A model of the basic particles and forces featuring six quarks, three charged leptons, three massless neutral leptons and four fundamental force carrying bosons. The twelve fermions are arranged into three generations, while the bosons serve to explain the electromagnetic interaction plus the strong ...

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29
votes
1answer
1k views

How close does a particle-antiparticle pair need to be for annihilation to happen?

I've most often seen the statement that the annihilation of a particle and its antiparticle occurs when they 'collide' with one another. So in other words when they get very close to one another ...
1
vote
0answers
33 views

Massless Dirac Field Chirality and CP

I have some very basic questions about Quantum Field Theory. So let's assume we have massless fermions. In 4 spacetime dimensions, due to the Group Structure of $SO(3,1)$ there exists the famous ...
-2
votes
1answer
61 views

Fundamentals for predicting the standard model? [closed]

. Now, the question(s). What must a theory include to be consistent with the standard model? What concepts/ fields must be predicted?(such as predicting a Higgs field, gauge groups, particles being ...
3
votes
1answer
93 views

Spontaneous symmetry breaking of anomalous global abelian symmetries and $U(1)$ of QCD

Let me restate the $U(1)$ problem of QCD: Let us forget about the $s$ quark, and consider the $u$ and $d$ massless. This is a good approximation since $m_{u,d} \ll \Lambda_{QCD}$. Then ...
2
votes
0answers
82 views

Is there any additional complexity in the physical laws that seems unnecessary for us to exist? [closed]

I am wondering if the universe is as simple as possible, at least given the constraint that humans exist on Earth. This is my second attempt at this question, which was marked as too broad, since I ...
3
votes
3answers
164 views

Are field theories special?

Our best descriptions of the microscopic world, that satisfy many fundamental requirements (as we know them today), are field theories. Is there something fundamental about field interactions, or are ...
2
votes
2answers
135 views

Simulation of everyday life based on standard model [closed]

If I were to model the standard model, say on a super powered computer (which does not necessarily have to exist in the real world), would I get molecules, chemistry, life? I want to understand the ...
1
vote
1answer
71 views

Three gauge bosons vertex

I was told that two $Z$ bosons could not decay to one (virtual) $Z$ boson at any loop level. Is it true? if so, why? Does it also hold for photons? Could we generalise the statement to "There cannot ...
3
votes
1answer
137 views

Quark mixing vs neutrino mixing, mass eigenstates, weak states and detection

I have some doubts regarding the CKM matrix in the quark sector and PMNS matrix in the leptonic sector. Let us call $(d^\prime, s^\prime, b^\prime)$ the weak basis for quarks and $(d,s,b)$ the mass ...
1
vote
2answers
328 views

Can all fundamental forces be repulsive?

If the electric force can be attractive (with opposite charges) or repulsive (same charges), and the magnetic force acts like this too, can all forces be repulsive in some cases? For example, could ...
2
votes
1answer
64 views

Evidence for standard model description of neutrons

as I don't know too much about experiments I have the following question concerning the evidence about the quark constituents in neutrons. After a quick google investigation I found some sentences ...
31
votes
7answers
2k views

How can the unstable particles of the standard model be considered particles in their own right if they immediately decay into stable particles?

How can the unstable particles of the standard model be considered particles in their own right if they immediately decay into stable particles? It would appear to a layman such as myself that these ...
1
vote
3answers
80 views

What are the six quark mass values when extrapolated to Planck energy?

Let us assume that the standard model is correct up to Planck mass. (Yes, I know, this is a big assumption.) If we continue the running of quark masses with energy (due to renormalization), what are ...
0
votes
0answers
64 views

What are the dominant decay products of upsilon meson?

Upsilon meson may decay to phi or omega meson but these should be OZI suppressed as in this case, bottom and antibottom quarks of upsilon meson will have to first annihilate to high energy gluon. ...
1
vote
1answer
253 views

Why is neutral sigma baryon more massive than lambda baryon?

