Tagged Questions
1
vote
1answer
45 views
Baryon wave function symmetry
If a baryon wavefunction is $\Psi = \psi_{spatial} \psi_{colour} \psi_{flavour} \psi_{spin}$,
and we consider the ground state (L=0) only.
We know that the whole thing has to be antisymmetric under ...
5
votes
2answers
96 views
What maintains quark spin alignments in baryons?
What maintains quark spin alignments in baryons?
The $uud$ proton and $udd$ neutron are both spin 1/2, implying that two of their spin 1/2 quarks are always parallel and the other is always opposed.
...
1
vote
1answer
50 views
Testing covariance of an expression?
This is something I've been unsure of for a while but still don't quite get.
How does one tell whether an expression (e.g. the Dirac equation) is covariant or not? I get it for a single tensor, but ...
1
vote
1answer
140 views
Symmetry and Conservation
According to Noether's theorem, "Every conservation law corresponds to an underlying symetry or vice-versa" . For example, conservation of linear momentum corresponds to translational symmetry, ...
0
votes
2answers
207 views
Scalar potential, vector potential, and spinor potnetial
In Particle Physics, I've seen Scalar potentials which look like this $$ V = a \Phi^2 + b \Phi^4$$
$\Phi$ is scalar (a number).
What about vector potentials, and spinor potentials? How are they ...
3
votes
1answer
177 views
Lepton Number Conservation
What is the global symmetry of the electroweak Lagrangian that gives rise to lepton number conservation?
As I understand it, electric charge is some linear combination of the conserved quantities ...
6
votes
4answers
295 views
What is meant by the phrase “the mass is protected by a symmetry”?
In a particle physics context I've heard this phrase used. I guess it means that the mass of a particle is less than you'd naively expect from $E=mc^2$ after computing the momentum uncertainty ...
2
votes
1answer
129 views
Similar masses and lifetimes of the $\Delta$ baryons
Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
1
vote
1answer
257 views
Understanding P-, CP-, CPT-violation etc. in field theory and in relation to the principle of relativity
I can never get my head around the violations of $P-$, $CP-$, $CPT-$ violations and their friends. Since the single term "symmetry" is so overused in physics and one has for example to watch out and ...
19
votes
1answer
66 views
Any use for $F_4$ in hep-th?
In high energy physics, the use of the classical Lie groups are common place, and in the Grand Unification the use of $E_{6,7,8}$ is also common place.
In string theory $G_2$ is sometimes utilized, ...
1
vote
4answers
383 views
Is “real” antimatter (odd under C, P, T) unphysical?
A positron is odd under charge conjugation and parity reversal but nevertheless even with respect to time reversal. Is a theoretical positron which would be odd under all three symmetries (C, P, T) ...
