Questions tagged [standard-model]
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 and weak nuclear forces (and the Higgs mechanism). Do NOT use this tag for the standard model of cosmology, etc..
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Is the weak quark mixing a consequence of electroweak symmetry breaking?
Because of the CKM matrix, the quark doublets that are changed by $W^{+}$ and $W^{-}$ include a linear combination of quark flavours, instead of the pure quark flavours. I was wondering if, before ...
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What experimental data do we have to plug into the Standard Model for it to work?
In the formulation of the Standard Model, I've always been told that we need experimental data to fix some parameters. What are these parameters and how vital is it that we have the exact value? In a ...
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Are all of the characteristics of elementary particles essentially symmetry differences?
I am trying to get a better conceptual grasp on the "splitting" of the fundamental forces at the beginning of the universe.
The first force to separate was the gravitational force. Am I ...
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Difference between $ SU(3)$ and $ SU(3)_c $ group
I am reading quark model. I don't understand what's the meaning of a color $SU(3)$ or $SU(3)_c$ group and how it differs from a general $SU(3)$ group. Please elaborate.
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Standard Model irreducible representation notations
Does anyone know what the significance/meaning of the subscripts on the following notations for the irreps. in the Standard Model?
an up, down left-hand fermion (quark) pair $(u,d)_L$ is denoted: $(\...
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What happens when an anti-electron collides with a neutrino?
What happens when an anti-electron collides with a neutrino? If something does happen, is a photon released after the collision?
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Why do the members of $SU(2)$ doublets gain different masses after spontaneous symmetry breaking?
Before spontaneous symmetry breaking (SSB) elementary particles belonging to the same $SU(2)$ doublets are indistinguishable, which clearly is not the case after SSB.
I am comfortable with the idea of ...
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If a $J/\psi$ decays to an electron-positron pair 5% of the time, how often would a $\phi$ meson decay to a electron-positron pair?
I know the mass of $J/\psi$ to be 3097 mev and the mass of phi to be 1018 mev. I know that $J/\psi$ decays to electron and positron 5% of the time. I also know the full width of j/psi to be 0.092mev ...
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How to write a reaction in terms quarks? [closed]
How do you write a reaction in terms quarks, especially where strange particles decay?
Eg. For lambda baryon --> p + negative pion
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How to determine the charge of a $W$ boson in a Feynman diagram?
As the title says, I am not sure in what situations there is a W$^+$ boson and when there is a W$^-$ boson. My lecturer explained to me that you can view it either as the $W$ boson supplying a charge ...
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$\Sigma^0$ baryon decay
I’ve seen it stated that the sigma baryon $\Sigma^0$ only decays to $\Lambda^0 \gamma$, and then $\Lambda^0$ decays to $p\pi^{-}$ or $n\pi^0$.
I understand that the weak interaction conserves weak ...
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In Peskin & Schroeder's QFT book page 704, the definition of electric charge is opposite?
In Peskin's book Chapter 4, the QED Lagrangian in Eq.(4.3) which contains the interaction term $$\mathcal{L}_{\mathrm{int}}=-q\bar{\psi}\gamma^\mu\psi A_{\mu}\tag{4.3}.$$ From this Lagrangian we can ...
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When do pairs of quarks form jets vs mesons?
For certain processes with low momentum transfer, such as the Kaon decay shown below, quarks will form bound states of mesons.
Whereas for higher momentum-transfer processes, such as the decay of an ...
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Do virtual particles share the same property values with the normal particles? [duplicate]
For example does a virtual electron have the same characteristic intrinsic values like mass, charge, magnetic moment etc. as a normal stable electron? Or can these range wildly and not having specific ...
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Can $W$, $Z$ and Higgs Bosons be also regarded as the first ever virtual particles experimental verified?
With a mean life time of E-25s for the $W$ and $Z$ Bosons and E-22s (predicted) for the Higgs boson nobody has directly observed these particles. Actually their life time is within the Heisenberg ...
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Feynmann diagram for $W$ boson decay
So a $W^{-}$ boson decays into right-handed antineutrino and left-handed lepton with "wrong" helicity. I found that textbook explanation of that process involves lots of handwaving.
I am ...
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Numerical simulations of standard model
Is standard model simulation a current and possible branch of research, or is it just lattice QCD?
