgs factory reveal something new besides testing existing theories?
After the discovery of Higgs boson at LHC, multiple lepton colliders like FCC-ee, ILC, CLIC, and muon colliders were proposed. These colliders can produce Higgs bosons under very clean backgrounds to ...
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Can the right-handed hypercharge participate in the fermion mass-generation mechanism?
In the Standard Model, fermion masses arise from Yukawa couplings after electroweak symmetry breaking, but these couplings are free parameters. They reproduce observed masses yet offer no theoretical ...
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Proving invariance of Yukawa sector under $SU(2)_L\times U(1)_Y$
As the title suggests I am trying to show this invariance. But before I do that I will explain what the crux of the problem, for me, is. This post might be a bit lengthy, but I believe it is necessary ...
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Why are chirality and helicity experimentally linked?
Here are some true statements about weak charged interactions in the Standard Model:
The weak isospin interaction is described by $\mathrm{SU}(2)_L$. This means that only left-chiral fermions ...
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If left-handed neutrinos cannot be Majorana because of $SU(2)$ how does the seesaw mechanism work?
I am reading many different papers and texts about Majorana neutrinos, specifically in the context of neutrinoless double beta decay and the seesaw mechanism, and I am becoming confused about the role ...
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What makes three generations of lepton so different in anomalous magnetic dipole moment?
I've read the questions discussing the differences among electrons, muons and taus. However, I am perticularly interested in their anomalous magnetic moment which seems not to be discussed in previous ...
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Positive kaon decay Feynman diagram and difference in branching ratios
Question: Help me draw the correct feynman diagram for reaction (ii)
I am trying to look at the branching ratios and feynman diagrams for the two following decays:
i) $K^+ \to \pi^+ + \pi^- + e^+ + \...
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Feynman diagrams: NLO real corrections versus LO diagram with additional radiation
I try to understand the NLO Feynman diagrams. I understand that, at NLO, we have the virtual, soft, collinear and real corrections.
Now suppose that there is a parton configuration, for example the ...
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What is the shape of the potential energy graph for the Higgs Field?
I know that the Higgs field is not in a symmetrical state and that its expectation values lie at the bottom of the 'Mexican hat' of the Higgs Field's potential energy graph. And this spontaneous ...
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Tuning of bare parameters in RG and the Hierarchy Problem
From what I understand about Wilsonian RG, one of the key insights involved is that if you start with (say a scalar $\phi^4$) theory on a lattice and wish to define a meaningful continuum limit (which ...
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Matter is defined as anything that occupies space and has mass, but electrons do not occupy space, so why is electron still considered matter?
In classical Physics Matter is defined as " anything that occupies space and has mass is considered matter" but according to latest theories of reality (the QFT), Electrons Etc are just ...
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Does strangeness have $U(1)$ symmetry?
I know that isospin has $SU(2)$ symmetry, meaning one can rotate $u$ quarks into $d$ quarks and vice versa without changing the underlying physics of a system when ignoring the mass difference.
In the ...
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What is the experimental evidence for the breakdown of Coulomb's law for small $r$ for the electron?
In Volume 2, Chapter 5, Section 8 of The Feynman Lectures on Physics https://www.feynmanlectures.caltech.edu Feynman states
"From measurements in nuclear physics it is found that there are ...
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What is the scientific community's take on causal fermion systems? [closed]
I recently came up to a podcast where Finster exposed his theory of "causal fermion systems" (CFS) and kind of intrigued me, here is the link. He seems pretty confident about his results so ...
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Quarks' motion inside the neutron [duplicate]
Neutron's quark structure is udd.
In the neutron, how do the quarks move?
Do up quarks rotate around the down quark?
Do the down quarks rotate around the up quark?
Do they move like the two-body ...
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Is the Choice of Minima in the Higgs Mechanism Arbitrary or Related To Producing a Massless Photon?
I'm trying to understand the choices made during derivations of the Higgs Mechanism. Particularly at the point where we have
$\phi^\dagger\phi = \frac{1}{2}\left(\phi^2_1+\phi^2_2+\phi^2_3+\phi^2_4\...
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Can neutral pions help lengthen the half-life of alpha decaying isotopes?
I was having a thought experiment and wanted to know the feasibility of it.
We know that a neutral pion ($\pi^{0}$) of rest energy 135 MeV decays into two gamma ($\gamma$) rays of 67.5 MeV each. ...
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Unitary gauge and how to obtain a real representation from a complex one
I was reading an article by Weinberg that introduced the unitary gauge ("General Theory of Broken Local Symmetries", 1) at the classical level for a lagrangian $L$ of standard model-type, ...
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Understanding the different $SU(2)$ symmetries [closed]
I am confused when it comes to the relation between some arbitrary gauge transformation/ internal symmetry and the different symmetries considered. I will illustrate this by considering the $SU(2)$ ...
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Electron electric charge not a parameter of standard model
Why is the electron electric charge not in the table of the standard model parameters?
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Derivation decoupling of GWB (Gravitational Wave Background)
In many textbooks we can found the detailed mathematical derivation of the time (~380’000 years) of CMB decoupling after the Big Bang.
