# Tag Info

0

I have to take issue with Demosthene's textual analysis in a comment on the question. To examine the physics rather than the way chemists talk, we should look at a tree level Feynman diagram for the reactions. Any reaction. Both the reactants and the products touch the participate in a vertex with the force carrying boson, so both have an equal claim to be ...

2

If certain reaction is allowed, the inverse reaction (if energy and momentum are conserved) will be allowed too. So neutrinos (not antineutrinos) can interact with neutrons to yield electrons and protons. For your second question: leptons can interact via electromagnetism, too. Electrons and positrons are leptons, and they interact mediated by photons: ...

-1

Is there a quark conservation law? No. In proton-antiproton annihilation (see Wikipedia) the quarks are destroyed. See this section: "...when a proton encounters an antiproton, one of its constituent valence quarks may annihilate with an antiquark, while the remaining quarks and antiquarks will undergo rearrangement into a number of mesons (mostly pions ...

2

In diagrams, you are just adding a disconnected non-interacting piece to the Feynman diagram (just a straight line for the added quark), so sure, just writing one or more additional quarks on both sides always yields an allowed reaction, although you can't be sure the quarks bind into a single state (e.g. if you added just a $u$ to your reaction instead of a ...

9

Yes, there are the quantum numbers Charm, Strangeness, Topness and Bottomness, which are conserved by strong and electromagnetic interactions, but not by weak interactions. Upness and Downness are simply the Isospin, which is also preserved for strong interactions, when the quark masses can be neglected, which is usually a very good approximation as ...

4

Charged hadrons, and neutral hadrons with nonzero magnetic moment, interact electromagnetically. A spinless, neutral hadron would not couple to the electromagnetic field at tree level, but the most obvious example of such a particle is the $\pi^0$, which decays electromagnetically to two photons. All particles with flavor participate in the weak ...

4

Quarks, the constituents of hadrons/mesons, interact via the strong, weak and electromagnetic force. So hadrons/mesons do interact via all this forces, too. Even if the total net-carge is zero. Take for instance the neutron, which has zero electric charge. Still it has a magnetic moment which gives rise to electromagnetic interactions. It can also decay via ...

1

In the context of nuclear or particle physics the phrase "the strong interaction" means the same thing as "the strong force". In fact we rarely write a formula for the strong force in the sense that we write Coulombs law for the electrostatic force. Both terms are refering to the strong nuclear force. In the context of perturbation theory (or the lack of ...

1

Usually such terms alter the Feynman rules in a subtle way through the measure in the functional integral. A non-linear sigma model in d=2 is a standard example. You have to add terms to the action containing $\delta^d(0)$ so as to cancel non-renormalizable loop diagrams with $k^{-2}$ in the propagator and two $k$'s in the numerator. If you omit these ...

0

The interpolating field couples to many states. This is summarized by the Lehaman-Kallen spectral representationfor the interacting propagator. Most field thoery books will have a discussion of this.

1

From an energy perspective, a free neutron sees a nucleus as a three-dimensional square well with a depth of a 5--10 MeV. The presence or absence of milli-eV thermal oscillations or eV-scale molecular bonds may change the details of the shape of that potential well, but in general the change is much less important than the uncertainty in the neutron's energy ...

Top 50 recent answers are included