Questions tagged [elementary-particles]

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6
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0answers
910 views

General equation of motion for elementary particles

Elementary particles can be grouped into spin-classes and described by specific equations, see below: Is there a general Lagrangian density from which all these equations can be derived? A ...
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2answers
646 views

Is muon muon annihilation already realised?

As muon colliders do not yet exist, has muon-muon annihilation already been realized experimentally?
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50 views

Parity of Particles

Like charge, spin,etc.. Parity is an intrinsic property of the particle. As I read in Grifith's introduction to elementary particles book , he states parity mathematically but I am not able to see it ...
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245 views

Nature of Microscopic space-time

I am going through the introductory chapter's of Schwinger's Source theory. He writes, It [Source Theory] is a phenomenological theory, designed to describe the observed particles. No speculations ...
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1answer
66 views

Do charges have spatial dimension?

I don't know much about anything in physics. I hope you can bear with that. Let me start with my question do charges have any dimension, by this I mean physical dimension like length, breadth, height ...
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62 views

Do photons form bound states?

Since photons do not have electric charge, they do not interact via the electromagnetic force. They are also reported to be devoid of any colour-charge, so interaction via the strong force is ruled ...
3
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1answer
98 views

Which are the obstructions for $E_8^L\times E_8^R$ unification?

After left-right symmetry extension of the standard model, $$G' \times SU(2)^L \times SU(2)^R$$ it would seem that a logical pathway to grand unification is to try to obtain it by breaking down from ...
3
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1answer
354 views

What effects would a finding of Gravitational Repulsion Between Matter and Anti-Matter in the ALPHA Experiment have on Mainstream Theory?

The actual nature of the gravitational force between matter and anti-matter (attractive or repulsive) remains unsettled: See Are there experiments taking place right now that might show evidence for ...
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220 views

Young Tableau Projectors: Does the order of symmetric and anti-symmetric projectors matter?

Given a Young Tableau we find the irreducible basis of an arbitrary tensor by projecting, The projectors are usually defined as first symmetrise over the row entries and then anti-symmetrise over the ...
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71 views

Can the mass of a SUSY particle depend on the process it participates in?

I believe that mass is property of every particle,as well as spin etc.Now I'm interested in SUSY particles in cMSSM model.Can it be,that mass of a SUSY particle (at one point in five parameter space) ...
3
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1answer
755 views

Thickness of electromagnetic waves

Radio wave photons and light photons have a different wavelength. But they also appear to have a much different "thickness" in that light photons "fit" cleanly through small pigeonholes, where the ...
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1answer
48 views

Standard boost for one-particle states in Weinberg's QFT chapter 2

Weinberg's approach to QFT starts with particles which are not necessarily more fundamental than fields but are known more for certain. A particle of a particular species can have different momenta $p$...
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1answer
92 views

Are all bound states entangled?

In QM, a bound state is a special state of a particle subject to ta potential such that the particle tends to remain localized in space. The potential may be external or it may be the result ...
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38 views

A question on the existence of elementary particles with relation to time

Suppose that the universe started existing at time $t = 0$ and we chose another arbitrary point in time $t =\tau$. Is it true that for every positive real number $\tau$ every single elementary ...
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Are there experimental arguments against elementary particles to have wobbling magnetic moment

Elementary particles having angular momentum and magnetic moment are observed or assummed as these are either always parallel or antiparallel. This condition could be satisfied even the instantaneous ...
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128 views

Are we able to store low energy positrons in a magnetic field for arbitrarily long time?

And if not, what prevents us? Is there a mathematical equation describing the loss rate?
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79 views

Nature of particle spectra at ALICE

I have a question regarding the nature of the particle spectrum at ALICE as a function of momentum. The spectra in question can be seen here. My question is, why is it that the particle spectrum in ...
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234 views

Parton Distribution Functions, average cross section of the nucleon

Say we are given the scattering cross section for neutrinos from $d$ and $\bar{u}$ quarks as $\frac{d\sigma^{d}}{dQ^2}=\frac{G_F^2}{\pi}$, $\frac{d\sigma^{\bar{u}}}{dQ^2}=\frac{G_F^2}{\pi} (1-y)^2$, ...
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44 views

Is there a good reason not to think of gravity as the signaling of particles inward motion?

