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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12
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2answers
834 views

Evidence of why the Standard Model is a successful theory of particle physics

When discussing physics with laypersons, I'm often in the situation where I have to explain what the Standard Model is, and why it's a successful theory of particle physics. To help in such ...
3
votes
2answers
65 views

Higgs Standard Model Parity

In the Standard Model, the Higgs boson is expected to have spin 0 and even parity. I know how to get the spin-0 approach, but how do I argue for the even parity? Could you give a simple and a more ...
36
votes
2answers
647 views

Symmetries of the Standard Model: exact, anomalous, spontaneously broken

There are a number of possible symmetries in fundamental physics, such as: Lorentz invariance (or actually, Poincaré invariance, which can itself be broken down into translation invariance and ...
5
votes
1answer
279 views

Labelling representations using isospin and hypercharge

Can someone explain how isospin and hypercharge can be used to label representations? What is the meaning of the term singlet, doublet etc in this context? In particular how can I use it to label ...
5
votes
1answer
48 views

Hypercharge of the complex Higgs doublet

I was wondering how one can see that the hypercharge of the complex Higgs doublet is $Y=\frac{1}{2}$. Complex Higgs doublet. $$ \Phi(x) = \begin{pmatrix}\ \Phi^{+}(x)\\ \Phi^{0}(x) \end{pmatrix} $$ ...
8
votes
3answers
189 views

What are particle multiplets in the Standard Model?

The particles of the standard model are often displayed in groupings known as multiplets. I know that this somehow relates to the underlying symmetries of the standard model, which can be viewed as ...
0
votes
1answer
46 views

Why doesn't a changed particle ever lose energy by interacting with others by radiation of virtual photons? Are all virtual photons exchanged?

I've had it explained to me in a separate post that charged particles are constantly exchanging virtual particles with other charged particles and their energy is a steady state. How it is a surety ...
9
votes
2answers
436 views

How does Annihilation work?

How does annihilation work? I'm wondering why matter and antimatter actually annihilates if they come into contact. What exactly happens? Is that a known process? Is it just because of their different ...
4
votes
1answer
64 views

Electroweak interaction: From $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ to $W^{\pm},Z_{\mu},A_{\mu}$

EDIT: Additional question at the end I am trying to illuminate how the "unphysical" gauge bosons $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ will be the "physical" $W^{\pm},Z_{\mu},A_{\mu}$ when ...
8
votes
1answer
214 views

Anomalously broken conformal symmetry

I'm trying to understand an argument made by Bardeen in On Naturalness in the Standard Model. The argument is about quadratic divergences in Standard Model. My notation is that the SM Higgs potential ...
1
vote
2answers
145 views

Lepton number conservation in standard model

Why is it said that in standard model lepton number is conserved? How do I know that Lepton number is an abelian charge? Why is this conservation not as sacred as electric charge conservation. How ...
2
votes
1answer
86 views

Foundations of the notion of elementary particle in the Standard Model

According to http://en.wikipedia.org/wiki/List_of_particles, the list of elemetary particles includes more than 30 particles (bottom of the page). Does the Standard Model explain (if yes, then how) ...
2
votes
1answer
46 views

Decuplet baryon resonances

Are all baryons from decuplet resonances?? Because all resonances decay by strong interaction; but omega minus baryon can't decay via strong, because any other bound state with strangeness -3 exists. ...
1
vote
2answers
72 views

For what rare events was the LHC built?

I understand that for low cross-section events a very high luminosity is necessary in order to obtain enough data to produce meaningful statistics. That is why the LHC was built. But which are these ...
1
vote
0answers
71 views

Renormalizability of standard model

I'm wonder what precisely is meant by the renormalizability of the standard model. I can imagine two possibilities: The renormalizability of all of the interaction described by the Lagrangian before ...
12
votes
2answers
1k views

What happens to matter in a standard model with zero Higgs VEV?

Suppose you reset the parameters of the standard model so that the Higgs field average value is zero in the vacuum, what would happen to standard matter? If the fundamental fermions go from a finite ...
8
votes
1answer
83 views

Would a high energy bottom quark 'decay' to a top quark?

The reason for the long life time of $B$-hadrons is that the CKM element $|V_{tb}| > 0.999$, meaning that the preferred decay of the $b$-quark is to a $t$-quark (and vice versa). However because ...
1
vote
2answers
86 views

Subatomic particle mass and Benford's Law

Nine out of 15 subatomic particle masses begin with the digit one. Benford's Law would imply 30% with one as the leading digit. Is there any significance to this frequency distribution, such as ...
8
votes
2answers
305 views

Are there massless bosons at scales above electroweak scale?

Spontaneous electroweak symmetry breaking (i.e. $SU(2)\times U(1)\to U(1)_{em}$ ) is at scale about 100 Gev. So, for Higgs mechanism, gauge bosons $Z$ & $W$ have masses about 100 GeV. But before ...
1
vote
2answers
140 views

Quantum field theory's completeness

I realize Quantum Field Theory doesn't include gravity at all. Other than that, does QFT completely describe all electromagnetic and nuclear interactions? In other words, does it describe (at least) ...
3
votes
2answers
50 views

Uniqueness of W,Z bosons

What is real reason for considering only ONE unique W and Z bosons, and not of 3 separate flavors, in the Standard Model?
8
votes
1answer
135 views

Why $SU(3)$ and not $U(3)$?

Is there a good reason not to pick $U(3)$ as the colour group? Is there any experiment or intrinsic reason that would ruled out $U(3)$ as colour group instead?
6
votes
0answers
61 views

From $U(3)$ to $SU(3)\times U(1)$ Color symmetry. There is a “gluon” photon-like?

Suppose that $U(3)$ was the gauge group. We can decompose this as $U(3)=U(1)\times SU(3)$, which implies that in addition to the $SU(3)$ that has eight generators corresponding to eight gluons, there ...
4
votes
1answer
229 views

Power counting with a cutoff

In Effective Field Theory video lectures found here, the professor explained power counting in effective field theories and the difficulties of power counting associated with loop diagrams. He then ...
3
votes
1answer
65 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
votes
0answers
25 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 ...
8
votes
2answers
265 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
54 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
323 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
65 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
votes
2answers
128 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?
7
votes
2answers
547 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
34 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
91 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 ...
8
votes
2answers
163 views

How do we measure meson decay constants?

I'm trying to understand how people actually measure decay constants that are discussed in meson decays. As a concrete example lets consider the pion decay constant. The amplitude for $\pi ^-$ decay ...
1
vote
2answers
49 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
82 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
70 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 $ ...
9
votes
1answer
332 views

Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...
15
votes
0answers
230 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 ...
18
votes
0answers
607 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
736 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
50 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
149 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
122 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
328 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
128 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
66 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
27 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 ...