Stack Exchange Network

Stack Exchange network consists of 174 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..

-1
votes
0answers
70 views

Is string theory inconsistent with the Standard Model of Elementary Particles?

According to (super)string theory, each fundamental particle represents a different vibrational mode of a relativistic string and each type of vibration pattern represents a different particle. But ...
1
vote
0answers
30 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 ...
-1
votes
0answers
43 views

Predicting the Frequencies of Visible Light [closed]

Why can't the Standard Model predict the frequency range of visible light; which must rather be inferred from measures of wavelength? Given that QFT is a gauge theory in which, since the fields are ...
35
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 ...
-2
votes
0answers
48 views

Why the Higgs mass has a upper and a lower bound?

in the above diagram what the $\Lambda$ axis is physically describing? How the graph will look like below 1TeV? why it is called new physics cut off scale?
0
votes
1answer
50 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
54 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
45 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
68 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 ...
0
votes
1answer
31 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
36 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
146 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
365 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
82 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
52 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 ...
0
votes
2answers
62 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
63 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
68 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
52 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
30 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 ...
0
votes
1answer
58 views

In the Standard Model of particle physics, why we ignore the gravitation force?

In the Standard Model of particle physics, we consider only three forces, my question is about the gravitation force why we ignore?
1
vote
1answer
50 views

The production of $b$ ($b$ bar) quarks

I have a question, please if there anyone helps me to understarnd how we distinguish the production pair of quarks $b$ ($b$ bar) it comes from a QCD background or comes from higgs decay?
2
votes
1answer
139 views

Why the photon doesn't acquire mass with the Higgs mechanism?

I did the computation that from $$(0,v)^{T}(\partial_\mu+igA_\mu^a\tau^a+i\frac{g'}{2}B_\mu)(\partial_\mu-igA_\mu^b\tau^b-i\frac{g'}{2}B_\mu)(0,v)$$ with $(0,v)$ being the expectation value of the ...
0
votes
2answers
88 views

Why does the pion live in a representation of isospin SU(2) and is the mediator of the strong force generated by color SU(3)?

Why does the pion live in a representation of isospin $\rm SU(2)$ and is the mediator of the strong force generated by color $\rm SU(3)$? I somehow find strange that this is the case. Given that $\rm ...
3
votes
2answers
46 views

High intensity laser and neutrino pair production

Given the very small rest mass of the neutrino, visible photons have plenty energy for neutrino pair creation. What would be the probability of $\gamma \to \nu + \bar\nu$? Would the neutrinos be ...
2
votes
1answer
81 views

Is this reaction even allowed? [closed]

$$p+p\rightarrow p+n+\pi^+$$ According to coservation laws, is this Allowed or Forbidden? If Allowed what type of interaction is this :- Strong, EM. or Weak? Why? From conservation of Charge &...
2
votes
0answers
27 views

Higgs decay at higher energies

If I look at the expected Higgs decay BR's vs. $m_H$ the WW and ZZ dominate over the tt decay mode in the over tt threshold region. From the mere couplings: $g_{ffH} = \sqrt2 m_f /v$ $g_{VVH} = 2 ...
1
vote
1answer
84 views

A question about isospin of pion and kaon

In Ch.18 of the textbook An Introduction to Quantum Field Theory by Peskin and Schroeder, on P.611 when discussing QCD renormalization of the weak interaction, two operators ${\cal O}^{1/2}$ and ${\...
1
vote
1answer
43 views

How accurate is the Standard Model at explaining everyday phenomena? How do we know the answer?

I've read many times that "the Standard Model can explain all everyday phenomena (except gravity)." But I haven't been able to find out what exactly is meant by this. If I were to simulate (...
3
votes
2answers
62 views

How do know that Goldstone Boson actually become the longitude degrees of freedom in W+,W- and Z boson?

In many Quantum Field Theory text books they says these about Spontaneous Breaking and Higgs mechanism like this In unitary gauge, the Goldstone Bosons are eaten by $W^\pm$ and Z and become their ...
3
votes
2answers
142 views

How do we know that gluons travel at the speed of light?

Since gluons are located within nucleons and immediately outside of them, how do experiments determine parameters like their speed? Is it possible we could be assuming they travel at the speed of ...
0
votes
1answer
35 views

Why does the upper component of a $SU(2)$ doublet has $T^3=1/2$ and lower component $T^3=-1/2$ and not the opposite?

