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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Is it possible that there is a third class of fermions?

There exist six types of quarks, and six types of leptons, both divided in three generations. Could there be some other new class of exactly six particles, similar to these, but with properties such ...
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Experiments check out theories but who or what checks out the experiments? [closed]

There is a classic saying which goes more or less like this: If your theory is not verified by the experiment then it is wrong! Specifically for the field of particle physics, lately experiments ...
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Tadpole VEV from a fermion loop?

We have one extra complex scalar $\Phi$ beyond the Standard Model (BSM) protected by an $U(1)$ global symmetry, which is broken by an Yukawa coupling $ y_\Phi \Phi \overline{\chi} \chi$, where $\chi$ ...
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2 answers
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Latest experimental evidence for properties of the Higgs boson

I'm trying to find out the most up to date properties for the Higgs boson (like its mass, charge, spin-parity). For now, just focussing on the mass of the Higgs boson, the most up-to-date information ...
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$W$ boson $0.1$% heavier than predicted by 7$σ$? [closed]

Quite recently more and more refined experimental results pile up that put the SM under stress and tend to disprove more and more its predictive power and potentially are the start-up point of new ...
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What would be the impact of slighty higher mass for the $W$ boson? [closed]

With the recent announcement from CDF https://cerncourier.com/a/cdf-sets-w-mass-against-the-standard-model/ placing it at the mass at $$80,433.5 \pm 6.4\; \text{(stat)} \pm 6.9\; \text{(syst) MeV},$$ ...
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3 votes
2 answers
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Phenomological vs empirical

"Thermodynamics is a phenomenological theory" I am not able to understand the difference between empirical and phenomenological descriptions, aren't all theories empirical?? Do we say some ...
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What would be the implications in the Standard Model if we experimentally verified that the electron charge has an intrinsic electric dipole moment?

It is known also by recent experiments that the electric charge distribution in space of an electron has been measured with great accuracy to be perfect homogeneous thus essentially geometrically a ...
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Does anyone know or knows how I can find papers with loop diagrams (one and more) that involve the Standard Model and $Z'$ only?

I have tried to search for them on arXiv and the Web of Science, but without having a specific reference I was not successful, even though invested some hours. What I am trying to find could well be ...
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How does the Higgs being a Goldstone Boson (in new models) protects its mass from quadratic corrections?

I understand how a symmetry protects a mass from this type of correction: It is known that a symmetry is not broken by corrections of any order -- this hints that if a mass term is forbidden by an ...
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How to plot the 95% CLs exclusions when working with MG5/MA5?

So I am a complete noob to phenomenology and I need to plot CL contours for a model I am working on. My model looks kinda like this $$\mathcal{L} = g_{1}\{Fields\} + g_2\{Fields\}$$ and I need to plot ...
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2 votes
1 answer
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Why do we use "vector-like" to mean "non-chiral", in particle physics?

I've been reading some stuff about searches for vector-like quarks and vector-like leptons, and I'm a little confused about the terminology. Also, I'm a little new to this, so bear with me. As far as ...
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1 vote
0 answers
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Composite Higgs $SO(5)\to SO(4)$ model: how is $H$ a composite particle?

I am reading this review on CH models by Wulzer and Panico. In Section 2.2.2, they write a minimal model of $SO(5)$ breaking into $SO(4)$, triggering electroweak symmetry breaking (EWSB) with a ...
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1 answer
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How to calculate the "observed" line in Brazil Band plots?

Look, for example, fig 5a in the following paper. My understanding was that, to calculate the 'expected' line, we would calculate the predicted signal+background cross section $\sigma_{s+b}$ (since ...
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1 answer
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How to find parameters $\theta_{12}, \theta_{13} $ and $ \theta_{23} $ for the lepton mixing matrix?

I am currently studying neutrino physics and read that the PMNS matrix can be expressed through $9$ real parameters. I especially see parameters such as $\sin\theta_{12}$ popping up though, and I don'...
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Is the historically adopted 'bare' model of elementary particles causing the infinities problem and main reason to use re-normalization method?

I'm interested to know if the so called non-physical 'bare' model especially for massive elementary particles, which treats the particles as mathematical dimensionless points without any volume and ...
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1 answer
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What equation does KATRIN use to measure neutrino masses?

