one of the four known fundamental forces of nature and the one responsible for beta-decay radioactivity. The weak interaction is very short-ranged and more weakly coupled than either the strong nuclear force or electromagnetism. At energy scales above the Z mass the weak and electromagnetic ...

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27 views

Fermi's theory of beta decay - Does Fermi's Hamiltonian have the wrong transformation properties?

I'm studying the theory of beta decays as proposed by Fermi in the 30's, and I found an inconsistency between the transformation properties that he claims for his Hamiltonian and the transformation ...
10
votes
2answers
740 views

Why couldn't the decay $\pi^- \to e^- + \bar\nu_e$ occur if electrons were massless?

If we assume that electrons (just like neutrinos) are massless, why can’t the decay $\pi^- \rightarrow e^- + \bar{\nu}_e$ occur under the weak interaction?
4
votes
1answer
110 views

SU(2) confinement picture

Preamble: In section 2 of these lecture notes (Gerard 't Hooft, 1998) an alternative interpretation of the weak interaction is presented, in which the weak force is confined, much like the strong ...
0
votes
0answers
18 views

Mass difference in particle oscillation from weak lagrangian

Looking for an answer to how an expression to $\Delta M = M_2 - M_1$ arise in QFT I have found the approximation \begin{equation} \Delta M_K \approx \frac{G_F^2}{4\pi} m_K f_K^2 \sum_{q=u,c,t} m_q^2 ...
0
votes
1answer
72 views

Strangeness of elementary particles

What is the property, whose violation led to the assumption of strangeness? Prior to the discovery of strangeness was it assumed that particles that are produced by strong interactions can decay only ...
0
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1answer
35 views

Is dark matter particle affected by weak interaction too?

Neutrino is affected by weak subatomic force and gravitational force and just like dark matter they don't easily interact with matter, if dark matter cannot be affected by the weak interaction how ...
2
votes
0answers
82 views

Feynman amplitude for electron-positron annihilation and $W^{\pm}$ production

I'm working with this interaction Hamiltonian density $$ H_{int}(x) = ig\bar{\Psi}_{\nu_e}(x)\gamma^\rho P_L \Psi_e(x)V_\rho(x) + igV^\dagger_\rho(x)\bar{\Psi}_e(x)\gamma^\rho P_L \Psi_{\nu_e} $$ ...
4
votes
1answer
366 views

Are there weak force waves?

In the same way as there are electromagnetic and gravitational waves that update the information on their respective field, is there an analogue for the weak and strong forces?
0
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1answer
46 views

Leptonic Decay of Muon and Tau

So the question asks: (a) Draw the Feynman diagrams showing the dominant leptonic decay mode of the $\mu^-$ and the $\tau^-$. (b) Assuming $m_\tau \gg m_\mu \gg m_e$, estimate the ratio of the rate ...
1
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1answer
22 views

Is the Electroweak theory chiral regardless of temperature?

Is the electroweak theory a chiral theory regardless of whether one is above the electroweak symmetry breaking temperature or not?
2
votes
0answers
47 views

Why is the D0 oscillation so different from the K0 and B0?

I have looked for this answer into many articles and books but I am not able to figure out why $D^0\to\bar{D}^0$ is so highly suppressed if compared to the $B^0 \to \bar{B}^0$ and $K^0 \to \bar{K}^0$ ...
0
votes
1answer
34 views

Wu experiment beta decay

maybe it's a stupid question. But in Wu experiment she showed that parity in not conserved in beta decay. So how to say on general that this is true for any weak force interaction?
0
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1answer
39 views

Do neutrinos ever turn back to something less ghostly?

The most notable source of neutrinos seems to be the Sun. Obviously, the neutrinos are created from something else. Now as I think of it, they can just fly away through the solar system and be gone. ...
0
votes
1answer
53 views

Why should we expect dark matter with weak scale masses?

The WIMP "miracle" is often used to motivate WIMPs: that a WIMP with a weak-scale mass naturally freezes out of thermal equilibrium after the big bang with the right relic abundance. I understand the ...
0
votes
4answers
61 views

Change in the half-life of a neutron

What would happen if the half-life of a neutron was much more less than it is now? How could this affect the nuclei?
4
votes
0answers
65 views

Distinguishing between left-handed and right-handed weak coupling from electron-neutrino scattering

This question comes from Schwartz's QFT book, exercise 13.6. In it we consider a coupling between fermions (neutrinos and electrons in this particular case) and the Z boson of the form $g_V \bar{\psi} ...
2
votes
1answer
39 views

What is the product of low energy neutrino annihilation?

