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 ...

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4
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88 views

Why is Quark Mixing forbidden in the Lagrangian (pre CKM)

The corresponding term in Lagrangian for the coupling of quarks to gauge fields reads: $$ \sum_{i} \bar Q_i D_\mu \gamma^ \mu Q_i .$$ Considering the Yukawa terms, it is generally stated that no ...
2
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0answers
105 views

What is the meaning of SU(2) triplet scalar field? [closed]

The following is an about a Left-Right Symmetric model. $SU(2)\otimes SU(2)$ $(2\otimes 2=3\oplus 1)$ will generate a triplet, which in Left-Right Symmetric model is $$\vec{\Delta}=\begin{pmatrix}\...
11
votes
1answer
576 views

Why is the charmed eta meson its own antiparticle, but the neutral kaon is not?

I have a limited understanding of antiparticles, so this may be why I am unable to explain why certain mesons are their own antiparticles, while others are not. My understanding is that antiparticles ...
0
votes
1answer
42 views

What are all charge-like quantum numbers?

What are all charge-like quantum numbers? In particle physics there are often things (like charge conjugation) that apply to all charge like quantum numbers. Everytime I read something about charge-...
1
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1answer
44 views

Why do the different lepton generations have different masses?

I've been reading Mark Srednicki's book on Quantum Field Theory, and toward the end (Chapter 88), he describes how the different generations of leptons acquire mass via Yukawa interactions. However, I'...
3
votes
1answer
94 views

Interpreting the Cross Section Ratio R

Below is experimental data for the ratio $$R=\frac{\sigma(e^+e^-\rightarrow hadrons)}{\sigma(e^+e^-\rightarrow\mu^+\mu^-)}$$ as a function of the centre of mass energy $\sqrt s$. I am interested in ...
0
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0answers
26 views

What is the difference between the generation of mass for Fermions compared with Bosons in the standard model?

I've seen a few questions asking how the Higgs mechanism generates mass for particles of the standard model. However, I haven't seen any which specify the differences between Bosons and Fermions in ...
2
votes
0answers
45 views

Lepton and strangeness conservation [closed]

Do I have a misunderstanding here at all? The question states: One of the following equations represents a possible decay of the K$^+$ kaon. \begin{align}\mathrm K^+&\to\pi^++\pi^0\\\mathrm K^+...
-1
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1answer
49 views

Can a massless quark exist?

Is there any possible way to extract all the mass of a quark? Probably under extreme Gs or heat or pressure?
2
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0answers
37 views

Identical Particle Wavefunctions

Consider the process $$\rho^0\rightarrow\pi^0+\pi^0$$ The $\rho^0$ has $J=1$ whilst the two pions have $S_{tot}=0$ and thus require $L_{tot}=1$ by conservation of angular momentum. Consequently this ...
7
votes
2answers
110 views

How can $\Lambda^0$ and $\Sigma^0$ both have $uds$ quark content?

Title says it all: How can $\Lambda^0$ and $\Sigma^0$ both have $uds$ quark content? Doesn't this make them the same baryon?
0
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1answer
46 views

Gluon to quark scattering

I am trying to calculate the $g g\to q \bar q$ amplitude but am finding it intractably complex. I have determined that there are only two independent polarizations that contribute non-zero ...
3
votes
2answers
266 views

Do Standard Model Yukawa couplings depend on the gauge choice?

In the standard model and the Unitary gauge, we write the Higgs field as $ \phi = \frac{1}{\sqrt{2}} \begin{pmatrix} 0 \\ v + H \end{pmatrix}$ and the Yukawa couplings (leaving out the neutrino ...
2
votes
0answers
100 views

Shouldn't there be 6 fundamental forces? [closed]

I'm listening to Leonard Susskind's The Black Hole War. In it he states (paraphrased) that a string wrapped around a compact dimension once imparts one unit of charge. Wrapped one way, it's a ...
2
votes
0answers
47 views

Are the pions really all that light?

I'm studying the sigma model where the pions are identified as the (pseudo) Nambu-Goldstone bosons of chiral symmetry breaking ("pseudo" from mild isospin symmetry violation). This argument usually ...
2
votes
1answer
277 views

$G$-parity in an electromagnetic decay

I am looking at the decay $\eta\rightarrow\pi^+\pi^-\gamma$ and I would assume that the decay itself (ignoring the $\pi\pi$ final state interaction that is obviously strong) is electromagnetic since ...
1
vote
1answer
55 views

Why don't all the gluon's get converted into energy in an uranium atom undergoing fission?

