Questions tagged [elementary-particles]

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2answers
126 views

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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0answers
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Is it possible that the Rishon model and a Mirror Universe are connected? [closed]

I'm not sure if both the Rishon Model and the Mirror Universe fall outside the realm of mainstream physics (though obviously, there are physicists paying attention to these concepts), but maybe it's ...
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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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0answers
18 views

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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0answers
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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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5answers
5k views

Are protons bigger than electrons?

In every text/ physics book that I've read, Protons are mentioned as particles that are bigger, way bigger 2000 times to be precise, than electrons...I believed that until a few minutes ago when I ...
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1answer
64 views

How to transform a given Lagrangian to a Nambu-Gorkov basis?

With reference to the Nambu (or famously, Nambu-Gorkov) transformation in this paper, could someone explain the reason behind using the 3rd Pauli matrix in the Lagrangian after equation (2.3) (would ...
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2answers
80 views

If virtual particles are considered to be just mathematical constructs, does this imply there are no corresponding physical processes?

Some people consider all elementary particles to be non-existent. They tell us that they are changes in the field configurations that last which are called "real particles", while those that ...
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1answer
45 views

How to prove the equivalence of two definitions of hypercharge?

Before introducing top bottom and charm quarks,Strong Hypercharge is defined in the following two ways--- $1.\,\,\,Y=B+S$ where $Y,B,S$ are the hypercharge, baryon number and strangeness respectively. ...
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1answer
48 views

Conservation of chirality in non-weak elementary particle interactions

Chirality is not conserved in propagation (e.g., electron oscillates between left and right chiral). But is chirality conserved in interactions? What is a good reference paper or book for this notion ...
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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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2answers
55 views

Entropy always increases. Then why did elementary particles come together to form an atom?

It is generally said that entropy always increases. But after the Big Bang elementary particles came together to form an atom. Isn't that paradoxical ?
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1answer
31 views

Why the mesons $\pi^0$ and $\eta$ are “degenerate”

I don't know anything about elementary particles, but reading the book by Zeidler on p158, table 2.8 one can observe the quark content of baryons and mesons. It is strange that the $\pi^0$ meson has ...
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1answer
63 views

Question about a relativisticaly accelerated harmonic oscillator

How can the speed of oscillation of a harmonic oscillator be affected if somehow it got accelerated to a relativistic speed perpendicular to its oscillation? Can this be compared with the effect on ...
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1answer
37 views

Which is the meaning of these masses?

When reading about the masses of neutrinos in the HDM (Hot Dark Matter) model of the universe, I came across the following equation: $$\tag{1} \sum_i m_{\nu_i} = 92 \Omega_\nu h^2 \text{eV}$$ My ...
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4answers
97 views

Do elementary particles last forever?

I have heard that not even black holes last forever, because of Hawking radiation. But what about elementary particles? Will an electron, for example, exist for all time?
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2answers
69 views

What principle of quantum mechanics tells us that harmonic fluctuations of a field act like localized particles? [duplicate]

"Quasiparticles" are ubiquitous in condensed matter physics, e.g. magnons and phonons, and more generally all particles in quantum field theory are considered the elementary harmonic ...
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4answers
1k views

Haag's comment on the relation between fields and particles

I am very confused by the statement made in Haag's, Local Quantum Physics: Fields, Particles, Algebras (page 46): ... the idea that to each particle there is a corresponding field and to each field a ...
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1answer
111 views

Which equations of 5 string theories show that elementary particles formed by strings?

It is commonly said that "elementary particles are indeed formed by strings." (from E Witten interview) Which equations of string theory show that elementary particles are indeed formed by ...
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2answers
94 views

Electric field associated with a stationary electron

In the framework of QFT, quantum fields are the fundamental objects instead of point-like notion of particles. Particles, at least fundamental ones like electron, are understood to arise as ...
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2answers
89 views

What is the evidence (experimental observation) that elementary particles have spin angular momentum?

From what I have read here, the concept of spin is attributed to a calculation based on a mathematical model using quantum mechanics. For example, How can a particle with no size have angular momentum?...
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1answer
41 views

Does tau decay to rho meson + tau neutrino?

In the particle data group table: http://pdg.lbl.gov/2020/tables/rpp2020-sum-leptons.pdf ,only $\tau \rightarrow \pi + \nu_{\tau}$ is documented. But does $\tau \rightarrow \rho + \nu_{\tau}$ as well? ...
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3answers
346 views

Why do the masses of fundamental particles seem to increase exponentially?

