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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Why is lightning considered a plasma?

I was wondering why a lightning bolt is coined as "plasma", or a "spark" from an electrical wire/device is as well, yet flares, molten lava, and burning buildings are not(flares are pyrotechnic, ...
8
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1answer
590 views

Charge neutrality of the Universe: evidences and theories

I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is ...
2
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0answers
83 views

What determines the probability of a pair of photons interacting, and producing a positron and an electron?

The second answer to this question describes how this process might occur, and I'm curious for more details about it: What is the probability distribution of the interaction producing electron-...
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0answers
350 views

Is total angular momentum conserved in particle interaction?

Imagine that two electrons interact by exchanging a virtual photon. I know that the total energy and linear momentum of the two electrons is conserved by the interaction. Is the total (orbital) ...
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1answer
159 views

Spinor representation restricted under subgroup, a formula from Polchinski

The question is about the spinor representation decomposed under subgroups. It's a common technique in string theory when parts of dimensions are compactified and ignored, and we are only interested ...
2
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1answer
142 views

Particles from String theory

I understand that the strings in string theory are posited to be many, many orders of size smaller than say, a quark, electron or any other particle. But if this is so, how does the string "expand" to ...
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1answer
179 views

Number of decays in a chain reaction

It is widely known that the probability of $n$ decays from one system to another $A \rightarrow B$ (e.g., electrons decaying from one atomic energy level to another or muons decaying into neutrinos ...
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1answer
85 views

Any known relationships among quark masses?

Here is some numerology: Gen 1 Mass(d)/Mass(u) = 2 = 2 * 1 Gen 2 Mass(c)/Mass(s) = 12 = 4 * 3 Gen 3 Mass(t)/Mass(b) = 40 = 8 * 5 Does standard model make any predictions of relations? Do any GUT ...
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1answer
200 views

Particle Spacing in a Vacuum

Four questions: (To start off, I know very little about physics it isn't even funny (I probably use a ton of wrong terms here and leave out vital information, if so I will try to edit it in as you ...
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1answer
90 views

momentum conservation and gluons

The process is the following: $$e^-e^+ \rightarrow photon \rightarrow quark + antiquark$$ Regarding the momentum conservation law, how come we have a photon of spin 1 and at the end some meson with ...
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0answers
165 views

Møller scattering: twisted?

I am studying the Møller scattering, but I don't know how to get the twisted diagram from the S-matrix. Has anybody a good explanation?
5
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1answer
104 views

Classical EM neglects electron recoil?

Imagine two electrons $A$ and $B$ at rest. Electron $B$ is at a vertical distance $r$ above electron $A$. Let us assume that the electrons are constrained to move on horizontal rails. At time $t=0$ ...
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2answers
384 views

Does our existence cost us energy?

Anything when it needs to inform its presense such as electromagnetic presense of charged particles and gravitational presense of particles due to their mass does so by sending information of its ...
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0answers
90 views

Fermi's weak interaction theory

In Fermi's theory, we have energy squared in the numerator of the cross-section which makes it diverge as energy increases. But isn't that the Fermi constant suppresses it with increasing order?
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2answers
387 views

Have we found a Higgsino?

In supersymmetry, for each particle (boson/fermion), there is a symmetric particle which is a fermion/boson. The MSSM predicts five Higgs bosons: two neutral scalar ones (H and h), a pseudo-scalar (A)...
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1answer
70 views

Simple photon recoil question

Imagine two charges A and B separated by some distance. Charge A emits a photon which is absorbed by charge B. Is the recoil momentum received by charge A always equal and opposite to the momentum ...
13
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1answer
565 views

Operator that describes particle detector

In non-relativistic QM, the position of a particle is an observable. In QFT, fields are the observables. However, particles must have some sort of position, otherwise we wouldn't see pictures like the ...
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2answers
605 views

Pair production of neutrinos

I learned that neutrinos have a much lower energy than electrons. Pair production of electrons occurs when the photon energy is above 2 times the energy of an electron. So I am wondering if pair ...
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1answer
74 views

Statistics followed by Neutrinos [closed]

What does the neutrino particles follow- Dirac or Majorana Statistics?
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1answer
1k views

Can two photons annihilate?

This is a question about definitions. When two photons interact to create an electron/positron pair, does this process 'count' as annihilation of the photons? I've struggled to find a good ...
29
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2answers
824 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 ...
5
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2answers
226 views

Photon particle/wave question

Imagine a source of photons at the center of a spherical shell of detectors at radius $R$. Assume the photons are emitted one at a time. Now if photons are particles that are highly likely to travel ...
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1answer
1k views

What is the precise statement of the OZI Rule?

What is the precise statement of the OZI Rule? I've heard that a diagram is OZI suppressed if it can be "cut in two by cutting only gluon lines", but I don't really understand. For example, consider ...
5
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1answer
439 views

Question about Neutrino Flavor and Mass Eigenstates

I know the flavor and mass eigenstates are different, but are they related? What I mean is, in a process like fusion where electron neutrinos are created, do they start in the 1 mass eigenstate? My ...
4
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3answers
205 views

Will the current carrying solid conductors emit light?