Since neutrinos are only subjected to weak interaction(ignore gravitation), thus the interaction of neutrinos are only governed by Z bosons, and photon is unlikely produced. If two neutrinos ...
3
votes
1answer
66 views

Why does virtual negative W boson decay mainly into antiup and down quarks during weak decays of lambda, Xi, omega and other baryons

Virtual $W^-$ boson may decay into $\bar{u}$ and $d$ quarks, $\bar{c}$ and $s$ quarks, $e$ and $\bar{\nu}_e$, $\mu$ and $\bar{\nu}_{\mu}$, $\tau$ and $\bar{\nu}_{\tau}$. Decay into $\bar{u}$ and $s$, ...
6
votes
1answer
143 views

Why does an interaction see the proton instead the quark mass?

When an interaction goes deep in the nucleus, should we have some way to interpolate between the proton mass and the quark mass which is going to be the ultimate destination of the interaction? For ...
0
votes
1answer
129 views

Why we unified electromagnetic and weak force?

We have unified electromagnetic and weak force into one single force called Electroweak force. I mean we can use these different forces within their respective domains like weak interaction for short ...
2
votes
1answer
103 views

How can we calculate pion decay constant in Chiral Perturbation Theory ?

Above diagram is an one-loop contribution to the Pion decay constant $f_\pi$. For example in this paper (Eq.7) they have written down the pion decay constant to one loop, but the calculation is not ...
2
votes
1answer
32 views

Is the mass of the Z due to mixing with the photon “precursor” B or to interaction with the Higgs?

I want to get something clear that I do not seem to understand. I used to read that the photon A and the Z boson are (different) linear combinations between the W^0 (neutral weak boson before SU(2) ...
2
votes
1answer
87 views

How do neutrons escape nuclei?

How do neutrons ejected from a nucleus gain kinetic energy if the they don't repel electrically and the nuclear force only attracts? Does it have something to do with the weak force?
2
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1answer
36 views

Gluon have colour-anticolour; what about weak bosons?

Gluons can be red-antiblue, or green-antired, etc. What about weak interaction bosons? (Say before symmetry breaking, to make matters simpler.) Is there a similar "weak charge" structure of ...
0
votes
1answer
47 views

Role of SU(2) group in isospin and in the weak interaction

I know that the SU(2) group describes internal symmetries such as isospin and the weak interaction. But isospin and weak interactions are quite different, so more precise what is the role of SU(2) in ...
2
votes
1answer
59 views

Why are bare mass terms for W-bosons forbidden, but coupling terms to Higgs doublets allowed?

The $W$ bosons live in the adjoint rep of $SU(2)$, which is three dimensional. The standard model Higgs lives in a $SU(2)$ doublet, i.e. the two dimensional rep. The $W$ bosons get their mass ...
1
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1answer
66 views

Experimental evidence of two neutrinos in muon decay?

We know that the pion decays into a lepton/neutrino pair while the muon decays into a muon neutrino, electron and electron neutrino. How do we distinguish them experimentally? Would the muon decay ...
7
votes
2answers
980 views

Is half-life a statistical average of variable decay times?

Is the half life of a material only accurate as long as you are still in a macroscopic regime? If I had 8 particles in a box would I observe a fluctuation in half lives, and what would occur within ...
0
votes
0answers
22 views

What is the entropy of strong and weak nuclear forces? [duplicate]

Can we determine the entropy of strong and weak nuclear forces? If so, what will be the formula to determine the strong and weak force entropy? Thank you :)
3
votes
0answers
119 views

Is there a relationship between force and entropy?

Is there any relation between force and entropy? If any, I would like to know what the equation of this relation will be. What is the entropy of strong and weak nuclear force? Can we determine it? If ...
3
votes
0answers
56 views

Matrix elements of four-quark operators [closed]

In weak interaction phenomenology, especially in strangeness changing processes, effective four-quark operators are used. Such as $Q_1 = (\bar{s}_\alpha \gamma_\mu (1-\gamma_5) d_\alpha) ...
2
votes
2answers
52 views

Ambiguity with reaction equations

I understand that if two particles are on the left hand side of a reaction equation they are said to "interact". For example, $p+e^{-}\rightarrow n+v_e$ is a proton and electron interacting (electron ...
1
vote
1answer
237 views

How to tell if a particle interaction is strong/weak?

Problem: Prove that the reaction $p+p\rightarrow p+K^+$ is impossible, where $p=\text{proton}$, $K^+=\text{kaon}$. (Side question: Is there a specific name for a positive Kaon, just like a "positive ...
0
votes
1answer
55 views

What does “interact via strong force” mean?