The (15 positive) masses of fundamental particles are measured inputs to the standard model. They seem to increase exponentially when ranked in increasing order, or perhaps follow a power law when ...
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1answer
46 views

Does a Meson hit earth or not hit earth? [closed]

I am told a $\mu$ meson with an average lifespan of $2 \times 10^{-6}$ is created in the upper atmosphere at an altitude of $6000m$. When it is created, it has a velocity of $0.998c$ in a direction ...
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0answers
25 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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0answers
27 views

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 ...
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4answers
113 views

If light is considered a wave, then what exactly is a photon? [duplicate]

So according to google: a photon is a particle that transmits light. Ok, but light is considered a wave, not a stream of particles(I'm pretty sure that this is what Young's double slit ...
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2answers
62 views

Why does the De Broglie Wavelength influence the scale in which a nuclear reaction occurs?

In high energy accelerator collisions, why does the De Broglie wavelength of the incident particle affect the type of interaction it has with the target nucleus? E.g. In 280 MeV proton, "direct ...
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2answers
90 views

How is the higgs field excited to give a Higgs boson?

I understand that the excitation of the Higgs field itself is the Higgs boson, and not the Higgs field itself, which does fit somewhat into the little String theory I've read (The excitations of the ...
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1answer
61 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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0answers
60 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 ...
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3answers
83 views

What are the necessary attributes that any elementary particle must have or have a defined value for it?

We know that each elementary particle/entity must have mass, charge and spin defined. Are there any other attributes (independent) that must be defined for every elementary particle? is there any ...
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1answer
51 views

Do charges' sign are conventional? [duplicate]

As we know in the universe there are two types of charges, positive for some elementary particles and negative for other. By inversion charge sign of elementary particles the world be the same this ...
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1answer
29 views

What can we conclude for the spin configuration of the quarks inside the baryon? [closed]

If yes, is there any way to reconcile this findings with Pauli's exclusion principle?
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1answer
92 views

Are elementary particles as old as the universe?

Lets take quarks for example. Are the quarks - that constitute the universe - as old as the universe? Or are particles always created? Or were they all created when the universe was born?
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1answer
39 views

Theoretical Enneaquark?

First of all I'm new to physics. I'm teaching my self as of late and I'm wondering if a particle composed of 4 up quarks and 5 down(= 1 charge) could theoretically form a 'stable' particle under the ...
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6answers
2k views

Can elementary particles be explained adequately by a wave-only model?

I have been watching quantum mechanics documentaries and reading a layman's book called "The Quantum Universe". I believe I understand why the double slit experiments exclude a particle only model. ...
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1answer
58 views

Why do macroscopic objects not move at the same speed their constituents are made of?

How can subatomic particles move at relativistic speeds while the things they make up are moving much slower?
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3answers
11k views

What is the evidence for 'billions of neutrinos pass through your body every second'?

This statement is repeated so often that it has become somewhat of a cliche: 'billions of neutrinos pass through your body every second'. For example see 1, 2, 3, 4, 5, 6. What is the evidence for it,...
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1answer
44 views

Would both life as well as elementary particles no longer exist upon “heat death?

Would the elementary particles in the standard model still exist upon “heat death”? Would electrons stop orbiting around the nucleus? Would the periodic table of elements still be relevant assuming ...
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3answers
106 views

Do all the elementary particles in the standard model have their own wave functions?

Is it possible to derive the wave functions of all particles in the standard model? Would this be through the Schrödinger equation?
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1answer
96 views

Can we split an electron (or any other elementary particle) like we split a photon?

On this site, there are many questions and answers about splitting a photon. Most of them right away clearly state, that the term splitting is not quite right, because in most cases, the original ...
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1answer
88 views

If an electron is a singularity do we talk about a black hole? [duplicate]

As the standard model states an electron is a pointlike particle. If it is really so it has all features to be thought of as a mini black hole but then there is the problem how a such black hole can ...
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2answers
55 views

Pressing questions about the annihilation of a particle & an antiparticle

A charged particle (e.g. proton) meeting with its own charged antiparticle (e.g., antiproton) annihilates and energy is given off in the form of radiation. Do we have any clue why this happens? Does ...
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0answers
80 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(1,...
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1answer
114 views

Are matter particles really excitations of fields?

So it is said that particles are excitations of fields. We are given examples like photons for electromagnetic field, gravitons for gravity, etc. We are also told that normal matter is an excitation. ...
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2answers
71 views

What is the simplest, smallest matter in the universe? [closed]

per wiki, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms. what is the simplest, smallest matter ...
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4answers
875 views

How would we know that Dirac equation does not describe composite spin-1/2 fermions?

How do we know that the quanta of a quantized Dirac field describe elementary spin-1/2 fermions (or point particles of spin-1/2) and not composite spin-1/2 fermions (or extended structure of spin-1/2) ...
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4answers
267 views

Are entangled particles indistinguishable?

I have read this question: https://physics.stackexchange.com/a/462620/132371 where John Rennie says: When the two particles become entangled the means the total wavefunction Ψ can no longer be ...
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2answers
84 views

Relative size of electrons and quarks

Today, we consider quarks and electrons (leptons) as point-like or fundamental (structureless). Is there any way to indirectly probe quark/lepton substructure and guess if they are composite of ...

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