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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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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
53 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
43 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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29 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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29 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
107 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
34 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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80 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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0answers
20 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
52 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
54 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
27 views

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
53 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 ...
3
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1answer
107 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
76 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
147 views

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
56 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
104 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
63 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
77 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
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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
61 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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0answers
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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
28 views

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
278 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
68 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 ...
3
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1answer
91 views

Matter effects contributing in solar, atmospheric and reactor neutrino oscillations

Neutrino oscillations are affected by the matter effects. For solar neutrinos, which are exclusively neutrinos of $\nu_e$ type, the matter effects can be contributed by (i) the solar plasma, (ii) ...
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1answer
234 views

Why should proton decay into positron rather than antimuon?

Grand unification theories, such as $SU(5)$/$SO(10)$/SUSY variants, suggest proton decay. The lack of observational evidence for proton decay rules out simple GUTs. But wait a minute! The GUT's ...
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2answers
124 views

What is meant by the absolute scale of the neutrino mass?

In this review titled "Pieces of the Flavour Puzzle" the author Ferruccio Feruglio wrote in the introduction that "The origin of the parameters in the flavour sector of the Standard Model (SM), ...
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1answer
656 views

Why does only gravity leak into extra non-compact dimensions?

This article K. Pardo, et. al., Limits on the number of spacetime dimensions from GW170817, Journal of Cosmology and Astroparticle Physics, Vol. 2018, 2018. which was published recently in JCAP ...
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1answer
68 views

Higgs Doublet Transformations

If we consider two complex Higgs doublets with $SU(3)_{c} ⊗ SU(2)_L ⊗ U(1)_Y$ quantum numbers $\phi_{A,B}$ ∼ (1,2,1), such that $\phi_A = \begin{pmatrix} \phi_{A}^{\dagger}\\ \dfrac{1}{\sqrt2} (Re \...
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1answer
53 views

Unification of the strong and electromagnetic interaction

Is it somehow possible to theoretically unify the electric charge in electromagnetic interaction with the colour charge in the strong interaction and how these charges give rise to the respective ...
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0answers
42 views

3 generations as extra unconventional dimensions?

Kaluza-Klein resonances arise in theories with extra dimensions like superstrings or old KK models. Usually, extra dimensions and KK states provide regular spacing in the spectrum. Question: can some ...
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1answer
218 views

Why is technical naturalness enough?

There are two notions of "naturalness" used in particle physics today. Dirac naturalness: all dimensionless parameters $g$ in a theory should be order $1$. Technical naturalness: an observed coupling ...
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0answers
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What is the status of SUSY GUTs in 2018?

Grand unification theories (GUTs) generically predict proton decay, and many of them have been under pressure for decades as experiments have failed to see it. I don't think there have been recent ...
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49 views

Are trans-Planckian field values a problem for the relaxion?

The relaxion is a new model-building gadget that solves the hierarchy problem by allowing the Higgs mass term to dynamically relax to zero. To describe it as simply as possible, leaving a lot out: we ...
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264 views

What motivates clockwork theory?

Clockwork is a new model-building gadget that produces very small couplings starting from a theory with no small numbers at all, in an attempt to solve the hierarchy problem. To describe it as ...
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1answer
75 views

U(1) Dirac string moved to the SU(2) or SO(3) gauge theory

Dirac string describes the string connecting the U(1) magnetic monopole to the U(1) anti-magnetic monopole in the U(1) gauge theory. Since U(1) is a subgroup of SU(2) and SO(3), we may embed the U(1) ...
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Computing hadronic cross sections with PDFs

I am trying to estimate the cross section for a BSM process at the LHC, and I would like to ask if anyone knows what is the simplest way to integrate over the PDFs, for example with Mathematica. I ...
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1answer
54 views

A fourth (sterile) neutrino existence and quark generations

Would the existence of a fourth (sterile) neutrino imply the existence of a fourth generation of quarks and a fourth lepton, beyond electrons, muons and tau particles?
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1answer
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131 views

Does the sedenion algebra offer a grand unification theory?

Stephane Bronoff in The Standard Model of Particle Physics from Sedenions claims that studying the left-multiplication map of unit doubly-pure sedenions solves several mysteries of the standard model. ...
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1answer
185 views

Why is the dark matter freeze-out temperature $T\sim \frac{m}{20}$ so generic?

For a dark matter of mass $m$, the typical freeze-out temperature is $T$ is usually assumed to be between $\frac{m}{20}-\frac{m}{25}$. But the freeze-out temperature depends upon the annihilation ...
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1answer
74 views

If $U$ determines the mixing between fields and $U^*$ determines the mixing between states-Why?

In this pdg review, Eq. (14.1), the mixing between the flavour neutrino fields and neutrino fields corresponding to mass eigenstates are denoted as $$\nu_{lL}=\sum\limits_{j}U_{lj}\nu_{jL}\tag{1}$$ ...
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1answer
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Is it sufficient to consider the uncharged dark matter and a $\mathbb{Z}_2$ symmetry to prevent its decay into photons?

Higgs boson, though electrically neutral, can decay to produce a pair of photons i.e., have electromagnetic interactions. See the answer here. Therefore, it appears that making dark matter ...
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1answer
89 views

Why can't the Higgs vacuum energy clump to galaxies and act as dark matter (instead of dark energy)? [closed]

The Higgs field has a nonzero vacuum expectation value which contributes to the energy density of the Universe. Energies contribute to the curvature of spacetime and affected by gravitational ...
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1answer
73 views

What distinguishes the behaviour of particle from its antiparticle: C violation or CP violation?

It is said that a CP violation would mean that the behaviour of the particle is different from the behaviour of antiparticle. Why is C violation not good/enough?
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2answers
110 views

Why is it assumed supersymmetry in nature is ${\cal N}=1$?

It is often presumed that if supersymmetry exists then there will be a single supersymmetry (${\cal N}=1$). Why do we assume this? What is wrong with additional supersymmetries (${\cal N}>1$)? For ...