Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [standard-model]

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..

0
votes
0answers
10 views

Electron capture cross-section at qualitative level

I would like to compute the cross-section of electron capture but, as I understand, it is impossible in terms of usual QED due to the hadronic structure of nucleus. But it seems that there is a ...
0
votes
1answer
27 views

Is quantitative knowledge of the Standard Model useful in the development of controlled fusion?

I have read articles about quantitative knowledge of particle physics, such as energies, cross sections and particle lifetimes, gained from work at the LHC and other accelerators. Is such quantitative ...
1
vote
1answer
46 views

Why does literature list the strong coupling at the scale of the Z-boson's mass?

In the 2004 edition of the book "QCD as a Theory of Hadrons" by S. Narison, the author provides a value for the strong coupling at a scale of the mass of the Z boson, $$ \alpha_s (M_Z) = 0.1181 \pm ...
0
votes
1answer
43 views

Are there theories that can predict the Yukawa couplings?

In the standard model, the Yukawa couplings, hence the masses of the fermions, are free parameters and are only determined by experiment. Are there beyond the SM theories that can "predict" the Yukawa ...
0
votes
3answers
81 views

Why is the proton (uud) lighter than the $Δ^0$ (uud) baryon?

Neutron has quark composition udd with spin $\frac 12$. $\Delta^0$ baryon has quark composition udd with spin $3 \over 2$. On Wikipedia it says that $\Delta$ baryons have mass of approximately $1232 ...
0
votes
2answers
50 views

Retrodiction of Particle Masses

While researching baryon asymmetry, I came across this article discussing problems with the Standard Model, where it is noted that: The Standard Model did not and cannot predict the masses of the ...
1
vote
2answers
65 views

Is the interaction $\gamma p \to \pi^+n$ allowed?

I'm doing an undergraduate lecture course in particle physics and I'm still getting to grips with the basics of interactions. One of the example interactions I've been given in an exercise is $\gamma ...
0
votes
2answers
64 views

What elementary particles have properties that vary by spin direction?

This table of elementary particles indicates that electron spin = 1/2. My understanding is that electron spin may proceed in two directions which may be denoted by spin sign and that electron spin ...
3
votes
1answer
55 views

How can matter and anti-matter coexist in a meson?

Whilst learning about the nature of subatomic particles, I came along a pion zero meson. What really stumbled me was that the quark configuration of the particles was up and anti-up or down and anti-...
3
votes
0answers
46 views

What is the origin of the electric charge? [duplicate]

What is the origin of the electric charge? In order to explain mass we had to postulate the existence of a quantum field (Higgs field), and we say that elementary particles get their mass by ...
2
votes
2answers
140 views

Electric charge of the Higgs field

The Higgs field is \begin{equation} \Phi = \left( \begin{array}{cc} \phi_{1} + i\phi_{2} \\ \phi_{3} + i\phi_{4} \end{array} \right) \tag{1} \end{equation} with $\phi_{1}$ and $\phi_{2}$ ...
0
votes
2answers
59 views

Layperson can not get his head around Force Carriers

I read all I can but, this is vexing me. It realtes to Quantum-Mechanics, and I believe Quantum Field Theory, and maybe even Quantum Chromodynamics. Before the Higgs the Model was 16 instead of 17 we ...
4
votes
5answers
129 views

Why are matter fields predominantly fermions?

Apart from the Higgs, all matter is made up of fermions. Is there any obvious reason why that is?
0
votes
0answers
30 views

How is the standard model actually quantized?

The standard model Lagrangian is well known. But there are several ways to quantize a theory starting from the Lagrangian. In particular there are several ways to quantize gauge theories (e.g. ...
1
vote
0answers
29 views

Gauge singlet under SM

What does it mean when they say something is a gauge singlet under the Standard Model group? I would like to understand this concept of Singlets and Doublets. Thanks in advance.
1
vote
1answer
77 views

$W$, $Z$ bozons and fermions gained their masses WHEN?