Source KATRIN weighs neutrinos produced by the nuclear decay of tritium, a radioactive isotope of hydrogen. When a tritium nucleus transmutes into a helium one, it ejects an electron and a neutrino (...
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Sterile neutrino decay into three active neutrinos

I have found several sources that provide the expression of the decay rate of sterile neutrinos into three active neutrinos. In https://arxiv.org/abs/0705.1729 (p.40),https://arxiv.org/abs/0901.3589 (...
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Right-handed neutrinos Lagrangian and drawing Feynman diagrams from it

The Lagrangian for the right handed neutrino field is: $$ L_{\nu} = y_{\alpha i} \bar{L_{\alpha}} H^{\dagger} N_{i} + m_{i} \bar{N^{c}_{i}N_{i}} $$ With $ L_{\alpha} $ being the left-handed lepton ...
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Normalization of Kallen-Lehmann spectral representation, comparison to 4D spectrum from 5D theory

The Kallen–Lehmann spectral representation for a quantum field $\phi(x)$ is normalized: $$\int_0^\infty d\mu^2\, \rho(\mu^2) = 1 \ ,$$ up to factors of $2\pi$ that are a matter of convention. See, for ...
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1 answer
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What is the total signal strength of the Higgs?

Dealing with the signal strength modifier of the Higgs, a few things escape my grasp : 1/ In the PDG booklet the combined result is presented with an uncertainty, although some of the measured signals ...
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0 votes
1 answer
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In an $SO(10)$ GUT, how many gauge fields acquire masses that are above the electro-weak scale?

The $SO(10)$ group is spontaneously broken down into the Standard Model gauge group at around $10^{16}$ GeV and the electroweak scale is ~246 GeV. I think there should be 45 gauge fields predicted by ...
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2 votes
1 answer
156 views

Why must $U(1)$ matrices commute with $SU(2) \times SU(3)$ matrices in embedding within $SU(5)$?

I'm a physicist taking a groups course. I can believe that the direct sum of the fundmental representations for the $SU(2)$ and $SU(3)$ matrices will work as an embedding of the $SU(2) \times SU(3)$ ...
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1 answer
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Gravitational and inertial mass seem to result from different fields, yet virtually the same. How do new physics theories attempt to reconcile this?

As best I understand it, internal mass (at rest) is due to interactions of particles with the Higgs field, and in equation terms, due to various chiral terms, sometimes described as swapping chirality....
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2 votes
0 answers
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Difference between right-handed and sterile neutrinos

Several SM extensions propose the addition of heavy, right-handed neutrinos to explain the smallness of neutrino masses. There are also theories adding a fourth, sterile neutrino in the context of ...
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2 votes
1 answer
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Deduction of weak boson hypercharge in Georgi–Glashow $SU(5)$ grand unified theory (GUT)

In the Georgi–Glashow model, the extra 12 bosons $X_\mu^a$, $Y_\mu^a$ that appear have weak hypercharge $y = -\frac{5}{6}$. I want to know how this is deduced from the weak hypercharge generator $$Y = ...
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A question on the electrostrong force

I understand that the strong nuclear force is carried by gluons, the electromagnetic force is carried by photons and the weak nuclear force is carried by the $W$ and $Z$ bosons. However, in the ...
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By which interaction will proton decay? [duplicate]

I learned that proton takes at least $10^{34}$ years to decay. If it will decay one day, will it decay via weak interaction or some other interaction?
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2 votes
0 answers
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Question about Kaluza-Klein excitations

In Randall Sundrum (RS) model-type 1 : A Large Mass Hierarchy from a Small Extra Dimension, it’s mentioned that: This result contrasts sharply with the scenario of large extra dimensions for solving ...
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1 answer
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Double charmed omega baryon to charmed omega baryon via muon capture?

Let’s think of the double-charmed omega baryon as a kind of second-generation proton, and the single-charmed omega as a second-generation neutron. I made up the names “puotron” and “muotron” for ...
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2 votes
0 answers
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Neutrino Oscillation and FCNC

We know that in the Standard Model (SM) neutrinos are massless. But the discovery of neutrino oscillation suggests that neutrinos must have masses because only then there will be a mass basis for ...
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0 votes
1 answer
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The effect of the fifth force of nature being detected?

The article https://www.sciencealert.com/physicists-may-have-discovered-new-force-of-nature-in-lhc-experiment speculates that possibly the effect of the fifth (so far unknown) force of nature has been ...
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0 answers
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Electroweak Precision Observables

I was reading some papers on electroweak theory. There I found the term "electroweak precision observables". My questions are the following: What are the electroweak precision observables? ...
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3 votes
1 answer
299 views

Indivisiblity of quarks

I have been researching the Standard Model of Particle Physics recently. According to the model, quarks are indivisible. Does this mean that quarks cannot be divided, or does it mean that if we were ...
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In context of resonances searches in particle physics, is Narrow Width Approximation meaning the same as Zero Width Approximation?

