All Questions
Tagged with phenomenology or beyond-the-standard-model
605 questions
0
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97
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Higgs particles and Dark Matter particles
Usually, it is mentioned that the Higgs field IS the origin of mass for known fundamental particles.
If very heavy dark particles are found (heavier or much heavier than the top quark), should it mean ...
- 6,727
0
votes
1
answer
1k
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Is this formula for the time-temperature relation in this universe correct, or is there a more appropriate one?
I'm trying to simplify an equation into a form that uses the ratio of the number density of sterile to active neutrinos.
For this, I need a relation between the time and temperature of the universe, ...
- 759
0
votes
0
answers
51
views
What is the reheating temperature of neutrinos during the BBN?
I want to integrate a differential distribution function of sterile neutrinos and the boundaries are the decoupling and the reheating temperature of neutrinos, but I don't know what is an acceptable ...
- 759
9
votes
3
answers
451
views
Do we have good reasons to believe that neutrino oscillations aren't the result of a new particle? If so, what are they?
The standard way of describing neutrino oscillations seems to be that the mass eigenstates differ from the flavour eigenstates, which leads to an oscillation of neutrino flavour over time.
However, ...
- 93
1
vote
1
answer
160
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Horizontal Gauge Symmetry?
Some physics literature says Horizontal Symmetry of gauge theory, such as this paper, available also at arXiv.
What does this Horizontal Symmetry of gauge theory or Horizontal gauge group mean? Does ...
- 4,376
2
votes
0
answers
343
views
Anticommutator of gauge covariant derivatives
I must convert some dimension-6 operators I've obtained to the SILH base (ref: this, "Review of the SILH basis", CERN presentation by R. Contino).
In this conversion I've got operators such ...
- 137
2
votes
0
answers
40
views
$ (5^* \times 5^*)_{asym}={10}$ in A. Zee's book p.409 versus PDG Sec.114
What is the mathematical or physical way to understand why the 4th and 5th components in the Georgi Galshow SU(5) model has the SU(2) doublet $(1,2,-1/2)$:
$$
\begin{pmatrix}
\nu\\e
\end{pmatrix}
$$
...
- 4,376
1
vote
0
answers
126
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Georgi statements about the symmetry breaking of $\rm SO(10)$
Here is a paragraph with some statements about the Gauge Symmetry Breaking from Georgi's book Lie Algebras in Particle Physics 2nd ed -- From Isospin to Unified Theories (Georgi, 1999) p.285.
Georgi ...
- 4,376
5
votes
0
answers
160
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$\rm SO(10)$ grand unified model restores the parity symmetry lost in $\rm SU(5)$ model
It is said in Lie Algebras in Particle Physics 2ed - From Isospin to Unified Theories (Georgi, 1999) p.285, Georgi said that
$\rm SO(10)$ grand unified model restores the parity symmetry that was ...
- 4,376
1
vote
0
answers
177
views
How to give left-handed neutrinos alone Majorana mass?
The Wikipedia page on Georgi–Glashow model says
Fermions transforming as a 1 under SU(5) are now thought to be necessary because of the evidence for neutrino oscillations, unless a way is found to ...
- 4,376
1
vote
0
answers
37
views
Light composite fermion as a bound state formed by $SU(4)$ gauge force attractions
In this paper https://inspirehep.net/literature/152400, in eq.(3.4), it claims that
the MAC (most attractive channel) in $SU(4)$ gauge theory will attract
fermions in $[1]_4$
and
fermions in $[3]_4$
...
- 4,376
0
votes
0
answers
41
views
Quark mass vs Lepton mass $m_d/m_e$
In Zee QFT in a nutshell book p.418, Zee said about Quark mass vs Lepton mass $m_d/m_e$
:
He first mentioned $m_d/m_e=1$ for unification scale.
Then he mentioned $m_d/m_e\sim 3 $ in eq.15.
Are ...
- 4,376
4
votes
1
answer
127
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Elegant theoretical way(s) to prove the $U(1)$ electric charge of electron + proton $Q_e+Q_p=0$?
In Zee's QFT in Nutshell book p/410, he uses the following method to show $U(1)$ electric charge of proton + electron $$Q_e+Q_p=0$$ in Grand Unified Theory (GUT):
However, Zee only shows
by the ...
- 4,376
1
vote
1
answer
255
views
Monopole problem: 't Hooft–Polyakov, Big Bang theory versus Cosmic inflation
I am not sure the validity of this claim from Wikipedia on 't Hooft–Polyakov_monopole
The "monopole problem" refers to the cosmological implications of grand unification theories (GUT). ...
- 4,376
2
votes
0
answers
196
views
Why isn't the triplet representation of $SU(2)$ symmetric?
By the Young Tableaux construction, a triplet of $SU(2)$ (diagramatically, two boxes side by side) is supposed to be a two indices symmetric tensor.
However, one of the most known and minimal ...
