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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1answer
77 views

Why is a tensor times its dual a derivative?

Why is a term like $$F \tilde{F}$$ or $$G \tilde{G}$$ considered to be a derivative? Where are the derivatives? This is said in a PRD article. Check section IV page 5.
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4answers
2k views

Could we make things out of newly discovered particles?

Right now, all of the "stuff" that has been created in the world is made of protons, electrons, and neutrons. I'm aware that particles other than these have much shorter lifetimes. But I've also heard ...
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0answers
34 views

Why do the gauge bosons fix the couplings of the SM?

In chapter Chapter 16: Grand Unified Theories in the very first paragraph, the author states Note the SM gauge interactions of quarks and leptons are completely fixed by their gauge charges. ...
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2answers
1k 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 ...
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0answers
27 views

If neutron would be lighter by 1 MeV, how stability of Hydrogen could be changed?

In current Universe proton is stable and the following reaction does not go $ p + e \rightarrow n + \overline{\nu_e}$ Currently proton is lighter than neutron by 1.293 MeV. If neutron would be ...
5
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2answers
320 views

Do all the particles acquire mass in the Standard Model due to the Higgs mechanism only?

I know that a mass term for an intermediate boson is not compatible with the gauge symmetry. But in principle a mass term for the electron field does not violate a gauge symmetry. However to build an ...
4
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1answer
146 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 ...
0
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1answer
72 views

Why is rho to two pions not allowed? [duplicate]

Why is the $\rho^0 \rightarrow \pi^0 + \pi^0$ decay not allowed? I have seen this question but I am not satisfied with the answers. The $J^{PC}$ of the $\rho$ and $\pi$ are $1^{--}$ and $0^{-+}$ ...
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0answers
124 views

Simplify QCD Lagrangian

How we can derive the electric charge of the field theory for each field? For example lets say that we have the u-quarks (3-colors) and electron that we know that has charge -e) free Lagrangian ...
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0answers
35 views

What is the physical meaning of U- and V-spin?

$SU(3)$ group has three $SU(2)$ subgroups. The first one (with generators $\lambda_{1}, \lambda_{2}, \lambda_{3}$ of corresponding algebra) is called I-spin, the second one (with generators ...
0
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1answer
184 views

Terminology of Higgs boson and Goldstone boson

I know, the from the Higgs Mechanism, or Spontaneous symmetry breaking, the massless Goldstone boson becomes massive. So in some sense Goldstone bosons are eaten by gauge "boson". Here I got ...
13
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4answers
699 views

Why do leptons and quarks mix?

Is the fact that weak eigenstates are not mass eigenstates completely arbitrary? Or is there a deeper reason for the existence of the PMNS and CKM matrices?
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2answers
161 views

Width of the decay of Higgs boson into dimuon

According to Standard model, the partial width of the decay of Higgs into dimuon (up to tree level) is: $$\Gamma\approx\frac{m_H}{8\pi} \left(\frac{m_{\mu}}{\nu}\right)^2$$ with the Higgs mass ...
2
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0answers
22 views

Has the formation of a new quark pair as we separate two quarks been observed or is it only a prediction? [duplicate]

Because of quark confinement we know that as we try to separate quarks appart the energy required will increase, but if the force is strong enough (I do not know if possible in the lab, but at least ...
15
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3answers
9k views

Your Mass is NOT from Higgs Boson

Your Mass is NOT from Higgs Boson? http://www.youtube.com/watch?v=Ztc6QPNUqls This guy can't be correct, right? He argues that because mostly of a nucleus' mass is made out of the space between ...
0
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1answer
123 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 ...
1
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1answer
108 views

How to explain electrons' interaction via the weak force?

What is the piece of theory which dictates that electrons interact via the weak force with other electrons and protons, and how can this force be understood in terms of what I am more familiar with ...
2
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0answers
47 views

Are there Planck units for weak or strong “charge”, similar to the electromagnetic Planck charge $\sqrt{4~\pi~\epsilon_0~\hbar~c}~$?

Are there Planck units for "charge" of weak or strong interaction, similar to the Planck unit of electromagnetic charge: $\sqrt{4~\pi~\epsilon_0~\hbar~c}$ ? Are there perhaps direct substitutes, ...
0
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1answer
135 views

Vector bosons: polar vectors or axial vectors?

The $W$ and $Z$ bosons are known as vector bosons, because they have non-zero spin. How do we know whether they are axial or polar vectors? Context: I am reading about a technique called Operator ...
5
votes
1answer
847 views

Introduction to Physical Content from Adjoint Representations

In particle Physics it's usual to write the physical content of a Theory in adjoint representations of the Gauge group. For example: $24\rightarrow (8,1)_0\oplus (1,3)_0\oplus (1,1)_0\oplus ...
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0answers
80 views

Is $\overline{B}^0$ really the antiparticle of $B^0$?

They have a different mass, which is apparently forbidden by $CPT$ symmetry. Does this have anything to do with them having two distinct energy eigenstates?
3
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1answer
186 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 ...
2
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1answer
113 views

Gauge SU(2) with real triplet

I have come across a model of gauge $SU(2)$ with a real triplet. The covariant derivative for $SU(2)$ complex doublet is written as $$D_\mu=\partial_\mu-igT^aA^a_\mu$$ where $T^a$ are generators of ...
7
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1answer
399 views

What part does the Higgs boson play in conveying mass?

