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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1answer
77 views

How do we know that weak isospin is an exact symmetry while strong isospin is not?

It is said in textbooks that if the $SU(2)_f$ or $SU(3)_f$ flavor symmetry were exact for sstrong isospin, then all members of the multiplets would be exactly equally massive. By looking at quark ...
-2
votes
1answer
107 views

Quantum Theory as a framework for other theories of nature

We know that Quantum Theory should be considered as a framework in which all other theories/forces (Strong, Weak, EM and Gravity) exist. For example, we have the Quantum Chromodynamics, Quantum ...
9
votes
1answer
261 views

Why does the eightfold way work?

Last year I attended an introductory particle physics course, in which the Eigthfold Way for classifying hadrons has been discussed. The main idea consists in grouping hadrons in multiplets (i.e ...
6
votes
1answer
263 views

Spin of 125 GeV Higgs boson

Can someone please explain to me why (according to decay of Higgs boson into 2 photons) Higgs boson cannot have spin $S=1$?
5
votes
2answers
270 views

Is ch. 2, sect. 4 of The Feynman Lectures on Physics, Vol. 1 still accurate?

The chapter 2 section 4 of volume 1 is on nuclei and particles. Here are a few things that trouble me. Dr. Feynman says that Another most interesting change in the ideas and philosophy of science ...
23
votes
5answers
2k views

Could gravity be an emergent property of nature?

Sorry if this question is naive. It is just a curiosity that I have. Are there theoretical or experimental reasons why gravity should not be an emergent property of nature? Assume a standard model ...
4
votes
3answers
346 views

In SUSY why does electroweak symmetry breaking only happen in the SM sector?

This is a difficult question to phrase succinctly, so I hope the title makes sense. What I want to understand is what seems like a lack of symmetry (besides SUSY-breaking) between the SM sector and ...
25
votes
1answer
370 views

Identification of particles and anti-particles

The identification of an electron as a particle and the positron as an antiparticle is a matter of convention. We see lots of electrons around us so they become the normal particle and the rare and ...
0
votes
0answers
34 views

Have there been more distinctive names suggested for neutrino mass states $\nu_1, \nu_2, \nu_3$?

The different mass states of neutrinos are generally named $\nu_1, \nu_2, \nu_3$. By comparison, the names of quark mass states (up, ...
55
votes
8answers
20k views

What's inside a proton?

What constitutes protons? When I see pictures, I can't understand. Protons are made of quarks, but some say that they are made of 99% empty space. Also, in this illustration from Wikipedia, what's ...
3
votes
1answer
226 views

Is Higgs mechanism necessary in QCD?

As we known, we introduce Higgs mechanism into Standard model to explain mass of Gauge boson, lepton and neutrino(maybe?). Higgs mechanism is necessary for electroweak theory because gauge symmetry ...
1
vote
1answer
189 views

What makes the quarks stay inside the proton?

Inside a single proton for example, what is the force(s) that keeps the quarks together? Why don't they leave the proton? If they do, how does that even happen? And maybe an additional sub question: ...
4
votes
3answers
108 views

Are the second and third generations of matter required or optional?

If the second and third matter families (so-called generations: muon, muon neutrino, tau, tau neutrino, ...) didn't exist, would that affect how the universe runs? Are they optional or required?
8
votes
2answers
459 views

What do the four components of Dirac Spinors represent in the Standard Model?

I've been trying to get my head around the formalisms used in the Standard Model. From what i've gathered Dirac Spinors are 4 component objects designed to be operated on by Lorentz Transformations ...
3
votes
0answers
90 views

Were fermions ever massless?

In a discussion of the Standard model and Higgs mechanism it was claimed that accordingly: "During an early phase of the cosmos all fermions were massless." I wonder whether this claim can be ...
1
vote
1answer
173 views

Conservation of mass-energy and nuclear transmutation

This may just be beyond the grasp of the everyman, but I'm trying, and failing, to grasp how conservation of mass-energy works in cases of beta decay and electron capture. A neutron has a mass of one ...
2
votes
1answer
109 views

Does the decay of the Higgs Boson create up or down quarks?

