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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31 views

Are gauge theories always renormalizable?

Speaking of quantum field theories. Is one of the following implications correct? gauge theory (gauge invariant) => renormalizable renormalizable => gauge theory (gauge invariant) If yes do you ...
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1answer
47 views

What does “Standard Model” really refer to?

I am reading the arXiv published paper by Frank Wilczek called "Physics in 100 Years". Apparently, this paper is the printed form of a talk given at Brown University earlier this year (2015). Right ...
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0answers
15 views

EW phase transition and baryogenesis

There are three Sakharov conditions of baryogenesis: CP symmetry violation. Baryon number conservation violation. Thermodynamical equilibrium violation. In SM the first one is satisfied by CKM ...
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0answers
13 views

Chemical potentials of SM particles at high temperatures

Recently I've heard the statement that chemical potentials of SM particles on $T > 1 \text{ GeV}$ are very small, so that Gibbs potential reduces to free energy. How to prove this statement? Does ...
4
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0answers
35 views

Why are $W$ bosons massless above electroweak scale? [duplicate]

Because of the Higgs mechanism, one must replace the Higgs field $\phi$ with $\phi_0 + \phi_1$ where $\phi_0$ is the vacuum expectation value. As far as I understand, the $\phi_0$ gives the mass term ...
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2answers
190 views

If mesons were stable could they form atoms?

if there were stable enough mesons similar to protons and neutrons could they capture electrons to form exotic elements. if not why is this not possible?
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1answer
57 views

Chiral Fermion Problem and the String Net Model

In Xiao-Gang Wen's book "Quantum Field Theory of Many-Body Systems", he mentions that (the string-net condensation picture)...has a problem: we do not yet know how to produce the $SU(2)$ part of ...
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0answers
33 views

Questions on QFT and SM

What are some question paper to solve/practice on Quantum Field theory and Standard model, I read the theory but not practiced?
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1answer
24 views

colliding point particles

when I draw e.g. the diagram of compton scattering I assume that the electron of given momentum gets 'hit' by a photon and interacts with it. How close does the photon have to get to the electron that ...
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28 views

What are the parity of particles? [duplicate]

When looking to see if particle collisions/decays are possible and what force they act through, how do you know the parity of particles to know whether they act through weak force? Is there a grouping ...
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0answers
38 views

One loop effective potential of Standard Model

The one loop Coleman-Weinberg contribution of a scalar field to the effective potential (in MSbar scheme) is: \begin{equation} const. \times m^4(\phi_c) \left( log \left( ...
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0answers
48 views

Are mass terms forbidden in the Lagrangian because of parity violation or because fermions live in a complex representation?

Normally one argues that we can't write down Lorentz AND gauge invariant mass terms, because of parity violation, i.e. l-chiral and r-chiral fields transform differently. This means that mass terms ...
3
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1answer
145 views

Can bosons have anti-particles?

Can bosons have anti-particles? In the past, I would have answered this question with a yes, primarily because I can imagine writing down a QFT for complex scalars that has a U(1) symmetry that ...
3
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0answers
61 views

Is Witten's claim that gauge group representations get exchanged with its dual under parity correct?

I'm currently reading Physics and Geometry by Witten, which I really liked up to the point where he claimed that we exchange representations $R$ and $\tilde R$ under parity transformations, where $R$ ...
2
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1answer
75 views

Why does the electromagnetic and weak coupling strength do not meet at the electroweak scale?

The running of the coupling strengths is usually visualized on a logarithmic scale like here What surprises me is that the weak and the electromagnetic coupling strength do not meet before the GUT ...
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1answer
61 views

Help for project on the basics of the Higgs field

I have a project for my university class on the Higgs fields and how it impacts the standard model. Also I was going to add some information on how the Higgs particle is formed and decays into ...
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0answers
20 views

How is the strength of a force quantitatively evaluated?

