Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.

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Classic mass predictions from Left-Right models with discrete symmetries?

I am covering the classic literature on predictions of Cabibbo angle or other relationships in the mass matrix. As you may remember, this research was a rage in the late seventies, after noticing that ...
35
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4answers
6k views

How do we know Dark Matter isn't simply Neutrinos?

What evidence is there that dark matter isn't one of the known types of neutrinos? If it were, how would this be measurable?
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1answer
598 views

Why the pion does not get mass under Spontaneus breaking of chiral symmetry, but the quarks do?

Some sources state that when the mass of a quark goes to zero, it allows for Spontaneous Breaking of Chiral Symmetry and gets a constituent mass of about $200\, \mathrm{MeV}$. Other sources state ...
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1answer
54 views

Which arguments for $m_u \approx 0$ are still in the market?

The RPP note on quarks masses has traditionally carried, and it is still there, the comment that It is particularly important to determine the quark mass ratio mu/md, since there is no strong CP ...
4
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1answer
76 views

What's the potential of the LHC's heavy ion experiment?

RHIC has been the dominant player in heavy ion physics, producing tantalizing evidence in support of the entropy/viscocity formula from AdS/CFT. What's the potential of the LHC's Pb ion collsions? ...
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45 views

GUT predictions for charm mass?

Most GUT models have some relationship between down-type quarks and leptons, that more or less agree with the observed values after running the renormalization equations. But, what about up-type ...
25
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4answers
1k views

“Slightly off-shell”?

I'm not new to QFT, yet there are some matters which are quite puzzling to me. I often come across the statement that real particles (the ones we actually measure in experiments, not virtual ones) are ...
9
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0answers
45 views

status of +4/3 scalar as explanation of $t\bar t$ asymmetry

One of the early proposals for the Tevatron asymmetry on $t \bar t$ was a "fundamental diquark" with a charge (and hypercharge) +4/3, either in a triplet or a sextet colour. I am interested on the ...
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1answer
617 views

Where to find experimental/theoretical value of (charge) radius of particles?

Where to find experimental/theoretical value of (charge) radius of particles like proton, neutron, $pi^+$, etc. ?
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1answer
101 views

Is the force between solitons with same charge always repulsive?

I know the one-dimensional case in which the force is proportional to $e^{-R}$ and the force is attractive for solitons with opposite charge and repulsive for solitons with same charge. I was ...
0
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2answers
227 views

Speed Distribution of The Particles

I want to know the distribution of the particles's speed. The particles what I mean are nucleons and electrons of element. Consume there is 1kg of iron on room temperature and it's shape is sphere. ...
0
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1answer
175 views

What is the dominant interaction in elastic collision pi- + neutron -> pi- + neutron?

What is the dominant interaction in elastic collision pi- + neutron -> pi- + neutron? Is it strong nuclear interaction or electromagnetism? Edit: sorry I meant to say "elastic". There is no matter - ...
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1answer
556 views

What final states can proton-proton collision generate?

What final states can proton-proton collision generate? Where to find listing of possible final states of a particle interaction, for example proton colliding with proton?
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1answer
421 views

Understanding P-, CP-, CPT-violation etc. in field theory and in relation to the principle of relativity

I can never get my head around the violations of $P-$, $CP-$, $CPT-$ violations and their friends. Since the single term "symmetry" is so overused in physics and one has for example to watch out and ...
2
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2answers
964 views

How do I rearrange dE/dt to find an electron's 'half-life' due to synchrotron radiation?

I know that $-\frac{\mathrm{d}E}{\mathrm{d}t} \propto E^2$ for an electron losing energy to synchrotron radiation, but I can't find how to arrange this to give the time it would take for the electron ...
4
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3answers
3k views

What is lepton number?

What exactly is a lepton number of a particle? With the charge (eg proton is just 1, not the exact charge), I can understand because it's a physical property, put a particle with charge + next to ...
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3answers
3k views

The amount of energy required to break the Coulomb Barrier

This web page says that only 3-10 keV of energy is required to break the Coulomb barrier for colliding hydrogen nuclei. Pretty far from what originally said. Is this true? Does this have something ...
2
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1answer
292 views

Can particle physics be represented as an algebra?