Does the decay of the Higgs Boson create up or down quarks?
7
votes
1answer
551 views

Proton Radius Puzzle, Is it possible that proton's radius differ depending on how you measure it? What does that even mean?

I just read this NewScientist article, and I was stunned by its results. So I found the original paper here on arxiv. In the introduction of the paper it is stated: The recent determination of ...
1
vote
1answer
1k views

Quark Radius Upper Bound

If quarks had internal structure (contradicting current beliefs), what is the lowest upper bound on their "radius" based on current experimental results? If possible, I'd prefer to only consider ...
10
votes
4answers
5k views

Why don’t photons interact with the Higgs field?

Why don’t photons interact with the Higgs field and hence remain massless?
18
votes
5answers
4k views

Are W & Z bosons virtual or not?

W and Z bosons are observed/discovered. But as force carrying bosons they should be virtual particles, unobservable? And also they require to have mass, but if they are virtual they may be off-shell, ...
0
votes
1answer
157 views

Symmetry groups [closed]

I am quite new to this subject. I am just repeating in a few words, what I have learned so far: There are 4 fundamental forces of nature: strong, weak, electromagnetism and gravity. Physicists are ...
3
votes
2answers
567 views

Equation of everything

Is this equation in the image true? Can you give some topics that I can cover the equation.
7
votes
1answer
274 views

How to understand the Lagrangian of the standard model, effective or “fundamental”

I have a question about understanding the Lagrangian of standard model, should we view it as a "fundamental" or effective theory? The "fundamental" theory here means the theory with physical cutoff ...
5
votes
2answers
259 views

Do I need to study the “Standard Model” before studying String Theory?

After this semester, I'll have a background up to a first course in QFT (first 5 or 6 chapters of Peskin and Schroeder). The next step in QFT will be something specific to the Standard Model ...
2
votes
1answer
181 views

The Higgs explains how particles acquire mass. Could it explain how much?

It's my understanding that nothing in the Standard Model predicts the mass values of the fundamental particles, so I guess that means we don't currently know how to make models of Higgs interactions ...
4
votes
1answer
161 views

Why does the pion half-life differ between the charged and uncharged species?

Why does the uncharged pion have much shorter half-life than the charged pion despite the fact that the uncharged pion has a little bit less mass than the charged one, so that according to the ...
2
votes
1answer
167 views

Fine-Tuning, the Hiearchy Problem, and Mass in the Standard Model

In Chapter 1 of his book String Theory in a Nutshell, Kiritsis states the following. The [Standard M]odel is unstable as we increase the energy (hierarchy problem of mass scales) and the theory ...
-6
votes
2answers
262 views

Why did Standard Model never sense a requirement to include gravitational quantum? [closed]

Standard Model is advanced (lorentz invariant) version of Quantum physics. It tried to include everything which came in the way while understanding quantum world. It even didn't bother to include ...
4
votes
2answers
485 views

Are electrons just incompletely evaporated black holes?

Imagine a black hole that is fast-approaching its final exponential throws of Hawking evaporation. Presumably, at all points in this end process there there will remain a region that identifiably ...
1
vote
0answers
123 views

“Original” coupling constant of the Higgs with the electron, taking into account renormalization

I read Peskin, Schroeder, "An introduction of quantum field theory". Formula (20.100) gives the electron mass after the Higgs mechanism as $m_e=\frac{1}{\sqrt{2}}\lambda_e v$ Here $v$ is related to ...
0
votes
1answer
293 views

How to calculate Rest Mass practically with Standard Model?

With relativistic physics, we can apply force to see resistance against acceleration. It'd give us relativistic mass and we have well established formula to get to the Rest Mass as long as we know the ...
8
votes
0answers
172 views

Chiral fermions from torsion flux in M-theory?

Witten's 1981 paper "Search for a realistic Kaluza-Klein theory" is frequently cited for its observation that, in a compactification of d=11 supergravity on a manifold with SU(3) x SU(2) x U(1) ...
6
votes
1answer
212 views

A Game Of The Number Of Space-Time Dimensions

Holger Bech Nielsen, one of the founders of string theory, has apparently just played some sort of game between different potential dimensions for space-time and reached the conclusion that D4 wins in ...
2
votes
0answers
84 views

What's the most precise test of electroweak unification in the standard model?

