What is Standard model: Definition and 269 Discussions

The Standard Model of particle physics is the theory describing three of the four known fundamental forces (the electromagnetic, weak, and strong interactions, and not including gravity) in the universe, as well as classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists around the world, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, confirmation of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.
Although the Standard Model is believed to be theoretically self-consistent and has demonstrated huge successes in providing experimental predictions, it leaves some phenomena unexplained and falls short of being a complete theory of fundamental interactions. It does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the accelerating expansion of the Universe as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses.
The development of the Standard Model was driven by theoretical and experimental particle physicists alike. For theorists, the Standard Model is a paradigm of a quantum field theory, which exhibits a wide range of phenomena including spontaneous symmetry breaking, anomalies and non-perturbative behavior. It is used as a basis for building more exotic models that incorporate hypothetical particles, extra dimensions, and elaborate symmetries (such as supersymmetry) in an attempt to explain experimental results at variance with the Standard Model, such as the existence of dark matter and neutrino oscillations.

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  1. casparov

    A Can Non-Commutative Geometry Describe Gluons?

    Hey, I have a question regarding the gluons. Is it possible for a non-commutative group/geometry to represent them mathematically ? Replacing the Gell-Mann matrices. I read that the frameworks for gluons /gluonic forces are various, depending on the context.
  2. ohwilleke

    I Update On Muon g-2 Research

    The E989 experiment at Fermilab recently made a high precision measurement of the anomalous magnetic moment of the muon (muon g-2), an observable quantity which can in principal be calculated using the Standard Model for the electron, the muon, and the tau lepton, respectively. The upshot of...
  3. DomDominate

    B What exactly is spin? Does the standard model work without spin?

    I did some research online and found that "When certain elementary particles move through a magnetic field, they are deflected in a manner that suggests they have the properties of little magnets." To explain this phenomenon, physicists invented the concept of spin. So far so good. What I...
  4. danielcmk

    B Is the Standard Model overfitted?

    Is the Standard Model overfitted? I hear that the standard model is the most accurate model that we have so far showing accuracy of 13 digits or so. However I am wondering if this accuracy comes from adding so many constants until it fits. First of all the standard model takes in 25 constants...
  5. G

    I Why does the QFT Lagrangian not already use operators?

    I've learned that in canonical quantization you take a Lagrangian, transform to a Hamiltonian and then "put the hat on" the fields (make them an operator). Then you can derive the equations of motion of the Hamiltonian. What is the reason that you cannot already put hats in the QFT Lagrangian...
  6. A

    A No CP-Violation for coinciding Quark-Masses

    Hello everyone, I know that if two of the quarks (e.g. strange & bottom) had coinciding masses, there would be no CP-violation in the standard model. Apparently the reason lies in the parameters of the CKM-matrix, but I don't understand how to show that. Can someone explain?
  7. J

    A The Generalized Capabilities of the Standard Model Lagrangian?

    If the standard model Lagrangian were generalized into what might be called "core capabilities" what would those capabilities be? For example, there are a lot of varying matrices involved in the standard model Lagrangian and we can generalize all of them as the "core capability" of matrix...
  8. S

    I From a false vacuum to a true vacuum?

    In theory (please correct me if I am wrong in any point), if our vacuum were metastable (i.e. in a "false vacuum" state), it could go through a phase transition into a stable state (a "true vacuum" state). Depending on the properties of the new vacuum, fundamental forces and particles could...
  9. W

    B Why are SU(3), SU(2) and U(1) groups used in the Standard Model?

    hi, i have studied Standard Model for particle physics - at present it is described by three groups - i have studied - these groups but could not establish what particular feature suggest of these group to be used to describe SM. Thanks
  10. Buzz Bloom

    I Observations fit poorly with the Standard Model of Cosmology

    Reference: https://scitechdaily.com/breaking-cosmology-too-many-disk-galaxies-a-significant-discrepancy-between-prediction-and-reality/ The following are quotes from the reference. 1. The Standard Model of Cosmology describes how the universe came into being according to the view of most...
  11. U

    Calculating Amplitude in Standard Model

    Hi! I'd like to ask you if my calculation of the amplitude on the mentioned process in the Standard Model is correct. The three diagrams contributing at lowest order should be where in the middle one the two Higgs boson are NOT forming a quartic interaction vertex. My attempt at calculating the...
  12. F

    I Why are free parameters bad for a theory?

