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 ...
32
votes
5answers
2k views
Why do we think there are only three generations of fundamental particles?
In the standard model of particle physics, there are three generations of quarks (up/down, strange/charm, and top/bottom), along with three generations of leptons (electron, muon, and tau). All of ...
28
votes
4answers
2k views
What is needed to claim the discovery of the Higgs boson?
As I understand the Higg's boson can be discovered by the LHC because the collisions are done at an energy that is high enough to produce it and because the luminosity will be high enough also.
But ...
19
votes
5answers
1k 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 ...
18
votes
2answers
160 views
Values of SM parameters at one certain scale
The general question is:
What are the values of Standard Model parameters (in the $\bar{MS}$ renormalization scheme) at some scale e.g. $m_{Z}$? As its parametrization in Yukawa matrices is not unique ...
16
votes
1answer
230 views
Why is there no theta-angle (topological term) for the weak interactions?
Why is there no analog for $\Theta_\text{QCD}$ for the weak interaction? Is this topological term generated? If not, why not? Is this related to the fact that $SU(2)_L$ is broken?
15
votes
6answers
2k views
Why should the Standard Model be renormalizable?
Effective theories like Little Higgs models or Nambu-Jona-Lasinio model are non-renormalizable and there is no problem with it, since an effective theory does not need to be renormalizable. These ...
15
votes
2answers
1k views
If the LHC doesn't find the Higgs Boson, what would be the implications for the Standard Model?
What would be the implications to the Standard Model if the Higgs Boson hadn't been found with the LHC?
Also, if the Higgs Boson had not been found with the LHC, would it have been successfully ...
15
votes
2answers
1k views
How does string theory reduce to the standard model?
It is said that string theory is a unification of particle physics and gravitation.
Is there a reasonably simple explanation for how the standard model arises as a limit of string theory?
How does ...
15
votes
3answers
496 views
Why is gravity so hard to unify with the other 3 fundamental forces?
Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force.
I've been told that ...
14
votes
7answers
1k views
What Do We Get From Having Higher Generations of Particles?
Background: I have written a pop-science book explaining quantum mechanics through imaginary conversations with my dog-- the dog serves as a sort of reader surrogate, popping in occasionally to ask ...
14
votes
2answers
655 views
Is there some explanation for $y_t=1$
The Yukawa coupling of the top quark is Dirac-natural in a too excellent way, it is within one sigma experimentally, and within 99.5% in absolute value, of being equal to one. Without some symmetry, ...
13
votes
2answers
1k views
Did the researchers at Fermilab find a fifth force?
Please consider the publication
Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV
by the CDF-Collaboration, ...
13
votes
4answers
913 views
What is the need for the Higgs mechanism and electroweak unification?
The Higgs mechanism allows massless fields to acquire mass through their coupling to a scalar field. But if the masses cannot be predicted because the couplings have to be fixed, what really is the ...
11
votes
5answers
2k 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, ...
11
votes
3answers
881 views
Why are quark types known as flavors?
There are six types of quarks, known as flavors.
Why where these types called flavors?
Why do the flavors have such odd names (up, down, charm, strange, top, and bottom)?
11
votes
1answer
88 views
Higgs Field - Is its discovery truly “around the corner”?
Rather surprised I haven't seen many questions or discussion regarding the rumored confirmation of the Higgs field. As I understand it, the energies where they saw things were actually quite a bit ...
10
votes
2answers
70 views
ATLAS Higgs Interpretation
I came across this abstract, and I am curious as to what the ATLAS Team has actually discovered:
Abstract Motivated by the result of the Higgs boson candidates at LEP with a mass of about ...
10
votes
4answers
2k views
Why do electron and proton have the same but opposite electric charge?
What is the explanation between equality of proton and electron charges (up to a sign)? This is connected to the gauge invariance and renormalization of charge is connected to the renormalization of ...
10
votes
1answer
190 views
Technical naturalness of Yukawa couplings
Naturalness in the sense of 't Hooft tell us that a small parameter is a signal of a symmetry such that the parameter will be zero when the symmetry is exact. I am puzzled about how this principle is ...
10
votes
1answer
987 views
What are the alternatives to the Higgs mechanism?
Can someone summarize, with references if possible, all of the alternatives to the simplest model (that requires only a single scalar Higgs field with the Mexican Hat potential) of spontaneous ...
10
votes
2answers
2k views
Shape of the Higgs branching ratio to ZZ
I've been looking at the, now very popular, graph of the SM Higgs decay branching ratios:
You see that the ZZ branching ratio has a funny dip around the $170\, GeV$, very different from the WW ...
10
votes
1answer
57 views
N=2 SSM without a Higgs
In arXiv:1012.5099, section III, the authors describe a supersymmetric extension to the standard model in which there is no Higgs sector at all, in the conventional sense. The up-type Higgs is a ...
10
votes
1answer
291 views
What does the latest $B_s^0\rightarrow \mu^+\mu^-$ results mean for SUSY?
