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Results tagged with standard-model
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user 36793
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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Trying to work out the $CP$-transformation property of the Higgs potential
The parity transformation property of a complex scalar field $\phi(x)$ is given by: $$P\phi(t,\textbf{x}) P^{-1}=\eta_P\phi(t,-\textbf{x})$$ where $\eta_P=\pm 1$. The charge conjugation property of a …
CommunityBot
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4
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answer
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Understanding CP-violation from a toy model of two fermions and a scalar boson
Consider a field theory given by the following Lagrangian $$\mathcal{L}_{int}=y\overline{\psi_1}\psi_2\phi+y^*\overline{\psi}_2\psi_1\phi^\dagger$$ where $\phi$ is a complex scalar field, and $\psi_1, …
3
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1
answer
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Phase transition and effect on leptogenesis
What is the effect on leptogenesis in the standard model if the electroweak phase transition is (i) first order and (ii) second order?
CommunityBot
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Can we derive the formula $Q=I_3+\frac{1}{2}(B+S)$ instead of accepting it as an empirical r...
The electric charge of a quark or lepton, $Q$, is related to the third component of the weak Isospin $T_3$ and weak hypercharge $Y$ according to the formula $$Q=T_3+\frac{Y_W}{2}.\tag{1}$$ This, in a …
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Anomalous baryon current in the Standard Model (SM) and the stability of free protons within...
In the Standard Model, the baryon number is not exactly conserved due to anomaly but the decay rate is extraordinarily small at ordinary temperatures. Does this make free protons unstable in the Stand …
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Physical meaning of the form factors $F_1(q^2)$ and $F_2(q^2)$ for $q^2\neq 0$
The charge form factor $F_1(q^2)$ and the anomalous magnetic moment form factor $F_2(q^2)$ have clear interpretations at the value $q^2=0$ i.e. $F_1(0)$ is equal to the charge of the electron and $F_2 …
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Anomalous magnetic moment form factor of $e^-,\mu^-$ and $\tau^-$ in QED
The anomalous magnetic moment form factor $F(q^2)$ of an elementary fermion at $q^2=0$, calculated at one-loop, is $$F_2(0)=\frac{\alpha}{2\pi}.$$ At least at this order (order-$\alpha$), $F_2(0)$ doe …
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Calculating the $\mu\rightarrow e\gamma$ decay and cancellation between diagrams
In the book “Gauge theory of elementary particles-Cheng and Li, section 13.3, the $\mu\rightarrow e\gamma$ decay amplitude is calculated in the $R_{\xi}$ gauge. Regarding this derivation, I'm stuck wi …
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Same $U(1)$ charge for the $SU(2)$ doublet
Consider the electroweak gaugesymmetry $SU(2)_L\times U(1)_Y$. The entries of $SU(2)_L$ doublet will have same $U(1)$-charge. How can this be shown mathematically?
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How to integrate out the $W$-boson fields?
What does it mathematically mean to 'integrate out' the $W$-boson fields to obtain the Fermi Lagrangian from the electroweak theory? How does one achieve this mathematically? It will be helpful if som …
- 213k
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Physical significance of the reality of an ${\bf N}$ representation: how the nature of inter...
Background The fundamental representation of ${\rm SU(N)}$ is denoted by ${\bf N}$ and the conjugate of the fundamental is denoted by ${\bar{\bf N}}$. If the representation ${\bf N}$ is related to ${ …
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A particle without gauge interactions
Sterile neutrinos do not have any gauge interaction (electroweak or strong) but only gravitational.
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Help me understand Lepton universality
In the limit of low momentum transfer i.e., $q^2\ll M_W^2$ and vanishing electron and muon mass, the electronic and muonic decay modes have equal decay rates i.e. $$\Gamma(\tau\to e^-\bar{\nu}_e\nu_\t …
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Higgs is neutral but decays into photons-Why?
Higgs is neutral and therefore cannot have electromagnetic interactions. Then how can it decay into a pair of photons? Does it mean that particles need not be charged to have electromagnetic interacti …
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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 …
