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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3
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1answer
70 views

What is meant by Proton Structure Function?

I am going to embark on a project involving deep-inelastic scattering but first I am trying to do some really basic background reading to get me up to task. My only background in particle physics is ...
0
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0answers
32 views

Why are quark up and down an isospin doublet?

I have some difficulties in understanding the isospin of quarks. As far as I am concerned, the isospin formalism is used to express the physical property of electric charge. I mean: what I know ...
9
votes
2answers
275 views

What's a lepto-diquark?

This questions refers to Slansky's Group theory for unified model building, page 106 of chapter 7. He assigns the weight $(1)(01)$, which is stepwise projected from $E_6$ to $SU(2)\times SU(3)$, to a ...
2
votes
0answers
59 views

Can all laws of physics derived by a single or lists of more general laws?

(This is actually my first question - please understand my lack of knowledge and bad English..) I have always been curious about deriving thousands of laws from more general ones.. Can general laws ...
3
votes
2answers
343 views

Higgs boson production via positron-electron collision

One of the suggested diagrams for the Higgs production is the following: so basically an electron-positron pair annihilates and forms an (excited?) Z boson, which then decays into another (less ...
4
votes
1answer
79 views

Tadpole diagram and vacuum

This statement may be well-known. For many massless theories, these tadpole diagram graphs vanish in dimensional regularization (by dimensional analysis and the absence of any inherent mass scale in ...
0
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2answers
134 views

Reasons for choosing $SU(3)$ as the color group vs. $SO(4)$

What are the reasons that $SU(3)$ is used for QCD? Why wouldn't the simpler & smaller group $SO(4)$ make a better candidate?
8
votes
2answers
608 views

Is there a “difference” between photons that act as virtual particles and photons that act as the quanta of EM radiation?

I) I know that virtual-photons are known to be the force-carriers for the Electromagnetic force, and that they are called "virtual" because the Energy-Time-inequality version of the Heisenberg ...
0
votes
1answer
36 views

quarks annihilation process

I am appreciating particle physics and I read about mesons. In quark's model, mesons are pairs of quark-antiquark. Now I think that in general matter-antimatter annihilate and so I don't understand ...
6
votes
1answer
97 views

Why more than one Higgs?

Since by introducing one Higgs Boson we can give a mass to the leptons and gauge bosons of the weak interaction: Why should we consider more than one Higgs (doublet) once we go beyond the standard ...
1
vote
2answers
58 views

Higgs doublet: a charged and a neutral component?

In the book 'Modern Particle Physics' byM. thomson the Higgs doublet is written as $$\phi = \left(\begin{matrix} \phi^+ \\ \phi^0 \end{matrix}\right)=\phi = \left(\begin{matrix} \phi_1 +i\phi_2 \\ ...
6
votes
1answer
88 views

Simplifying a seemingly simple gamma matrix identity

When studying from the book by Wise and Manohar, Heavy Quark Physics (pg 102), I came across a seemingly simple identity that I am not able to prove. It's likely an easy problem but I can't for the ...
3
votes
0answers
98 views

Why is the $\theta$ term of QCD violating charge and parity (CP) symmetries?

From the non-trivial nature of the QCD vacuum, the Lagrangian is augmented with a term like \begin{equation} \theta \frac{g^2}{32 \pi^2} G_{\mu \nu}^a \tilde{G}^{a, \mu \nu} \end{equation} where $ ...
16
votes
0answers
251 views

Finding the vacuum which breaks a symmetry

I will start with an example. Consider a symmetry breaking pattern like $SU(4)\rightarrow Sp(4)$. We know that in $SU(4)$ there is the Standard Model (SM) symmetry $SU(2)_L\times U(1)_Y$ but depending ...
19
votes
0answers
643 views

A dictionary of string - standard physics correspondences

Motivated by the (for me very useful) remark ''Standard model generations in string theory are the Euler number of the Calabi Yau, and it is actually reasonably doable to get 4,6,8, or 3 ...
14
votes
3answers
755 views

Alternatives to electromagnetism for communication?

