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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23 views

Can we duplicate a human being with 100% accuracy down to the atomic level? [duplicate]

Similar to my last question asked here - Can an arrangement of particles be duplicated precisly? Would it be possible to clone or duplicate a biological system with 100% accuracy. It seems there is ...
2
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2answers
148 views

Increased likelihood of photon emission due to “nearby” absorber?

Is an excited atom more likely to emit a photon if there is a similar atom in the ground state nearby ready to absorb it? When I say "nearby" I guess I mean that the absorber has an approximately ...
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2answers
72 views

Does yukawa potential of two particles have effect on each other? [on hold]

Okay,a novice here.Suppose two particle interact with Higgs field.Does The Yukawa potential created by each of them affect each other or the interaction in any way.If so,what is it physical ...
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2answers
474 views
+250

Quarks as preons for the whole standard model

This is a sequel to an earlier question about Alejandro Rivero's correspondence, the "super-bootstrap". The correspondence itself was introduced in his "Supersymmetry with composite bosons"; see the ...
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0answers
68 views

General definition of vector spinor and spin

I am looking for basic and exact definitions of fundamental physical consepts in graduate level. I reach this following definitions. Could you please help to improve these definitions. Spin: ...
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1answer
26 views

Difference between Urca process and $\beta$-decay in neutron stars cooling

I was reading about the Urca process and its importance in the cooling of astrophysical compact objects. Indeed, it is supposed to be one of the major contribution to the cooling of neutron stars ...
2
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1answer
56 views

Fierz identity for Weyl spinors in tensor currents

Using Fierz identity I found that certain four-fermion operator with left $l_i$ and right-chiral $r_i$ Weyl spinors vanish $\bar{l}_1\sigma_{\mu\nu} r_2 \bar{r}_3 \sigma^{\mu\nu} l_4 =$ $ ...
2
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1answer
60 views

What are the quantum numbers of an exchange particle in the t channel?

i know that for an s channel reaction, the quantum numbers of the intermediate particle have to be the same as those of the particles coming in, for example in the reaction $\gamma \pi \rightarrow a_2 ...
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1answer
71 views

Do massive particles exchange Higgs bosons?

Do massive particles exchange virtual Higgs bosons between themselves? If they do does the resulting Higgs force decay exponentially with distance?
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1answer
447 views
+100

Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...
6
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3answers
2k views

Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...
2
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2answers
86 views

Dashed lines in Feynman diagram

In this article, in e.g. figure 2, what does these dashed lines across the Feynman diagram mean?
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1answer
821 views

Does photon have size measurement because of its particle nature

Does photon have size measurement because of its particle nature like electron's 3.86*10^-13m etc..
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1answer
97 views

Polarization vectors in scattering amplitudes

The annihilation ($e^+ e^-\rightarrow 2\gamma$) diagrams are I'm just wondering if the amplitudes should be $$(-ie)^2\left[\bar v(p_2)\gamma^b\epsilon_b^*\frac{-i(-(\gamma^\mu p_{1\mu}-\gamma^\nu ...
3
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3answers
47 views

Isotropic neutrino-lepton scattering

I'm a physics student and I'm attending an introductory course of particle physics. My professor stated that, in center of mass frame, the $\nu_\mu e^- \to \nu_\mu e^-$ elastic scattering has an ...
1
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0answers
32 views

Lie theory and particle physics [duplicate]

I have recently been reading Intro to Lie algebras and representation theory by Humphreys, and when I am finished I am interested in reading about Lie groups and Lie algebras and their applications to ...
56
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5answers
6k views

How literally should you take “The Higgs boson gives other particles mass”?

A standard phrase in popular discussions of the Higgs boson is that "it gives particles mass". To what extent is this a reasonable, pop-science, level of description of the Higgs boson and it's ...
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2answers
1k views

How does one experimentally determine chirality, helicity, spin and angular momentum?

If I've got an instance of a fundamental particle, how can I separate out the measurements of these three concepts? (I think) I understand the theory behind them, and why the particles in the ...
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1answer
47 views

Higgs Boson revealed video

I'm newbie here, no background in physics, just trying to understand a bit about the Higgs Boson. I guess the key moment of this video (https://www.youtube.com/watch?v=RC-apKhWNDE) is when Fabiola ...
2
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2answers
205 views

Why is it called “annihilation”?

The term "annihilate" literally means "turn into nothing". However, when a particle and antiparticle collide, they clearly do not turn into nothing; they simply transform into different particles. ...
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1answer
231 views

Physical -> Chemical -> Nuclear -> (what comes next)

If a splitting atoms / fusing isotopes (fission bomb, fusion bomb) yields more energy than chemical changes (TNT, et al) yields more energy than physical change (hydrogen bonds forming during water ...
21
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3answers
935 views

Why is the (free) neutron lifetime so long?

A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ ...
2
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1answer
58 views

Deriving Feynman rules from a Lagrangian for vertex factors for “more complicated” interactions

I am trying to derive Feynman rules from a given Lagrangian and I got stuck on some vertex factors. What for example is the vertex factor that corresponds to the four-scalar interaction that is ...
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2answers
53 views

Photon striking a molecule and getting reflected

I am writing a simple simulator which simulate absorption of UV light in solution. The idea is to see if I can see Beer-Lambert laws in my model. It is not intended to be a precise simulator but ...
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2answers
701 views

What is the current status of the anomalous muon magnetic moment?