I have read these questions: How does the Higgs mechanism work? How does the Higgs boson give mass to other elementary particles like electrons? What is the difference between the Higgs Boson ...
1
vote
0answers
22 views

Interpretation of a CLs exclusion plot

I have some trouble with the interpretation of this plot. The plot on the right shows the CLs values for the SM Higgs boson hypothesis as a function of the Higgs boson mass in the range 110–145 GeV. I ...
0
votes
3answers
115 views

Difference between $W^-$ and $\pi^-$

Maybe it's a very naif question, but what is the difference between a $W^-$ and a $\pi^-$? I mean they both change a $d$ into a $u$ right? $d \rightarrow u W^- \quad \text{and} \quad d \rightarrow ...
1
vote
1answer
41 views

Maximal Parity violation in Weak interactions

In 1956 Lee and Yang proposed parity violation of the weak interactions to explain the $\theta-\tau$ puzzle. The following year, 1957, Madam Wu and collaborators found that in the $\beta$ decay of ...
0
votes
3answers
143 views

Why do quarks and gluons have colour?

I asked a question here a few days ago and got some fantastic answers so I'm going to continue. Let me preface this by saying I know quarks do not actually have 'colour', but colour is some sort of ...
2
votes
1answer
95 views

Beta function in the Standard Model

In Srednicki's textbook "Quantum Field Theory", Problem 89.4 asks us to compute the leading terms in the beta function for each of the three gauge couplings of the Standard Model. These gauge ...
3
votes
1answer
41 views

Relationship between compactification moduli and generations in standard model

The situation I am describing is a $10D$ heterotic string theory which is compactified on a Calabi-Yau to get a $N=1$, $4D$ effective theory. It is mentioned in Ashoke Sen's notes on string ...
2
votes
1answer
69 views

When can you simplify the $W$ boson propagator?

I have seen in several sources that the propagator of the $W$ boson is: $$\frac{- i \left( g^{\mu\nu} - \frac{P^\mu P^\nu}{m_W^2} \right)}{p^2 - m_W^2} . $$ But then in some calculations (usually ...
0
votes
1answer
53 views

Why is the Higgs $CP$ even?

Why was it always assumed that the Higgs boson is a CP even particle? I understand that experimentally, it just is so but I am under the impression that before its discovery people took it to be CP ...
0
votes
1answer
75 views

Comparison between $\rho^0$ and $J/\psi$ decay mode

Why must a hadronic decay of the $J/\psi$ meson include (at least) three gluons? Why is the decay mediated by a single gluon allowed for the $\rho^0$ meson?
0
votes
1answer
79 views

How do Fermions with $0$ weak hyper charge couple to electro-weak force?

If you have two fermions (with spin $\pm \frac{1}{2}$) that form a weak-isospin doublet and their respective right-handed fermions which are weak-isospin singlets, what would it imply if the doublet ...
0
votes
0answers
80 views

Products of Lie-Groups versus Lie-Group Extensions in Physics

The Standard Model of elementary particle physics is a gauge theory based on the Lie group $U(1) \times SU(2) \times SU(3)$. From the mathematical perspective I read that: Simple Lie groups have ...
-1
votes
2answers
40 views

Naive question about lepton/quark energy states

I understand there are 3 energy states for quarks and leptons (electron, muon, tauon... Up, charm, top etc.) And we have 3 forces (not including gravity, em, strong and weak). This naively seems ...
1
vote
0answers
32 views

Shape of electron [duplicate]

Today, in the BBC Science section, a headline reads that the Imperial College of London has determined that the shape of the electron is completely spherical. In a physics book I'm reading now, the ...
3
votes
2answers
80 views

How are composite hadron fields related to elementary quark fields?

(This question is related to: A pedagogical exposition of the hadron physics?) I'm a mathematician who has been trying to learn quantum field theory for a while. I've gone through large parts of ...
1
vote
1answer
39 views

What was the prediction of the standard electroweak theory about the $W$ and $Z$ boson masses?

The standard electroweak theory has two coupling constants $g$ and $g^\prime$. In this theory, the $W$ mass and $Z$ mass are given by $$M_W=\frac{1}{2}gv,~M_Z=\frac{1}{2}(g^2+g^{\prime 2})^{1/2}v$$ ...
1
vote
2answers
68 views

Why are the generations of leptons/quarks regarded as fundamental particles?

My understanding is that 'fundamental' pertains to there being a distinct quantum field corresponding to the particle. I ask the question above based on the fact that the heavier generations of ...
8
votes
2answers
2k views

What is the difference between a neutrino and an electron neutrino?

So, what is the difference between a neutrino and an electron neutrino? Like how does the term 'electron' made a difference? Also, what is the difference between an antineutrino and an electron ...
0
votes
0answers
52 views

How does Alain Connes NCG compare phenomenologically with superstring theory?