It seems, from my (weak) understanding of the standard model that the only field suitable for long range communication is the one we actually use, electromagnetism. (Gravity waves could be used as ...
0
votes
1answer
55 views

Monopoles in non-abelian semi-simple gauge groups

Relative to the following Indeed, the modern point of view is that the operator of electric charge is the generator of a U(1) group. The charge quantization condition arises in models of ...
1
vote
1answer
48 views

Read-off particle from (projected) Dynkin labels

In the review of Slanksy "Group theory for unified model building" in chapter 6: How do one relate the projected Dynkin diagrams from for example $\overline{5}+10$ of $su(5)$ to the corresponding ...
4
votes
3answers
150 views

Is there a table that sums up the parameters, the assumptions/symmetries, and the predictions of the standard model?

The title says it all: is there a table that sums up the parameters, the assumptions/symmetries, and the (most important) predictions of the standard model?
5
votes
1answer
127 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 ...
4
votes
3answers
343 views

Does the Standard Model require neutrinos to be massless?

I am an undergraduate student in Physics, I have a basic understanding of Particle Physics and Quantum Mechanics but none whatsoever of Quantum Field Theory. I know that Neutrino mixing requires ...
3
votes
2answers
134 views

What exactly is the weak portion of the SM gauge group?

This Wikipedia article: http://en.wikipedia.org/wiki/Left%E2%80%93right_symmetry states that the weak part of the SM gauge group is not $SU(2)_L \times U(1)_Y$ but $ \frac{ SU(2)_L \times ...
3
votes
1answer
76 views

Conservation of total angular momentum in $\Phi$-meson decay

I am looking into the decay of a $\Phi$-meson decaying into $K^+$, $K^-$. My problem is, the $\Phi$-meson has a total angular momentum of 1 and the two Kaons have a total angular momentum of 0. On the ...
1
vote
0answers
32 views

How to find Lepton Number? [closed]

is a Standard Model particle with (u, d, b) quark content. What are the electric charge, baryon number and lepton number of this particle? Is this the only particle expected to exist with this quark ...
14
votes
2answers
275 views

Infrared-free QED and Higgsless standard model phenomenology

This is one of those "what if" fantasy world type questions. I like hard sci-fi so please no "well, you changed one thing about the world so now anything goes." :) What if the Higgs had no vev? That ...
4
votes
2answers
320 views

“Periodic Table” of Particles of the Standard Model?

What is a good, single, "periodic table" of all the particles of the Standard Model? I thought Particle Data Group would have a single-page PDF of this, but I couldn't find a single table listing all ...
15
votes
1answer
466 views

Does the existence of Higgs imply the existence of Magnetic Monopoles?

I am aware that in theories with spontaneous symmetry breaking, Magnetic Monopoles can exist as topological solitons. Can the same be done with the Standard Model gauge group. I am familiar with the ...
6
votes
3answers
1k views

Why do quarks have a fractional charge?

I am aware that evidence exists that strongly suggests the existence of quarks and do not doubt it. It is just simply really weird to me that they can have a fractional charge. While other ...
3
votes
1answer
231 views

Notation for Standard Model Charges?

Does anybody know what these following numbers describing an electron $(1, 1, -1)$ represent in $SU(3) \times SU(2) \times U(1)$? Or, these numbers that describe an up quark: $(3, 1, 2/3)$? I'm ...
-1
votes
1answer
62 views

What does this notation mean? [duplicate]

Terminology question. Reading this, in the middle of the second page, when it says Left-handed quarks form 3 (3; 2; + 1 6 ) multiplets Qn (n = 1; 2; 3); What does this (3;2;+1/6) mean?
0
votes
1answer
78 views

Need help solving a task - laws of conservation (leptons, baryons, charge)

We got a task from our teacher, a multiple choice task; and here it is: Which of the following reactions is correct, considering the conservation laws? Note: We have only learned to use the ...
3
votes
1answer
134 views

Effective theories and dimension six operators

What is the importance of dimension six operators in the study of physics beyond the Standard Model? Are these operators more relevant than dimension five operators like $HHFF$ or operators with ...
3
votes
1answer
172 views

Rigorous mathematical formalism of particle physics

Can anyone provide me with a rigorous mathematical definition of the fundamental particles (all fundamental bosons and fermions), reflecting the analogy of action of groups with interaction of ...
4
votes
4answers
112 views

why do the electroweak vacuum have to be charge and color neutral?