I have following questions and arguments. why do only gluons get converted into energy in an uranium atom undergoing fission? why don't all the gluons get converted into energy? which conditions ...
4
votes
1answer
167 views

Pion decay: V-A vs. V coupling

For the Decay $$ \pi^- \to \mu^- \bar{\nu}_\mu $$ the Feynman rules for this tell us that the vertex couples with $\gamma^\mu (1-\gamma^5) / \sqrt{2} $. This gives me the reduced amplitude of $$ M = \...
6
votes
1answer
164 views

Why did it take so long to find the Higgs?

The $W$ and $Z$ boson took a long time to be discovered because they were so heavy; we couldn't produce them in a particle collider until the 80's. But the Higgs boson isn't that much heavier than the ...
3
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0answers
71 views

Few questions regarding String-Net theory and the Standard Model

A friend today showed me this post and after reading Prof. Wen's answer, few questions came to my mind. Prof. Wen says: all fermions (elementary or composite) must carry gauge charges (see cond-...
12
votes
2answers
686 views

What's the deepest reason why QCD bound states have integer charge?

What's the deepest reason why QCD bound states have integer electric charge, i.e. equal to an integer times the electron charge? Given that the quarks have the fractional electric charges they do, ...
3
votes
2answers
68 views

Are the properties assigned to quarks meaningful?

Suspect this may have been asked before, but can't find it. My question is: If you can never have a free quark, what sense does it make to attribute properties to them, since you can never ...
1
vote
0answers
29 views

How do I go about understanding particle physics? [closed]

My science project has tasked me in creating a research paper on the standard model of particle physics, but I'm not in highschool yet. I don't know how to go about learning the math and the concepts ...
1
vote
1answer
50 views

The charges of the forces

I am trying to establish a simplified understanding of the fundamental forces to explain them to a young audience. If we say that gravity has one charge (attractive), electromagnetism has two charges ...
0
votes
1answer
124 views

Why are quarks fundamental particles? [closed]

A neutron decays into a proton by changing one of its down quark into an up quark and releasing energy, positron and neutrino particle. So, a down quark can decay into an up quark. If a quark decays,...
7
votes
1answer
137 views

The process $\mu^+\mu^-\rightarrow hh$

I am doing some calculations in the Standard Model. I have a question that seems rather simple but makes me think a lot. I want to compute the cross section of the following process at the leading ...
4
votes
1answer
277 views

Computing box diagrams with non-vanishing external momenta

I'm trying to explicitly compute the following box diagram in the Feynman-t'Hooft gauge: If I neglect the impulsion of the $s$ quark, then the final amplitude is given by $$\mathcal{A} \propto [\...
1
vote
1answer
72 views

Is there a standard resource that lists all understood particle-particle relationships?

I am just starting to dig a little deeper into particle interactions, and just have an introductory college physics background (no quantum mechanics). But I am interested in the conditions of the ...
4
votes
2answers
147 views

Top quark mass $m_t$ at energy scales $\mu < m_t$?

Edit - Maybe formulated differently: Does it make sense to talk about the top mass at energies below $m_t$, although in all processes the corresponding energy scale is above $m_t$, because of the rest ...
1
vote
1answer
92 views

How do Higgs field provide mass to other particles? [closed]

I know this question has been posted so many times here but still I have some confusions about Higgs mechanism. I watched some videos relating to Higgs mechanism and they says the Higgs field provide ...
1
vote
0answers
35 views

Where does the square root of two in the conversion between the Fermi constant and the weak coupling constant come from?

As in the title, where does the square root of two in the conversion $$ G_{F}=\frac{\sqrt{2}g^{2}}{8m_{W}^{2}} $$ between the Fermi constant and the weak coupling constant come from? I was able to ...
5
votes
2answers
243 views

What is the exact relation between $\mathrm{SU(3)}$ flavour symmetry and the Gell-Mann–Nishijima relation

I'm trying to understand how the Gell-Mann–Nishijima relation has been derived: \begin{equation} Q = I_3 + \frac{Y}{2} \end{equation} where $Q$ is the electric charge of the quarks, $I_3$ is the ...
2
votes
2answers
277 views

Is $SU(2)$ really broken by the Higgs VEV or just hidden?

