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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 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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1 answer
70 views

Loops and UV divergences

I read when asked whether a force could only exist at a certain phase transition or high energy: "I am not aware of a coupling that only exists at high energies or in a phase transition -- in ...
Jtl's user avatar
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35 views

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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How can baryonic CP violation contribute to the explanation of the large matter-antimatter asymmetry in our universe?

I have been doing baryonic CPV experimental search in the past few years. However, I never really get a good clue on this fundamental question. The thing is that CPV has only been found in the meson ...
RedQuark's user avatar
2 votes
1 answer
397 views

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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0 answers
32 views

Can a particle have properties of both Dirac and Majorana particles?

Dirac fermions have antiparticles of opposite properties, and only a particle and an antiparticle can annihilate. Majorana fermions have no antiparticles because they can annihilate with themselves. ...
哲煜黄's user avatar
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36 views

Can you explain the Georgi–Jarlskog mass relation?

I am trying to understand the Georgi Mass relation in $SU(5)$ As far as I was aware the symmetry breaking occurs only with the various charge quantum numbers (colour, weak charge, electromagnetic). So ...
bob's user avatar
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Equivalence of axion to fermion couplings

In order to solve the Strong CP problem through the axion, we introduce the axion-gluon coupling $$ \dfrac{a(x)}{f_a} \text{Tr}\, G\tilde{G}.\tag{1} $$ In a similar fashion, we may introduce the axion-...
Gabriel Ybarra Marcaida's user avatar
2 votes
0 answers
35 views

General formula for a $f1\to f2$ gamma processes (e.g. $\mu \longrightarrow e\gamma$), understanding the detailed calculation in the paper by Lavoura

I want to work out in detail the paper by Lavoura to get some real practice as a beginning student. I have stumbled upon several problems as I am moving along with the arguments. Firstly, I am not yet ...
Hubert John's user avatar
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Vertex factor type-I seesaw

Consider the following interaction term: \begin{equation} \mathcal{L}_\text{int} = y_{ij}\bar{\ell}_{iL}\tilde{\eta}N_{jR} + \text{h.c.} \end{equation} where \begin{equation} \ell_{iL} = \begin{...
SNC92's user avatar
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Is there any reason for the mass of the electrons? [duplicate]

I've recently read Feynman's QED in which he mentioned the possibility that the seemingly random numbers that correspond to the mass of the electron and heavier charged particles (mu and tau electrons)...
danielzl's user avatar
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1 answer
144 views

$SU(5)$ Gauge Field Theory, symmetry breaking

If I start with an $SU(5)$ gauge group and discover that the vacuum is preserved only by matrices of the form $G$ $$\begin{bmatrix} A & 0 \\ 0 & B \\ \end{bmatrix}$$ where ...
Klaus's user avatar
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1 answer
40 views

Does the number of right chiral neutrinos always need to be the same as the number of anti left chiral neutrinos?

Neutrinos are only observed to have a left handed chirality and anti neutrinos are only observed as having a right chirality. In some beyond the standard model hypotheses neutrinos of right chirality ...
The Burger King's user avatar
2 votes
2 answers
98 views

Why does the mechanism producing matter-antimatter asymmetry keep our universe electrically neutral? Any general argument?

I've noticed what seems to be a fine-tuning issue. To be more specific, electric neutrality implies that the amount of lepton asymmetry produced through some unknown processes precisely cancels out ...
Bababeluma's user avatar
-1 votes
1 answer
221 views

Is there a clean mathematical way to deduce grand unification from string theory?

The question says it all. Simply stated: Can one prove grand unification from string theory? What is the argument chain of such a proof? The textbooks I read so far only appear to give hand-waving ...
KlausK's user avatar
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87 views

Distinction between majorana neutrinos and sterile neutrinos

I am a bit confused about Majorana neutrinos. A generic Dirac spinor can be written in terms of his left and right-chiral components as $$ \psi = \begin{pmatrix} \psi_L \\ \psi_R \end{pmatrix} $$ A ...
Crucio's user avatar
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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 ...
iwab's user avatar
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0 answers
40 views

Which statistical methods are better than basic random scans for studying and exploring the parameter space of extensions of the standard model?

Given a lagrangian of a new model beyond the standard model, and given a set of constraints, say the oblique parameters for instance and the decay of the higgs boson and some signal strengths and ...
Collector101's user avatar
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0 answers
16 views

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 ...
Troy Dube''s user avatar
1 vote
0 answers
267 views

Degrees of freedom in the early universe with MSSM?

