models:standard_model
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models:standard_model [2018/03/30 14:08] jakobadmin [Concrete] |
models:standard_model [2019/02/03 08:46] 77.180.211.234 [History] |
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| - | ====== The Standard Model ====== | + | ====== Standard Model of Particle Physics ====== |
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| **Particle Content** | **Particle Content** | ||
| - | {{ :models:standardmodel.png?nolink&400 |}} | + | {{ :models:paper.journal.40.png?nolink&800 |}} |
| + | |||
| ---- | ---- | ||
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| <tabbox Concrete> | <tabbox Concrete> | ||
| - | --> Particle Content# | + | At the heart of the Standard Model is the [[advanced_tools:gauge_symmetry|gauge symmetry]] |
| + | $$ | ||
| + | G\ =\ SU(3)_C\times SU(2)_L\times U(1)_Y\, . | ||
| + | $$ | ||
| + | The $SU(3)_C$ mixes the three colors of the quarks and antiquarks, | ||
| + | the $SU(2)_L$ the weak isospin, and the $U(1)_Y$ | ||
| + | couples to the weak hypercharge $Y$. | ||
| - | * {{ :models:sm-overview.pdf |The field content of the standard model is nicely summarized here}} | + | The electroweak symmetry $SU(2)_W\times U(1)_Y$ |
| + | is spontaneously broken by the scalar field $\langle H \rangle \neq0$ down to $U(1)_{EM}$. | ||
| - | <-- | + | As a result, the $W^\pm$ and $Z^0$ vector particles become |
| + | massive ($M_W\approx80.4$ GeV, $M_Z\approx91.2$ GeV) while the | ||
| + | photon $\gamma$ remains massless. | ||
| + | |||
| + | |||
| + | |||
| + | ---- | ||
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| + | <-- | ||
| + | |||
| + | -->Particle Content# | ||
| + | |||
| + | {{ :models:sm-overview.pdf |The field content of the standard model is nicely summarized here}} | ||
| + | |||
| + | |||
| + | **The Gauge Bosons** | ||
| + | |||
| + | The __photon__ couples to the electric charge which is a linear combination of hypercharge and weak isospin | ||
| + | $$ | ||
| + | q\ =\ T^3\ +\ Y . | ||
| + | $$ | ||
| + | |||
| + | The photon is responsible for electromagnetic interactions. Since it is massless the electromagnetic forces are long-ranged. | ||
| + | |||
| + | The __$W^\pm$ and $Z^0$ bosons__ are responsible for the weak interactions. Since both are massive the weak force is short-ranged. | ||
| + | |||
| + | The bosons responsible for the strong force are called __gluons__. This name stems from the fact that they ``glue'' the quarks and antiquarks together. Bound states made of quarks and antiquarks are called baryons and mesons. The strong forces become stronger with rising distance between two color-chared particles. As a result individual quarks, antiquarks, or gluons can't be isolated. This is known as confinement. Only $SU(3)_C$ singlets can be observed. | ||
| + | |||
| + | ---- | ||
| + | |||
| + | **The Fermions** | ||
| + | |||
| + | All __quarks__ come in 3 colors $c=1,2,3$ and 6 additionally six flavors $f=u,d,s,c,b,t$ | ||
| + | called `up', `down', `strange', `charm', `bottom', and `top'. | ||
| + | |||
| + | The left-handed quarks form 9 $SU(2)_L$ doublets: | ||
| + | $$(u,d)_L, (c,s)_L, (t,b)_L$$ | ||
| + | (3 for each color) | ||
| + | |||
| + | The right-handed quarks are $SU(2)_L$ singlets. | ||
| + | |||
| + | This curious difference between left-handed and right-handed quarks means that weak interactions disrespect the parity symmetry. The bosons $W^\pm$ only couple to the left currents $J^\mu_L=V^\mu-A^\mu$ | ||
| + | and don't care about the right currents $J^\mu_R=V^\mu+A^\mu$. | ||
| + | |||
| + | The same is true for the __leptons__ $e^-$, $\mu^-$, $\tau^-$, and the 3 neutrino species. | ||
| + | |||
| + | The left-handed leptons live in three $SU(2)_L$ doublets: | ||
| + | $$(\nu_e,e^e)_L, (\nu_\mu,\mu^-)_L, (\nu_\tau,\tau^-)_L$$. | ||
| + | |||
| + | The right-handed charged leptons $e^-_R$, $\mu^-_R$, $\tau^-_R$ | ||
| + | are $SU(2)_L$ singlets. So far right-handed neutrinos were never observed. | ||
| + | |||
| + | <-- | ||
| + | |||
| + | -->Standard Model Interactions# | ||
| + | |||
| + | [{{ :models:586px-standard_model_feynman_diagram_vertices.png?nolink |Source: Image by Garyzx published under the [[https://creativecommons.org/licenses/by-sa/3.0|CC BY-SA 3.0]] licence}}] | ||
| <-- | <-- | ||
| ---- | ---- | ||
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| <-- | <-- | ||
| - | --> Questions left open by the standard model?# | + | --> What questions are left open by the standard model?# |
| See [[:open_problems|Open Problems]] | See [[:open_problems|Open Problems]] | ||
| + | <-- | ||
| + | |||
| + | --> What symmetries do exist in the standard model and what is their experimental status?# | ||
| + | see https://physics.stackexchange.com/questions/97896/symmetries-of-the-standard-model-exact-anomalous-spontaneously-broken | ||
| <-- | <-- | ||
| <tabbox History> | <tabbox History> | ||
| * The Rise of the Standard Model: A History of Particle Physics from 1964 to 1979 by Lillian Hoddeson | * The Rise of the Standard Model: A History of Particle Physics from 1964 to 1979 by Lillian Hoddeson | ||
| * Resource Letter: The Standard Model and Beyond by Jonathan L. Rosner | * Resource Letter: The Standard Model and Beyond by Jonathan L. Rosner | ||
| + | * https://inference-review.com/article/the-standard-model by Sheldon Glashow | ||
| + | |||
| </tabbox> | </tabbox> | ||
models/standard_model.txt · Last modified: 2019/07/03 08:12 by jakobadmin
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