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...
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...
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...
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} =...
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...
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!
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...
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...
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...
Not the best at physics but trying to understand the standard model. So can someone please tell me if this is right or not and if not, can you explain me why?
Higgs bosons reacts with everything that has mass.
Electromagnetic force reacts with everything that has charge.
Weak force reacts with...
This is a homework problem in a course in particle physics at Cornell University.
Assume the Left Right Symmetric (LRS) model for leptons. The gauge group is GLR = SU(2)L×SU(2)R×U(1)X. The Standard Model group SU(2)L×U(1)Y has to be included in the LRS group. Namely, U(1)Y ⊂ SU(2)R×U(1)X. Find...
This T-shirt I bought at a physics conference displays the following equation. It looks like the Lagrangian of the Standard Model of particle physics but I only recognise lines 1 (electroweak) and 3 (Higgs mechanism). What are lines 2 and 4 and what is/isn't included? eg. are quarks, gluons...
The covariant derivative in standard model is given by
Dμ = ∂μ + igs Gaμ La + ig Wbμ Tb + ig'BμY
where Gaμ are the eight gluon fields, Wbμ the three weak interaction bosons and Bμ the single hypercharge boson. The La's are SU(3)C generators (the 3×3 Gell-Mann matrices ½ λa for triplets, 0...
In a thesis, I found double sided arrow notation in the lagrangian of a Dirac field (lepton, quark etc) as follows.
\begin{equation}
L=\frac{1}{2}i\overline{\psi}\gamma^{\mu}\overset{\leftrightarrow}{D_{\mu}}\psi
\end{equation}
In the thesis, Double sided arrow is defined as follows...
This is a question that I have tried to pose several times without any success but, anyway, I would like to try again for the very last time.
Asume for a moment that EW-SSB (electroweak spontaneous symmetry breaking) actually happened in our early universe. Imagine that our Standard Model of...
How do we know the spin of an elementary particle? For example, a fermion has spin 1/2; a photon has spin 1; and even the ficticious graviton has spin 2. How do we know these spins? In other words, how are these spins determined?
I was reading the following article that tries to use some equations originally proposed by Pauli in 1951 to reason from one of two reasonably plausible axions that there are tight constraints on the fundamental particle content and mass spectrum of the Standard Model together with BSM...
It is my understanding that the task of enumerating all of the divergent diagrams in a quantum field theory can be reduced to analyzing a hand full of diagrams (well, at the moment I know that this is at least true for QED and phi^4 theory), and that all other divergent diagrams are divergent...
Gluons are often depicted as fundamental particles in the Standard Model. But in looking at their mechanism, it seems they are not really fundamental particles in the sense that they are fundamental, indivisible, building blocks. They are mesons- a composite quark-antiquark pair, where their...
This question is about the use of bar on a fermionic field in a Lagrangian, the use of arrows on external fermion lines and the particle-antiparticle nature of a fermion.
For illustration of my question, I will use the following the charged-current interaction of the Standard model...
The decay processes of the ##W## bosons are completely governed by the charged current interaction terms of the Standard model:
$$\mathcal{L}_{cc}
= ie_{W}\big[W_{\mu}^{+}(\bar{\nu}_{m}\gamma^{\mu}(1-\gamma_{5})e_{m} + V_{mn}\bar{u}_{m}\gamma^{\mu}(1-\gamma_{5})d_{n})\\...
Just found this new book on amazon. Looks interesting. I purchased.
https://www.amazon.com/dp/0691167591/?tag=pfamazon01-20
The TOC, Preface, and intro could be found here
http://press.princeton.edu/titles/11050.html
I wish they included a sample chapter as well (the book in not cheap), but I...
Last year I finished the undergraduate course in Mathematical Physics. This year, more precisely in March, I'm going to start the graduate course to acquire a master's degree in Physics.
Now, for this course I must choose a research topic and find an advisor. This is being a little bit...
I have seen the derivation for Unruh radiation for a massless, non-interacting scalar field (Carroll). Are there interesting differences that arise for more realistic standard model cases. For example, what does QCD look like for an accelerating observer? Any papers that detail this would be...
Hello! Can someone explain to me what exactly a local gauge invariance is? I am reading my first particle physics book and it seems that putting this local gauge invariance to different lagrangians you obtain most of the standard model. The math makes sense to me, I just don't see what is the...
I'm in a deep discussion with a friend. He says that the Standard Model of particle physics is actually known by Standard Model of cosmology and that both are the same and that the SM of particle physics is in the Minkousky geometry.... I disagree about this, I do think that the SM of particle...