All Questions
Tagged with phenomenology or beyond-the-standard-model
605 questions
0
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50
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UV cancellation in $S$, $T$, $U$ (oblique parameters) in unitary gauge in the SM
I am PhD student in particle physics and I am trying to compute the three oblique parameters in a BSM theory (a $\mathrm{SU}(5)$ theory with KK modes).
In order to check my calculation, I always ...
0
votes
0
answers
57
views
Neutrino oscillation via some unknown interaction mechanism
My query is based on this post. Similar to the Feynman diagram proposed in the problem, why don't we consider a similar mechanism in beyond standard model to explain the neutrino oscillation? It would ...
- 378
1
vote
1
answer
126
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Fermion Charges and Intermediate $B-L$ Charge in Trinification
We have a Trinification Model, $$SU(3)_C \times SU(3)_L \times SU(3)_R.$$ The first group is the colour group, the second is the Left Weak force and the third is the Right Weak force. There are 27 ...
- 55
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0
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47
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Why do we try to extend the Standard Model with new quantum fields (special relativity) in regions where gravity dominates, like the Big Bang?
The way we define particles nowadays is trough quantum fields. These fields are representations of the Poincaré group (symmetries of the Minkowski space). In this sense, we can only merge strong and ...
- 39
2
votes
1
answer
116
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If the universe at one point had a 'superforce' composed of all fundamental forces, would that force have a boson, or bosons, that mediate the force?
I know that every fundamental force has a boson that is responsible for mediating the force, those being the Photon, Gluon, $W^-$, $W^+$, $Z$, and possibly graviton. I also know that during the re-...
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1
answer
78
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Goldstone Matrix for $SO(3) \longrightarrow SO(2)$ breaking
In these lecture notes (https://arxiv.org/abs/1506.01961) on composite Higgs models, on page 22, the authors calculate the Goldstone Matrix $U[\Pi]$ for an abelian composite Higgs scenario i.e. $SO(3)$...
- 311
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50
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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 $SU(2)\times U(1)$ ...
- 21
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votes
1
answer
81
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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 ...
- 455
1
vote
0
answers
43
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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, ...
- 2,210
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0
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41
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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 ...
- 1
2
votes
1
answer
407
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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 ...
- 455
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votes
0
answers
41
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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. ...
- 1,537
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0
answers
107
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Symmetry breaking/Phase transitions
I have completly edited the question to focus on one problem.
I have seen on different places that it is claimed that the inflation was triggered by a phase transition/symmetry breaking of strong ...
- 368
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0
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43
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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 ...
- 287
1
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0
answers
53
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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-...
- 2,210
2
votes
0
answers
38
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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 ...
- 31
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0
answers
40
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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{...
- 168
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votes
0
answers
46
views
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)...
- 1
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1
answer
147
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$SU(5)$ 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 ...
- 3
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votes
1
answer
42
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 ...
- 377
2
votes
2
answers
103
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 ...
- 631
-1
votes
1
answer
225
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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
...
- 805
0
votes
0
answers
124
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 ...
- 131
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votes
0
answers
182
views
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 ...
- 153
1
vote
0
answers
325
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 ...
- 1,496
1
vote
0
answers
45
views
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
224
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)?
- 11
4
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1
answer
326
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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 ...
- 1,845
4
votes
0
answers
146
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 ...
- 531
1
vote
1
answer
164
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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 ...
- 311
2
votes
0
answers
53
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 ...
- 585
-1
votes
1
answer
130
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 ...
- 11
0
votes
1
answer
28
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.
1
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0
answers
90
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 ...
- 195
1
vote
1
answer
169
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 ...
0
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0
answers
65
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 ...
- 1
2
votes
0
answers
62
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&...
- 53
2
votes
0
answers
61
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 ...
- 53
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 ...
- 2,754
3
votes
1
answer
163
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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 ...
- 71
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1
answer
106
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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 ...
- 1,280
10
votes
3
answers
477
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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 ...
- 1,845
3
votes
0
answers
88
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 ...
- 13.4k
6
votes
0
answers
140
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 (...
- 268
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votes
2
answers
125
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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 ...
- 145
2
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0
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94
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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 ...
user367500
-1
votes
1
answer
257
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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?
2
votes
0
answers
42
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 ...
- 13.4k
0
votes
0
answers
251
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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 ...
- 8,296
0
votes
1
answer
66
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 ...