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Why is the lifetime of $\phi$ meson much longer than $J/\psi$
So the mass of $J/\psi$ is 3096Mev while the $\phi$ meson is 1018 Mev and yet the phi meson lives 50 times longer than $J/\psi$ meson. I dont understand why this is, can anyone explain why?
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Gauge Boson Self-Interactions with covariant derivative
Self-Interactions of the unphysical gauge bosons $W_1, W_2, W_3$ are written within the gauge term
$L_\mathrm{Gauge}=-\frac{1}{4} W_{\mu \nu} W^{\mu \nu}$
with $W_{\mu \nu}= \partial_\mu W_\nu - \...
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Does the standard model predict $\alpha_G^{-1}\approx c_5$ for $m_{proton}$? [closed]
Given $$\alpha_G^{-1} = \frac{m_{planck}^2}{m_{particle\ of\ interest}^2}$$
$$particle\ of\ interest = proton$$
$$c_5 = fifth\ Catalan\ Mersenne\ prime = 2^{(2^{(2^{(2^2-1)}-1)}-1)}-1$$
Does the ...
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Lagrangian for quarks and pions
I need to understand how starting from the free Lagrangian
$$
\mathscr{L} = \bar{q}(i \not\partial - \hat{m})q
$$
and based on the chiral angle associated with the pion field and the quark field ...
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Inverse muon decay on Mandl shaw- Help on $W$ boson propagator
Hello, I cannot understand why here the other term of the propagator of $W$ boson $k^{\alpha} k^{\beta}/m_{W}^{2}$ is not present, and how/if this absence is linked to the fact that we neglect terms ...
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Nonconservation of hypercharge in Higgs decay
From Wikipedia, Higgs boson has hypercharge of +1 and isospin of -1/2.
W bosons have hypercharge 0 and isospin +-1.
Now Higgs boson can decay into 2 W bosons of opposite electric charge. No matter how ...
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How would I estimate the partial width for the decay of upsilon meson into an electron-positron pair?
I cam across a question that stated the total decay width for the phi meson was 4300 kev and the partial decay of it into an electron-positron pair was 1.3kev. How would I estimate the partial width ...
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$(g-2)/2$ The anomalous magnetic moment [closed]
Does anyone know how to calculate the anomalous magnetic moment of the muon?
The Fermilab result is 3 standard deviations from the standard model calculated value. Quantum electrodynamics to 10th ...
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Why is the fermionic sector of Standard Model the way it is? [closed]
"Because it works!" will be considered too broad an answer. I want to precisely know which experiments forced to consider the model construction the way it is. For example, I can see Wu's ...
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Can two $W$ bosons convert a proton into an antiproton by becoming two $W^+$ bosons?
Would this process have been more or less likely in the high energy conditions around the time of the big bang?
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What is the connection between matter in the universe and the baryon number not being conserved?
Towards the end of "Quarks, the Stuff of Matter", the author discusses the implications of the proton is not stable and ultimately decays. He states, that if the proton decays, then the ...
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Why not put the anti-quarks in the conjugate representation?
The isospin doublet consisting of $u$ and $d$-quark is defined as
$$
\begin{pmatrix}
u\\
d
\end{pmatrix}.
\tag{1}
$$
But the isospin doublet consisting of the antiquarks, $\bar{u}$ and $\bar{d}$, is ...
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Concluding that local $SU(2)$ symmetry implies that we have charged and uncharged fields
In Samoil Bilenky's (2nd. ed) "Introduction to the Physics of Massive and Mixed Neutrinos," he constructs the $SU(2)$ Yang-Mills model.
He starts by introducing the doublet (section 3.2, ...
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Why is the vacuum state $|0\rangle$ invariant under parity?
I was studying the leptonic pion decay $\pi\rightarrow l\nu_{l}$, and usually the amplitude is computed by
$$\mathcal{M}(\pi\rightarrow l\nu_{l})=-i\frac{G_{F}}{\sqrt{2}}V^{*}_{ud}\langle0|\bar{d}\...
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Understanding $\mathscr{L}_Y^{\text{down} }=-\sqrt{2}\sum _{a,q}\overline{\psi }_{iL}Y^{\text{down} }_{iq}q'_RH+\text{h.c.} $
Currently reading Bilenky's "Introduction to the Physics of Massive and Mixed Neutrinos." (2nd ed.)
On page 56 (Section 3.4 on the Standard model) elaborates
"Let us assume that in the ...