    It is often said that one of the drawbacks of the standard model is that it has many free parameters. My question is two-fold: What exactly is a free parameter? My understanding is that the free parameters of a model/theory are the ones that cannot be predicted by the theory and need to be...
  13. Safinaz

    A How to find the value of the baryon asymmetry in this paper

    I'm trying to understand from this paper https://pdg.lbl.gov/2020/reviews/rpp2020-rev-bbang-nucleosynthesis.pdf What is the value of the baryon to photon ratio ##\eta=n_b/n_\gamma## as named in figure 24.1, but I can't get from the figure or the paper how ##\eta## is of order ##10^{-10}## Any...
  14. Safinaz

    A How Randall-Sundrum model has solved the hierarchy problem?

    I'm trying to understand how the RS model solved the hierarchy problem from this mass relation $$ M^2_p = \frac{M^3}{k} \Large[1- e^{-2k\pi r} \Large],$$ Equ. 16 in their paper: https://arxiv.org/abs/hep-ph/9905221 With k as large as the Planck scale, the exponential will be so small and...
  15. C

    UAP Report and the Standard Model

    Here is the report submitted https://www.bbc.com/news/world-us-canada-57619755 "UFO report: US finds no explanation for sightings The US government has said it has no explanation for dozens of unidentified flying objects seen by military pilots. A Pentagon report released on Friday says of...
  16. M

    A Just standard model and gravity, up to high energies? An update

    A recurring topic in particle physics, is the possibility of a "desert" above the electroweak scale: no new physics (new particles, new forces) until the grand unification scale or the Planck scale. It's important to remember that the Higgs boson mass was correctly predicted three years in...
  17. JD_PM

    High Energy Books on the Standard Model of elementary particle physics & beyond

    Hello! I am taking a course on Electroweak & Strong Interactions (you could equally call it Standard Model I) and I find it absolutely fascinating! 😍 We studied how weak interactions violate parity, introduction to QCD, flavor physics (CKM matrix, CP violation, …) and neutrino physics...
  18. ChrisVer

    A What is the problem with the particle masses in the Standard Model?

    Hi, Several times I encounter the argument that there is a "problem" with the masses in the Standard Model that we try to "understand". From the one side, you have people who ask why the neutrino masses are so small, and from the other side they ask why the top quark mass is so large. The...
  19. john baez

    A Octonions and the Standard Model

    I've slowly been writing a thread on octonions and particle physics, just to explain some facts in a self-contained way, with all the proofs. I don't know where this will lead. I'm certainly not presenting a theory of physics, much less advocating one. Mainly it's just fun. Octonions and...
  20. DarkMattrHole

    B Question regarding 'beauty' in the theories that go beyond the standard model

    There has been a lot of talk about the value of beauty in theoretical physics. There seems to be a lot of little things that are beautiful because they make sense, according to what we already know, like the discovery of anti-particles, and recently the Higgs. The standard model was revealed...
  21. sbrothy

    B Beyond the Standard Model Explanations of GW190521

    Title says it all. Maybe it belongs more in Astrophysics but given the title... "Beyond the Standard Model Explanations of GW190521" - - - - https://arxiv.org/abs/2009.01213 If this is for real I'm surprised it's gotten so little attention..? EDIT PS: (for my own convenience mostly) ...
  22. AndreasC

    I What are the most important phenomena that the Standard Model can't explain?

    I guess the crux of the question is, where are we more likely to encounter new physics? The standard model already explains almost every experimental result, but not EVERY result. But what are some of the most important results that are either incompatible with the standard model or just...
  23. J

    A Griffith's Elementary Particles Section 9.7 Electroweak Unification

    1. On pg. 343 Griffith's expresses the weak current in terms of left-handed doublets. jμ± = ##\bar χ_L##γμτ±##χ_L## ##χ_L## = ##\begin{pmatrix} ν_e \\ e \end{pmatrix}_L## ##\tau^+## = ##\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}## , ## \tau^- ## = ##\begin{pmatrix} 0 & 0 \\ 1 & 0...
  24. Jehannum

    Gap in the market for a book on the Standard Model

    Summary:: Is there a primarily non-technical book covering all aspects of the Standard Model of particle physics? The Standard Model comes up a lot in YouTube videos. There must be a decent amount of public interest. I think there would be a market for a semi-technical but accessible for the...
  25. FourEyedRaven

    Particle Beyond the Standard Model

    Hi. I'm looking for recommendations of books, surveys, or lecture notes, that deal with physics beyond the standard model all in one place. The starting point is someone who already knows QFT and the SM at the level of Schwartz's book on QFT and the SM...
  26. fresh_42

    Quantum Article about the Standard Model

    I thought this might be worth a read: https://iopscience.iop.org/article/10.1088/1361-6552/aa5b25/pdf
  27. bland

    I Why isn't the Goldstone boson on the Standard Model map?

