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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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3
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1answer
78 views

How can electrons and quarks be composite?

There are theories suggesting that the electrons and quarks are not elementary particles, but instead are composite particles of two or more yet undiscovered elementary particles. However ...
0
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1answer
48 views

Has it ever been possible to measure the fluxes of $\nu_e$, $\nu_\mu$ and $\nu_\tau$ separately?

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 ...
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1answer
65 views

Dark matter in the time window between freeze-out and kinetic decoupling

Background After the freeze-out, when all annihilations have stopped, the abundance ($Y=\frac{n}{s}$) of thermal dark matter species no longer changes with time. However, it is still kept in kinetic ...
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0answers
57 views

Mixing matrix in particle physics

It is familiar for us that the diagonalization of a mixing matrix which is written in the neutral basis gives the masses of the neutral particles. If I construct a mixing matrix which is written in ...
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0answers
27 views

Jacobian peak in particle physics

The question is related to the derivation of equation (42) in the lecture note of (https://arxiv.org/pdf/1709.04533.pdf). I discussed this with my professor and he seems not interested in such "...
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0answers
24 views

SM particles connection to their corresponding superpartners

Is it correct to say that what Supersymmetry predicts is, among others, that for each SM particle there exists a superpartner? Or is it more rigorous to say that in fact for each SM state there is a ...
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0answers
38 views

Vev's in Beyond the Standard Model

Recently, I read a paper, the authors have mentioned that if we have $n$ stand for VEVs which are singlets of the SM gauge group, $k$ are associated with SM doublets, and $S$ is the VEV of the SM ...
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1answer
48 views

How the hierarchy of forces is explained by Supersymmetry?

The hierarchy problem is often stated in two ways: First, the divergent corrections to the Higgs bare mass, second, why is gravity so much weaker than the other three forces. The solution to the ...
2
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1answer
161 views

Why is the smallness of Higgs mass not technically natural?

Technical naturalness The smallness of a parameter $\theta$ in the Lagrangian of a quantum field theory is said to be technically natural, if in the limit of vanishing $\theta$, the theory has some ...
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3answers
114 views

How is there no hierarchy problem without UV cutoff?

I can understand the quadratic divergent corrections to Higgs bare mass which is referred to as the hierarchy problem. But I don't understand how there won't be any hierarchy problem if we do not ...
22
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4answers
2k views

Why do all fields in a QFT transform like *irreducible* representations of some group?

Emphasis is on the irreducible. I get what's special about them. But is there some principle that I'm missing, that says it can only be irreducible representations? Or is it just 'more beautiful' and ...
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0answers
34 views

The importance of dimensions in the effective Lagrangian

I would like to examine the contributions from the new physics in any process in particle physics with the help of the Effective Lagrangian method. In this method, the standard model Lagrangian plus ...
5
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0answers
249 views

Do we care about CFTs in particle physics?

This question is related to these others: mostly this one, but also this one and this one. Do we care about CFTs in particle physics? Let me explain. Suppose we don’t know anything about string ...
3
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1answer
58 views

Fierz identity for symplectic group

For the fundamental representation of $SU(N)$, there is a Fierz identity: $$ \sum_iT^i_{ab}T^i_{cd}=\frac{1}{2}\left(\delta_{ad}\delta_{bc}-\frac{1}{N}\delta_{ab}\delta_{cd}\right) $$ where $T^i$ is ...
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0answers
50 views

Heirarchy problem

Can anyone explain the hierarchy problem in context to Higgs mass corrections by scalar loop and fermion loop (the problem arising when we try to treat SM as an EFT)? and how do these corrections ...
2
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1answer
50 views

Why are there no particles with charge, but no isospin?

The standard model has two parallel series of leptons: the charged leptons (electron, muon, and tau) with -1 electric charge and -1/2 weak isospin, and the neutrinos, with 0 electric charge and +1/2 ...
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1answer
79 views

Right-handed neutrinos in Standard Model

Does SM allow for the right-handed (Majorana) neutrinos? Or right-handed neutrinos are beyond SM?
2
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1answer
101 views

In relativistic QFT, is it ever possible that the bare mass be finite and equal to the physical mass?

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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1answer
31 views

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
78 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
76 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
31 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
45 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 ...
0
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1answer
53 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
86 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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1answer
34 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?
2
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1answer
80 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
100 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
67 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
135 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
28 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
25 views

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
25 views

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 ...
0
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1answer
88 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 ...
8
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3answers
314 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 ...
1
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1answer
59 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 ...
3
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0answers
30 views

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
125 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 ...
6
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1answer
138 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 ...
2
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1answer
84 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+...
4
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1answer
79 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
51 views

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
143 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
45 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
42 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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0answers
58 views

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 ...
3
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1answer
216 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 ...
2
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1answer
52 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
104 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
38 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