This is not about inventing new theories, let alone rejecting canonical ones. I am just wondering if general relativity (GR) could be interpreted like the following, or if there is something in GR ...
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51 views

Considering the negative energy density in the Casimir effect and general relativity worm holes, are these experiments feasible?

The question came after I answered the question here, and reading the link provided where negative mass is needed to create wormholes, Microlensing by natural wormholes: theory and simulations We ...
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1answer
104 views

Wigner's classification in curved space

Wigner classfied elementary particle as unitary irreducible representations (UIR) of the Poincaré group. Suppose the spacetime is curved with symmetries $G$. Should the elementary particles in this ...
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91 views

Particles in curved space-time and group representation

It is well-known, that particles in Minkowski space can be constructed as unitary projective representations of the Poincaré group, i.e. isometry group of Minkowski space: $$M_d= \frac{Poincare_d}{SO(...
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1answer
71 views

Question about quantum fields, elementary particles, and quantum numbers, and fundamental forces

As I understand it the allowable spin states of elementary particles is tied to the number of space and time dimensions, so for any two universes with the same number of space and time dimensions the ...
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141 views

Why don't strings have a Planck mass?

I understand that strings have a size of roughly the Planck length $l_P$ of $10^{-35}$ m. If that is the case then one would expect that their mass would be roughly the Planck mass which is an ...
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86 views

Possible Feynman diagram for $\tau^+ \rightarrow p \mu^+ \mu^-$ and $\tau^+ \rightarrow \bar{p} \mu^+ \mu^+$?

I want to know the possible Feynman diagram for these two lepton family, lepton and baryon number violating tau decays. These decays are forbidden in the Standard Model. But the further extension of ...
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84 views

Is there a weak hypercharge : spin-3/2 analogy?

So I was not trained as a particle physicist, but I left a table of particles on a post on Hacker News based on what little I do understand about the conservation of weak hypercharge and weak isospin. ...
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1answer
66 views

Are particles of fields that arise from compactification and strings treated differently in string theory?

I am aware that particles in string theory are different vibrating modes of strings. I am also aware that compactification leads to emergent fields from the parts of the metric of the compactified ...
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Role of higher fermion generations in ordinary matter

Do the second and third generation fermions play any significant role in ordinary, everyday matter or physical processes? Could a hypothetical alternate universe without higher generation fermions (...
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51 views

Can a particle be identified when one knows $\left<dE/dx\right>$ and the Cherenkov angle $\theta_c$?

I have a question about if it would be possible to identify a particle by measuring the energy loss due to ionization $\langle dE/dx\rangle$ and the Cherenkov angle $\theta_c$. I assume that we know ...
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58 views

The structure of the electron as a particle

has anyone found the minimum radius of the electron including the magnetic field ( dipole moment) ? The 'classsical' radius only uses the electric field, and so is a minimum radius for a purely ...
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80 views

Do all particles have radiative transitions?

Everybody knows that excited electrons can emit photons upon relaxation. A nucleus too (which is not an elementary particle), can be in an excited state and emit gamma rays upon relaxation: (source) ...
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55 views

Voltage drop along electron beam

A focused electron beam represents a current and unless the charges (electrons) meet no resistance to their movement there should be a voltage drop along the length of the beam. So, assuming the beam ...
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128 views

What are these arcs in bubble chamber photos?

In photos such as this one, or this one (too large to fit inside post), what are the highly frenzied arcs that are really prominent in these photos? Are they simply physical walls in/of the chamber, ...
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114 views

Identifying interaction responsible for this particular Eta-prime decay

$$\eta ' \rightarrow \eta + \pi^{-} + \pi^{+}$$ To identity the interaction responsible for the above reaction/ decay, observe that the strangeness number sums to zero on both sides. Conservation ...
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106 views

Why doesn't the decay mode of negative omega conserve rest mass?