As I understood, there is a coincidence of the weak coupling constant $g$ calculated in two different ways: 1) The muon lifetime $\tau_{\mu}$ is related to $g$ by the formula $(m_{\mu} c^2)^5 ...
-1
votes
1answer
230 views

Is the Standard Model experimentally verified? [closed]

Has the Standard Model of Particle Physics been experimentally verified? Or is it still waiting for experimental verification? OR, What aspects/predictions of the Standard Model have been ...
2
votes
1answer
190 views

Is the Higgs mechanism needed for Quantum Field Theory?

The NY Times article on Firewalls today has the following paragraph: Quantum field theory is how the world works [quoting a physicist]. It had a major triumph just a year ago, when the Higgs ...
7
votes
2answers
606 views

Was the Higgs mass correctly predicted by asymptotic safety of gravity?

This paper was published in Phys Lett B in 2009, and predicted the Higgs mass to be 126 GeV based on the asymptotic safety of gravity. Is this prediction taken seriously by the theory community, or is ...
8
votes
3answers
1k views

Other possible theories (other than string theory) which are generalizations of the standard model with incorporation of gravity

The only finite mathematical framework that incorporates both the standard model of particle physics and gravity under one umbrella that I am aware of is string theory. I would like to know whether ...
5
votes
4answers
791 views

Why are neutrino oscillations considered to be “beyond the Standard Model”?

Is this just a historical artifact - that the particle physics community decided at some point to call all of the pre-oscillation physics by the name the "Standard Model"? The reason I ask is because ...
6
votes
1answer
239 views

Fundamental Higgs vs. pseudo-Nambu-Goldstone boson: experimental fingerprints

If we consider the 126 Higgs-like boson as a pseudo-Nambu-Goldstone boson, what are the experimental fingerprints of that case? What are the main differences, in a purely effective field theory ...
7
votes
2answers
766 views

How do I know the proton isn't made of 3 anti-down quarks?

I have a proton, how do I know that it is made of 2 up quarks and 1 down quark or if it is made of 3 anti-down quarks, each with different color charges? This question is also applicable to the ...
1
vote
0answers
372 views

Running of gauge couplings in the Standard Model [closed]

I'm sure many of us are familiar with the following plot showing the running of the inverse of the fine-structure constants of the SM. (I got the picture from google) At one-loop, the expressions ...
6
votes
1answer
188 views

Is color confinement detected?

I'm a graduate student studying QFT. I'm quite interested that is color confinement detected or proved? (both directly and indirectly) Or it is just an assumption?
11
votes
1answer
260 views

Why do we only have complete particle generations?

There are 3 generations of fermions in the standard model. I know that there is a theorem that states, that only complete generations are allowed. This means that there have to be quarks with three ...
1
vote
0answers
63 views

Baryogenesis - P and CP Violation

There are 4 requirements for baryogenesis to happen: 1. A process that violates baryonnumber conservation 2. The universe has to be out of equilibrium 3. P has to be violated 4. CP has to be violated ...
2
votes
2answers
179 views

$\left(H^\dagger H\right)^2$ is invariant under $U(1)\times SU(2)$?

Is it true that $\left(H^\dagger H\right)^2$ is invariant under $U\left(1\right) \times SU\left(2\right)$ where $H$ is the Higgs field $(1,2,1/2)$? Does this invariance imply that its hypercharge ...
15
votes
5answers
920 views

String Theory and Standard Model in CERN

I don't know how to say it, but in the TV dominatrices and the popular science books we see the string theory as "the best theory to explain everything", and as "the only game in town"... etc. And ...
2
votes
1answer
546 views

Why some particles interact with the Higgs field and others don't?

Why some particles interact with the Higgs field and others don't? Higgs doesn't explain that much: why some particles have mass and others don't? is like why some particles interact with the Higgs ...
13
votes
2answers
1k views

115 GeV, 170 GeV, and the noncommutative standard model

Several years ago, noncommutative geometry was used to describe the standard model, somehow yielding a prediction of 170 GeV for the mass of the Higgs boson, a prediction which was falsified a few ...