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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Are fields intuitive choices to explain forces?

Fields are used to explain all the forces with respective particle being their facilitators. However, are fields intuitive choice to explain the forces? The physical significance is not very apparent. ...
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1answer
18 views

Number of free parameters in a Standard Model with Neutrino oscillation

In two related questions, it was asked how many free parameters the standard model has. Without neutrino oscillation, there are 19 free parameters. Now it turned out that neutrinos have a mass aswell, ...
4
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1answer
35 views

What does a physical surface look like at a subatomic level?

At the macroscopic level, we are all quite familiar with the concept of a physical surface. From wikipedia: https://en.wikipedia.org/wiki/Surface_(topology) In mathematics, a surface is a ...
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2answers
47 views

Difference between measurement and expectation value?

Does measurement mean simply acting on a wave function by a physical observable? Or finding the expectation value of the physical observable? I understand the result is same if the function is an ...
9
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2answers
1k views

How does the LHC explore extra dimensions?

The Large Hadron Collider (LHC) has been smashing particles for a long time and sometimes people say that it has found new dimensions. How is it even possible for a particle accelerator to find new ...
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4answers
59 views

Resource Recommendations: General relativity, local tetrads and particle physics

I'm still self-learning general relativity. I have been a huge fan of Andrew Hamilton's amazing lecture notes on GR, black holes and cosmology. He goes through GR in pretty much full tetrad formalism. ...
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41 views

Interesting question to figure it out [on hold]

A 50-cm-long iron rod is heated from 20 °C to 100 °C. The linear coefficient of expansion for iron is $1.2 × 10^{-5} K^{-1}$. How to determine the change in length of the rod. By which formula?
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2answers
98 views

Why can we approximate massive particles as massless or vice versa?

Our descriptions of massless and massive particles are very different. For example: Massless particles have only two polarizations, which we call helicities. Spin projection on axes different than ...
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2answers
91 views

What is the decay width and why is it given in energy units?

I'm reading Thomson, Modern Particle Physics, and in chapter 16 author says that the decay width of the Z boson is $\Gamma_Z =2.452 \pm 0.0023 \,\mathrm{GeV}$. He also says the total width of the ...
2
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2answers
357 views

What's smaller: a neutrino, or a string from string theory [on hold]

I've recently read an article that stated "If an atom were as big as the solar system, a neutrino would be the size of a golf ball". I watch the science channel, and on (I believe) the show How the ...
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1answer
78 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
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0answers
24 views

Does Compressing Energy over a Multiverse Dimensional Rupre Create Mass? [closed]

my question is only on a specific method of creating mass through super collapsation of enormous amount of energy in at a singular point or point of singularity.
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1answer
57 views

Doesn't quantum uncertainty disprove string theory? [duplicate]

String theory states that the oscillations of little strings are responsible for all the particles in and the evolution of the universe. The specific type of particle created by a string depends on ...
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2answers
110 views

Sufficient conditions for a interaction to be classified as weak, strong, …?

Let us say I have been given the equation of a interaction/decay/etc. between particles: $$X+Y\rightarrow A+B$$ Are their any sufficient conditions that we can use to determine the type of interaction ...
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1answer
47 views

The interpretation of bubble and oyster Feynman diagrams?

I am reading 'A Guide To Feynman Diagrams in the Many Body Problem' By R.D.Mattuck, in which their is reference to oyster and bubble Feynman diagrams, shown respectively below. In these diagrams I ...
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1answer
50 views

How to understand CP-violation in kaon systems with Feynman diagrams and matrix elements?