Physicists often talk about the 'strength' of a force. For example, gravity is weak, the strong force is of course strong. The hierarchy is summarized on this wikipedia page, which lists strengths in ...
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1answer
27 views

How to tell if a particle interaction is strong/weak?

Problem: Prove that the reaction $p+p\rightarrow p+K^+$ is impossible, where $p=\text{proton}$, $K^+=\text{kaon}$. (Side question: Is there a specific name for a positive Kaon, just like a "positive ...
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1answer
29 views

Higgs mass and EW precision tests

I'm trying to understand how the Higgs mass can influence EW precision tests. In order to do that I'm using the following document (section 4.3): http://arxiv.org/pdf/0706.0684v1.pdf There are a ...
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1answer
196 views

Is the exact form of the Higgs potential known?

Usually the Higgs potential is given as $$ \frac{1}{2}\mu^2\phi^2 - \frac{1}{4}\lambda^2\phi^4 $$ but I never quite understood if this just serves to give us an idea of how symmetry breaking works, or ...
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2answers
49 views

What is the property of neutrino? [closed]

If mass of a particle is due to Higgs boson, spin is due to Z boson and translational energy is due to photons, what exactly is the innate property of a neutrino? If none exist, is neutrino truly a ...
2
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3answers
93 views

Why are complex fields in the Lagrangian?

I know that a complex field has twice the number of degrees of freedom of a real field, and that fields (in QFT) aren't observables so we don't really care if they are real. But why the need for ...
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1answer
93 views

Scale invariance in QFT?

I was reading the following paper http://arxiv.org/abs/hep-ph/0703260 for Georgi and I have a conceptual question about it. Howard Georgi was talking about this Unparticle Physics theory and at the ...
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0answers
18 views

Wu experiment and masses of neutrino

Wu experiment have shown that there are only left-handed neutrinos (and right-handed antineutrinos) take part in weak interactions. My question is about the significance of this experiment in a ...
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1answer
80 views

Poincaré' lemma and EM potential $A^{\mu}$

My lecturer said that given the sourceless Maxwell's equations $$ \partial_{\mu}\, ^ *F^{\mu\nu} = 0 $$, we can find a solution $$ F^{\mu\nu} = \partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu},$$ that ...
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4answers
12k views

Why do electrons, according to my textbook, exist forever?

Does that mean that electrons are infinitely stable? The neutrinos of the three leptons are also listed as having a mean lifespan of infinity.
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1answer
383 views

Why do we need complex representations in Grand Unified Theories?

EDIT4: I think I was now able to track down where this dogma originally came from. Howard Georgi wrote in TOWARDS A GRAND UNIFIED THEORY OF FLAVOR There is a deeper reason to require ...
4
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1answer
86 views

Where would the dark matter particle fit inside a picture of the standard model of particle physics?

Where would the dark matter particle fit inside a picture of the standard model of particle physics? While I am particularly fond of the Sterile Neutrino, I have not been able to find any example of ...
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1answer
76 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 ...
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3answers
150 views

Why is the “real” gauge group of the standard model $SU(3) \times SU(2) \times U(1) /N$?

In this paper John Baez says the real gauge group of the standard model is $SU(3) \times SU(2) \times U(1) /N$. Can someone explain the logic behind this line of thought? Firstly, does this group ...
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1answer
335 views

Is color charge a quantum mechanical observable?

If I had 2 pions that were identical, except one was comprised of a red and anti-red, and the other was comprised of a green and anti-green, would I be able to perform an experiment that distinguishes ...
1
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1answer
36 views

Real and virtual photons in the standard model

In the Standard Model, the mass of the photon is zero, while the photon becomes massive if it acts as a mediator between two electrons. Why does this happen? Does it mean that the Standard Model ...
2
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1answer
47 views

Experimental determination of $\Lambda_{QCD}$

I have a question about $\Lambda_{QCD}$, the energy scale at which there is a transition from the regime of perturbative QCD to quark confinement. How it is measured experimentally?
4
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1answer
62 views

Origin of the quark condensate VEV

Consider the QCD lagrangian : $$L_{QCD}=-\frac{1}{4}G^a_{\mu\nu}G^{a\mu\nu}+\sum\bar{\psi}_q(i\not{D}-m_q)\psi_q$$ Textbooks explain that this lagrangian is spontaneously broken by the VEV of quark ...
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0answers
23 views

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants?