For a $SU(2)$ doublet, why does the upper component have $T^3=1/2$ and lower component $T^3=-1/2$? I know that this can be answered in the Standard Model by using $Q=T^3+Y/2$. But that is because we ...
-5
votes
1answer
84 views

Do gauge bosons really exist? [closed]

Do gauge bosons really exist or are they only a mathematical model? Have we ever detected them?
2
votes
1answer
104 views

Light neutrino number from the invisible decay width of $Z$ boson, and precluding heavy neutrinos as dark matter candidate

The $Z$ boson decays into pairs of quarks and leptons. While the decays to quarks pairs and charged lepton pairs can be observed, the decays to $\nu\bar\nu$ are cannot be. By subtracting the visible ...
1
vote
0answers
26 views

Symmetry breaking with Kinetic term dominating the Potential on a Lagrangian

Suppose a Lagrangian $L$ for a scalar field $\phi$, consists of a kinetic term and a Mexican-hat type potential. I am aware that if the vacuum has symmetry $H \subset G$ while the Lagrangian has ...
5
votes
1answer
108 views

Is the electroweak $SU(2)$ gauge symmetry an exact symmetry in Standard Model before spontaneous symmetry breaking?

In Standard model, components of a $SU(2)$ doublet (for example $u$ and $d$) have different masses. This means there is no $SU(2)$ symmetry, but I think it is okay because the $SU(2)$ symmetry is ...
0
votes
1answer
64 views

Pion decay constant: How to know which convention to follow?

As summarized by Wikipedia, different sources use different choices for the (pion) decay constant. This means that the numerical value can vary between $$ \sqrt 2\ f_\pi \quad\leftrightarrow\quad f_\...
12
votes
5answers
2k views

Why do we say there are four fundamental forces in the Standard Model (if gravity is included)? [duplicate]

In my physics textbook (and in popular science culture) it is stated that there are four fundamental forces: electromagnetism, strong, weak, and gravity. But Wikipedia tells me that there is a ...
0
votes
3answers
352 views

Is spinor the sum of scalar, vector, bi-vector, pseudo-vector, and pseudo-scalar?

Is spinor $\psi$ actually the sum of scalar, vector, bi-vector, ..., pseudo-scalar? Before talking about spinors, we have to differentiate two kinds of spacetime, demonstrated with the example of ...
8
votes
1answer
810 views

Is it a coincidence that quarks have exactly -1/3 or 2/3 the electron's charge? [duplicate]

I have read these questions: Why do quarks have a fractional charge? Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges? Hypercharge for $U(1)$ ...
0
votes
0answers
24 views

What Standard Model extensions are getting constrained by today's new measurement of the electron's EDM?

As published today in Nature: Improved limit on the electric dipole moment of the electron (free to view) and summarized on Live Science. They improve on the previous measurements by an order of ...
0
votes
1answer
61 views

Coefficients of Color Potential in Quarks [duplicate]

I was wondering if there was a relation between the fractional coefficients $$2/3, 1/3$$ obtained when calculating color potential for quarks and the value of electric charge for the up and down quark....
1
vote
1answer
73 views

Displacement current quantum mechanical interpretation?

while there are quite many classical explanations of displacement current to make Maxwell's equations work, see e.g. here: Displacement current - how to think of it , it sounds just a little bit like ...
1
vote
1answer
52 views

Electroweak to Electro/Weak Bosons?

I apologise in advance, this is something I just can't seem to get my head around. So it's my understanding that before the electroweak force split, there were four bosons - $W1$, $W2$, $W3$ and $B$ - ...
0
votes
1answer
108 views

Is this Feynman diagram possible?

I have been introduced to Feynman diagrams in a particle physics University module and I just created this diagram to practice checking conservation laws: I have been told that charge, baryon and ...
1
vote
2answers
91 views

Why is boson spin number related to attraction and repulsion?

The accepted answer to this question says Since the electroweak interaction is mediated by spin 1 bosons, it is the case that "like (charge) repels like and opposites attract". Another answer ...
-1
votes
1answer
19 views

Question about the spin of the antiparticle of $Δ^-$

Ι came across a statement in a physics book that the spin of the antiparticle of baryon $Δ^-$ is 1/2. I know that the spin for regular $Δ^-$ is 3/2, and - as far as I know - the spin of particles and ...
1
vote
1answer
94 views

Rho and Omega meson mixing

I am new to particle physics. So this might seem to be a trivial question. I read about $\omega$ and $\phi$ meson states being written in terms of octet and singlet state. In the same way, can $\...
0
votes
0answers
36 views

Is there a published list of particles that can be produced from the fundamental particles in the Standard Model?

I read an article that has made me curious to ask if there is a list of all the possible particles that can be generated by the fundamental particles in the Standard Model. Here is the article http:...
0
votes
1answer
70 views

Does the weak force obey the CPT symmetry? How?

I have read that the weak force does not obey the charge symmetry, the parity symmetry, and the time reversal symmetry. Then how does it obey the CPT symmetry?