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Questions tagged [beyond-the-standard-model]

Use this tag for questions beyond the standard laws of physics (General Relativity and the Standard Model) if a more specific tag, like "string-theory", "loop-quantum-gravity", "supersymmetry", etc. do not apply.

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How a discrete z2 symmetry removes flavour changing neutral current from Two Higgs Doublet Model?

By applying a discrete Z2 symmetry to the theory of Two Higgs Doublet Model it is ensured that fermions of one type couples to only one doublet. But how FCNC is removed by doing so? Because if all ...
3
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1answer
67 views

How do we know that the $W$ and $Z$ bosons aren't composite?

Background to my reasoning: When the strong force was first discovered, it was considered to be the force that interacts between nucleons to keep the nucleus together and that the mediator bosons of ...
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2answers
69 views

Dark matter composition [closed]

I assume that dark matter is made of heavy neutrinos.But wouldnt they be converted into neutrinos with less mass throygh weak interaction?So dark matter isnt made of neutrinos.I think there is truly ...
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1answer
25 views

What is the way to work out the running of lepton masses?

If we assume the GUT unification energy is some value E, (say $10^{16}GeV$). Can we work out the running of the particle masses for example the electon, muon and tau at various energies? And will ...
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1answer
40 views

How do we know the group property of a new particle?

Suppose I have a particle $W'$ which can decay into $\mu$ and $\nu_{\mu}$ and $e$ and $\nu_{e}$. Suppose we know such new gauge bosons come from some additional gauge group added to the Standard ...
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1answer
48 views

Dark matter and supersymmetric particles

Is there a possibility to consider supersymmetric particles of fermions and bosons as the unknown dark matter?
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2answers
73 views

Some neutrino anomalies that need explanation

It is inferred that the neutrino must have mass, but beyond saying this mass is incredibly minute nobody has ever measured it. All other particles which have mass also have charge,can be slowed down,&...
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0answers
17 views

Veto algorithm in particle decays and Monte Carlo techniques

What is the main concept behind Veto algorithm and how does it contribute to efficiency in Monte Carlo methods like when used in designing a parton shower?
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1answer
71 views

What mechanism will generate Dirac neutrinos?

Giving mass to neutrinos is not a problem. The problem is to explain its smallness. Once right-handed neutrinos $\nu_R$'s are included in the Standard Model (SM), the Majorana mass for $\nu_R$ must ...
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0answers
80 views

Can someone explain Technicolor?

I read Wikipedia on Technicolor (and understood some of it - I am not a scientist) Can someone give me a layman's definition? Is the technicolor theory dead now that the Higgs has been found? Can ...
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0answers
57 views

Hierarchy problems: calculating the mass of the Higgs vs. other SM particles

While reading up on hierarchy problems in particle physics (wikipedia), I stumbled onto the statement that in the Standard Model, there is no hierarchy problem (or at least it cannot be formulated) ...
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2answers
96 views

Hypercharge normalization for $SU(5)$ GUT

Reading about $SU(5)$ unification, texts says that they use the renormalization factor $\sqrt{3/5}$ for weak hypercharges in order to embed SM into a $SU(5)$ group. This implies a new $U(1)_Y$ ...
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1answer
20 views

Why do we need a two-Higgs doublet model and why only one extra doublet is added to the extension?

The general two higgs doublet model can neither give masses to neutrinos without considering a see-saw mechanism nor it can unify gravity with other three forces. To explain dark matter also we have ...
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0answers
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Correlation diagram for related branching ratios. How to interpret?

I wonder how to interpret the following diagram and how one can see where to place the diagonal lines? Source:https://arxiv.org/pdf/0809.0608.pdf So my thoughts on this: The two axis are two ...
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0answers
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Could electroweak interactions derive from higgsing of gauged chiral symmetry?

A recent question discussed the practice of introducing electroweak interactions into chiral perturbation theory by gauging part of the chiral symmetry. Gauging chiral symmetry is normally regarded as ...
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1answer
60 views

Fierz identities and Weinberg operator

I've been told that $$ (\bar{L_i^c}\widetilde{\phi}^{\ *})(\widetilde{\phi}^\dagger L_k) = -\frac{1}{2}(\bar{\widetilde{L}}_i \vec{\sigma}L_k)(\widetilde{\phi}^\dagger \vec{\sigma} \phi) \tag1 $$ by ...
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3answers
295 views

What really enforces technical naturalness of electron mass?

