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Results tagged with particle-physics
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user 36793
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. DO NOT USE THIS TAG for point particles in classical mechanics.
3
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Can we derive the formula $Q=I_3+\frac{1}{2}(B+S)$ instead of accepting it as an empirical r...
The electric charge of a quark or lepton, $Q$, is related to the third component of the weak Isospin $T_3$ and weak hypercharge $Y$ according to the formula $$Q=T_3+\frac{Y_W}{2}.\tag{1}$$ This, in a …
- 27.2k
2
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answers
191
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Anomalous baryon current in the Standard Model (SM) and the stability of free protons within...
In the Standard Model, the baryon number is not exactly conserved due to anomaly but the decay rate is extraordinarily small at ordinary temperatures. Does this make free protons unstable in the Stand …
- 27.2k
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How to tell whether a Feynman diagram is $t$-channel or $s$-channel by looking?
For a two-body scattering process denoted by $$a_1(p_1)+a_2(p_2)\to a_3(p_3)+a_4(p_4)$$ the tree-level Feynman diagrams can be classified into three categories. A tree-level scattering diagram is call …
- 27.2k
0
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Physical meaning of the form factors $F_1(q^2)$ and $F_2(q^2)$ for $q^2\neq 0$
The charge form factor $F_1(q^2)$ and the anomalous magnetic moment form factor $F_2(q^2)$ have clear interpretations at the value $q^2=0$ i.e. $F_1(0)$ is equal to the charge of the electron and $F_2 …
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1
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What sort of observations constrain the QCD interactions of dark matter?
Within our current limits of observation, dark matter (DM) is nonluminous i.e., it neither absorbs nor gives off electromagnetic (EM) radiation. This tells that DM is electrically neutral having no EM …
- 27.2k
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0
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Possibility of reaching equilibrium starting with a nonequilibrium initial condition in the ...
Update after @knzhou's comment
If in a theory, the coupling of the dark matter (DM) field to the Standard Model (SM) fields is small enough, the rate of interaction of the DM particles in the primordi …
- 27.2k
2
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answer
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Physical significance of the reality of an ${\bf N}$ representation: how the nature of inter...
Background The fundamental representation of ${\rm SU(N)}$ is denoted by ${\bf N}$ and the conjugate of the fundamental is denoted by ${\bar{\bf N}}$. If the representation ${\bf N}$ is related to ${ …
- 27.2k
2
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In this example, how can we have CP conservation with C violation?
Consider a simple two-body decay process $X\to Y+Z$ where $X$ is a boson, and $Y,Z$ are fermions. If $C$ is violated, $$\Gamma(X\to Y+Z)\neq \bar{\Gamma}(\bar{X}\to\bar{Y}+\bar{Z}).\tag{1}$$
However, …
- 27.2k
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Why don't the nuclear fusion processes inside the sun produce electron antineutrinos $(\bar\...
Why don't the nuclear fusion processes inside the sun produce $\bar\nu_e$ despite having the same mass as $\nu_e$? Is the reason as simple as "there is no production channel for $\bar\nu_e$s." ?
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About the spontaneous breakdown of an anomalous symmetry
If a global symmetry is anomalous, classically it is still possible to talk about spontaneous breakdown of that symmetry. In particle physics, do we have such an anomalous symmetry (or symmetries) whi …
- 27.2k
2
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How is a T-violation inherited in a QFT?
CP violation
In quantum field theory (QFT), ${\rm CP}$ symmetry or ${\rm CP}$ violation is a property of the Lagrangian. For a ${\rm CP}$ violating QFT, in general, the absolute square of the Feynman …
- 27.2k
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Neutrino mass hierarchy
I disagree with the answer provided by @StefanoGariazzo.
Oscillation probabilities are insensitive to the signs of $\Delta m_{ij}^2$ for all $i$ and $j$.
However, the numbering of massive neutrinos …
- 27.2k
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Has it ever been possible to measure the fluxes of $\nu_e$, $\nu_\mu$ and $\nu_\tau$ separat...
This is a follow-up of the question asked here.
After going through the Wikipedia page on SNO experiment, I need further clarifications about the accepted answer here.
First, the SNO experiment wa …
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0
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109
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Bare mass versus the mass form spontaneous symmetry breaking
Consider renormalization in $\phi^4$ theory $$\mathscr{L}=(\partial\phi)^2-\frac{1}{2}m^2\phi^2+\frac{\lambda}{4}\phi^4$$ where $m$ and $\lambda$ are respectively the unobservable bare mass and bare c …
- 27.2k
3
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In relativistic QFT, is it ever possible that the bare mass be finite and equal to the physi...
In renormalization, one follows the philosophy that the bare mass is unobservable and could be infinite, and the physical mass comes from the pole of the two-point function. Is it possible that in any …
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