Questions tagged [grand-unification]

A Grand Unified Theory is a model in particle physics in which at ultra-high energy, the 3 gauge interactions of the Standard Model (electromagnetic, weak, and strong) merge into a single one, characterized by one larger encompassing gauge symmetry and one unified coupling constant. After SSBreaking, force carriers differentiate themselves and are driven by the RG to their values and numbers in the lab. Use for gauge GUT and gravity unification.

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$\text{SU}(5)$ GUT Higgs sector and symmetry breaking

The Higgs sector of minimal $\text{SU}(5)$ GUT consists of scalar fields in two representations, a $\mathbf{24}$ and a $\mathbf{5}$. All the $\mathbf{5}$ non-derivative terms form the potential $V(\...
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Proton decays in Pati Salam model or Georgi Glashow model

This Pati-Salam model doesn't predict gauge mediated proton decay, according to Wikipedia. However the Georgi-Glashow model predict gauge mediated proton decay, according to Wikipedia. I thought the ...
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SUSY $SU(5)$ GUT chiral adjoint repersentations

when you have a chiral superfield in the adjoint representation in your theory (i.e the Higgs $\Sigma_{24}$ in $SU(5)$), you can write it as a $5\times5$ Matrix: $(\Sigma_{24})_i^j=\Sigma^a (t^a)_i^j$ ...
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Has the number of particle types changed in the GUT era and after?

The Wikipedia article on Grand Unified Theory says: "GUT models predict that at even higher energy, the strong interaction and the electroweak interaction will unify into a single electronuclear ...
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Are there massless bosons at scales above electroweak scale?

Spontaneous electroweak symmetry breaking (i.e. $SU(2)\times U(1)\to U(1)_{em}$ ) is at scale about 100 Gev. So, for Higgs mechanism, gauge bosons $Z$ & $W$ have masses about 100 GeV. But before ...
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There was no electromagnetic field at the moment of the Big Bang. Did it appear later?

After the big bang, the fundamental interactions were one, but over time they began to separate. This is evidenced by the Grand Unification model. Do I understand correctly that at the time of the big ...
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Zee QFT book on the neutrino mass

in p.102 of Zee QFT book, "As of this writing, it is not known whether the neutrino mass is Dirac or Majorana. We will see in chapter VII.7 that a Majorana mass for the neutrino arises naturally ...
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Is there any relation between weak and strong forces, similar to electric and magnetic forces?

Is it possible to unify the strong, weak, electric and magnetic field just by Maxwellian-type equations? (Maxwell by adding a small change - unified electric and magnetic field, then Einstein's ...
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Adjusting the rate of proton decay in the standard $\rm SU(5)$ grand unified theory

The proton decay rate in the standard $SU(5)$ grand unified theory is given by $$ \Gamma \sim \left(\frac{g^2}{M_x^2}\right)^2 m_p^5 =\frac{g^4}{M_x^4}m_p^5 $$ Naively we could push up the bound for ...
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Magnetic Monopoles and the Inflationary Epoch

What leads to magnetic monopoles existing before the Inflationary Epoch and becoming infinitely diluted during inflation (if indeed that is the explanation to their absence), but the electric ...
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What is string theory? Why was a new theory required when modern Physics was only one step away from establishing a G.U.T.? [closed]

What is string theory ? (correct me if i am wrong) Why a new underlying theory was required when modern Physics was only one step away from establishing a G.U.T. (unification attempt for four ...
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Why don't $\rm SO(10)/Spin(10)$ or larger GUTs permit electron-pair decay?

$\rm Spin(10)$ unifies all left-handed fermions and anti-fermions, and all right-handed fermions and anti-fermions. And its Pati-Salam subgroup unifies quarks with leptons (SU(4)) and complements SU(...
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$ (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 $(1,2,-1/2)$: $$ \begin{pmatrix} \nu\\e \end{pmatrix} $$ ...
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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 ...
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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 ...
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Parity $P$ symmetry restored by 1 in the $1 \oplus \bar{5} \oplus 10$?

In Lie Algebras in Particle Physics 2ed - From Isospin to Unified Theories (Georgi, 1999) p.283 Georgi wrote: When we include the $1$ in the $\rm SU(5)$ Unified Theory model, we get the 16 $$ 1 \...
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How to give left-handed neutrinos alone Majorana mass?

On Wikipedia, it says https://en.wikipedia.org/wiki/Georgi–Glashow_model#Breaking_SU(5): Fermions transforming as a 1 under SU(5) are now thought to be necessary because of the evidence for neutrino ...
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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 $[3]_4$ ...
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Electroweak Unification and Electroweak scale

We said that the EM and weak interactions are unified as Electroweak Unification. However, for usual Grand Unification, it requires that the gauge group G is simple Lie group -- which means the G has ...
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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 ...
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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). ...
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$SU(5)$ 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 ...
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${\rm SU}(5)$ doublet-triplet splitting problem and disagreement with phenomenology

The statement from Wikipedia about ${\rm SU}(5)$ Georgi–Glashow seems very puzzling to me. Here are the text from https://en.wikipedia.org/wiki/Georgi–Glashow_model#Decomposition: It is the Higgs ...
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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 $$ (\...
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Why are both C and CP violation necessary for baryogenesis?

Sakharov condition states both C and CP violation is necessary for baryogenesis. Now consider, for example, a theory with B-number violating interaction and C-violation. Therefore, if $p\to e^+\gamma$ ...
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Unification of Forces

I was reading that unification of Forces is the most important task in the entirety of Physics. My question is why do the forces have to Unified. Why can't they be different forces what makes us think ...
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Are X and Y boson gauge mediator of X and Y gauge symmetry? With zero X and Y charge?