I am trying to understand CP-Violation in the Kaon system using feynman diagrams and matrix element. Here is a slide from Mark Thomson corresponding exactly to what I am looking for (http://www.hep....
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0answers
55 views

Internal structure of electrons and quarks

I have some questions about experiments to probe the internal structure of electron and quarks. What type of experiments were done, in the recent years, to probe the internal structure of the ...
1
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1answer
34 views

Alpha Particle moving through a magnetic field [closed]

How would I find the acceleration of an alpha particle moving through a magnetic field given the force of the magnetic field, the charge, the initial velocity and the strength of the magnetic field.
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0answers
46 views

Running of $\alpha$ and scattering amplitudes

Consider a QED scattering process $e^-+e^-\rightarrow e^-+e^-$. The scattering crosssection at the tree-level depends on the square of the fine-structure constant $\alpha$ (apart from the electron ...
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3answers
500 views

How would cold neutrinos get trapped by stars?

Continuing on from the cool physics Q&A'd on the threads Where are all the slow neutrinos?, Is it possible that all "spontaneous nuclear decay" is actually "slow neutrino" ...
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0answers
65 views

Connection between Veneziano amplitude and Regge amplitude

I have tried to read about Regge theory, and I continue to run my head against the Veneziano formula, which is said to produce correct Regge trajectories by eg. t'Hooft at page 6 here: http://www....
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3answers
44 views

Can we give particle with no mass, mass? [duplicate]

Is it possible to take a particle with no mass and give it mass. For example light? Or increase mass?
0
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1answer
66 views

Definition of a meson? [closed]

I am looking for a definition of a meson that does not include the quark model. After some research I have come across this definition: A meson is a particle that is (1) believed to be ...
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1answer
28 views

Particle Data Group book

Many PDG data books have 'July' marked on their covers, does this mean they are published (and made available on their website) in July? When is it expected to be available this year? (date or month ...
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1answer
68 views

Which theoretical models are there between quantum mechanics and cosmology? [closed]

I'm an enthusiast/hobbyist right now and I'm quite curious about the subject of understanding which scales come between the quantum scale (ab initio/first principles) and the macroscopic scale. After ...
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5answers
6k views

If particles are points, then aren't atoms empty space?

Zero dimensional points do not take up space, so then wouldn't everything in the universe be literally empty? Or is there something that I'm missing?
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3answers
345 views

Why Do Glueballs Have Mass, When Individual Gluons Are Massless?

From Wikipedia Glueballs Glueballs are predicted by quantum chromodynamics to be massive, notwithstanding the fact that gluons themselves have zero rest mass in the Standard Model. Glueballs with ...
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2answers
349 views

Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced?

This thought was inspired by a comment from the current leading answer, by @Sentry, to the question Where are all the slow neutrinos? This [slow-neutrino induced nuclear decay] will still be an ...
29
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5answers
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Do massless particles really exist? [duplicate]

I was in doubt, so I went to wikipedia. There it says "the photon has zero rest mass", but on the side description it says the mass is $<1.10^{-18} \:\mathrm{eV}/c^2$. So is the mass of the photon ...
46
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2answers
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Where are all the slow neutrinos?

The conventional way physicists describe neutrinos is that they have a very small amount of mass which entails they are traveling close to the speed of light. Here's a Wikipedia quote which is also ...
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0answers
33 views

Basic calculus of the adjoint spinor being transformed under parity

In Modern Particle Physics (p.287) Thompson says that under the parity transformation of the adjoint spinor we have $$\bar u=u^\dagger\gamma^0\rightarrow^p (\hat Pu)^\dagger\gamma^0= u^\dagger\gamma^{...
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1answer
32 views

Constructing singlet from doublets

Can we construct a gauge invariant term using the SU(2) doublet $l_L=(\nu_e e)^T$ and $(l_L)^c=C\bar{l}^T_L$? Since, both are doublets under SU(2), and $2\times 2=3+1$, I wonder what will be the ...
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Calculating photon number density inside a volume on whose surface the energy flux is known

I have the power spectrum for a galaxy of radius $R$, which we can approximate as a sphere at some distance $D$. Now, on earth we can measure the power spectrum which is given as a list of tuples, ( $...
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28 views

How to calculate off shell decay channel's branch ratio

I know for the on shell decay, the branch ratio equal partial decay width divide by total decay width. But for off shell decay, for example , $H\to WW^*$, one of the $W$ is off shell, how to calculate ...
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1answer
71 views

Is there a problem with our currently known fundamental particles?