Many years ago, a discrepancy was found between the experimentally measured value of the muon magnetic moment, and the theoretically calculated value. Shockingly, most physicists were blase about it. ...
2
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2answers
110 views

How to explain spin of electron? [duplicate]

How can we explain spin of electron, or the spin of other fundamental particles? If we think the spin of electron is similar to the spin of a ball or planet we make a mistake. We say it is an ...
2
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1answer
53 views

Magnetic moment of uncharged particles

As we know that particles, only having charge, can have magnetic moment, then how particle like neutrino (having mass) can have magnetic moment? Don't bother about neutron because it has charge ...
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2answers
65 views

How does a structureless particle decay?

As we know that particles having structure (quarks) decays to lighter products. We can show the decay of them by quark level Feynman diagram. But what about muon decays to electron, neutrino (muon ...
2
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2answers
293 views

Why does Matter occupies space? Matter and space are two things… If Space does not has mass, why should matter have space-ful nature?

This thought has completely changed my perspective towards matter. If the matter in a star can collapse to a point to form a Black hole, surely the true nature of matter should be able explain this ...
7
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2answers
114 views

What are the main algorithms the LHC particle detectors use to reconstruct decay pathways?

I am just starting to look into how we understand the data from particle collisions. My question is, what are the algorithms or ways that these detectors interpret the data? Are there standard ...
4
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3answers
170 views

Where does the electron get its high magnetic moment from?

I have always found the concept of spin a little weird. I had read somewhere that for the charge or size of electrons, their magnetic field is very high. In order to produce such fields, they must be ...
11
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2answers
507 views

Why can the Euler beta function be interpreted as a scattering amplitude?

The Wikipedia article on the Veneziano Amplitude claims that the Euler beta function can be interpretted as a scattering amplitude. Why is this? In another word, when the Euler beta function is ...
2
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2answers
81 views

Constructing SUSY algebra via index structure

Often in literature the SUSY algebra is simply given, but various books, for example Bailin and Love, goes through the trouble of showing how the SUSY commutation relations are the only possible ones ...
31
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6answers
2k views

If there were fundamental forces weaker than gravity, would we know about it?

We know that gravity is a very weak force compared to electromagnetic forces and the nuclear forces. We know about the other forces because they're necessary to explain atoms, and we can detect ...
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2answers
55 views

How is photon time of flight/range over sub-millimeter distances measured?

I was reading a paper that described how the force a low-thrust torsion pendulum was measured. In it, the paper states a laser is bounced off a mirror and the displacement is "...based upon the beam ...
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2answers
68 views

What's the difference between energy and temperature in field theory?

I'm familiar with the formalisms for both zero temperature and finite temperature field theory, but (somewhat embarrassingly) I don't actually have a good physical intuition for when physical ...
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2answers
160 views

From where this number of 14 Tev has arised for proton-proton head on collision in LHC?

I am interested in finding out, why are collisions at 14TeV done in the LHC, instead of some other energy?
3
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3answers
150 views

Unitarity of PMNS matrix

Why should the neutrino mixing matrix (PMNS matrix) be unitary? Is the unitarity dictated by experiments or is it a theoretical demand?
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5answers
1k views

What is the difference between a neutron and hydrogen?

Differences? They are both an electron and a proton, since the neutron decays to a proton and an electron, what's the difference between a neutron and proton + electron? so is it just a higher binding ...
3
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1answer
141 views

What is the idea behind counting the number of excited states and the representation of a group ?

While reading Polchinski's Chapter 1, I encountered the following on page 24, "For example, the $(D-1)$ dimensional vector representation of $SO(D-1)$ breaks up into an invariant and a $(D-2)$-vector ...
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0answers
36 views

Is spin an observable quantity for fundamental particles? [duplicate]

How we know that the spin of fundamental particles? For example spin-0, 1/2, 1,2.. What is the experimental facts about spin?
7
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2answers
125 views

Is there a fundamental particle that gives rise to energy?

I was wondering if there exist a particle analogous to the Higgs boson that gives rise to energy, I´m sorry it´s not the big question but I feel confused about how the universe works, also I have been ...
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0answers
49 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?
2
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2answers
74 views

Higgs field and masses of particles

Interaction of particle with Higgs field provides mass to the particles, then why still some particles are massless?
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0answers
28 views

About Paschos-Wolfenstein relation (Weinberg angle measuring)

There is Paschos-Wolfenstein relation: $$ \tag 1 \frac{\sigma^{NC}_{\nu_{\mu}} - \sigma^{NC}_{\bar{\nu}_{\mu}}}{\sigma^{CC}_{\nu_{\mu}} - \sigma^{CC}_{\bar{\nu}_{\mu}}} = \frac{1}{2} - ...
0
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0answers
44 views

Size of an elementary particle [duplicate]

Do we have a well defined mathematical expression denoting the size of a fundamental particle with no internal structure (electron for example) ? If we do, how does it fit in with the uncertainty ...
3
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2answers
108 views

Scalar field divergent mass correction interpretation question (hierarchy problem)

Simple power counting tells you that a scalar field coupled to some fermions at one-loop picks up a correction to the mass of the order $\Lambda^2$. Based on this people say things like "it's natural ...
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1answer
47 views

Is there a standard resource that lists all understood particle-particle relationships?

I am just starting to dig a little deeper into particle interactions, and just have an introductory college physics background (no quantum mechanics). But I am interested in the conditions of the ...
6
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2answers
2k views

Where does the number “380,000 years for electrons to be trapped in orbits around nuclei” come from?

How does this number get calculated? About 380,000 years after the Big Bang the temperature of the universe fell to the point where nuclei could combine with electrons to create neutral atoms. ...
2
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0answers
37 views

How do I calculate integer and half integer spin? [closed]

How do I calculate integer and half integer spin, and how do I use the calculations?