Technical or 't Hooft naturalness A parameter $\theta$ in the Lagrangian of a field theory is said to be natural, if in the limit of vanishing $\theta$, the theory has some enhanced symmetry. If this ...
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1answer
49 views

“Pure” Yang-Mills and the absence of light matter

I am researching various models of Neutral Naturalness which involve the addition of an additional gauge group whose matter content is uncharged under SM color. Many of these theories state that their ...
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0answers
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How to break softly a symmetry

If you start from a theory (non-SUSY) with whatever symmetry and you break it by adding a soft term. Do you have to add to your Lagrangian all possible soft terms that break the symmetry? If so, why? ...
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2answers
87 views

Can charged leptons undergo oscillation?

Neutrino oscillation is an observed fact while charged lepton oscillation is not. Unlike neutrinos, is it possible for the charged leptons to oscillate, theoretically? In other words, is there ...
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1answer
136 views

Does the Planck Spacecraft end the question of sterile neutrinos?

The 2015 results of the Planck satellite only found evidence of 3 neutrino's with the 4th (sterile neutrino) unlikely. However, in May 2018, physicists of the MiniBooNE experiment reported a stronger ...
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1answer
70 views

Lepton flavor violating process on loop level $\mu \rightarrow e \gamma$ via Higgs, Divergent integral

I am stuck with calculating the proces $\mu \rightarrow e \gamma$ as in this diagram: I wrote down the matrix element like this: $$ \mathcal{M}=\bar{u}(p-q)\left[\int \frac{d^4k}{(2\pi)^4}A\frac{(k+...
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1answer
68 views

What paper experimentally ruled out the original Peccei-Quinn axion?

Could someone please refer me to the paper that ruled out Peccei-Quinn axions experimentally. Most literature mentions this happening but doesn't refer to the original paper where it was proven so.
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1answer
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Are there theories that can predict the Yukawa couplings?

In the standard model, the Yukawa couplings, hence the masses of the fermions, are free parameters and are only determined by experiment. Are there beyond the SM theories that can "predict" the Yukawa ...
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1answer
142 views

What is a String Wall?

This question has nothing to do with sound waves, physical strings or walls... I am reading: https://arxiv.org/abs/1709.07091 It states "In the post-inflationary PQ symmetry breaking scenario, ...
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0answers
39 views

Gauge singlet under SM

What does it mean when they say something is a gauge singlet under the Standard Model group? I would like to understand this concept of Singlets and Doublets. Thanks in advance.
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0answers
34 views

Charge operator applied to matrix multiplets

In the context of SM ($SU(3)_C\otimes SU(2)_L\otimes U(1)_Y$) the charge operator is $Q_{SM} = T_3 + \frac{Y}{2}\mathbb{I}_2$ and gives us the fermions charges. Here $T_3=\frac{1}{2}\sigma_3$ is the ...
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Vector-like Representation of fermions

In the literature, they often extend the Standard Model by adding a so-called vector-like fermion which is a multiplet invariant under $SU(2)_L\times U(1)$. The left- and right-handed components of ...
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1answer
151 views

How do we see that the axion is a pseudoscalar?

The axion is the pseudo-Goldstone boson associated to the breaking of the conjectured Peccei-Quinn Abelian symmetry. The axion couples to the SM gauge fields in a CP-invariant manner (e.g. $aF\tilde F ...
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1answer
47 views

Does two Higgs doublet model predicts two Higgs bosons?

Does 2HDM predict two higgs boson? Why two doublets are needed? I need a simplified answer as i am new to BSM
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0answers
89 views

Products of Lie-Groups versus Lie-Group Extensions in Physics

The Standard Model of elementary particle physics is a gauge theory based on the Lie group $U(1) \times SU(2) \times SU(3)$. From the mathematical perspective I read that: Simple Lie groups have ...
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1answer
34 views

What is the difference between supersymmetry and MSSM?

What is the difference between supersymmetry and MSSM? Please explain in a simple language i am just a beginner of supersymmetry
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0answers
63 views

How does Alain Connes NCG compare phenomenologically with superstring theory?

In Veltmans book on QFT, diagrammatica, the full SM Lagrangian is published. There are more than a hundred terms and it looks pretty uninspiring and not quite the kind of equation one would want to ...
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1answer
57 views

Is there a bound on the number of sterile neutrinos from cosmological observations?