- 1,782
2
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0
answers
74
views
$SU(5)$ model and flipped $SU(5)$ model
It seems that both $SU(5)$ model and flipped $SU(5)$ model are legal grand unified theories (GUT) for the standard model gauge group. In Wikipedia, it says that:
The flipped $SU(5)$ model has a gauge ...
- 4,376
4
votes
1
answer
140
views
Why is gravitational wave production in early Universe disfavoured for crossovers?
Production of gravitational waves in the early Universe (for example, in the electroweak phase transition) is favoured only if the Universe undergoes a first-order phase transition but not favoured if ...
- 27.2k
2
votes
0
answers
136
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Lectures by Susskind versus Zee on the ${\rm SU}(5)$ grand unified theory notations
I was comparing two lectures about ${\rm SU}(5)$ grand unified theory.
a lecture of Susskind
He showed how to write
$$
(5 \times 5)_{asym}=\bar{10}
$$
as
a lecture of Zee showed how to write
$$
(\...
- 4,376
2
votes
1
answer
168
views
Why supersymmetry can only be verified in high energy level?
I'm wondering why supersymmetry can only be verified in high energy level,can we check supersymmetry in low energy physics?
- 547
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votes
1
answer
39
views
Why does this distribution function depend on time and not temperature?
When reading Sterile neutrino hot, warm, and cold dark matter I came across the following momentum distribution function for a neutrino species $\alpha$:
$$\tag{5.8} f(p,t) = \frac{1}{e^{E(p)/T + \...
- 759
7
votes
4
answers
1k
views
Why is it assumed that the Big Bang produced equal parts matter and antimatter?
It is well-known that a major open question in physics is why the Universe appears to be made almost entirely out of matter, with next to no antimatter, despite the two being strictly symmetrical ...
user268803
0
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0
answers
46
views
Good book on the standard model for theoretical mathematicians [duplicate]
I am a mathematician who specialises in algebraic geometry and algebraic topology. I am looking for a good textbook on the standard model that gears towards readers with more of a math rather than a ...
0
votes
1
answer
257
views
What is the gauge boson mass term for a theory with a matrix of scalars?
If we have a theory with gauge group $SU(3) \times SU(2)$ with a set of six complex scalar fields grouped in $\Phi=\begin{pmatrix}
a & d\\
b & e\\
c & f
\end{pmatrix}$, where, for instance,...
- 313
-5
votes
1
answer
148
views
Why is the neutrino considered a composite particle? [closed]
The existing model predicts it should have no mass but observation says otherwise, it is known that the neutrino can change flavor over time but how does it qualify as a composite particle? Does it ...
- 13.1k
0
votes
1
answer
178
views
How do I solve Schroedinger's equation for sterile neutrinos?
When reading Light singlet neutrinos and the primordial nucleosynthesis the following equation is given:
$$\tag{5} i \frac{\partial}{\partial t } \begin{pmatrix} c_e (t) \\ c_x (t) \end{pmatrix}= \...
- 759
0
votes
0
answers
58
views
Neutrino oscillations
It seems well documented that neutrinos oscillate between flavours. In the link there are some figures which show probabilities but it isn't clear to me why the abscissa is measured in $L/E$. Is it ...
- 3,906
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0
answers
43
views
Proton decay through a $(3,1)^{-1/3}$ complex scalar
Suppose we add to the Yukawa sector of the SM a complex scalar $T^\alpha(3,1)^{-1/3}$, where $\alpha=1,2,3$ is a $SU(3)_C$ index and the charges assignment means that it transforms as a triplet under $...
- 123
1
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1
answer
226
views
What is the meaning of a non-resonant neutrino production?
What is the meaning of non-resonant production in the following context:
They assumed a negligible primordial lepton number,or asymmetry, so
the neutrinos are produced non-resonantly. [1]
I thought ...
- 109
4
votes
2
answers
99
views
What are ordinary mass-terms (of neutrinos)?
When reading the introduction to Sterile neutrino hot, warm, and cold dark matter I came across the following definition of sterile neutrinos:
We can define sterile neutrinos generically as spin-$\...
- 759
4
votes
1
answer
235
views
How did Supersymmetry (incorrectly) predict the mass of the Higgs Boson?
In an article by CERN states
The minimal version of supersymmetry predicts that the Higgs boson mass should be less than 120-130 GeV
How was this conclusion reached? I could not find any answers on ...
- 41
1
vote
2
answers
1k
views
Fermion current and gauge interactions in Lagrangian density
I believe the answer to this is quite simple, perhaps so simple that I cannot find it in any book.
Usually, if there is a gauge symmetry in the theory, we add an interaction term in the covariant ...
- 102
2
votes
2
answers
184
views
Approaches to Model Building [closed]
I often see references to 'model building' in the particle physics literature, presumably to refer to creating new QFTs which go beyond the Standard Model.
How exactly does this process of model ...
- 1,433
3
votes
1
answer
59
views
What causes neutrinos to be weakly coupled?
When reading about "active-sterile mixing", which requires some Dirac mass ($m_D$) and some Majorana masses ($M_R$) to be very small but not zero, the seesaw limit model is discussed ($M_R \gg m_D$).