However i can’t found an equivalent derivation for the GWB.
Any ...
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Cancellation of the quartic divergences in vector boson loop correction to Higgs mass
The vector boson loop corrections to the Higgs 2-point function are given by one diagram with one $hhVV$ vertex $ g_{hhVV} = 2im^2/v^2 $ and another diagram with two $hVV$ vertices $g_{hVV} = 2im^2/v$....
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Question about chirality conservation in a model beyond SM
In this paper Lagrangian equation (1), there is a term
$$ \lambda_S \bar{\nu}_R^c \chi S_2 $$
to give the right handed neutrino mass in the B-L ISS model.
But since $\chi$ is a singlet scalar , and $...
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What Constants in the SM Lagrangian Are Relevant to the Shape of the Higgs Potential?
So for the Higgs potential, I'm aware that, before symmetry breaking, the specific values of $\mu^2$ and $\lambda$ in $V(\phi)=\mu^2 \phi^\dagger\phi+\lambda (\phi^\dagger\phi)^2$ define its shape. ...
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Quantum waves of collection of particles [closed]
According to the de Broglie relationship, the wavelength of an object is inversely proportional to its mass. As a result, protons possess a smaller wavelength than their constituent quarks and gluons. ...
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Higgs decay into $ZZ$ or $WW$ [duplicate]
I was studying this graph:
(Source)
I was wondering why there is such a big difference in the branching ratio of $H \to WW$ and $H \to ZZ$. I know that for the Higgs mass of $125\,\text{GeV}$ both ...
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Can someone explain Higgs boson intuitively? [duplicate]
I know that Higgs boson gives mass to all other particles but how exactly does that happen?
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Action of charge conjugation on charged mesons
The charge parity isn't defined for charged mesons, and we define the G-parity instead which is given by:
$${G} \equiv {C} \exp{i\pi \tau_2}$$
However, I am stuck at how to apply it.
For example, if ...
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Cross-section of $\pi^0$ mesons in Pythia
I simulated 10,000 events in PYTHIA 8.3 for p-p collisions (14 TeV High Luminosity run). I get the cross-section for 101.512 mb, which seems reasonable (with certain error) as ATLAS cites 104.7 ± 1.1 ...
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Equivalent proton-neutron Feynman diagrams
Are the following Feynman diagrams equivalent?
I would assume not given the different numbers of gluons involved.
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Need for two gluons in $\phi$ meson decay
According to the Feynman diagram for $\phi$ meson decay, two gluons are required.
Why can a single gluon not be emitted from one of the initial-state quarks, creating the needed quarks to produce the ...
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Can anyone tell me what the magnetic dipole moment of the muon is?
Is the magnetic dipole moment of the muon the same as the electron's ?
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Why should we add Ricci scalar to Lagrangian of Standard model when we try to quantize gravity?
Naively, I think the simplest way to include gravity in the Standard Model is to treat the metric $g$ as a variable in the Lagrangian $\mathcal{L}_{SM} $ defined on a (compact) time-orientable ...
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Most probable Feynman diagram
I am trying to find the most proabale feynman diagram for the following reaction:
$$\pi^- + p \rightarrow \bar\Sigma^- + \Sigma^0 + p$$
with contents
$\overline{\Sigma}^- (\overline{uus})$, $\Sigma^0 (...
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The Physics of Strong Sphalerons
I recently came across the term of "strong sphalerons" [1]. I am aware of the electroweak sphaleron(s) and I am also aware of some useful resources for electroweak sphalerons. However in ...
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What is the most stringent argument to guarantee $N_c=3$? [closed]
There is strong evidence that "color quantum number" is needed in order not to break some well established principles of physics (e.g. $\Delta^{++}$ antisymmetric wavefunction). There is ...
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Is observation of high energetic cosmic rays excluding possibility that parameters of the Standard Model are in a metastable vacuum?
Measurements of the Higgs and top mass allow us to establish constraints on the instability scale at which the Higgs potential starts to become negative, or, said similarly, meaning that there exists ...
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Could you image something using a quark microscope?
As all quarks are fermions, just like electrons, would it be possible to use them to image things smaller than can be imaged using electron microscopes through similar means?
(This question may not ...
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Two flavour Nambu-Jona-Lasinio model: lagrangian and derivation of the mass gap equation
Consulting a lot of literature about the Nambu-Jona-Lasinio model (NJL model), I have run into many different choices - even at the level of writing the Lagrangian, so I would like to clear some ...
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Why is the excess at the $t\bar t $-threshold, seen by CMS, a surprise?
Recently the CMS Collaboration reported on an $\approx 5\sigma$ excess in the $t\bar t$-threshold [1]. There are two papers published, one is a BSM search that fits a heavy $\mathcal{CP}$-odd Higgs ...
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When should one consider parity and charge conjugation and how does it work?
As written above the main question is: How does parity and C-parity work and when do I need to consider it?
I feel like parity and $C$-parity is not very well defined. I know for parity that it's a ...