My question is why the electroweak vacuum of the Standard Model have to electroweak charge and QCD color neutral? What goes wrong if electroweak vacuum has either non-zero charge or color quantum ...
6
votes
1answer
235 views

Why is $SU(3)$ chosen as the gauge group in QCD?

Why is $SU(3)$ chosen as the gauge group. Why not $U(3)$? Why does it even have to be unitary?
1
vote
0answers
25 views

How can a pion with neutral charge exist? [duplicate]

A $\pi^0$ consists of an up and anti-up quark. However, I also learned that when a particle and its anti-particle meet, energy is produced. So, my question is that how can $\pi^0$ exist? Won't it ...
2
votes
3answers
322 views

why cannot fermions have non-zero vacuum expectation value?

In quantum field theory, scalar can take non-zero vacuum expectation value(vev). And this way they break symmetry of the Lagrangian. Now my question is what will happen if the fermions in the theory ...
5
votes
1answer
176 views

Pion decay in particle physics

I'm taking a particle physics course and we're using Perkins Introduction to High Energy Physics as the text. I am looking at problem 1.7. It asks whether $$\pi^0\rightarrow e^- + e^+$$ is allowed or ...
10
votes
1answer
145 views

Chirality, helicity and the weak interaction

From what I'm understanding about Dirac spinors, using the Weyl basis for the $\gamma$ matrices the first two components behave as a left handed Weyl spinor, while the third and the fourth form a ...
5
votes
3answers
543 views

Does the Higgs field really explain mass or just reformulate it? What about charge?

The mass of a particle used to be considered a fundamental and intrinsic property of the particle; on the same level as other properties such as charge, spin, chirality/helicity. Due to the Higgs ...
2
votes
1answer
63 views

Mass scales in See-saw mechenism

Are both types of Majorana masses $$\mathcal{L}^L_M=-\frac{m_L}{2}[\overline{(\psi_L)^c}\psi_L + \overline{\psi_L}(\psi_L)^c]$$ and $$\mathcal{L}^R_M=-\frac{m_R}{2}[\overline{(\psi_R)^c}\psi_R + ...
1
vote
3answers
191 views

Can virtual particles, in particular gravitons, interfere?

Question 1. Can virtual particles, in particular gravitons, interfere? Virtual particles are created and annihilated in a distance too small and a time too short to be measured. Their existence is ...
5
votes
2answers
319 views

One Loop Higgs Mass Correction

I am attempting to compute the one loop correction to the Higgs mass, which requires the evaluation of a scattering amplitude, namely $$\require{cancel} \mathcal{M} = (-)N_f \int \frac{\mathrm{d}^4 ...
4
votes
1answer
195 views

CP violation from the Electroweak SU(2)$_{weak,flavor}$ by $\int \theta F \wedge F $

Question: Why there is NO Charge-Parity (CP) violation from a potential Theta term in the electroweak SU(2)$_{weak,flavor}$ sector by $\theta_{electroweak} \int F \wedge F$? (ps. an explicit ...
6
votes
1answer
104 views

Anomalous Dimensions of Gauge Interactions

Peskin and Schroeder mention a few times that the anomalous dimension of a gauge interaction operator is zero. The justification for this is that the charge operator shouldn't get modified under ...
4
votes
1answer
201 views

What parity has an electron?

I couldn't find anything about the parity of an electron. Neither in the german, nor in the spanish and nor in the english version of Wikipedia. I only found one sentence in the parity article of ...
0
votes
1answer
66 views

Could elementary particles join to create bound states?

I recently had question, can 2 elementary particles be "attached" together using Strong and weak nuclear forces to create a bound state. For example can Electron and some other stable elementary ...
2
votes
0answers
65 views

Electromagnetic force interaction

As far as I know, the electromagnetic force only interacts on particles with electrical charge, but I was told that the electromagnetic force was involved in the following reaction: ...
6
votes
1answer
104 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 ...
3
votes
1answer
39 views

Renormalizing with external momenta set to zero

I've often seen in textbooks that authors renormalize diagrams by setting external momentum to zero. Under what conditions is this justified? An example of this is done in Manohar and Wise's book on ...