Many scientists are searching for particles even more fundamental than leptons, quarks, gluons, etc. and (from what I know) string theory tries to hypothesize one elementary "thing" that everything is ...
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20 views

LHCb Peaking Background

I was reading a paper on the estimation of the branching fraction of B+ to K pi pi gamma. I was wondering whether you could clarify the meaning of peaking background. Thanks!
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1answer
15 views

Is in the area where the aurora's are also more cosmic ray?

On our poles the aurora's are the effect of high energy particles and photons comming from the sun (solarwind) and of cosmic ray. Those rays are interacting with the oxygen and nitrogen molecules/...
2
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1answer
28 views

Why are vector mesons identified by the adjective vector?

vector mesons are mesons with total spin 1 and odd parity (usually noted as JP = 1−). Compare to a pseudovector meson, which has a total spin 1 and even parity. coming from a mathematics ...
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1answer
32 views

Pair production of quarks

I was reading about pair-production of particles by photons, and in every place that I read, only the electron/positron production was said. So I had the following doubt, is it possible to have a ...
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3answers
724 views

Is there strong interaction between electrons?

I am not familiar with quantum mechanics at all. But I remember when I was at high school, we learned that strong interaction keeps protons next to each other while they repel each other because of ...
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16 views

How to know the cross section in this Fig

I wonder how to calculate the cross section of ( p p > gamma gamma b b~) (blue region) in the opposite plot, the y-axis is the number of events divided by 100 GeV with luminosity = 100 $\mbox{fb}^{-1}...
3
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1answer
269 views

Understanding CP-violation from a toy model of two fermions and a scalar boson

Consider a field theory given by the following Lagrangian $$\mathcal{L}_{int}=y\overline{\psi_1}\psi_2\phi+y^*\overline{\psi}_2\psi_1\phi^\dagger$$ where $\phi$ is a complex scalar field, and $\psi_1,\...
2
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4answers
124 views

How can fields interaction give rise to particles?

We say light a matter-wave, meaning along with its wave property it shows particle nature. But how can fields interaction (electric and magnetic) give rise to particles (photon)? I wish someone could ...
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2answers
77 views

Can we see/detect things which don't have electrons

Whenever we sees a thing the process happening at atomic level is the electrons of that stuff absorbs the energy from packets and goes to higher state and then comes to ground state and emits ...
3
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0answers
21 views

Why Weyl fermion in Weyl semimetals(WSM) have high mobility only at low temperature?

I read several papers reporting high Weyl fermion with very high mobility in WSMs such as TaAs, NbAs, WTe2 and so on. However, this high mobility looks like (=Weyl fermion) always appears at only low ...
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0answers
27 views

What is meant by interactions being mediated by force-carrier particles?

When a photon interacts with an electron, what is observed to happen? Force-carrier particles are described as the mediators of these interactions. What does this mean and how is this concluded?
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1answer
67 views

Do photons interact with everything?

Suppose you shoot a beam of photons in a particle collider. Are there any particles in which the photons do not interact with? Q2: What is an interaction between particles?
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56 views

Why isn't proton radiation by decay on earth known in nature?

Perhaps asking for why isn't appropriate in physics, but as there is neutron and alfa radiation what causes proton radiation not to be very common in nature (in laboratory it is seen although)
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1answer
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Weak decay iff or if strangeness changes? [duplicate]

I know that for a decay if the strangeness changes then the decay is a weak decay because strangeness is conserved in both strong decays and electromagnetic decays. However, is it also true that if a ...
2
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2answers
129 views

What is the meaning of the size of an elementary particle in QFT? What is the meaning of a point particle? [duplicate]

I have often seen people refer to the size of a particle being at most a given value, or a particle being a point particle, in the context of quantum field theory. Examples are the Wikipedia entry on ...