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants? If any, which (types of) ones? For the ones that do, what are the relations ...
0
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1answer
36 views

Experimental evidence for Z boson coupling to right handed fermions

I do have a question about electro-weak interactions. I know the Z boson is an admixture of two fields, one that couples only to the left-handed part of the fermions (the neutral field introduced to ...
1
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1answer
65 views

Virtual particles and the scaling effect on valence quarks

Inside a proton there are 3 valance quarks. In addition, there is constant creation and annihilation of gluon, quarks and anti-quarks. The number of virtual particles we observe depends on how ...
3
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1answer
43 views

Decay Feynman diagram

$$D^0 \to K^+ +\pi^- + \pi^0 + \pi^0$$ cannot occur by first order weak interactions. Could anybody help me confirm this? What I currently have is that the initial charm goes to anti-strange and the ...
2
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3answers
98 views

Discovery of spin-3 particle at LHCb

I just read a discussion on the CERN website regarding first observation of a heavy flavored spin-3 particle at LHCb. This appears to be a post from last July. Is there anyone knowledgeable enough in ...
2
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1answer
110 views

Free parameters in the Standard Model

From my understanding of the standard model, I understand that there are 19 or 20 free parameters that we need to put in by hand as, and I'm guessing here, there is as yet no theoretical basis for ...
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0answers
48 views

W boson one loop electroweak contribution to muon g-2

I want to calculate the one loop W boson contribution (triple gauge boson vertex WW-Photon) to the muon anomalous magnetic moment g-2 with the help of Dimensional Regularization. Diagram given below: ...
1
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1answer
27 views

CKM matrix - Unitarity triangles

I currently read an article and they mentioned, that using the unitarity relation between the 1. and 3. column of the CKM matrix, one can easily show that the area spanned of the unitarity triangle is ...
2
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4answers
185 views

What is the difference between the Higgs Boson particle and an electron moving through the Higgs field?

I am watching a lecture by Sean Caroll titled "Particles, Fields, and the Future of Physics". I am not a physicist by any means but enjoy the subject in my spare time hoping to understand it. This ...
2
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1answer
36 views

How is the the lower-limit of the proton lifetime measured experimentally?

Wikipedia says : Recent experiments at the Super-Kamiokande water Cherenkov radiation detector in Japan gave lower limits for proton half-life, at 90% confidence level, of 6.6×10^33 years via ...
2
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2answers
59 views

What are the “generations of matter”?

After a series of clicks on New Scientist and Wikipedia, I ended up on the Wiki article for "generations of matter", and I didn't quite understand it. I believe (and this may be wrong) that different ...
3
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1answer
106 views

Number $g(T)$ of relativistic degrees of freedom as a function of temperature $T$

Let us consider the total number of relativistic degrees of freedom $g(T)$ for particle species in our universe: $$g(T)=\left(\sum_Bg_B\right)+\frac{7}{8}\left(\sum_Fg_F\right)$$ Where the sums are ...
2
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1answer
34 views

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states?

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states? My textbook states that this is because "only then is the wave function at the origin non-vanishing". Could anyone ...
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0answers
66 views

Understanding $ee\to h \to ff$ process

can anyone tell me where to find a good reference that talks about $$e^+ e^-\rightarrow H \rightarrow f\bar{f}$$ where this describes an electron-positron annihilation into a Higgs that in term ...
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1answer
59 views

Difference between Higgs mechanism and Higgs decay

What is the difference between Higgs Mechanism and Higgs decay? I know that Higgs mechanism is a process which provide the mass to gauge boson. In general, many literature explain Higgs mechanism ...