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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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What force or field is associated with the weak hypercharge?

So what is the force or field associated with the weak hypercharge in post-SSB?
Positron99's user avatar
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1 answer
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Parity transformation of the $\pi^{0}\rightarrow\gamma\gamma$ process

I want to prove that the amplitude $$\mathcal{M}^{\mu\nu}=\epsilon^{\mu\nu\alpha\beta}q_{1\alpha}q_{2\beta}$$ is violating parity. Here $q_{i=1,2}$ are the external momenta of the photons. The total ...
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$ \pi^0\to \gamma\gamma$ parity conservation

Let's consider the decay process $\pi^0\to \gamma \gamma$. After we spontaneously broke the chiral symmetry of QCD coupled to an abelian gauge field $A^\mu$, we end up with the Goldstone boson ...
Alex's user avatar
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1 answer
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What is the associated charge for the weak neutral current?

So for the strong force, there's color charge; for electromagnetism, there's electric charge; and for weak charged current, there's weak isospin. How about the weak neutral current? Is there an ...
Positron99's user avatar
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Question about pion EFT interaction with the proton [closed]

I have encountered the following Lagrangian describing the interaction between pions and some nucleon N $$\mathcal{L}=\frac{F_{\pi}}{4}Tr(∂_{\mu}U^{\dagger}∂^{\mu}U)+\bar{\psi}_{L}i\not\partial\psi_{L}...
Filippo's user avatar
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Standard Model Generational Disparity [closed]

This may appear to be opinion based at first glance, but I believe it has conceptual merit. The Standard Model contains 3 generations of particles: $e~–\mu~–\tau$, Up–Charm-Top, etc. But the 2nd and ...
RC_23's user avatar
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3 votes
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Parity violation via symmetry breaking?

(Apologies in advance for a poorly formulated question.) In Physics, if something can be equally well found in state A or state B, but for whatever reason is in state A, we sometimes observe the ...
mavzolej's user avatar
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Jet events and Deeep Inelastic Scattering (Scaling Behavior) at the same time?

I am a philosopher of physics, so I already apologize for potential ignorance. I have also graduated in physics, but I now analyze problems on another level and also forgot some of the mathematical ...
Dontwastetime's user avatar
1 vote
2 answers
105 views

Checks of anomaly cancellation

In a textbook I read that if $G$ is a global symmetry of the classical Lagrangian, then one has to check $G\times H^2$ anomalies, where $H$ is one of the SM gauge groups. For example, when $G$ refers ...
Fern's user avatar
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Does electroweak theory have mass gap (not just Higgs mechanism)?

I am extremely confused by seemingly contradictory statements. In this PE answer, the electroweak sector in the Standard Model does NOT have a mass gap (or at least not observed). In fact, the gauge ...
Keith's user avatar
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How to add a non-chiral lepton doublet to the Standard Model?

How would the Standard Model Lagrangian (before symmetry breaking) change if we were to add a non-chiral lepton doublet $\ell_{L,R}$ with weak hypercharge $y=-\frac{1}{2}$ to the $SU(2)\times U(1)$ ...
spiderhouse's user avatar
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2 answers
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How can a virtual $W$ boson turn into an electron and electron antineutrino?

This is specifically with regard to beta decay. My current understanding is that in one type of beta decay, a neutron turns into a proton, an electron, and an electron antineutrino. In order to change ...
save environment's user avatar
3 votes
0 answers
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Is there a sigma for unexplained hypothetical discoveries?

I recently read that the Koide formula relating electronic leptons rest masses is often considered to be numerologic, since unexplained, even though recent years experiment data tend to narrow the ...
olivierlambert's user avatar
2 votes
1 answer
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Could there be states of matter that could avoid "matter decay"?

Regular structures of matter may decay over extremely long periods of time (especially if proton decay occurs, which is not proven but it remains a possibility) Even if that happens, are there any ...
vengaq's user avatar
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2 answers
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Why does the up and anti-up quark combine into a pion and not a photon?

im currently studying a level particle physics and im confused about this. Particle annihilation occours when a particle meets its corresponding particle, converting their mass energy into two photons,...
liv.ysf's user avatar
12 votes
4 answers
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What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

I am asking this question for theoretical understanding of the topic: What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance? I understand ...
Devansh Mittal's user avatar
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Doubt in $e^{+}e^{-}\rightarrow W^{+}W^{-}$ scattering

I am trying to understand how to compute the scattering amplitude for the process $e^{+}e^{-}\rightarrow W^{+}W^{-}$, as a reference one could look at Peskin chapter 21. What I do not understand is ...
Filippo's user avatar
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Do GUT's really explain parity violation?

Every book on the Standard Model introduces early on the concept of left and right-handed quantum fields, defined as \begin{align} (\psi_L)_{\alpha} = \left(\frac{1-\gamma_5}{2}\right)_{\alpha \beta}\...
user38680's user avatar
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3 votes
1 answer
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How to be sure that when a muon passes a detector it is actually a muon?