In Veltmans book on QFT, diagrammatica, the full SM Lagrangian is published. There are more than a hundred terms and it looks pretty uninspiring and not quite the kind of equation one would want to ...
36
votes
6answers
10k views

Is the Higgs boson an elementary particle? If so, why does it decay? [duplicate]

The Higgs boson is an excitation of the Higgs field and is very massive and short lived. It also interacts with the Higgs field and thus is able to experience mass. Why does it decay if it is ...
0
votes
1answer
54 views

Scalar particles are described by a real scalar field or by a complex one?

Well, in the title is already stated my main question. I know you can use a complex scalar field to describe two real scalar fields, by using just one that involves both of them. But, in the modern ...
0
votes
1answer
56 views

How to analyse the LHC signal for Higgs?

With increasing energy the collision decreases in the plot for signal in LHC. why is that? and at an energy 125GeV the no of events suddenly increases. How this proves that higgs has a mass of 125GeV?
2
votes
1answer
50 views

Can the EM field self-interact in the Standard Model?

Since the EM field is a linear combination of the electroweak $U(1)$ gauge field and one of the $SU(2)$ gauge fields, does this mean that it has self-interaction terms carried over from the ...
3
votes
2answers
72 views

Leptons during Electroweak Epoch

Prior to the electroweak force splitting, did charged leptons still carry a charge of $e$? I was under the impression that, since electromagnetism didn't exist in its current state prior to ...
-1
votes
1answer
45 views

Are Generations and Families of elementary fermions one and the same?

I've seen both terms being used in papers and it seems to me they essentially mean the same thing referring to three generations of leptons and quarks as families. Is this true or are there some ...
0
votes
0answers
37 views

Elementary particles & their reactions: literature

I would like to find a book which contains lot of examples of different reactions with elementary particles (for instance, electron-electron scattering, electron-positron annihilation, electron ...
0
votes
3answers
181 views

Left Handed / Right Handed Particles and the Weak Force

Good Afternoon, I am a 50-year-old guy who was never a scientist or physics student. Just a person who loves to read books on particle physics. I have a question on the Weak Force and particles. (...
3
votes
2answers
423 views

Why is neutron slightly heavier than the proton? [duplicate]

With latest knowledge of QCD, is there any explanation for why the neutron is slightly heavier than the proton? Can it be boiled down to a simple formula?
2
votes
2answers
99 views

Is this feynman diagram possible? $e^- + e^+ \to \nu_\mu + \bar{\nu}_\mu$

I am starting to learn about Feynman diagrams and I have been told that flavour has to be conserved at vertices in the case that the exchange particle was neutral. Since here the exchange particle is ...
1
vote
1answer
55 views

When is $Q= B/2 + I_3$ true in particle physics?

I have seen stated that for unflavoured quarks, the relation between baryon number, electric charge and third component of isospin can be written as $Q= B/2 + I_3$. However, I have also seen this ...
1
vote
2answers
74 views

Why is the relative angular momentum of quark+antiquark in a pion equal to zero?

In a set of lecture notes provided by my lecturer, it says that a pion consists of a quark ($q$) and an antiquark ($\bar{q_2}$) with relative $L=0$. The negative parity and the fact that $S=0$ makes ...
1
vote
0answers
67 views

Lecture notes by Rudolf Mössbauer

Rudolf Mössbauer was an excellent lecturer. He gave lectures on Neutrino Physics, Neutrino Oscillations, The Unification of the Electromagnetic and Weak Interactions and The Interaction of Photons and ...
2
votes
0answers
70 views

Why is the standard model renormalizable if we believe it is an effective theory? [duplicate]

We believe that the standard model is only an effective field theory of its true UV completion. However, effective theories have dimensionful couplings and are not renormalizable. The standard model ...
3
votes
1answer
57 views

Scattering matrix symmetries and standard model

I am not able to get around the following question (if it make sense): Suppose I can derive the scattering matrix S for any particle scattering process. Suppose that the standard model is actually ...
1
vote
1answer
33 views

Which direction does “the mirror” in the Wu experiment flip?

I have seen two different setups for the Wu experiment: One where the "imaginary" mirror flips the experiment along a plane parallel to the magnetic field and one where the mirror is aligned ...