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0answers
116 views

Range of forces from mass of force carrier?

Why is $\frac{\hbar}{mc}$ a good estimate of the range of the four forces, where $m$ is the mass of the carrier particle of the force? Inputting the pion mass gives $1.4\ \mathrm{fm}$ for the hadronic ...
1
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1answer
157 views

A strange particle, $X$, decays in the following way: $X → π^– + p$. State what interaction is involved in this decay

A strange particle, $X$, decays in the following way: $X → π^– + p$. State what interaction is involved in this decay. I know the answer to be weak interaction, but why is it weak interaction? What ...
4
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1answer
310 views

How are forces related to decays?

How are decays related to forces, what is meant by particle X decays through the, say, strong force? The way I understand forces is by how they change the acceleration of particles with the right ...
11
votes
1answer
981 views

Interpretation of derivative interaction term in QFT

I am trying to understand what a term like $$ \mathcal{L}_{int} = (\partial^{\mu}A )^2 B^2 $$ with $A$ and $B$ being scalar fields for instance means. I understand how to draw an interaction term in ...
4
votes
2answers
157 views

Interpretation of an “interaction” term

In QFT a polynomial (of degree >2) in the fields is said to be an interaction term, Ex.: $\lambda\phi^4$. Question Is it possible to give an interpretation to terms like $\frac{1}{\phi^n}$? (for ...
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1answer
296 views

How does the dressed Klein-Gordon propagator look in position space?

The free Klein-Gordon propagator in momentum space $\sim (p^2-m^2+i\epsilon)^{-1}$ has just a single pole at $p^2=m^2$. The passage to Fourier space is difficult but possible. The result is very ...
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3answers
1k views

Long/short-range interaction

A potential of the form $r^{-n}$ is often considered long-range, while one that decays exponentially is considered short-range. Is this characterization simply relative/conventional, or is there a ...
2
votes
2answers
568 views

Why $\lambda\phi^4$ theory, where $\lambda>0$, is not bounded from below?

Why the following interaction, in QFT, $$\displaystyle{\cal L}_{\rm int} ~=~\frac{\lambda}{4!}\phi^4$$ where $\lambda$ is positive, represents a theory that is unstable (or unbounded from below as it ...
2
votes
2answers
222 views

Interaction speed between electric charges and magnetic materials

Einstein said that the speed of a matter in universe cannot exceed the speed of light. Is it correct for electric force transmission speed from one electric charge to other one? What is ...
3
votes
1answer
200 views

Interacting system and relaxation times

I got a question I'm not sure how to state precisely or is it even valid. Any help is most welcomed. I stripped the question of all details because I wanted to emphasize my problem, but should ...
14
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7answers
456 views

Macroscopic laws which haven't been derived from microscopic laws

Can you think of examples where a macroscopic law coexists with a fully known microscopic law, but the former hasn't been derived from the latter (yet)? Or maybe a rule of thumb, which works but ...
4
votes
1answer
117 views

Intuitive picture for spin-fluctuations contribution to specific heat of He3

Usually when discussing Fermi liquid theory, it is stated that due to the quasiparticles effectively behaving like a free electron gas with effective mass, the specific heat is linear in $T$ at small ...
1
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3answers
497 views

How do magnets work?

I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works. I mean, magnetic substances ...
3
votes
2answers
136 views

Interacting classical strings?

May classical strings be interacting? I would guess no, I can not see any way to break a classical closed string in two of them (the "pants" diagram); but maybe I'm missing something.
2
votes
1answer
115 views

What's the meaning of the coupling change after a renormalization (in the 1-dim Ising Model)?

What does it mean that after the theory (1-dim Ising model here, but the question is general) is renormalized one time and $g_i\rightarrow g_i'$, that the couplings are weaker, even if the theory ...
6
votes
1answer
115 views

Expectation values of interacting fields

I was motivated to ask this question by the equality claimed in equation 10.3.3 of Weinberg's volume 1 of QFT books. My interpretation of that, If $O_s$ is a quantum field of spin $s$, $\psi_s$ is ...
5
votes
2answers
362 views

Lorentz transformation in light cone coordinates in string theory

What is the explicit form of the Lorentz transformation changing the light cone coordinates in the light cone gauge in string theory? The extended nature of the strings complicate matters, especially ...
3
votes
4answers
1k views

How can I explain why the weak nuclear interaction between individual nucleons is 'weak'?

By considering the energy-time uncertainty principle, estimate the range of the weak nuclear interaction at low energies. Compare this range to the size of a typical nucleon (for example, a proton) ...
6
votes
2answers
781 views

How do Leptons arise from Lambda decay?

I have a question for an assignment: Use your understanding of the quark model of hadrons and the boson model of the weak nuclear interaction to explain how leptons can arise from lambda decay, ...
2
votes
3answers
354 views

Fermionic interaction potentials

Are there any examples of fermionic particles or quasiparticles for which the interaction potential is a globally smooth function? i.e. no singularities or branch points. As an example, in Flügge's ...
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votes
3answers
839 views

What is physical in the principle of local gauge invariance? [closed]

Modern theories of interactions in particle physics are gauge ones. I know how the gauge fields are introduced in equations ($D = \partial + A$). I just do not see any physical motivation in it. I am ...