...
- 759
0
votes
2
answers
100
views
Is it possible to falsify the $SU(2)_{lepton, left}*SU(2)_{quark, left}*U(1)$ symmetry group as an alternative candidate for GSW Model?
We know that the current symmetry of GSW is $SU(2)_{fermions, left}*U(1)$, and the correct representation of the $SU(2)_{fermions, left}$ is the $2+2$ representation.
I want to know what is the reason ...
- 1,280
3
votes
2
answers
320
views
Why does the observation of $Z$-boson decay imply active neutrinos to be heavy?
Whilst reading Light Sterile Neutrinos: A White Paper it is stated on the bottom of p.3 without an explanation that:
"The observed $Z$-boson decay width implies that any additional active neutrinos ...
- 759
1
vote
2
answers
50
views
Example of weak interactions induced by mixing
I understand that weak interactions are the exchange of W and Z bosons between leptons and quarks (as explained in this other question: Weak Interaction), but when I read Light Sterile Neutrinos: A ...
- 759
0
votes
1
answer
231
views
Is this $CL$ or $CL_S$ method?
I have already posted this problem here, closed for asking too many questions. I will reproduce the introduction and contextualization here, and try to ask a more specific one that I hope will be ...
- 1,782
3
votes
2
answers
459
views
Is lepton number conserved by definition?
In ordinary beta decay, an electron and an anti-neutrino, together with a proton, are emitted. The proton has zero lepton number, the electron +1 lepton number, and, it is said, the neutrino-type ...
- 141
2
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1
answer
300
views
How SUSY solves the hierarchy problem?
I am struggling to understand the argument for why the introduction of a stop in SUSY can solve the hierarchy problem. The quadratic divergence from the top loop in the higgs mass calculation gives a ...
2
votes
1
answer
78
views
How can we know that there are no other elementary particles at the mass-level of the SM particles?
Well, if they exist, there is a very small probability to generate them in a nuclear reaction. But, what is an estimate for a bound to this probability based in accelerator experiments?
user232333
1
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1
answer
276
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What is an effective field theory (EFT)? Is the standard model (SM) an EFT? Till which scale? How is included gravity?
What is an effective field theory (EFT)? and why all the observable interactions until one scale are only a finite number that we know? Is the standard model (SM) an EFT? till what distances? I real "...
user232333
2
votes
1
answer
797
views
$B$-$L$ global symmetry in the grand unification theories
What are the precise $B$-$L$ (baryon - lepton) global symmetry in the standard model?
Is this a $U(1)$ global symmetry or a discrete finite group $\mathbb{Z}/N$ global symmetry for the following ...
- 4,376
1
vote
1
answer
170
views
Data analysis on particle physics: what am I formally doing in this specific case? [closed]
I have performed an analysis of the exclusion(discovery) perspectives for a BSM particle at the LHC. However, my focus of study (and understanding) was until little time ago the purely theoretical and,...
- 1,782
1
vote
0
answers
25
views
Extensions to Minimal Gauged UBLM Model
Recently I have been reading a bit about BSM physics and came across the minimal gauged $U(1)_{B - L}$ model, where the gauge group of the Standard Model is extended to a larger product with another $...
- 1,433
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1
answer
102
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What would we have to find to prove supersymmetry correct? [closed]
What would we have to find to prove that supersymmetry is true?
- 125
0
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1
answer
149
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Help counting the number of real parameters in simple seesaw Lagrangian
The seesaw Lagrangian is $$-\mathcal{L}_{\rm mass}=\frac{Y^\ell_{ab}\langle H^0\rangle}{\sqrt{2}}\bar{\ell}_{aL}\ell_{bR}+\frac{Y^\nu_{ab}\langle H^0\rangle}{\sqrt{2}}\bar{\nu}_{aL}\nu_{bR}+\frac{1}{2}...
- 12.3k
6
votes
1
answer
201
views
Does our failure to detect neutrinoless double beta decay spell trouble for the seesaw mechanism?
The seesaw mechanism is a theoretical model of neutrino masses that has the side benefit of (arguably) naturally explaining why neutrinos are so much lighter than the other massive Standard Model ...
- 49.4k
3
votes
3
answers
203
views
How does the baryon asymmetry control temperature fluctuations of CMB?
The temperature fluctuations of the Cosmic Microwave Background (CMB) have a sensitive dependence on the quantity of baryon asymmetry of the universe. In fact, analysis of CMB fluctuations is one of ...
- 27.2k
0
votes
0
answers
50
views
Why does the "expected" line varies with the unknown new physics parameter on Brazil-band plots?
There are two similar questions here, but they could not help me (I could not relate their answers to my problem, at least). I hope that I can make myself clear in the following.
Take, for instance, ...
- 1,782
0
votes
1
answer
521
views
How do neutrino masses change the shape of the $\beta$ decay spectrum?
It is more-or-less established that neutrinos have masses. But as of now, $\nu$-masses have not been directly measured in the laboratory. But I heard a talk where the speaker said that efforts are ...
- 12.3k