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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30 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 ($M_R \gg m_D$). ...
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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 ...
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2answers
158 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 ...
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2answers
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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 ...
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1answer
49 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 ...
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Heavy resonance BSM

I recently came across the idea of Heavy resonance BSM theory and their particles. A quick summary would be great about what the theory predicts. Given I’m not exactly sure about its nature from my ...
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9 views

Benchmark model in particle physics [closed]

What are Benchmark models in particle physics? What is the significance of Benchmark models?
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2answers
63 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 ...
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1answer
35 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 ...
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1answer
63 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?
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1answer
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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 "...
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Theoretical interest in Lorentz invariance violation

I believe I understand the experimental spirit of searches for Lorentz invariance violation as described for example in Searches for Lorentz Violation and works quoted therein. However is there any ...
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1answer
150 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 ...
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1answer
75 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,...
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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 $...
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Amplitude of an operator in BSM physics

I am currently working on effective field theory within the standard model (SMEFT). In this formalism, one introduces higher dimensional operators to the standard model Lagrangian, typically operators ...
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1answer
77 views

What would we have to find to prove supersymmetry correct? [closed]

What would we have to find to prove that supersymmetry is true?
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1answer
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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}...
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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 ...
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3answers
63 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 ...
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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, ...
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1answer
35 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 ...
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0answers
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Neutrino flavor models from irreducible representations of discrete groups [duplicate]

I am starting ph.D in neutrino physics-ph. I've read some papers on discrete symmetries and neutrino mass models. Neutrino flavor models are built using irreducible representations of discrete groups, ...
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3answers
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Does theory allow that one neutrino is massless and the other two not?

The question says it all. Is there the theoretical possibility that one of the neutrino mass eigenstates have zero mass, whereas the other two have not? Is there a theory that allows this option? I ...
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0answers
32 views

$\Delta {b_{L}}$, $\Delta {b_{Y}}$ and $\Delta {b_{C}}$ and unification of couplings

In any standard book on QFT, I understand how to find out the beta function for Standard Model and for Minimal Supersymmetric Standard Model, but i could not understand how this beta function changes ...
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1answer
50 views

Why processes involving virtual loops probe higher energy BSM physics at higher scale than those not having loops?

Why processes involving virtual loops (so-called indirect searches) allow to probe higher energy scale Beyond Standard Physics than those processes (so-called direct) that are typically of tree order ?...
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1answer
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New Physics contributions to the Wilson Coefficients

In this article (arXiv:1507.06660v1 [hep-ph]), the authors tried to extend the SM by adding a new sector, consisting of vector-like quarks and leptons $Q$, $L$ and two scalars $\phi$, $\chi$. They ...
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59 views

Why are rare decays a good probe for New Physics?

It is often said that decays that are suppressed by the SM are an excellent probe for searches for New Physics. Why is that the case? I understand that if a process is forbidden by the SM, such as ...
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1answer
64 views

Sensitivity of observables to New Physics

I am currently reading a PhD thesis on experimental particle physics and at some point the author talks about the sensitivity of a given observable $Q$ to New Physics (NP). The idea is that ...
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1answer
51 views

What mechanism gives mass to elementary particles in string theory?

Nowadays it's assumed (it can still turn out to be different) that elementary particles are "given" mass by interaction with the Higgs field. I read in the only answer to this question: If you ...
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0answers
40 views

Can we falsify photons having a tiny mass, experiencing subjective time, and traveling slightly slower than $c$ (like neutrinos)? [duplicate]

The measured speed of neutrinos can't be separated from $c$ within experimental limits. The standard model includes no mechanism to grant neutrinos mass. The mass of neutrinos can't be detected. ...
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2answers
75 views

Why neutrino mass hierarchy scenario do not include the case $m_2<m_1<m_3$ and the case $m_3<m_2<m_1$?

The neutrino mass hierarchies are made of two hypotheses/scenarios: the normal hierarchy: $m1<m2<m3$ the inverted hierarchy: $m3<m1<m2$ Why neutrino mass hierarchy scenario do not ...
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1answer
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Is there any evidence that dark matter interacts with ordinary matter non-gravitationally?

As far as I understand it, dark matter direct detection experiments are based on the idea that dark matter interacts with ordinary matter, it just has a very small cross-section. So far, there's been ...
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0answers
29 views

MSSM in 2020 and naturalness, state of art?

My question is simple. Given the current LHC and pre-LHC data bounds, can we safely say (an under what odds or conditions) that (pick one) The MSSM is unlikely to be true. The MSSM can yet be true ...
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0answers
41 views

Two Higgs doublet model

Are there any papers which explain introduction of two Higgs doublet model? I would like to know the introduction. I am not working on the theory side but on the experiment side.
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0answers
64 views

Deriving the effective Standard Model Lagrangian augmented with QCD axion

I am reading Section $3$ of this review titled The Strong CP Problem and Axions by R. D. Peccei and also the question and answer of this post. A famous solution of the Strong CP problem in QCD is ...
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22 views

How to prove that $E=2 \text{ GeV}$ drives to maximum of neutrino oscillation for $L=811 \text{ km}$ of NOvA experiment?

How to prove that E=2 GeV drives to maximum of neutrino oscillation for L=811 km of NOvA experiment (as NOvA claims) ? The dependence for $\nu_\mu\rightarrow\nu_\mu$ is $\sin^2{\frac{\Delta m^2_{32}L}...
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0answers
42 views

The phase space suppression for 3 body decay

In particle physics, what does it mean the phase space suppression?
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0answers
53 views

Why the SUSY particles of fermions have spin 0 but not 1? [duplicate]

As the supersymmetric particles have spin which differs by half, why cant the superpartners have a spin = 1. Why does it always have to be 0?
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2answers
110 views

How come Goldstone boson, PQWQ axion, be able to have mass at all?

Quote: Goldstone's theorem: For every spontaneously broken continuous symmetry, there is a massless particle created by the symmetry current. However, under $U(1)_{PQ}$ symmetry, I read that PQWW ...
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0answers
23 views

Friedman equation with non-negligible neutrino masses

I have heard that the Friedman equation (for lambda-cdm) with significant neutrino masses is modified from its simpler form (sum over various densities of c.c., curvature, matter and radiation) to a ...
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0answers
63 views

Non-flat Galaxy rotation curves?

The galaxy rotation curve is stated as being constant, hinting towards the presence of dark matter. But few galaxy rotation curves are not constant but it keeps rising (an example shown in image), can ...
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2answers
99 views

In layman terms, what would it mean if a magnetic monopole was observed?

I am a CS student so I don't really understand all the nuances surrounding this subject but I have heard of magnetic monopoles a couple of times and found them to be extremely interesting. I have ...
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0answers
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Why is technical naturalness a natural expectation?

In first few minutes of this lecture by Nathaniel Craig, he explains the idea of Dirac naturalness in the following way. Let us consider a QFT as an effective theory with a UV cut-off $\Lambda$. Let $...
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1answer
68 views

Layman's questions about Supersymmetry

Please help me with two very silly questions. Assuming supersymmetry is correct, why don't we observe the superpartners of the Standard Model particles at ordinary energies? Why do we have to search ...
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1answer
69 views

About the spontaneous breakdown of an anomalous symmetry

If a global symmetry is anomalous, classically it is still possible to talk about spontaneous breakdown of that symmetry. In particle physics, do we have such an anomalous symmetry (or symmetries) ...
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1answer
110 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 ...
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1answer
60 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
72 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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75 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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