Possibly the most useful thing anyone could tell me about particle physics: Naively, one could try and make an algebra by enumerating all the types of particles and defining equivalence relationships ...
20
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3answers
323 views

Twistors in Curved Spacetime

I am looking for good and recent references to constructing twistor space for curved spacetime. This could be a general spacetime, or specific ones (say maximally symmetric spaces different from ...
13
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3answers
2k views

Hypercharge for $U(1)$ in $SU(2)\times U(1)$ model

I understand that the fundamental representation of $U(1)$ amounts to a multiplication by a phase factor, e.g. EM. I thought that when it is extended to higher dimensional representations, it would ...
6
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1answer
695 views

Is there a concise-but-thorough statement of the Standard Model?

I’m a grad student in high-energy physics. I’m familiar enough with the Standard Model, but I’ve always wondered whether there existed a canonical statement of, effectively, “what we talk about when ...
20
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3answers
7k views

Why you need a graviton when you have the higgs boson?

Since I studied General Relativity I had this question running on my mind. As I see it (just taking lectures of Quantum Field Theory right now) "Why you need a gauge boson for gravity when the higgs ...
2
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2answers
908 views

What is the correct term for the “polarity” of matter (matter vs. antimatter)? Are fractional polarities allowed?

What is the correct term for the "polarity" of matter (matter vs. antimatter)? Are neutral polarities allowed? (1,0,-1) Are fractional polarities allowed?
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2answers
6k views

Speed of a particle in quantum mechanics: phase velocity vs. group velocity

Given that one usually defines two different velocities for a wave, these being the phase velocity and the group velocity, I was asking their meaning for the associated particle in quantum mechanics. ...
10
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4answers
23k views

What are quarks made of?

So atoms are formed from protons and neutrons, which are formed from quarks. But where do these quarks come from? What makes them?
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1answer
373 views

Do Killing spinors know global information?

The conformal Killing spinor equations on $R\times S^3$ in Minkowski signature are \begin{equation} \nabla_\mu \epsilon=\pm \frac{i}{2}\gamma_\mu\gamma^0\gamma^5\epsilon \end{equation} whose solution ...
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1answer
1k views

Why should bosons be in the adjoint representation of the gauge group?

Is there a deep mathematical reason for why bosons should be in the adjoint representation of the gauge group rather than any other representation?
4
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1answer
968 views

Does the speed of sand flow in a hourglass depend on a height of a sand column above the hourglass neck?

In a hourglass, does the sand flow through the neck depend on the amount of sand in the upper glass? If we consider a sand flow analogous to fluid flow, then it should depend linearly, but in that ...
13
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1answer
282 views

realization of: CFT generating fuction = AdS partition function

An important aspect of the AdS/CFT correspondence is the recipe to compute correlation functions of a boundary operator $\mathcal{O} $ in terms of the supergravity fields in the interior of the ...
20
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1answer
193 views

Any use for $F_4$ in hep-th?

In high energy physics, the use of the classical Lie groups are common place, and in the Grand Unification the use of $E_{6,7,8}$ is also common place. In string theory $G_2$ is sometimes utilized, ...
14
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1answer
131 views

Instanton Moduli Space with a Surface Operator

I would like to understand the mathematical language which is relevant to instanton moduli space with a surface operator. Alday and Tachikawa stated in 1005.4469 that the following moduli spaces are ...
2
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2answers
132 views

Question about interpreting PDG particle cross section data sets' metadata fields

I have some question about interpreting PDG particle cross section data sets' metadata fields. The data sets I'm having questions for are http://pdg.lbl.gov/2011/hadronic-xsections/hadron.html For ...
8
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1answer
71 views

Are lens spaces classified via a Weinberg angle?

I am thinking about Kaluza Klein theory in the 3 dimensional lens spaces. These have an isometry group SU(2)xU(1), generically, and in some way interpolate between the extreme cases of manifolds $S^2 ...
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1answer
556 views

Fundamental particles with spin > 1

I am in undergraduate quantum mechanics, and the TA made an off-hand comment that currently no one knows how to describe fundamental particles with spin > 1 without supersymmetry. I was curious and ...
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1answer
1k views

What's jet multiplicity?