As nicely summarized on P4 in On effective degrees of freedom in the early universe here; at high temperatures where all the particles of the Standard Model are present, we have 28 bosonic and 90 ...
Mr Anderson's user avatar
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1 vote
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Toolkit to generate the most general gauge invariant Lagrangian for a given particle content

I am currently working on a BSM model for unification where I am adding scalars for unification. I add many scalars, so finding the most general gauge invariant lagrangian is becoming difficult. Is ...
1 vote
1 answer
183 views

Does NFW profile work for any galaxy?

We use Navarro–Frenk–White (NFW) to calculate Dark Matter (DM) density. Can we use it for DM halo in any galaxy or is it used only for Milky Way (MW)?
Peyman's user avatar
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4 votes
1 answer
305 views

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 ...
LolloBoldo's user avatar
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4 votes
0 answers
137 views

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 ...
M. Winter's user avatar
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1 vote
1 answer
128 views

The chirality of the standard model fermions

I read 'The Standard Model Effective Field Theory at Work' by Isidor, Wilsch, and Wyler. In a footnote, they say that, in principle, right-handed neutrinos could be included in the Standard Model by ...
Lelouch's user avatar
  • 309
2 votes
0 answers
48 views

Slope in interaction strength vs mass for QCD axion

The theory models of QCD axion, i.e. those who solve the strong CP problem, all have a prediction that follows a band with a slope in the space interaction strength vs. axion mass. (1) What does cause ...
Stefano Barone's user avatar
-1 votes
1 answer
123 views

Integral on phase space

I'd like to integrate the square amplitude in the phase space( in $d^3k/(2\pi)^3 2E_k$ and $d^3k'/(2\pi)^3 2E_k$) where $p$ and $p'$ are the 4-momentum of the input particles, $k$ and $k'$ 4-momentum ...
Andrea's user avatar
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0 votes
1 answer
26 views

Experimental method for measuring electric dipole momentum of electron

Is there any experiment for finding the electric dipole momentum of electron? Provided that, The Standard Model predicted EDM for leptons including electrons.
Hewa Ahmed Mustafa 's user avatar
1 vote
0 answers
77 views

Effective field theory of massive spin-1 and spin-2

I'd like to understand what could be the use of an effective field theory (EFT) of a single massive particle of spin 1 or 2, or simple modification of these (see below). By EFT, I mean the most ...
Rubilax96's user avatar
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1 vote
1 answer
139 views

Feynman diagram: Two-way arrow in the fermion propagator line?

I have encountered some diagrams (like the example below) where two lines coming out of a single vertex (in this context, right-handed neutrino $N^c$) have opposite direction. In a usual diagram, a ...
lost-neutrino's user avatar
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0 answers
57 views

Why are there no diccussions of hypercharge conservation or Dirac hypercharge monopoles?

The Maxwell equations can be derived from an equation for a spin 1 field with $U(1)$ symmetry. From this field equation is possible to postulate Dirac monopoles by simply roting the real and complex ...
yeaton's user avatar
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2 votes
0 answers
56 views

Doublet-triplet splitting in GUT: how can the "color triplet" have mass?

I'm hopelessly perplexed about the $SU(5)$ doublet-triplet splitting. I read that the color triplet part of the Higgs quintuplet needs to have extremely high mass compared to the "electroweak&...
SgtJohn74's user avatar
2 votes
0 answers
53 views

Is $SU(N)$ with $N>5$ ruled out as a GUT?

Reading the "mainstream" sources, the candidates for GUT gauge groups are $SU(5)$, $SO(10)$ and $E_6$ Yet I understand for ranks 5 and 6, $SU(6)$ and $SU(7)$ also have complex ...
SgtJohn74's user avatar
2 votes
0 answers
30 views

Lifetime of a WIMP [duplicate]

I have been watching videos of WIMP's and have a simple question.. The larger the particles, the shorter their lifetime. A top quark is so massive that it cannot form a "stable" bond with ...
Rick's user avatar
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3 votes
1 answer
155 views

How do the different Neutrino masses come about?

The determination of the Neutrino mass can be roughly divided in three strategies: The neutrino mass from cosmological observations: $$m_\nu = \sum_{i} m_i $$ The neutrino mass from the neutrinoless ...
Marc's user avatar
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0 votes
1 answer
104 views

Are there enough parameters in standard model to falsify SUSY?