The question is as follows: when you have any kind of detector for muons you just take measurements and you say, for example, the number for the muon flux but how you're sure that all particles ...
Francisco Santiago's user avatar
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Hierarchy Problem vs ratio of masses in the Standard Model

In the Standard Model, the ratio between the top quark's mass to the neutrinos is at least about $2 \times 10^{11}$. It could rise by at least an order of magnitude in the coming years as the ...
tomdodd4598's user avatar
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The origin of the Hierarchy Problem

In the answer to this question on the origin of the hierarchy problem, it is stated that: The low-energy parameters such as the LHC-measured Higgs mass 125 GeV are complicated functions of the more ...
tomdodd4598's user avatar
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1 answer
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Where is antineutrino in standard model Lagrangian?

I'm somewhat confused by the content I studied in Srednicki's work, where the neutrino is described as a Majorana field. In this framework, there shouldn't technically be antineutrinos, given the ...
Bababeluma's user avatar
1 vote
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One-Loop beta function for gauge couplings

I am currently doing my homework on Standard Model one-loop correction. When I am reading Quantum Field Theory by Mark Srednicki and Journeys Beyond the Standard Model by Pierre Ramond, I notice some ...
quantumology's user avatar
1 vote
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Is there a Higgs-pole like the $Z$-pole?

Why isn’t there studies of direct Higgs production like for the $Z$ boson? Looking for future colliders, they all aim for $$e-e+ -> HZ $$ which for me makes sense for measuring a physical Higgs but ...
VirtuallyOnShell's user avatar
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Regarding vanishing of a triangle diagram

Furry's theorem ($C$ symmetry) is very important in calculations in QCD, Electroweak theory. Primarily it says everything about QED (three photon triangle diagram), but can be extended to QCD, and ($Z$...
Tanmoy Pati's user avatar
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Evidence of more generations in the QCD beta function

We know that the beta function for QCD is $$ \beta = -\left(11 - \dfrac{2N_f}{3}\right), $$ where $N_f$ is the number of fermions in the theory. We have $\beta_{\text{SM}} = -7$. Now, my question is, ...
Gabriel Ybarra Marcaida's user avatar
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1 answer
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Is the set of possible elementary particle types equal to the set of all combinations of their properties? [closed]

I'm playing around with a mnemonic system for a fantasy language I'm working on, for remembering the properties of elementary particles. Each letter represents a unique sound. i a u These 3 are the &...
Lance's user avatar
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2 votes
1 answer
63 views

Field redefinitions in the Higgs mechanism

Consider the Higg's mechanism for a simple $U(1)$ theory. Leaving aside the lagrangian which consists of a kinetic term for the gauge field, a covariant derivative term and the potential term for the ...
Nakshatra Gangopadhay's user avatar
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1 answer
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Why is isospin utilized in determining the branching fraction of $K_1(1270)\to K\pi\pi$ final states?

The branching fraction of $\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}$ is determined by $$\mathcal{B}_{K_1 \rightarrow K^{+} \pi^{+}\pi^{-}}=\frac{1}{3} \times \mathcal{B}_{K_1 \rightarrow K \...
realTyao's user avatar
2 votes
1 answer
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Contribution of dark matter to running of physical constants

I read that "essentially everything in the Standard Model impacts the running of every physical constant in the Standard Model. So, if there is even a single particle missing from the Standard ...
Jtl's user avatar
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2 votes
1 answer
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Can glueballs and bosons survive indefinetely in space (forming structures)?

I have been recently interested in looking for possible structures (ranging from clumped structures like "stars" to diffuse clouds of gas or halos) made from standard model-particles other ...
vengaq's user avatar
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1 vote
1 answer
42 views

Matrix element including weak currents

If a $\overline{B^0}$ meson decays into $D^+$, $e^-$ and $\overline{\nu}_e$ we have a matrix element $$\langle{D^+ \, e^- \, \overline{\nu}_e |\, (\overline{c_L} \gamma^{\mu} b_L) \, (\overline{e_L} \...
Newstudent's user avatar
1 vote
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How to interpret a branching fraction diagram?

I'm confused as to how can I (student in master 1 class of particle physics) interpret such diagram: Where $q^2 = m^2(l^+l^-)$. I understand that the y axis represents the variation of the ...
Ducktective's user avatar
1 vote
0 answers
56 views

Is the Higgs sector in the Standard Model also asymptotically free?