A paper from the LHCb collaboration just came out last week, stating basically that the $B_s^0\rightarrow\mu^+\mu^-$ decay matches standard model predictions, and people are already shouting that SUSY ...
10
votes
1answer
808 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 ...
10
votes
0answers
278 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
...
9
votes
1answer
97 views
Is the fine-structure constant a parameter of the standard model?
According to the wikipedia entry on the fine-structure constant:
In fact, α is one of the about 20 empirical parameters in the Standard Model of particle physics, whose value is not determined ...
9
votes
1answer
277 views
The physics community's take on noncommutative geometry
Connes's noncommutative geometry program includes an approach to the Standard Model that employs a noncommutative extension of Riemannian metric. In recent years I've heard physicists say that this ...
9
votes
0answers
89 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 ...
8
votes
4answers
2k views
Why don’t photons interact with the Higgs field?
Why don’t photons interact with the Higgs field and hence remain massless?
8
votes
2answers
306 views
Do current models of particle physics explain the chemical properties of elements/compounds?
I have a particle system of seven protons and seven (or sometimes eight) neutrons (each formed by their appropriate quarks, etc.) bound together in a state that can be macroscopically described as a ...
8
votes
1answer
360 views
Do color-neutral gluons exist?
If I'm correct a quark can change color by emitting a gluon. For example a blue up quark $u_b$ can change into a red up quark by emitting a gluon:
$$u_b \longrightarrow u_r + g_{b\overline{r}}$$
...
8
votes
4answers
409 views
strange modulation of radiactive decay rates with solar activity
Recently i found out this uber strange article about nuclear decay rates being somehow showing seasonal variations with a high correlation with sun activity. Two very precise questions:
1) has this ...
7
votes
2answers
1k views
Why is the Higgs boson spin 0?
Why is the Higgs boson spin 0? Detailed equation-form answers would be great, but if possible, some explanation of the original logic behind this feature of the Higgs mechanism (e.g., "to provide ...
7
votes
2answers
179 views
Particles mass determined by SO(D-2) vs SO(D-1)
I've recently come across this statement that massless particles arise from $SO(D-2)$ symetry and massive particles from $SO(D-1)$.
I would have guessed that it would be the exact opposite way, but ...
7
votes
3answers
661 views
Left and Right-handed fermions
Is there a simple intuitive way to understand the difference between left-handed and right-handed fermions (electrons say)?
How to experimentally distinguish between them?
7
votes
2answers
116 views
Simulation of QED
Can anyone point me to a paper dealing with simulation of QED or the Standard Model in general? I will particularly appreciate a review paper.
7
votes
2answers
500 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?
7
votes
1answer
110 views
Is the LEP B meson asymmetry evidence for higher dimensions and/or string theory?
According to this blog, new standard model calculations have changed the 3 sigma B meson forward and backward production asymmetry observed at LEP into two anomolies:
A 2.5 sigma B meson production ...
7
votes
1answer
194 views
Is there literature on a continuous mass spectrum for the Higgs field?
Various masses for the Higgs field are compatible with experiment, but is it possible that the Higgs field is not observable because it has a continuous mass spectrum?
Work in the 60s and 70s on free ...
6
votes
3answers
189 views
Origin of lepton/quark generations?
What theoretical explanations exist for the fact that there are three generations of leptons and quarks?
I'm not so much asking why there are exactly 3 generations, but rather what makes electron, ...
6
votes
3answers
417 views
How are the masses of unstable elementary particles measured?
I am interested in knowing how (Q1) the particle's masses are experimentally determined from accelerator observations.
What kind of particles? They must be as far as we know elementary and unstable ...
6
votes
1answer
330 views
Anti particles: What exactly is inverted?
http://en.wikipedia.org/wiki/Antiparticle says "Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge."
and
What is anti-matter?
...
6
votes
2answers
322 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 ...
6
votes
4answers
265 views
AQFT and the Standard Model
The German physicist Rudolf Haag presented a new approach to QFT that centralizes the role of an algebra of observables in his book "Local Quantum Physics". The mathematical objects known as operator ...
6
votes
1answer
186 views
Weinberg angle measurement methods
I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
6
votes
1answer
160 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 ...
6
votes
1answer
138 views
What is the origin of flavor? [duplicate]
Possible Duplicate:
Origin of lepton/quark generations?
In the standard model (and in nature), Fermions appear in different generations, or flavors. Besides up and down quarks and ...
6
votes
1answer
458 views
What is the difference between 'running' and 'current' quark mass?
When looking at the PDG, there is a difference between the 'running' and the 'current' quark masses.
Does anyone know which is the difference between these two?
6
votes
2answers
209 views
Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?
I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...
5
votes
2answers
333 views
More questions on string theory and the standard model
This is a followup question to
How does string theory reduce to the standard model?
Ron Maimon's answer there clarified to some extent what can be expected from string theory, but left details open ...