    They seem to have something to do with Z or W particles, maybe, and they have something to do with mediating weak iso spin, I think, and they may be related to the Higgs field. But they don't have a box dedicated to them on the Standard Model of particle physics. Can someone tell me why this is...
  28. M

    A Seeking the Standard Model in E8 plus Supersymmetry

    This is just a quick alert regarding a paper today https://arxiv.org/abs/2005.03048 Exceptional Unification of Families and Forces Alfredo Aranda, Francisco J. de Anda, Stephen F. King [Submitted on 6 May 2020] This work considers the remarkable suggestion that the three families of quarks and...
  29. H

    I Right chiral vs left chiral electrons in the standard model

    Sometimes I hear particle physicists refer to left/right chiral electrons as different particles that are 'mixed' by the mass term. Maybe I misunderstood entirely, but if there is even a handwavy sense in which this is the case, clarifications would be appreciated. In high energy collisions...
  30. tomdodd4598

    I Form of the Standard Model: Higgs-Fermion Yukawa Coupling

    Hey there, I was looking at the Higgs sector of the standard model, particularly its coupling to the fermions: ##\mathscr{L}_{ yukawa }=-\sum _{ a,b=1 }^{ 3 }{ \left( { Y }_{ ab }^{ u }{ \bar { Q } }_{ a }{ \hat { \varepsilon } }_{ 2 }{ H }^{ \dagger }{ u }_{ b }+{ Y }_{ ab }^{ d }{ \bar { Q }...
  31. P

    A Why is there no distance-measure in the standard model?

    The standard answer: “In GR, only average density matters.” That is what Friedmann’s equations (1) say—mathematically—but he does not derive that conclusion. He starts with it. Friedmann does not start with a messy, real-world model of the universe, one that has fractured into galaxy clusters...
  32. S

    A Standard Model and number of fundamental forces

    Just a curious question, is there a limit within the standard model on how many fundamental forces there can be? I have some familiarity with particle physics/QFT(not quite mastery obviously otherwise Id probably be able to answer this myself) and the thought popped in my head when reading about...
  33. takunitoche

    A Derivation of the Yang-Mills 3 gauge boson vertex

    Hello everyone, I am stuck in the derivation of the three gauge-boson-vertex in Yang-Mills theories. The relevant interaction term in the Lagrangian is $$\mathcal{L}_{YM} \supset g \,f^{ijk}A_{\mu}{}^{(j)} A_{\nu}{}^{(k)} \partial^{\mu} A^{\nu}{}^{(i)} $$ I have rewritten this term...
  34. bhobba

    I Is Gravity Part Of The Standard Model?

    I am watching a show about the Standard Model and The Theory of Everything (which of course we do not have right now) and the lecturer mentioned gravity is not part of the Standard Model. Yet other books include it. What is the general consensus? Thanks Bill
  35. D

    I Why does a Lagrangian matter for the standard model?

    Hi, I don't know much about the standard model but I'm asking out of interest. Why do we actually need a Lagrangian for the standard model? Surely when you apply the relevant Euler-Lagrange equations, you end up with a variety of equations like the Maxwell equations or Dirac equations. Why...
  36. A

    A Renormalization (Electron self energy)

    Hello everybody! I have a big question about the renormalization: I do not understand why the "renormalization condition" is to impose the tree level result. Now I will explain it better. Let's take, for example, the electron self energy. The tree-level contribution is the simple fermionic...
  37. A

    A The product of a matrix exponential and a vector

    Hello everybody! I was studying the Glashow-Weinberg-Salam theory and I have found this relation: $$e^{\frac{i\beta}{2}}\,e^{\frac{i\alpha_3}{2} \begin{pmatrix} 1 & 0 \\ 0 & -1 \\ \end{pmatrix}}\, \frac{1}{\sqrt{2}}\begin{pmatrix} 0\\ v \\ \end{pmatrix} =...
  38. S