I know that the search for Higgs would be quite pointless if there was no estimation of its mass. Namely the perturbative violation of unitatity, gave us an upper bound on its mass.Unitarity ...
Bastam Tajik's user avatar
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10 votes
3 answers
449 views

Is a QFT always an EFT coming from something deeper?

(I have already read this post but my question is different) Reading Ch. 12 of Weinberg's Quantum Field Theory Vol. 1, he states that all realistic (interacting) QFTs are now believed to be EFT of ...
LolloBoldo's user avatar
  • 1,611
3 votes
0 answers
84 views

Is the Higgs VEV unnatural?

Is there some way to argue that the Higgs VEV is unnatural, without even bringing up the Higgs boson mass? For example, can one show that the Higgs vev receives large corrections from new physics? The ...
Mitchell Porter's user avatar
6 votes
0 answers
129 views

Conceptual dobuts about EFTs and the decoupling of heavy fields

I've tried to synthetize some of my misconceptions in the following statements. I just like to know which of them are true and get some intution about them. EFTs exist only if heavy fields decouple (...
JuanC97's user avatar
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0 votes
2 answers
105 views

Why was the Higgs boson included in the standard model, but not supersymmetry?

This is a soft question so may not be suitable for this site. The LHC famously discovered the Higgs boson several years ago, but also seems to have ruled out several hoped for versions of ...
Nethesis's user avatar
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2 votes
0 answers
78 views

CalcHEP and FeynCalc giving different amplitudes--spin averaging?

I've done a simple amplitude calculation involving neutrinos and fermions scattering or annihilating through a BSM gauge boson. I'm checking with FeynCalc and CalcHEP, but the two are giving ...
user avatar
-1 votes
1 answer
223 views

Jarlskog Invariant

Jarlskog Invariant is directly proportional to CP violation. I want to know why it's called "an invariant". What is the nomenclature of the Jarlskog Invariant?
Anil Sharma 's user avatar
2 votes
0 answers
39 views

How did this generalized NJL model from 1993 predict Higgs boson and top quark masses?

Since the Higgs boson was found in 2012, at a mass around 125 GeV, it has often been remarked that this is curiously close to "criticality" or "metastability" or a false vacuum, if ...
Mitchell Porter's user avatar
0 votes
0 answers
206 views

Is there an explanation for why electric charge, or hypercharge, are rational multiples of each other? [duplicate]

Electromagnetic charges are obviously quantized - I suppose the lowest charge being the $d$ charge of $e/3$. Every other charged particle has a multiple of that charge (actually all stable free ...
AXensen's user avatar
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0 votes
1 answer
65 views

Would observed limit on resonant double Higgs production the same if the scenario considered is spin $0$ scalar or spin $0$ radion particle?

At LHC, some analyses search for resonant HH production, from an unknown particle labelled $X$. They typically make the limit on cross-section of resonant HH production as a function of the spin of ...
Mathieu Krisztian's user avatar
1 vote
1 answer
96 views

Holographic self-energy for a scalar field in a slice of AdS

I am confused about a key step in Gherghetta's "TASI Lectures on a Holographic View of Beyond the Standard Model Physics" in the derivation of the holographic self-energy in the strongly ...
Henry Deith's user avatar
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0 votes
1 answer
244 views

Do we think we know how to match the Standard Model from String Theory?

String theory admits a vast number of vacuum solutions, which I gather come from the all the ways of compactifying the geometry of spacetime down to 3+1 dimensions using Calabi-Yau manifolds. I have ...
user34722's user avatar
  • 2,504
1 vote
1 answer
208 views

Lagrangian with negative mass

I was reading a paper https://arxiv.org/abs/1707.03094 considering the SM extension with $SU(2)$ singlet and doublet fermions. After EWSB, the mass eigenstates are the linear combinations of gauge ...
Tsukishima's user avatar
3 votes
1 answer
119 views

Could a fourth family of quarks and leptons account for dark matter?

In the early universe, could a family of quarks and leptons have formed an electrically neutral particle that is dark matter?
user avatar
1 vote
0 answers
107 views

Finite quotient of standard model group [closed]

In chapter three, p. 31, of this paper (https://arxiv.org/abs/0904.1556) Baez and Huerta show that the standard model's structure group contains, in a sense, superfluous parts. They show that one can ...
Moguntius's user avatar
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