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Results tagged with standard-model
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user 42937
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..
8
votes
Accepted
Higgs is neutral but decays into photons-Why?
The fact that the Higgs boson is electrically neutral means that it is a singlet under the $U(1)$ electromagnetic gauge group. Since the whole Lagrangian must be a singlet as well, any coupling to the …
- 2,194
7
votes
Accepted
Expected consequence of the term $\theta F^{\mu\nu}\tilde{F}_{\mu\nu}$ in the Standard Model
To answer point $2$, $\theta$ is derived from the neutron elecric dipole moment that is measured to be like $ <10^{-18}\,\text{e}\cdot\text{m}$. You can prove that the dipole moment is proportional to …
- 2,194
2
votes
Accepted
Unitarity gauge in Higgs mechanism in P&S's QFT
What P&S are saying in that section is just that starting from the general parametrization
$$ \phi(x)= U(x)\frac{1}{\sqrt{2}} \left(\begin{array}{c} 0 \\ v+h(x) \end{array}\right)$$
You can go to the …
- 2,194
5
votes
Accepted
Term in Lagrangian Invariant under $SO(n)$ but not $O(n)$?
Take a field theory with a scalar field $\phi_i$ as a multiplet of $O(N)$, where $i$ is the $O(N)$ index.
You can construct two scalar combinations:
$\phi_i \phi^i$ that is both $O(N)$ and $SO(N)$ …
- 2,194
2
votes
Why does the upper component of a $SU(2)$ doublet has $T^3=1/2$ and lower component $T^3=-1/...
A possible 2 dimensional representation of $SU(2)$ is the one for which
$$T_3 = \frac{1}{2}\sigma_3= \frac{1}{2}\left(\begin{array}{cc} 1&0\\0&-1\end{array}\right)$$
In this representation is obviou …
- 2,194
1
vote
Accepted
What's the difference between these two 'process'?
Aside from all the discussion in the comments, I'll answer your question.
Pair Production is a process in which some energy gets converted into a particle and an antiparticle. There are several exa …
- 2,194
4
votes
Accepted
Can we derive the formula $Q=I_3+\frac{1}{2}(B+S)$ instead of accepting it as an empirical r...
If you take pure QCD with massless $u$, $d$ and $s$ quarks, hadrons form multiplets of $U(3)$. This means that they can be characterized by three quantum numbers that are the eigenvalues of the three …
- 2,194
9
votes
A common standard model Lagrangian mistake?
It's not really a mistake, just a non-canonical normalization for $\psi$. The physics with and without the $h.c.$ is literally the same.
The canonical way of normalizing $\psi$ is such that
$$\mathcal …
- 2,194