    I Interpreting SM Lagrangian "differential particle" terms

    The Standard Model Lagrangian contains terms like these: ##-\partial_\mu \phi^+ \partial_\mu\phi^-## ##-\frac{1}{2}\partial_\nu Z^0_\mu\partial_\nu Z^0_\mu## ##-igc_w\partial_\nu Z^0(W^+_\mu W^-_\nu-W^+_\nu W^-_\mu)## How should one interpret the "derivative particle fields" like...
  39. FourEyedRaven

    I Particle Physics vs Quantum Field Theory vs Standard Model

    Hi. I'd like to ask what are the differences between Particle Physics, Quantum Field Theory and the Standard Model. I see these names of physics courses but I want to confirm if I understand the difference. My understanding is that when students learn particle physics in their undergraduate...
  40. H

    A Clarification about conserved currents in the Standard Model

    I'm currently doing a course on the Standard Model and I think I've gotten confused on some of the symmetries and resulting currents. Here's my current understanding: Before SSB: Electroweak - U(1) symmetry on fermion spinors and Higgs complex doublet, 1 conserved current Electroweak - SU(2)...
  41. Radwan Parvez

    A Neutrino Electron Scattering In The Standard Model Approach

    Previously I posted a problem concerning Electron-neutrino scattering, but as I couldn't describe the problem clearly, so I am trying to post the problem using latex codes to present it in the correct way. For a couple of months, I am trying to calculate the invariant amplitude of the Neutrino...
  42. Radwan Parvez

    A Neutrino Electron Scattering In The Standard Model Approach

    For a couple of months, I am trying to calculate the invariant amplitude of the Neutrino electron scattering in the standard model (SM) approach where I am not considering any kind of approximation and using the SM propagator for W Boson and Z Boson. I tried to do as following, find out the...
  43. atyy

    I Lattice standard model (Wang & Wen)

    There is a proposal for a generalized lattice standard model by Juven Wang and Xiao-Gang Wen. Could this be correct? I've put this under BTSM because it also mentions grand unified models. https://arxiv.org/abs/1809.11171 A Non-Perturbative Definition of the Standard Models Juven Wang...
  44. C

    I Is this outline of particle physics right?

    Just a quick query here: Is the outline of particle physics at the link below right? I have found it very helpful in a general way, but I am only just learning this stuff and don't want to be misled. https://physics.info/standard/concept-map.pdf Thanks!
  45. YoungPhysicist

    I Is there a simple explanation for Fermi-Dirac statistics?

    Is there a simple explanation for fermi-dirac statistics? I can't understand how a particle can "follow" a statistic.
  46. A

    B Why is the Higgs boson considered a boson?

    Bosons are described as force carrier particles and, as I understand it, the Higgs mechanism explains why photons are massless, just as all the carriers of the strong nuclear force, the gluons, whereas the weak force bosons have mass. A peculiar type of field is postulated, the ‘Higgs field’. It...
  47. M

    A A standard model wormhole?

    Apparently the Internet hasn't noticed this paper yet: http://arxiv.org/abs/1807.04726 Traversable wormholes in four dimensions Juan Maldacena, Alexey Milekhin, Fedor Popov (Submitted on 12 Jul 2018) We present a wormhole solution in four dimensions. It is a solution of an Einstein Maxwell...
  48. R

    Do photons carry the electric field?

    In basic electrostatics any charged particle will produce an electric field at every point in space, and will have electric filed lines spreading out radially. E = kQ/r^2 The Standard model of particle physics says that the Photon is the force carrier for the Electromagnetic force, just like...
  49. R

    A Electron charge vs quark charge

    I have been trying to understand some of the basic differences in the fundamental nature of leptons and quarks. One article on this issue compares leptons and quarks as "oranges vs apples" to which I basically agree except for one aspect. How can the charges of the quarks be 1/3 or 2/3 the...
  50. diegzumillo

    This wikipedia article on the standard model is really good

    I just wanted to get this out of my system. I'm not talking about the main article on SM but the mathematical formulation one: https://en.wikipedia.org/wiki/Standard_Model_(mathematical_formulation) Very, very hard to find good summarized material on SM out there. It's either good coverage but...