Neutral sigma-star baryon, neutral sigma baryon and lambda baryon have masses 1387 MeV, 1192 MeV, 1116 MeV respectively, whereas each of these 3 particles are composed of 1 up, 1 down and 1 strange ...
5
votes
2answers
831 views

Quarks in a hadron- where does the mass come from

We know that the sum of the masses of the quarks in a proton is approximately $9.4^{+1.9}_{-1.3}~\text{MeV}/c^2$, whereas the mass of a proton is $\approx931~\text{MeV}/c^2$. This extra mass is ...
-2
votes
1answer
51 views

Are there different colors of leptons? [closed]

Are there different colors of leptons? The Pauli Exclusion principal made it necessary for quarks to have 3 different colors. However, although leptons don't undergo the strong interaction they still ...
5
votes
2answers
765 views

Each elementary particle has its own field. What about antiparticles?

I understand how particles correspond to their respective fields. What about antiparticles though? Do they have separate fields as well?
0
votes
2answers
101 views

Color Force & Nuclear Force [closed]

I was wondering if the color force and nuclear force are both sub-forces of the Strong Interaction? If so is the Strong Interaction responsible for any other forces?
0
votes
0answers
65 views

Quantum Flavordynamics and messenger particles

My question is about messenger particles and how they relate to the concept of flavordynamics. I know that messenger particles travel between other particles to "communicate the force" like a photon ...
0
votes
0answers
44 views

Does core of a proton exist? [duplicate]

I understand a proton is made up of quarks/gluons. I want to know if a proton has an actual core? Also whether protons have a core/surface temperature.
10
votes
2answers
256 views

Can the up quark still be massless?

It used to be commonly discussed that the bare mass of the up quark can be $0$. This was because we can't observe its effect directly. To my knowledge the up quark can only be measured by its effect ...
1
vote
2answers
105 views

How do protons and neutrons interchange?

I recently read in a book that a nucleon with +1/2 isospin is a proton and if the isospin is changed to -1/2, it is a neutron, so it is the same particle in different states. If a proton has a ...
1
vote
2answers
112 views

Why do we assume that particles and their antiparticles have the same half-life?

Has it been proven experimentally? What would the consequences be if their half-lives were different?
5
votes
1answer
89 views

How do symmetries break in cosmology?

The way I understand spontaneous symmetry breaking in thermodynamic systems is that the symmetry is actually explicitly broken by an infinitesimally small field. The system chooses one of the ...
3
votes
0answers
92 views

Intrinsic parity

When we apply parity on a field two times, we demand that we should get back the same field. This gives us, $P^{2} =1$, which implies, $ P \psi = e^{i \theta} \psi$ . This extra phase factor is ...
2
votes
2answers
101 views

Quark model in particle physics

As we all know that baryons are made up of three quarks while mesons are made up of a quark and an anti-quark. Is it possible for a particle to exist with five or seven quarks? Can a particle exist ...
1
vote
0answers
37 views

Can non-color-neutral nucleons exist?

In a proton or neutron, one quark is red, another blue, and the last green, making it color neutral. Is it possible for a nucleon to consist of colors rgg, rbb, rrb, etc? If three quarks of such color ...
0
votes
0answers
64 views

About equivalence of two ways of “derivation” of Standard model

Two ways of SM derivation I know two methods of SM lagrangian "derivation". The first one, which I will call as Weinberg way, is based on approaches of SM as theory with spontaneusly broken ...
2
votes
0answers
59 views

How to let Pythia to output the complete event record in LHEF or StDHep format?

I am currently using Pythia 6.4 to simulate some processes (I do not have the intention to upgrade to 8). Now, I need Pythia to output its event record in the format of LHEF or StDHeP. I accidently ...
4
votes
2answers
214 views

Can quarks be considered real and elementary?

In our current theories all hadrons are made up of quarks and gluons. This view reduces considerably the big family of hadrons by providing a very logical structure in which all quantum properties ...
1
vote
1answer
192 views

What type of neutrinos do we detect

There are three types of neutrinos known today. When detecting them, how can we tell which type we are detecting?
1
vote
1answer
124 views

Why standard model particles cannot be dark matter particles

I'm interested if any of the particles in the standard model could be potential candidates for dark matter? I know that we do not see dark matter, therefore dark matter does not interact ...
5
votes
2answers
146 views

What is it exactly that conflicts when trying to unify all 4 fundamental forces?