That's a basic thing, but, surprisingly, it is very difficult to find concise explanation of: What is the definition of jet multiplicity? Why is it interesting?
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2answers
410 views

Where did the idea of a neutrino come from?

Exactly what paper by W. Pauli introduced the idea for the existence of a neutrino and how was its existence confirmed experimentally (who did that and in what paper)?
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2answers
315 views

What is the highest accuracy of measuring time differences achievable today?

I was wondering if it would be possible to shorten the distance between detectors when measuring the speed of neutrinos to, say, 7m rather than the current ~700km? In this way the distance traveled ...
6
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2answers
220 views

How is the distance between Geneva detector and the Gran Sasso one measured?

Does anyone know how is the distance between detectors in the now famous neutrino experiment measured? Also, how was the time of flight measured?
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1answer
157 views

$\frac{1}{(1-x)_+}$ type distributions and parton distribution functions

I am trying to get to grips with Altarelli-Parisi-type equations. In chapter 17 of Peskin/Schroeder, they first develop the equations for a similar problem in QED. Equation $(17.123)$ introduces the ...
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2answers
979 views

What is the “shape” of atomic/subatomic particles?

I apologize in advance for my ignorance if this is a question with an obvious answer... I am not experienced in this field. But are such particles in the universe points with a charge, or are they ...
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1answer
464 views

Do the particles that were found to break the speed of light really break Einstein's theory of relativity? [duplicate]

Possible Duplicate: What would be the effects on theoretical physics if neutrinos go faster than light? Update: Loose cable caused faulty results Apparently, researchers at CERN have found ...
9
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1answer
64 views

Dual Pairs in Four Dimensions

Following the conversation here, I am wondering if anyone knows of an example of dual pair with 4-dimensional N=1 SUSY which relates a non-Abelian gauge theory on one side to a theory with a ...
10
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1answer
364 views

Does the ruling out of TeV scale SUSY breaking disfavor grand unification?

One of the arguments in favor of TeV scale SUSY breaking is that it leads to the appropriate running of the gauge coupling strengths leading to grand unification, i.e. $k_Y = \frac{5}{3}$ instead of ...
13
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1answer
403 views

How are neutrino beams emitted at CERN?

As far I know they come from accelerator collisions, but I have read confusing things like magnetically focused. How could neutrinos be guided magnetically if they aren't affected by the ...
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0answers
300 views

What are the implications of superliminal neutrinos? [duplicate]

Possible Duplicates: What would be the immediate effects if light does not go at the maximum speed possible? Superluminal neutrinos Do we re-write physics? Or can it be fitted in current ...
34
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4answers
337 views

Models of neutrinos consistent with OPERA's results

I guess by now most people have heard about the new paper (arXiv:1109.4897) by the OPERA collaboration which claims to have observed superluminal neutrinos with 6$\sigma$ significance. Obviously this ...
20
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1answer
1k views

What happened to the idea of tachyonic or other superluminal neutrinos?

While hunting around for information about the recent OPERA measurement that hints at superluminal neutrinos, I discovered that this idea was actually considered back in the 1980s. Wikipedia lists as ...
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6answers
4k views

What would be the effects on theoretical physics if neutrinos go faster than light?

Earlier today, I saw this link on Facebook about neutrinos going faster than the speed of light, and of course, re-posted. Since then, a couple of my friends have gotten into a discussion about what ...
3
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1answer
170 views

What does “single inclusive” mean exactly?

I thought I knew what single inclusive scattering was, but today when I went to look up a definition to check my memory, I couldn't find one. A Google search yielded no shortage of papers that use the ...
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2answers
189 views

What is a proton-rich atom?

http://wiki.chemprime.chemeddl.org/images/e/e4/Plot_of_Neutron_Number_vs._Proton_Number_.jpg The above graph shows that all elements have more neutrons than protons in this nucleus. So how is there ...