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Results tagged with particle-physics
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user 36793
Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales. DO NOT USE THIS TAG for point particles in classical mechanics.
19
votes
2
answers
1k
views
Why is Higgs particle detected much later than top quark when it's lighter? [duplicate]
The Higgs boson is lighter than the top quark. But the top quark was discovered in the mid-1990s where the Higgs boson escaped detection for two more decades. So if the energy has already been achieve …
- 27.2k
15
votes
Accepted
Why does the Higgs field fall into the same ground state at all points across space?
If I understand it correct, then in a nutshell, you are asking why is the VEV independent of spacetime. If the Higgs field had different values at different points in space i.e., if it had a spacetime …
- 27.2k
14
votes
1
answer
18k
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Majorana mass vs Dirac Mass
Why is it said that the Dirac mass term conserves the fermion number but the Majorana mass term does not? Can someone explain this mathematically?
Which breakdown of symmetry is responsible for Major …
- 27.2k
11
votes
1
answer
2k
views
How does chirality of a massive fermion change with time?
For a massive fermions, like the electron, chirality is not conserved in time. It is not a good quantum number although it is Lorentz invariant. The Dirac Hamiltonian (in particular, the mass term in …
- 27.2k
9
votes
1
answer
717
views
effect of a simultaneous local and a global $U(1)$ symmetry breaking
EDIT : I am trying to figure out the effect of symmetry breaking in a $U(1)_Y\times U(1)_Z$ invariant lagrangian where $U(1)_Y$ is local symmetry of the Lagrangian and $U(1)_Z$ is a global symmetry of …
- 27.2k
8
votes
1
answer
981
views
Why is baryon or lepton violation in standard model is a non-perturbative effect?
The baryon number B or lepton number L violation in the standard model arise from triangle anomaly. Right? Triangle diagrams are perturbative diagrams. Then why the B or L violation in Standard model …
- 27.2k
8
votes
2
answers
2k
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How are strings of String theory different from particles in quantum field theory?
I'm not very familiar about String theory but just curious. I wanted to know, in what sense are the strings of string theory different from quanta of relativistic fields (which we interpret as particl …
- 27.2k
7
votes
3
answers
741
views
Criterion for a Feynman loop diagram to give a finite value
The contribution of loop diagrams in QFT are often divergent and sometimes convergent as well. For example, the self-energy corrections in QED are divergent. On the other hand, the Zee model of radiat …
- 27.2k
7
votes
1
answer
1k
views
Quark mixing vs neutrino mixing, mass eigenstates, weak states and detection
I have some doubts regarding the CKM matrix in the quark sector and PMNS matrix in the leptonic sector. Let us call $(d^\prime, s^\prime, b^\prime)$
the weak basis for quarks and $(d,s,b)$ the mass ba …
- 27.2k
7
votes
1
answer
887
views
Is $CP$ instead of $C$ responsible for changing a particle to its antiparticle?
The charge conjugation operator $C$ reverses the charge of a state. But it may or may not convert a particle to its antiparticle. For example, consider a neutrino which is charge-neutral and left-hand …
- 27.2k
6
votes
2
answers
1k
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What forbids off-diagonal elements in the kinetic terms of the Standard Model?
In the Standard Model, the gauge covariant kinetic term for the left-handed lepton doublets $\psi_{iL}=(\nu_{iL},e_{iL})^T$, for example, is given by $$i\overline{\psi_{iL}}\gamma^\mu D_\mu\psi_{iL}.$ …
- 27.2k
6
votes
1
answer
384
views
Difference between "C-violation without CP-violation" and "C-violation with CP -violation"
Consider two possible decay channels of a massive particle as $X\to A+B$ and $X\to C+D$ with decay rates $r$ and $1-r$ respectively. Let the decay rates of its antiparticle into channels $\bar X\to \b …
- 27.2k
6
votes
1
answer
530
views
Why is the Standard model Higgs not a candidate of dark matter (in particular, a WIMP)?
Please consider me as a naive self-learner in this field.
The Standard Model (SM) Higgs boson is electrically neutral and has a mass of around $125$ GeV (which lies in the WIMP window i.e., between 1 …
- 27.2k
6
votes
4
answers
1k
views
If a Goldstone boson is an excitation moving between degenerate vacua, how do symmetries rem...
In spontaneous symmetry breaking, moving around the circular valley of the Mexican hat potential doesn’t change the potential energy. These angular excitations are called Goldstone bosons. But doesn't …
- 27.2k
6
votes
3
answers
2k
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Unitarity of PMNS matrix
Why should the neutrino mixing matrix (PMNS matrix) be unitary? Is the unitarity dictated by experiments or is it a theoretical demand?
- 27.2k