Everyone knows that there are 4 fundamental forces: Gravity Electromagnetic Weak Strong At school and university you're taught that no one has been able to unify these 4 fources. However, not a ...
1
vote
1answer
77 views

What makes neutron heavier than a proton? [duplicate]

The mass of proton is 1.672*10¯²7 kg while it is 1.675*10¯²7 kg. Both are made up of 3 quarks each. Then what makes proton lighter than a neutron?
1
vote
1answer
47 views

Feynman rule for current-current operators

I wanted to know what is the Feynman rules for current-current vertex like this one: $$ {\cal{ L}} = G^\prime_F \hspace{2mm} \bar{d} \gamma^\mu (1-\gamma^5) u\hspace{3mm} \bar{s}\gamma_\mu ...
4
votes
1answer
209 views

Anomaly cancellation in the standard model (calculating the symmetrized trace of generators)

The Problem We can show that the condition for the Standard Model to be anomaly-free is that the symmetrized trace over the generators of the gauge group vanishes: \begin{align} \text{tr} ...
2
votes
1answer
55 views

Particle masses

if there is no theory to predict/calcukate the masses of the fundamental particles, where do they get the values for the quarks, as quoted in the standard model? And since the composite particles get ...
0
votes
0answers
30 views

Experimental sensitivity to variance of the fine-structure constant

If some of the fundamental parameters of the Standard Model had quantum uncertainties, they should manifest mainly as a minimum width in the experimental sensitivity of measurement of some of them, ...
2
votes
3answers
528 views

Is the Higgs field needed to explain the mass of the electron?

The self energy of the electron can be represented in two ways: the energy required to bring a charge distribution from infinity to the size of the electron (assuming it is a point charge with no ...
6
votes
1answer
530 views

Can two colliding photons create a Higgs Boson?

The LHC discovered the Higgs using the following decay mode: $$ H^0 \rightarrow \gamma \gamma $$ This got me thinking: if we reverse this mode, will it be valid? In some annihilation/decay pairs, ...
1
vote
1answer
76 views

Charge of $W$-bosons in Feynman diagrams

When looking at Feynman diagrams of particle decays, how would I be able to find out the charges of the $W$-bosons involved in the decay?
2
votes
2answers
239 views

How many of the Standard Model free parameters are mutually independent: (all of them)?

My knowledge of the standard model is very limited so please let me spell out my assumptions first (and please let me know when I have mangled concepts, terminology or I am plainly just out of my ...
2
votes
0answers
53 views

Physical proceses before the breaking of $SU(2)_L\times U(1)_Y$ symmetry

The energy scale which the electromagnetic and the weak interaction were unified, there were 4 massless gauge bosons: 3 corresponding to the unbroken generators of $SU(2)_L$, say $W_{\mu}^{1,2,3}$ ...
5
votes
3answers
242 views

The Makeup of the Pentaquark

Why is it that when they have the artist's rendition of the Pentaquark it shows two downs, two ups, and one anti-strange quark? Is this or is this just for show? Follow up to this question: if this ...
2
votes
1answer
114 views

How unique are the quantum numbers we commonly use?

We use the eigenvalues of the Cartan generators (=diagonal generators) of a given gauge group as quantum numbers in physics. Are these numbers somehow fixed and if not, what transformations are ...
1
vote
2answers
278 views

Radioactive decay as pure radiation of neutrinos and antineutrinos?

Is it possible with radioactive decay as pure radiation of neutrinos and antineutrinos? From a theoretical point of view? I'm not asking for processes since I'm convinced there are no known processes ...
3
votes
1answer
65 views

Can the effective vertex for $\gamma\to3\pi$ be derived directly from the anomaly?

My question is whether the effective vertex for $\gamma\to3\pi$ can be derived directly from the anomaly (given in the first equation below), in analogy with the $\pi^0\to2\gamma$ vertex? As far as I ...
3
votes
1answer
58 views

A pedagogical exposition of the hadron physics?

I am looking for a textbook/lecture notes/etc. on the basics of hadron physics. I wish to understand how to construct the effective Lagrangian for pions and nucleons starting from the QCD Lagrangian. ...
2
votes
0answers
108 views

Isospin In Kaon Decay

The decay $ K \to \pi \pi $ at zero-strong interaction level is calculated by considering the matrix element of the operator $ Q_2 = (\bar{s}u)_{V-A} (\bar{u}d)_{V-A} $ for two kinds of processes: ...