I am a high school physics teacher and did my physics degree a while ago, well before the Higgs boson was on in the physics undergraduate syllabus. Now, I am a little confused. The recent discovery ...
2
votes
2answers
173 views

What's the symbol for the antiparticle of the delta plus baryon?

It can't be $\Delta^-$ since that is another particle also made up of quarks (not antiquarks). I can think of four possibilities: $\overline\Delta^+$ $\overline{\Delta^+}$ $\overline\Delta^-$ ...
2
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2answers
55 views

At what energy do up and down quarks unbind?

At what energy do up and down quarks unbind? Google does not seem to have a clear answer. Could someone please represent this mathematically?
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1answer
95 views

Can we observe proton decay?

I know that the half life of a proton is more than $6.6\cdot 10^{33}$ years (antimuon decay). I have found this data on Wikipedia proton decay but I do not know the probability distribution that leads ...
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0answers
71 views

How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim ...
3
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2answers
330 views

Is there a connection between gluons and photons?

I was wondering if there is any sort of connection between a gluon and a photon since they are both considered massless.
10
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2answers
162 views

Why do fermions come in generations, but not bosons?

Why does the $1/2$ spin of fundamental fermions (electrons, quarks, and neutrinos) split them into three variants that differ only in mass, while the integer spins of massless fundamental bosons (e.g. ...
2
votes
1answer
234 views

Is this summary of modern theoretical physics correct?

This is not exactly a physics question; it's more of a question about physics. You'll see what I mean in a minute. My understanding of modern theoretical physics is below. What I want to know is: Is ...
4
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0answers
28 views

What are hadronic uncertainties?

I am reading articles about recent findings at CERN and the possibility of New Physics contributions, and they keep saying that the discrepancies may be due to hadronic uncertainties... What are ...
3
votes
1answer
143 views

Group theoretical reason that Gluons carry charge and anticharge

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) ...
3
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0answers
65 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 ...
10
votes
3answers
1k views

Why does the weak force distinguish left and right handedness?

I'm wondering why the weak interaction only affects left-handed particles (and right-handed antiparticles). Before someone says "because thats just the way nature is" :-), let me explain what I find ...
5
votes
2answers
436 views

What prevents photons from getting mass from higher order Feynman diagrams

The Higgs boson and gluons have no electric charge and photons couple to charge, so there is no tree level interaction between them and photons. But what prevents higher order diagrams from ...
0
votes
1answer
42 views

Why is a “Semi-leptonic” Decay Mode called so?

Why is a semileptonic decay mode called so? I mean, if there is one lepton amongst the decay products, it should be leptonic, right? If there are two, that should be called bi-leptonic or something ...
0
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1answer
45 views

Unitarity of CKM matrix?

The CKM matrix is known to be unitary. Now, is it just found experimentally? Is the following idea correct? We know that the weak force eigenstate $ \left( \begin{array}{c} d' \\ s' \\ b' ...
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0answers
67 views

Origin of CP violation in CKM matrix?

I have already seen this question but I am not very familiar with the group theoretical framework of the Standard Model and was hoping for a more diluted answer. So I have come across this slide: ...
2
votes
1answer
90 views

Why does the $Z$ boson not change quark flavour?

Is it just an observation from Particle Accelerators data? I was trying to understand what is it that mathematically stops the $Z$ boson from changing quark flavour, if it is known?
5
votes
1answer
377 views

Chiral anomalies

Recently I have read that there is contraction of chiral anomalies in SM. But people are working on chiral anomalies theory. So I have the question: what is the importance of development of the theory ...
15
votes
2answers
1k views

Is the Standard Model consistent (UV complete)?

This is a question about the self-consistency of the Standard Model - which I believe is the same as asking whether it is UV complete - in other words, can it be used to predict experimental results ...
2
votes
1answer
34 views

What theory unifies the electroweak and the strong forces? [closed]

As the title itself suggests, here's my question: What theory unifies the electroweak and the strong forces?
9
votes
1answer
281 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
1answer
75 views

What does the first column in the “decay modes” table mean (in Particle Data Group documents)?

As a follow-up to this more general question, what are the values in the first column of each of the "decay tables" in a PDG document describing? What are those things in the first column? Are they ...
8
votes
2answers
750 views

Neutrino oscillations versus CMK quark mixing

I wish to describe in simple but correct terms the analogy between the Cabibbo–Kobayashi–Maskawa (CMK) and Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrices. The CMK matrix describes the rotation ...
1
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0answers
105 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 ...
4
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3answers
373 views

Majorana Mass For Neutrinos In Standard Model

Neutrinos can't be given Dirac masses because there is no $SU(2)_L$ singlet right handed neutrinos in the standard model. But can neutrinos be given Majorana masses in the standard model? EDIT: Why ...
3
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0answers
96 views

Understanding the effective low-energy Lagrangian for hadrons

My course in Higgs Physics is discussing a two-nucleon low-energy effective theory of hadron interaction. With $\psi=(p,n)$, the pion is defined as $\vec{\pi}= i \bar{\psi}\vec{\tau} \gamma_5 ...
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2answers
112 views

What is the reason for the $ i \tau_2 $ - factor in the higgs coupling with up-type quarks?

The quark mass term in the Standard Model Lagrangian looks like this: $$ L = - \lambda_d \bar{Q}\phi d_R - \lambda_u \bar{Q} i \tau_2 \phi^* u_R $$ What is the reason for the $ i \tau_2 $ - ...