I was just wondering if the words "strong force" and "strong interaction" are interchangeable? Also, these are referring to "strong nuclear force", correct? Then what does it mean for particles to ...
3
votes
1answer
113 views

Could the 4 Forces Split Off or “Decay” into Other Forces in the Distant Future? [duplicate]

From my basic understanding of popular-level physics articles and books and such, the 4 forces (Electromagnetism, Gravity, Strong and Weak Force) used to be 1 force in the early universe, then split ...
2
votes
0answers
114 views

About generator of $SU(2)$ flavor symmetry group

I am reading the textbook, "weak interactions" by Howard Georgi which can be founded in his homepage. Here i am trying to solve the problem 1b-2. The problem is given as follows. Consider the ...
1
vote
1answer
29 views

Mass dimensions and weak interaction

The Fermi constant has a mass dimension of $-2$ and a value of $10^{-5}GeV^{-2}$. How can I infer from this information that the mass scale of the weak interaction is about $10^2 GeV$?
3
votes
1answer
56 views

Decay Feynman diagram

$$D^0 \to K^+ +\pi^- + \pi^0 + \pi^0$$ cannot occur by first order weak interactions. Could anybody help me confirm this? What I currently have is that the initial charm goes to anti-strange and the ...
0
votes
1answer
195 views

What are the equations for the weak and strong forces?

What are the equations for the strong and weak force, like how for the Electrostatics the equation is $F_c= k*Q*q/(r*r)$. I understand to an extend what the strong and weak forces are. However, I ...
1
vote
1answer
70 views

What are the quantum numbers of Majorana neutrinos?

I have a question about majorana neutrinos. Majorana particles are particles that are their own antiparticle. From this I would argue that they need to have all quantum numbers equal to zero. My ...
0
votes
2answers
33 views

What would happen if weak bosons wouldn't interact with higgs field?

I have a silly question - what would happen if weak bosons wouldn't interact with higgs field? What would happen to weak interactions? How it would affect mass of other particles?
3
votes
2answers
308 views

$\mathrm{\rho^0}$ meson decay via the weak interaction?

Of course, the $\mathrm{\rho^0}$ meson can decay in $\mathrm{\pi^{+}\ \pi^{-}}$ through the strong interaction. Using Feynman diagrams, I cannot understand why the same decay couldn't happen through ...
5
votes
1answer
80 views

What CP violating processes do we know of?

So, after going over my particle physics notes and some introducing literature, it seems the currently known processes we experimentally confirmed to be CP violating are Kaon mixing (an indirect ...
0
votes
1answer
98 views

Reaction in Particle Physics

I'm currently checking some reactions if they are allowed. One of them is $$\nu_\mu p\to\mu^-\Delta^{++}$$ Since this is a weak interaction I've checked the Baryon and Lepton number, Spin and the ...
-1
votes
1answer
1k views

Can we manipulate gravitation? [closed]

When I studied general relativity, my teacher said that what we knew today about gravitation was no better than what we had already known since Newton's time, because so far we could only propose ...
3
votes
1answer
136 views

Pion decay: V-A vs. V coupling

For the Decay $$ \pi^- \to \mu^- \bar{\nu}_\mu $$ the Feynman rules for this tell us that the vertex couples with $\gamma^\mu (1-\gamma^5) / \sqrt{2} $. This gives me the reduced amplitude of $$ M = ...
1
vote
1answer
168 views

How to explain electrons' interaction via the weak force?

What is the piece of theory which dictates that electrons interact via the weak force with other electrons and protons, and how can this force be understood in terms of what I am more familiar with ...
1
vote
2answers
182 views

Why is the Fermi coupling constant always expressed in units of $(\hbar c)^3$?

Everywhere I've looked so far (such as NIST) the Fermi coupling constant $G_F$ is always expressed as $$\frac{G_F}{(\hbar c)^3} = 1.166 364(5) \times 10^{-5} \textrm{ GeV}^{-2}$$ never as just ...
3
votes
1answer
90 views

Are there Planck units for weak or strong “charge”, similar to the electromagnetic Planck charge $\sqrt{4~\pi~\epsilon_0~\hbar~c}~$?

Are there Planck units for "charge" of weak or strong interaction, similar to the Planck unit of electromagnetic charge: $\sqrt{4~\pi~\epsilon_0~\hbar~c}$ ? Are there perhaps direct substitutes, ...
0
votes
1answer
124 views

Reference for the value of the axial vector coupling constant, $g_A$

This paper (I don't know if it is available for free or not) defines the axial-vector coupling constant (a constant important in calculations involving the weak interaction) as $g=1.26$. My advisor ...