All Questions
89
questions
0
votes
1
answer
112
views
Yukawa Interaction with Chiral Fermions
I understand that an interaction like
$$g\overline\psi_L\psi_R\phi$$
is allowed in the SM (for the sake of this discussion lets ignore gauge charges and focus only on Lorentz invariance).
I want to ...
3
votes
0
answers
49
views
How does crossing symmetry affect the value of an electroweak vertex (e.g. $u+W^-\to d$ vs. $W^-\to\pi^-$)?
Two of the weak charged current vertices I often encounter in my first foray into particle physics are $u+W^-\to d$ and $W^-\to\pi^-$, shown in the following Feynman diagrams:
These feel like the ...
- 2,680
2
votes
0
answers
35
views
General formula for a $f1\to f2$ gamma processes (e.g. $\mu \longrightarrow e\gamma$), understanding the detailed calculation in the paper by Lavoura
I want to work out in detail the paper by Lavoura to get some real practice as a beginning student. I have stumbled upon several problems as I am moving along with the arguments. Firstly, I am not yet ...
- 31
11
votes
2
answers
2k
views
Feynman diagrams vs old fashioned peturbation theory (OFPT) vs reality
As far as I understand, our best picture of the world is that it is comprised of universe-spanning fields (one for each type of particle) that can interact with each other. The interactions are local, ...
- 525
0
votes
1
answer
81
views
Why is there a $u$ in the middle of the feynman diagram for a quark and an antiquark annihilating?
There is a feynman diagram in chapter 2 of Griffiths Introduction to elementary particles, where a pair annihilation is taking place. I am confused as before it was written that internal lines are ...
- 11
3
votes
1
answer
431
views
Calculation of the decay rate of the $W$ boson
I am trying to calculate the decay rate of the $W^-$ boson to a charged lepton and the corresponding antineutrino.
I denote the four momentum of the $W$ boson with $q = (M_W, \vec{0})$. The momenta of ...
- 33
1
vote
0
answers
56
views
Understanding Classical Contributions to the Quantum Field Theory Path Integral
I'm a data scientist with no physics background who sometimes reads about physics in my spare time, so please take it easy on me, I know these are really obvious questions to physicists but feel free ...
- 51
0
votes
1
answer
146
views
Imaginary Contribution to Diagrams with one $\gamma^5$ Vertex
It is possible to write down a Feynman diagram as below for production of a Higgs boson.
I am slightly confused because the fermion-fermion-$Z$ vertex has a factor of $c_V - c_A \gamma^5$, but the $...
- 1,410
5
votes
0
answers
181
views
How do you understand displaced vertices rigorously in quantum field theory?
When you produce a long-lived particle (like charged pions, muons), it enters your detector. When you produce a short-lived particle (like the higgs, tau), the production of the particle is only seen ...
- 7,434
2
votes
1
answer
407
views
Can someone explain this Feynman Diagram in the picture?
I don’t understand this diagram at all, and what is the meaning of the $g$?
- 47
0
votes
0
answers
59
views
Numerators in LoopTools
I want to calculate the diagram
$$ \int \text{d}^D q \frac{q_\mu q_\nu q_\rho q_\eta}{(q^2-m_1^2)((q_1+p_1)^2-m_2^2)((q_1+p_1+p_2)^2-m_3^2)((q_1+p_1+p_2+p_3)^2-m_4^2)((q_1+p_1+p_2+p_3+p_4)^2-m_5^2)} $$...
- 55
-1
votes
1
answer
142
views
Deriving mathematical solutions from Feynman diagrams [duplicate]
So I know that we can represent mathematical expressions using Feynman diagrams, however, I wonder if we could derive mathematical solutions from a Feynman diagram.
For example, if we have the Feynman ...
- 625
3
votes
1
answer
165
views
Creation and destruction of particles in the Path integral
Reading Zee's QFT book he defines the interacting partition function as follows
$$Z(J,\lambda)=\int\mathcal{D}\varphi \exp{\left(i\int d^4x \left[\frac{1}{2}((\partial\varphi)^2-m^2\phi^2)-\frac{\...
- 775
1
vote
1
answer
582
views
Electron–positron annihilation (Quantum electrodynamics)
I'm trying to learn a bit about quantum particles interactions and I've found something in Wikipedia that I find confusing. There are two different examples with different results about the same ...
- 13
1
vote
1
answer
48
views
Meaning of "coupling" in the context of Dark Matter decay?
I often hear the term "coupling" when people speak of a potentially decaying dark matter (DM) particle. I don't understand what a (hypothetical) DM particle should couple to when we consider ...
- 447