There are 3 modes of decay via which a $$\Omega ^{-}$$ particle can decay This is one of the decay: $$\Omega ^{-} \rightarrow \Xi ^{0} + \pi^{-}$$ Baryon number is conserved. Strangeness number is ...
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2answers
99 views

Number of different massless particle an odd number

Why are there only three massless particles and not four? I thought for each kind of matter particle there is a corresponding particle. What makes this any different from everything else?
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337 views

Matrix element approximation

In the formula for the decay width of $\Upsilon(4S)$ to B-mesons from $\text{e}^+\text{e}^-$ collisions: $$\Gamma_{\Upsilon(4S)\to B\bar{B}}=\frac{\left|\underline{P}_B \right|}{8\pi M_{\Upsilon(4S)}^...
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1answer
221 views

Do elementary particles have a density?

The SM supposes elementary particles are structureless unless composite objects like hadrons. For bosons, that can occupy the same state, we can define energy or mass density. The same happens but ...
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Possible reactions / decays in the standard model

If we are in the Standard Model and we have the following processes: $$e^+ + e^- \to \mu + \mu^-\\ p + p \to K^+ + \Sigma^+ \\ p + n \to \Lambda^0 + \Sigma^+ \\ e^+ + e^- \to u + \tilde{t} $$ And ...
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Radioactive decay and particle collisions

I've been reading some popular science books regarding particle physics where they mention how collisions of subatomic particles at high speeds can create new particles. Also radioactive decay creates ...
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1answer
10 views

Particle Energy Correlation with Probability Cloud

Is there a relationship between a particle’s momentum/energy and it’s wavelength? I know the Planck Equation for photon energy, but does this also apply to Leptons, Quarks and other Bosons?
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Formalizing the Askar'yan Effect

Wikipedia defines the Askar'yan Effect as... [The] Askaryan effect is the phenomenon whereby a particle traveling faster than the phase velocity of light in a dense dielectric... produces a shower of ...
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1answer
61 views

Traces at pion decay

A negative pion breaks down into a muon and a muon antineutrino. What do the traces of the pion decay look like in a bubble chamber with a vertical, static homogeneous magnetic field? My ideas: The B-...
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1answer
53 views

Conserving angular momentum in elementary decay/reaction

I am trying to understand how to conserve angular momentum in a elementary decay/reaction. Consider the elementary reaction: $$ K^{-}(J = 0) +p(J = 1/2) ~\to~ \Omega^{-}(J = 3/2) + K^{+}(J = 0) + K^{...
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2answers
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Can a massless particle have both spin and charge?

Can a hypothetical elementary particle, at least in theory (according to the current science), have 0 mass and yet also have both spin and electrical charge (at the same time)?
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QCD methods - Dirac trace, trace in color space, trace in flavor space

What is meant by the following terms in QCD - Dirac trace, trace in color space, trace in flavor space, etc. Could someone explain with an example (For eg. what's the diffrerence between something ...
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Calculating the quark propagator while dealing with the color, Dirac & flavor matrices all together

$S^+$ is a diagonal matrix in color space, and is given as : $S^+ = S_{rg} ^+ \hat{P_{rg}} + S_b ^+ \hat{P_b}, where, \hat{P_b} = 1_c - \hat{P_{rg}}$ is the projector on blue quarks, $\hat{P_{rg}}$ ...
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Frequency of photons and speed in media

I'd like to ask a few questions about photons, not as a professional of physics. Frequency: Since it's connected to the frequency of the wave composed by the stream of photons but can be defined for ...
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29 views

Need help in deriving Boltzmann Equation for $3\to3$ scattering

This is the first time I am posting a question here, so please forgive me if I make any mistake. I am trying to derive the Boltzmann Equation for $3\to3$ scattering, which means there are 3 particles ...
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Question about gluons and the W-boson regarding Feynman diagrams

My questions are: 1) Does a gluon always have no charge? 2) Is the W-boson always positive or negatively charged? I thought these two statements were correct, but I came across an exercise that ...