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Results tagged with standard-model
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user 36793
A model of the basic particles and forces featuring six quarks, three charged leptons, three massless neutral leptons and four fundamental force carrying bosons. The twelve fermions are arranged into three generations, while the bosons serve to explain the electromagnetic interaction plus the strong and weak nuclear forces (and the Higgs mechanism). Do NOT use this tag for the standard model of cosmology, etc..
5
votes
1
answer
1k
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Higgs is neutral but decays into photons-Why?
Higgs is neutral and therefore cannot have electromagnetic interactions. Then how can it decay into a pair of photons? Does it mean that particles need not be charged to have electromagnetic interacti …
- 27.2k
1
vote
Help me understand Lepton universality
In the limit of low momentum transfer i.e., $q^2\ll M_W^2$ and vanishing electron and muon mass, the electronic and muonic decay modes have equal decay rates i.e. $$\Gamma(\tau\to e^-\bar{\nu}_e\nu_\t …
- 27.2k
0
votes
Origin of CP violation in CKM matrix?
different phases in the CKM matrix for quarks and antiquarks results in CP violation... First off, why? how?
This is because if the mixing matrix for the quark fields is $V$, then that for the an …
- 27.2k
0
votes
1
answer
462
views
Why is the Fermi coupling $G_F$ is measured from muon decay?
The decay rate of all weak processes, calculated from the $V$-$A$ theory will contain a factor of $G_F$, the Fermi coupling constant. However, $G_F$ is usually measured from $\mu^-$ decay which is in …
- 27.2k
2
votes
2
answers
347
views
Expected consequence of the term $\theta F^{\mu\nu}\tilde{F}_{\mu\nu}$ in the Standard Model
There is a coupling in the standard model of the form $\theta F^{\mu\nu}\tilde{F}_{\mu\nu}$ where $F^{\mu\nu}$ is the QCD field strength. I've read that $\theta<10^{-8}$, which is speculated to be rel …
- 27.2k
4
votes
1
answer
237
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A question about the notation of the Standard model
The ${\rm SU(2)_L}$ doublets, for example, the left-handed quark doublets $Q_{iL}\equiv(u_{iL}, d_{iL})^T$ are assigned quantum numbers $(\textbf{3},\textbf{2})_{+1/6}$, which means $Q_{iL}$ are tripl …
- 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
0
votes
1
answer
462
views
Uncertainty principle and measurement of the mass of Virtual particles
We can have real photons as well as virtual photons. However, I think we can have only virtual weak gauge bosons $W^{\pm},Z$. Is that correct?
If virtual particles are just a manner of interpreting t …
- 27.2k
3
votes
1
answer
174
views
Lowering the type-I seesaw scale without fine-tuning
The type-I seesaw mechanism yields the effective neutrino mass $$m_\nu\sim -M_DM_N^{-1}M_D^T.$$ Here, $M_D$ is the Dirac neutrino mass coming from Yukawa coupling of the left-chiral neutrino with the …
- 27.2k
1
vote
A particle without gauge interactions
Sterile neutrinos do not have any gauge interaction (electroweak or strong) but only gravitational.
- 27.2k
2
votes
0
answers
191
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Anomalous baryon current in the Standard Model (SM) and the stability of free protons within...
In the Standard Model, the baryon number is not exactly conserved due to anomaly but the decay rate is extraordinarily small at ordinary temperatures. Does this make free protons unstable in the Stand …
- 27.2k
5
votes
1
answer
167
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Current knowledge of Higgs
What is the current knowledge about the Higgs field after its discovery in the LHC? Does it exactly mimic the standard model Higgs? Does this knowledge rules out the possibility of other Higgs particl …
- 27.2k
3
votes
2
answers
351
views
Global symmetry and particle multiplets
In chapter 20, of Peskin and Schroeder's quantum field theory book, they start with a comment that a global symmetry that is manifest lead to particle multiplets with restricted interactions. Can some …
- 27.2k
7
votes
1
answer
1k
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Quark mixing vs neutrino mixing, mass eigenstates, weak states and detection
I have some doubts regarding the CKM matrix in the quark sector and PMNS matrix in the leptonic sector. Let us call $(d^\prime, s^\prime, b^\prime)$
the weak basis for quarks and $(d,s,b)$ the mass ba …
- 27.2k
5
votes
1
answer
649
views
Noether Charge Operators In Electroweak Theory
In electroweak theory, for the first generation of leptons, in the doublet
$$\psi_L=\begin{pmatrix}
\nu_{eL}\\
e_L
\end{pmatrix}$$
we assign a non-abelian charge $I=\frac{1}{2}$. Is this a Noether ch …
- 27.2k