All Questions
23
questions
1
vote
0
answers
148
views
QFT Scattering Cross Section Integral
I came across this integral studying QFT regarding what I think it may be the calculation of a 2$\rightarrow$2 particle scattering cross section.
$$I = \int \frac{dp_3}{(2\pi)^32E_3} \frac{d p_4}{(2\...
- 11
3
votes
1
answer
495
views
Phase space factor for a two-body decay
I was trying to understand how pion decays to muons and not electrons because of helicity suppression. So I was trying to figure out the ratio of the decay widths.
PDG review for kinematics (...
- 131
1
vote
0
answers
137
views
If we had a Higgs triplet with hypercharge $Y=1$, would we get three Higgs bosons?
In the Standard Model, the Higgs field is a doublet of SU(2) and hypercharge $Y=1/2$. We have four real scalar degrees of freedom (since $H$ is a complex doublet); three of these get "eaten" ...
- 61
0
votes
1
answer
67
views
How many free parameters can there be in the mass matrix of the $X$ bosons?
Let the GUT symmetry $SU(5)$ break spontaneously to $SU(3) \times SU(2) \times U(1)$ at a scale $M$ much higher than the masses of $Z$ and $W$ bosons. Then, at this scale, $Z$, $W$ bosons can be ...
- 1,669
2
votes
1
answer
131
views
Why does the term $i\epsilon^{\alpha\mu\beta\nu}p_{\alpha}q_{\beta}$ vanish in the squared amplitude of the top decay?
I would like to calculate the squared of the amplitude of a top-decay $t-> Wb$. I know already the solution, but I can't get there: I get stuck with the Levi-Civita-Tensor on my way. Can you help ...
- 45
1
vote
1
answer
704
views
How to show that the charge conjugation reverses the charge of a state?
How to show that the charge conjugation operator reverses the charge(s) of a (fermionic or bosonic) state?
Let us consider a spin-$\frac{1}{2}$ fermionic state of momentum $\textbf{k}$ and spin ...
- 26.8k
4
votes
2
answers
485
views
Simplify quantum electrodynamics expression
I have a quantum electrodynamics exercise on the one-loop electron self-energy correction in which I need to show that
$$
\tag{1}
ie^{2}\Sigma(p)=\frac{\left(-ie\right)^{2}}{\left(2\pi\right)^{4}}\...
- 171
1
vote
1
answer
760
views
Breaking of a commutator involving Dirac spinors and gamma matrices
I'm trying to understand a particular step in the solution to problem 27 in THIS solution sheet. By the middle of the page, they start with the simplification of this expression
$$\left[s^{\mu}\left(...
- 171
0
votes
1
answer
457
views
Trace from Casimir's trick (muon neutrino- electron inelastic scattering)
Griffiths defines Feynman amplitude for the CC process $\nu_\mu + e \rightarrow \mu + \nu_e$ as
$$\mathscr{M} = \frac{ g_w^2}{8M_W^2} \left[\bar \nu_e \gamma^\mu (\mathbb{1} -\gamma^5) e\right] \...
- 15
1
vote
1
answer
134
views
Annihilation operator of a particle at $\bf x$ for canonically qauntized Klein Gordon field
I am now reading the David Tong's lecture notes on quantum field theory.
http://www.damtp.cam.ac.uk/user/tong/qft/two.pdf
And I have some questions on whether there is some well-defined particle ...
- 766
2
votes
2
answers
824
views
Feynman Diagrams for a quadratic interaction term
Consider the Lagrangian
$$\mathcal{L} = \dfrac{1}{2} (\partial_{\mu}\phi_{1})^2 + \dfrac{1}{2}(\partial_{\mu}\chi)^2 - \dfrac{M_1^2}{2}\phi_{1}^2 -\dfrac{M^2_\chi}{2} \chi^2 - \dfrac{\mu_\chi}{2} \...
- 319
2
votes
1
answer
985
views
Decay of a scalar Particle-Symmetry factors
Consider the Lagrangian
$$\mathcal{L} = \dfrac{1}{2} (\partial_{\mu}\phi_{1})^2 + \dfrac{1}{2}(\partial_{\mu}\chi)^2 - \dfrac{M_1^2}{2}\phi_{1}^2 -\dfrac{M^2_\chi}{2} \chi^2 - \dfrac{\mu_\chi}{2} \...
- 319
3
votes
1
answer
3k
views
Feynman diagrams for Yukawa Interaction
I'm solving some QFT problems and one of them deals with the Yukawa coupling. It asks to consider three processes, namely, $\psi\psi\to\psi\psi$, $\psi\bar{\psi}\to\psi\bar{\psi}$ and $\phi\phi\to\phi\...
- 36.4k
2
votes
1
answer
364
views
$\Omega^0_c \to \Sigma^+ K^-K^- \pi^+$ Feynman diagram
How can I work out the Feynman diagram for the decay process, $\Omega^0_c \to \Sigma^+ K^-K^- \pi^+$?
user147457
1
vote
2
answers
3k
views
Strange quark decay into two down quarks and an anti-down quark
I saw that a $\Sigma^+$ can decay into $n+\pi^+$, which means that the $s$-quark must decay into $dd\bar{d}$. However, is there a Feynman diagram to represent this? I cannot find one for either the $\...
- 2,122