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Is there a spin-1/2 hadron composed entirely of up quarks? [duplicate]
I am curious to know if there exists a spin-1/2 hadron that is composed of three up quarks. I understand that in quantum chromodynamics, baryons are formed of three quarks, each carrying a distinct ...
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How to obtain the amplitude for the leptonic pion decay?
Consider the leptonic decay of the pion
$$\pi^{+}\rightarrow l^{+}\nu_{l}$$
In my notes there's written that in order to compute the associated rate we can use the effective Lagrangian
$$\mathcal{L}^{\...
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Another "real vs virtual particle" one: calculate the full diagram or $\sigma \times \mathrm{BR}$?
I have recently been forced to think about something I always thought that I understood but that, in reality, I could not be more confused about.
Suppose I want to study the LHC prospects for ...
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Beyond sexaquarks?
There are some candidates for tetraquarks, pentaquarks or even now sexaquarks/hexaquarks. But, I wonder, what are the highest molecular quark states taking into account QCD? Are there heptaquarks, ...
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Is there a phenomenological Lagrangian which can reproduce the long-range potential between quarks?
The long-range potential between quarks in a confining gauge theory increases linearly with the potential:
$$
V(r)=\sigma r \tag{1}
$$
where $\sigma$ is the string tension.
In QFT, one can calculate ...
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How can simple classicall things be described with string theory?
It is of course overkill to use string theory for this, but I am still interested in how, for example, the trajectory of a horizontal throw of a mass point could be derived from string theory, after ...
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${}$Higgs mechanism
Is is correct to say that, elementary particles have different masses, because they have different coupling strengths to Higgs field? And if yes. Does it make sense to question, why they have ...
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What led physics to "anticipate" the tau particle?
Wikipedia writes
The tau was independently anticipated in a 1971 article by Yung-su
Tsai.[8] Providing the theory for this discovery, the tau was detected
in a series of experiments between 1974 and ...
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How Fast Can Toponium Form?
I understand that Toponium is only theoretical because the T quark decays too quickly.
My question is this, would a right handed T quark live long enough to form a meson? If not, how long would it ...
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Where does the motivation for discovering a 5th force come from? Has there been any evidence found yet? [duplicate]
Electromagnetism, nuclear strong, nuclear weak, and the weird notably weaker force of gravity. Now a force is something fundamental to reality, gravity described as the bending of spacetime causing ...
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Amplitude of the process $q \bar q \rightarrow \tau^+ \tau^-H$
I want calculate the cross section of the process $q \bar q \rightarrow \tau^+ \tau^-H$, where the Higgs takes the $vev$. My question is: if the Higgs takes the $vev$ the amplitude of the process is ...
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What kind of a space is $\mathbb{C}_{-1}$?
In the first paragraph on page 24 of this paper: https://arxiv.org/abs/0904.1556, it's written
the left-handed leptons $\nu_L$ and $e^−_L$ both have hypercharge $Y=−1$, so each one spans a copy of $\...
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Introductory text to atomic onto std. model
My wife mentioned today that she would love to know more about 'how the world is made up'. She stopped learning science at a young age and finds most stuff meaningless or incomprehensible.
She is not ...
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Is there a "unification" explanation of why the mixed gauge-gravitational anomaly cancels in the standard model?
Quoting the Review of Particle Physics (93.2.3):
all representations of SO(10) are anomaly free in four dimensions... the absence of anomalies in ... a SM generation can be viewed as deriving from ...
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Standard model and gravity gauge theory
I will briefly explain my understanding on the subject.
In the following explanation i refer to the Poincarè group meaning the group:
$$\mathcal{P}_{1,3} = \mathbb{R}^{1,3} \rtimes Spin^+(1,3)$$
The ...
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Higgs Boson and Chirality
I have seen some statements that the Higgs boson is not responsible for particles gaining mass, but rather the Higgs field is. However, as I understand it, the Higgs boson is just an excitation in the ...
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Do we know a reason for why exactly $\rm U(1)$, $\rm SU(2)$ and $\rm SU(3)$? [duplicate]
I always found it a curiousity that in the symmetry groups of the known fundamental forces we find the nice arithmetic progression $1,2,3$: first there is $\DeclareMathOperator{\U}{U}\...
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How can strings be more fundamental than quantum fields?
I had the feeling that physics has moved on from the idea that spacially bounded objects located in spacetime (such as particles) can be fundamental. Instead, QFT describes everything by quantum ...
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