Recall that the electron carries U(1) gauge charge -1. the U(1) is gauged and mediated by the U(1) gauge boson which is the photon with zero U(1) gauge charge, thus $0$. Now let us take this ...
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Bern-Carrasco-Johansson (BCJ) Double Copy and Color-Kinematic duality

According to the wikipedia page on Strong Gravity, the theory is considered "non-mainstream", but from what I can gather there have been some very interesting progress and results since it ...
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$B$-$L$ 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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How to prove $Q_u = -2Q_d$ from $SU(5)$?

I'm a beginner, and I'm trying to figure out how to prove that charge of Up quark is equal to 2 times the charge of down quark from the 10 representation of $SU(5)$. Please help.
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Unification of forces in black hole singularity?

If at the center of a black hole a singularity or singularity-like state is reached, wouldn't you have the fundamental forces reaching unification energy? In which case, it would seem that a black ...
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Can a GUT be spontaneously broken mutiple ways?

Say we have a GUT e.g. $SU(5)$, if the Higgs field breaks this it can break it down to $SU(3)\times SU(2)\times U(1)$ if the Higgs field acquires values proportional to the weak hypercharge. But can ...
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Is there a symmetry breaking model possible for mirror fermions in $E_8$?

I've often been struck by how nicely the Standard model seems to fit into (supersymmetric) $E_8$. Specifically if we write the root vectors of $E_8$ as $(R,G,B,W,H,F,S,T)$. With colour being the ...
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Are there fermionic bound states that are gauge neutral to all gauge forces?

Puzzle: In our standard model particle physics, are there fermionic bound states that are gauge neutral to all gauge forces? Here we concern strong SU(3) color, electromagnetic U(1) EM, hyper U(1), ...
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Why do we need complex representations in Grand Unified Theories?

EDIT4: I think I was now able to track down where this dogma originally came from. Howard Georgi wrote in TOWARDS A GRAND UNIFIED THEORY OF FLAVOR There is a deeper reason to require ...
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Why are magnetic monopoles hard to find (if exist)?

I understand the Yang-Mill perspective of $U(1)$-gauge theory. In that, you can easily write down the field of a Dirac magnetic monopole. What interests me is the fact that it's so hard to find (if ...
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$\Delta {b_{L}}$, $\Delta {b_{Y}}$ 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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Why do physicists believe that there exist magnetic monopoles?

One thing I've heard stated many times is that "most" or "many" physicists believe that, despite the fact that they have not been observed, there are such things as magnetic monopoles. However, I've ...
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Where does in GUT symmetry breaking $U(1)$ come from?

In GUTs one starts with some larger group, like $SU(5)$, which is then broken into smaller groups, for example $$SU(5) ~\longrightarrow~ SU(3) \times SU(2) \times U(1)$$ This can be seen, for ...
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Hypercharge normalization for $SU(5)$ GUT

Reading about $SU(5)$ unification, texts says that they use the renormalization factor $\sqrt{3/5}$ for weak hypercharges in order to embed SM into a $SU(5)$ group. This implies a new $U(1)_Y$ ...
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Why does inflationary expansion of the very early universe require time duration?

If the grand unified force symmetry breaking separation into the strong force and electroweak force leads to a change in scale of the metric that defines distance within space is the cause of the ...
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How the hierarchy of forces is explained by Supersymmetry?

The hierarchy problem is often stated in two ways: First, the divergent corrections to the Higgs bare mass, second, why is gravity so much weaker than the other three forces. The solution to the ...
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In which representation are monopoles of grand unifying theories classified?

In the context of grand unification theories A.Zee's book states that $SU(5)$ (or $SO(10)$ if $SU(5)$ is considered as outdated as GUT candidate) as GUT and as spontaneously broken non-abelian gauge ...
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Representation of the $\rm SU(5)$ model in GUT

In Srednicki's textbook Quantum Field Theory, section 97 discusses Grand Unification. On page 606, it states: In terms of $\rm SU(5)$, we have \begin{equation} 5 \otimes 5 = 15_{S} \oplus 10_{A} ...
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Are there any good books about Grand Unified Theories?

I'm starting to get a little desperate, because I can't find any introductory treatments of Grand Unified Theories (GUT). So far the only books I found are Mohapatra Unification and Supersymmetry ...
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What processes conserve (and don't conserve) GUT $X$-charge?

I've been Wikipedia-ing the weak interaction and GUTs and I came across 2 seemingly conflicting pieces of information. In the page for Weak Hypercharge it says this: one of the interactions is with ...
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What is the way to work out the running of lepton masses?

If we assume the GUT unification energy is some value E, (say $10^{16}GeV$). Can we work out the running of the particle masses for example the electon, muon and tau at various energies? And will ...
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Interaction range of fundamental forces at a unification energies

At low energies, all fundamental forces have different coupling constants as well as an interaction ranges. As one know, at a some high energy (GUT energy $10^{14}$ GeV), all the coupling constants ...
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Mass splitting for leptons and down quarks in $SU(5)$ model?

In the minimal $SU(5)$ GUT model, the masses of the leptons and the corresponding down-type quarks must be equal. i.e. $m_e=m_d$, $m_\mu=m_s$, $m_\tau=m_b$. Whereas this is approximately correct for ...
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Why does the conclusion that protons are monopoles has led us to believe that they specifically may have a half-life? [closed]

from Zeldovich, Ya. B.; Khlopov, M. Yu. (1978). "On the concentration of relic monopoles in the universe": "The majority of particles appearing in any quantum field theory are unstable, and they ...