I have always thought that the Higgs sector, which is $\phi^4$ theory in essence, is not asymptotically free. However, I ran into the following statement from this paper: The standard model is, in ...
Keith's user avatar
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0 votes
1 answer
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$W$ and $B$ bosons when choosing a different minimum of the Higgs doublet

When comparing the experimental phenomenology with the standard model, one usually takes a combination of the $W^a_\mu$ and $B_\mu$ gauge bosons to obtain the physically observable ones ${W^+}_\mu$, ${...
SrJaimito's user avatar
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3 votes
1 answer
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Measurable effects of the global structure of the SM

It is known that the Lie algebra of the SM is $$ \mathfrak{su}(3)\oplus \mathfrak{su}(2)\oplus \mathbb{R}\,, $$ so that the Lie group is $$ G_{\text{SM}} = \dfrac{SU(3)\times SU(2) \times U(1)}{\Gamma}...
Gabriel Ybarra Marcaida's user avatar
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0 answers
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Would it be possible to build the standard model in terms of Joos-Weinberg spinors?

The Joos-Weinberg equation describes spinors of arbitrary spin. Could we replace all of the existing matter fields (scalar, fermionic, gauge, Rarita Schwinger, etc.) with JW spinors and still end up ...
Djjehdijwjw's user avatar
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1 answer
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Seeking references for giving geometrical interpretations of electromagnetism and the nuclear forces

From this thread, we have the following comment: To further blur the line, it is possible to give geometrical interpretations of electromagnetism and the nuclear forces, such that they appear to be ...
3 votes
2 answers
144 views

A confusion: Why are composite bosons possible?

I am not a physicist, but trying to understand the standard model to some extent. My understanding is that the essential property of Bosons and Fermions is that two distinct Bosons can occupy the same ...
user56834's user avatar
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21 votes
8 answers
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Do we understand chemistry from particle physics?

My chemistry knowledge is of a high-school level. In high-school, the properties of atoms were mostly presented as empirical phenomena. We learned some physical principles such as the idea that ...
user56834's user avatar
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2 answers
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Renormalizability of Quantum Gravity

At the end of chapter 6 on p. 210 in David's Griffiths' book Introduction to Elementary Particle Physics he says that 't Hooft proved that all gauge theories are renormalizable. I have also read ...
KaraboMadisa's user avatar
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1 answer
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Custodial symmetry of the standard model symmetry group $SU(2)_L \times SU(2)_R$

I am studying the standard model including the Higgs sector and electroweak interactions. Here, all of my terms have their usual meanings. Therefore my symmetry group is $SU(2)_L \times SU(2)_R \times ...
Chris G's user avatar
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0 answers
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Understading dimensions in quark bilinears

I have encountered myself with the following definition for $\pi$-fields as quark bilinears: $$ \pi^a = i\bar{q}\tau^a \gamma_5 q \ ,\quad\text{with }\ q = \left(\begin{array}{c}u\\d\end{array}\right) ...
SrJaimito's user avatar
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0 votes
1 answer
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Different representations of the Yukawa interaction

during studying Yukawa sector of the SM, I got confused with different reps of the Yukawa interaction. First, this is what I am familiar with(let me show only electron mass term): $$y_e \bar{L}_e H ...
김승현's user avatar
3 votes
1 answer
101 views

Why can't we insist that the strong interactions must preserve $CP$?

I'm having some trouble wrapping my head around the strong $CP$ problem. I know that the non-trivial vacuum structure of QCD induces the topological theta term in the strong sector of the SM, which is ...
qavidfostertollace's user avatar
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1 answer
55 views

Why don't we include diagrams with fermion and gauge boson external lines while calculating the effective potential of Standard model?

While calculating the effective potential of Higgs boson, we aim at $V_{eff}(h)$ instead of $V_{eff}(h, W^{+}, W^{-}, Z, quarks, leptons)$. I think the true vacuum should be the minimum of this ...
Bababeluma's user avatar
1 vote
1 answer
97 views

Quark condensate and VEV of $\pi^0$

In David Tong's lectures on the Standard Model I saw that there is a quark condensate, which is just a Vacuum Expectation Value (VEV) of the $\bar{q}_{Li}\, q_{Ri}$ operator, $$ \left< \bar{q}_{Li}...
Gabriel Ybarra Marcaida's user avatar
3 votes
1 answer
349 views

Is there really a strong CP problem?

The strong CP problem is considered one of the major unsolved physics problems. A non-vanishing value of $\theta$ in QCD $\theta$-term violates CP-symmetry. A primary strong CP violating observable is ...
MadMax's user avatar
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22 votes
2 answers
2k views

Have all the symmetries of the standard model of particle physics been found?

Background The standard model of particle physics is entirely determined by writing down its Lagrangian or, equivalently, writing down the corresponding system of PDEs. Every set of PDEs has a ...
William Wright's user avatar
1 vote
1 answer
81 views

Quark Combination of Hadrons

I am trying to understand the different combinations of quarks in a hadron. I have seen that the positive pion is written as $\pi^{+}=u\bar{d}$, but I have not seen it written in the opposite order. ...
Anant Badal's user avatar

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