In context of resonances searches at colliders, in thematics of particle physics, is Narrow width Approximation meaning the same as Zero Width Approximation? Is Narrow width Approximation meaning ...
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4 votes
1 answer
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Fermilab $g-2$ muon experiment: How to obtain $a_{\mu}$?

In the $g−2$ muon experiment, we measure the anomalous precession frequency $$\omega_a = \omega_s − \omega_c,$$ where $$\omega_s = \frac{g_{\mu}\left\vert q\right\vert B}{2m} + \frac{\left( 1-\gamma\...
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2 votes
1 answer
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Fermilab $g-2$ muon experiment: How to choose the momentum of the muons?

In the $g-2$ muon experiment, we measure $\omega_a = \omega_s - \omega_c$, where $\omega_s$ is the spin precession frequency and $\omega_c$ the cyclotron frequency. Since we can relate $\omega_a$ with ...
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Standard Model Effective Field Theory: when studying SMEFT, are we looking for deviations?

The Standard Model consists of renormalizable interactions (dimension 4) between the known fermions and bosons. The Standard Model Effective Field Theory (SMEFT) includes additional higher dimension ...
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1 vote
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On further probing beyond quarks, will we uncover more fundamental particles? [duplicate]

All matter as we know is made of protons neutrons and other particles which are fundamentally made of quarks. On further probation theoretically can we say quarks are made of more fundamental ...
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0 votes
1 answer
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What is the value of the baryon asymmetry? [duplicate]

Define the baryon asymmetry, which sometimes is called the baryon density, as the baryons to photons ratio $\eta = n_b/n_\gamma$. I found in Ref. 1, published in 2018, that the value of $\eta$ is of ...
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0 answers
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Have Preon models been ruled out? [duplicate]

Preons are hypothetical sub-components of quarks and leptons, however it looks to me they are not discussed much. Has some experiment proved they do not exist or are they simply not popular?
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-2 votes
1 answer
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The scale of new physics, where could it be from good theoretical reasons? [closed]

Supposing that the Standard Model is valid up to certain scale of energy $\Lambda$. Historically, the hierarchy problem was a motivation to propose new physics at TeV scale. No new physics is yet at ...
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1 answer
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What is the relation between custodial symmetry and $m_W = m_Z \cos \theta_W$?

In Wikipedia, we can read that custodial symmetry is responsible for keeping $m_W = m_Z \cos \theta_W$ in the SM. However, in 2HDM, the most general scalar potential doesn't have custodial symmetry (...
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How to know the minimal coupling and how to find eigenvalues of arbitrary representations?

I'm dealing with the following problem. In a $ SU(3)_L\times U(1)_X$ model, the scalar representation content accomodates the following anti-sextet $$ S \equiv \begin{pmatrix} \sigma_1^0 & \frac{...
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3 votes
1 answer
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Oscillation of charm meson [duplicate]

In the LHC they have found a meson(the charm meson) which oscillates between itself and its antiparticle and they have also found there is a difference in mass between the charm meson and the ...
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3 votes
1 answer
76 views

Can the gauge boson respective of a spontaneously broken generator remain massless in the context of the Higgs Mechanism?

I'm studying a 3-3-1 model which is an extension of the standard model. The breaking $$SU(3)\times U(1) \to SU(2)\times U(1)'$$ occurs in a single step and through a single scalar VEV. The problem is ...
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3 votes
1 answer
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Have we ruled out the Minimal Supersymmetric Standard Model (MSSM)?

This question is inspired by a Physics Stackexchange question posted 8 years ago (The future of supersymmetry). The question that I have is very similar to the question in the above link, except that ...
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2 votes
1 answer
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Meaning of "Minimal" in "Minimal Supersymmetric Standard Model"

From what I am aware of, the LHC has ruled out the Minimal Supersymmetric Standard Model (MSSM), or at least highly constrain it. "Minimal" means that supersymmetry is introduced into the ...
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5 votes
1 answer
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Future Plans for Searches for Supersymmetry in the LHC

Due to the failure of the LHC to discover supersymmetry so far (July 2021), the simplest and the likeliest supersymmetric models (e.g. the MSSM) have been ruled out, and the confidence in ...
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Effective field theory relevant to $B \rightarrow X_s l^+ l^-$ decay

In effective field theory, the local operators of dimesion $ \le 6 $ built out of the light fields relevant to the $ B \rightarrow X_s l^+l^- $ decay are \begin{align} O_1^u&=\left( \overline{s}...
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