The right-handed sterile neutrinos $\nu_{R}$ are electroweak singlets. They do not contribute to the electroweak anomaly, and therefore, their number is not fixed by the requirement of the anomaly ...
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Where can I find the detailed calculation for the mass of the lights Higgs boson in MSSM?

can somebody mention where the mass of the lights Higgs boson in MSSM (minimal supersymmetric standard model) is discussed? I need a detailed and thorough explanation of the subject mater. I ...
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0answers
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Is anti-sterile neutrino possible?

Due to the surplus of electron neutrino led people to suggest the possibility of 4th neutrino flavour, and it is thought to only interact with gravity and nothing else not even weak interaction. So is ...
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1answer
57 views

Can neutrinos change chirality by oscillating?

Active neutrinos are left-handed while sterile neutrinos are right-handed. There are speculations that active neutrinos can oscillate into sterile neutrinos. Can neutrinos change chirality by ...
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1answer
150 views

Is anything expected to be found at CERN with 14 trillion electron volts that wasn't found at 13?

Based on this article the accelerator has smashed together approximately 16 million billion protons since 2015, when it reached its current energy of 13 trillion electron volts. Planned ...
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1answer
78 views

Why should $\nu_\mu\to \nu_e$ oscillations be expected to be unobservable in short baseline experiments?

The blog here says On the other hand, several rogue experiments refuse to conform to the standard 3-flavor picture. The most severe anomaly is the appearance of electron neutrinos in a muon ...
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2answers
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If neutrinos are disfavoured as DM candidates why aren't axions?

Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer here). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot ...
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1answer
58 views

Estimate of neutrino masses from the values of $\Delta m_{21}^2$ and $\Delta m_{13}^2$ only!

The blog here says that The measured mass differences between the eigenstates are $\Delta m_{21}^2=7.5\times 10^{-5} {\rm eV}^2$ and $\Delta m_{13}^2=2.5\times 10^{-3} {\rm eV}^2$, suggesting that ...
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2answers
108 views

Could there be elementary particles with electric charge $> 2e$?

There are many quantum field theories, which extend the Standard Model and have new particles. For example, X boson of Georgi-Glashow model has charge $4e/3$ and some Higgs models involve a Higgs ...
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1answer
68 views

Constraints on RH component of fermion triplet under $SU(2)_L$

Consider a fermion $\chi$ whose left-handed part is in a triplet representation of $SU(2)_L$: $$ \chi_{L} = (\chi^1,\chi^2,\chi^3)_L^{\ \ \text{T}}. $$ The charged current of $\chi_L$ (i.e. its ...
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1answer
78 views

Can $E_8 \times E_8$ contain the standard model?

I know $E_8$ by itself can't be gauge group because it has no complex representation and so would not be chiral. But assuming the existence of mirror matter which also would have $E_8$ gauge group ...
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1answer
72 views

Emergent physics in the gap between the Planck scale and the “size” of quarks [closed]

The smallest probed length scale to date is around $\Delta x \approx 10^{-18} m$ (see here). If we compare this to the Planck scale of $\Delta x \approx 10^{-35} m$ we are left with almost 20 orders ...
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1answer
68 views

Which experiment could resolve the neutrino mass hierarchy problem?

Neutrino oscillations are sensitive to $\Delta m^2$, but not to the absolute mass scale, therefore we have the problem of the mass hierarchy. Which experiment could resolve this problem? Is there any ...
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Inclusive vs exclusive br fractions

Consider the inclusive process $$ q \to X, $$ where $q$ is the quark inside some hadron $H$, and $X$ is some fixed final state. Corresponding exclusive processes are $$ H \to X_{1}, \quad H \to X_{...
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1answer
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Can the CKM matrix supply the CP asymmetry as required by baryogenesis, in principle?

In the process of Baryogenesis through Leptogenesis from the decay of heavy Majorana neutrinos, the necessary CP violation is perhaps provided only by the CP phases in the PMNS matrix. But the Weak ...
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3answers
360 views

Given the transformation of $SU(2)$ triplet $\vec{\phi}$ how to find the transformation of ${\Phi}\equiv\vec{\phi}\cdot\vec{\tau}$?

Given the transformation of a $SU(2)$ triplet $\vec\phi$ $$\phi\to \exp{(-i\vec{T}\cdot\vec{\theta})}~\vec\phi\tag{1}$$ (in the question here by @physicslover) how does obtain the transformation of $\...
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1answer
70 views

Like the Higgs sector of the standard model, is there a SUSY sector which is also such a sector?

This question arose from an application of the virial theorem that showed how Bose-Einstein condensates of astrophysical dimension could arise from condensing clouds of normal phase bosons. If these ...