If we pass current through a gas, like in the discharge tube, the electrons will accelerate in the electric field. The accelerated electrons will collide with gas molecules, and transfer some of their ...
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1answer
692 views

Muon 3 Body Decay

I'm trying to calculate the maximum energy of the electron in the decay muon >electron + electronantineutrino +muonneutrino in the reference frame of the muon having no kinetic energy. $m_m$=mass of ...
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3answers
809 views

Why are all force particles bosons?

All of the force-particles in the standard model are bosons, now my question is pretty short, namely: Why are all force particles bosons? This can't be a coincidence.
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2answers
887 views

Why don't we normally see the Higgs boson?

I am a physics student and my dad just asked me about the Higgs Boson. I've told him the little I know, that the Higgs field is a field that is supposed to give mass to elementary particles, and that ...
9
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1answer
336 views

Rank of the Poincare group

There are two Casimirs of the Poincare group: $$ C_1 = P^\mu P_\mu, \quad C_2 = W^\mu W_\mu $$ with the Pauli-Lubanski vector $W_\mu$. This implies the Poincare group has rank 2. Is there a way to ...
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0answers
531 views

Smallest minimum feature size possible for transistors printed by photolithography

I'm doing a project about Moore's Law, one of the subtopics I've come to is photolithography. The way I understand it is that the MOSFET transistors are currently printed on a silicon wafer by ...
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1answer
458 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: ...
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1answer
120 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?
5
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3answers
391 views

Nobel Prize 2013: What is it about? [closed]

I would really like to understand Higgs-Englert’s discovery that earned them the 2013 physics Nobel prize. I tried reading their work, but understood nothing of it unfortunately. The reason why I’m ...
2
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0answers
109 views

Spin of a decay product

A particle A decays into particles B, C and D. The spin of A, B and C particles is 1/2 each. What are the possible spins of particle D? My attempt is the following: Since B and C have spin 1/2 each,...
3
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1answer
106 views

Specific Heat of Nano Particles

Specific heat of nano particles is less than bulk specific heat of them. Why?
6
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1answer
2k views

How to tell theoretically whether an electron behaves as wave or particle

I have seen many questions on SE on the dual nature of electrons behaving in certain circumstances as particles and as waves in some other circumstance. There is one thing I couldn't get a clear ...
26
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1answer
690 views

How does the Super-Kamiokande experiment falsify SU(5)?

In his book "The Trouble With Physics", Lee Smolin writes that he is still stunned by the falsification of the $SU(5)$ Georgi-Glashow model by the null results of proton decay experiments. I should ...
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1answer
493 views

Elastic collision of photon [closed]

Consider an elastic collision of a photon with 100 eV energy hitting a mirror. How much momentum is exchanged in the collision? Also, can one model the reflection of an elastically colliding photon ...
6
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1answer
265 views

What is a “reggized gluon”?

I'm reading a paper in which the author used these words many times assuming that the reader knows what he is talking about. Can someone please explain what it is? What is the difference between a ...
12
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2answers
713 views

Why are there no particles in conformal theories?

In Matt Strassler's recent post (here) he makes the statement that scale invariant (I assume he means conformally invariant, more generally) theories have no particles in them. What's the reason for ...
6
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2answers
904 views

What is the significance of Lie groups $SO(3)$ and $SU(2)$ to particle physics?

I was hoping someone could give an overview as to how the Lie groups $SO(3)$ and $SU(2)$ and their representations can be applied to describe particle physics? The application of Lie groups and their ...
6
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1answer
321 views

Has non-conservation of baryon number been observed?

CP violation (as I understand it) allows for non-conservation of baryon number, and thus can contribute (at least a little) to the baryon asymmetry in the universe today (far more matter than ...
3
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5answers
2k views

What really is the smallest “mass” or “object” in the universe?

As the Wikipedia article Subatomic particles shows, with respect to the sciences, the atom is obviously not the smallest piece of mass. Apparently, if people have already broken down the atom in to ...
3
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1answer
123 views

How quickly do neutrinos change flavor?

DOE’s Fermilab has switched on its newly upgraded neutrino beam. This is in preparation for the NOvA experiment, which will study neutrinos using a 200-ton particle detector at Fermilab and a 14,000-...
5
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1answer
374 views

What are the strongest sources of collimated neutrons and protons?

I am imagining an unusual experiment which will require intense beams of either protons or neutrons. The experiment would work better with neutrons, but neutron sources are much weaker messier so I ...
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0answers
96 views

How do I build an alpha emitter?

I would like to build an alpha emitter. I suppose I had some vague idea of knocking the electrons off of some helium. But upon further examination the idea does strike me as...naive? My question is ...
0
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0answers
142 views

What the quantum spin refers to? How we calculate the angular momentum $\omega$ from the spin quantum number?

How we calculate the angular momentum $\omega$ from the spin quantum number, to know how fast a particle rotating on its own axis?
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1answer
78 views

If an Electrical Field can jump over a point on its stright path of propagation?

Consider point B between points A and C on a stright line in vaccum(or any other environment). If the electrical fild $\vec E$ (or an EM wave) should necessarily pass through B to affect C and appear ...