It's generally stated in the textbooks that whent the Higgs field acquires a certain vev the corresponding symmetry is spontaneously broken. For example in A. Zee - QFT in a Nutshell: But none of ...
3
votes
2answers
173 views

Origin of Mexican hat potential in Higgs mechanism

I have recently read a layman's version of the Higgs mechanism with a Mexican hat potential. The only thing I don't get is what actually causes the Higgs potential to have a Mexican hat shape?
1
vote
3answers
69 views

How is each neutrino associated with a specific charged lepton?

For instance, why is an electron neutrino called that and what is its relationship with an electron?
1
vote
3answers
141 views

What is the difference between toy models and normal models? [closed]

Here is the short description of scientific model: an imperfect or idealized representation of a physical system And the definition of toy model: a simplified set of objects and equations ...
0
votes
1answer
60 views

Computing the pole mass from a given $\overline{MS}$ mass?

Given a Yukawa coupling as a function of scale $\mu$ and a vev, therefore $m_R(μ)=Y(μ)⟨ϕ⟩$, how can I compute the corresponding pole mass $m_p$? Relations I was able to find are (page 39) $$m_p=m_R−Σ(...
1
vote
1answer
130 views

Mirror/Parity symmetry in spin

We just saw parity symmetry and we were told about the experiments to see the non parity symmetry of disintegration, in particular one involving the reaction: $$^{60}Co\longrightarrow^{60}Ni+ e + \...
1
vote
1answer
74 views

Why only left-handed neutrinos have been observed yet?

This is what I understood (it may be wrong, so please correct me): since every particle is "divided" into a lefthand and a righthand partner, which is what guarantees the particles to have mass, and ...
-1
votes
1answer
309 views

Is the neutral pi meson a relativistic electron positron pair?

Is the neutral pi meson a relativistic electron positron pair? An electron position pair orbiting at relativistic speeds is proposed as a model of a neutral pi meson by Ernest Sternglass. However, ...
16
votes
1answer
3k views

Origin of electric charge

Baryons have charges that are the result of a polynomial calculation of their building blocks (quarks)'s fractional charges. But what gives these quarks electric charges? What interactions do they ...
1
vote
1answer
76 views

Why do we say that gluons carry color charge?

We know that gluons are Lie algebra $su(3)$-valued one-form fiels $A_{\mu}$. And because of $[A_\mu,A_\nu]$ does not vanish generally for the non-Abelian case, gluons have self-interactions. Now how ...
2
votes
1answer
210 views

Group theoretical reason that Gluons carry color-charge and anti-colorcharge

I was wondering how it is possible to see from the $SU(3)$ Gauge Theory alone that Gluons carry two charges colors: $g\overline{b}$ etc. Some background: The W-Bosons (pre-symmetry breaking) ...
18
votes
2answers
1k views

What is (meant by) a non-compact $U(1)$ Lie group?

In John Preskill's review of monopoles he states on p. 471 Nowadays, we have another way of understanding why electric charge is quantized. Charge is quantized if the electromagnetic $U(l)_{\rm em}...
1
vote
2answers
103 views

How is an electron “recycled” in a neutron?

A proton is made up, they say, by 2 up and 1 down quark, drowned in a sea of virual paricles: when an electron is captured this process thereby changes a nuclear proton to a neutron and ...
3
votes
1answer
53 views

Does the Peccei-Quinn (PQ) mechanism require fine-tuning?

The strong CP problem: the QCD theta parameter can not be arbitrarily small due to 't Hooft's doctrine of naturalness (a parameter can be arbitrarily small only when putting it to zero provides an ...
0
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0answers
51 views

Mass of an imaginative stable top quark at low energies? [duplicate]

Masses are not fixed quantities, but change with energy because of the renormalization group running. These can be calculated in a given renormalization scheme, for example, the MS scheme: Imagine ...
17
votes
5answers
9k views

Why don’t photons interact with the Higgs field?

Why don’t photons interact with the Higgs field and hence remain massless?
1
vote
3answers
85 views

What are the six quark mass values when extrapolated to Planck energy?

Let us assume that the standard model is correct up to Planck mass. (Yes, I know, this is a big assumption.) If we continue the running of quark masses with energy (due to renormalization), what are ...
0
votes
1answer
79 views

What maximum energy can be stored in a gluon field flux tube

Question is as clear as stated in title. What is the maximum energy that can be stored in a gluon field flux tube without production of an quark anti-quark pair? And how much it usually store in a ...