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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status of +4/3 scalar as explanation of $t\bar t$ asymmetry

One of the early proposals for the Tevatron asymmetry on $t \bar t$ was a "fundamental diquark" with a charge (and hypercharge) +4/3, either in a triplet or a sextet colour. I am interested on the ...
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(Why) Can we simply assume a given alignment of VEVs?

In GUT theories, one often assumes that Higgs fields take VEVs in given representations, of a given magnitude at a given scale. While I am well aware that this is one of the weak spots in such ...
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1answer
95 views

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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Is the conjectured noncommutative heavy scalar “brother” of the already detected Higgs boson is a pseudo scalar?

This is a technical (may be trivial?) question about this sigma scalar field advertised by Chamseddine and Connes to improve the electroweak vacuum stability involved by the weak mass of the already ...
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717 views

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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51 views

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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55 views

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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66 views

$\mathbb{Z}_6$ symmetry in the Standard Model

It's a well-known result that the spontaneous symmetry breaking of $SU(5)$ would lead not to the usual $G_{SM}=SU(3)\times SU(2)\times U(1)$, but to $G_{SM}/\mathbb{Z}_6$. However, it's also often ...
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98 views

Which are the obstructions for $E_8^L\times E_8^R$ unification?

After left-right symmetry extension of the standard model, $$G' \times SU(2)^L \times SU(2)^R$$ it would seem that a logical pathway to grand unification is to try to obtain it by breaking down from ...
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63 views

Doublet-triplet splitting : Meaning of some mechanism names

In order to solve the Doublet–triplet splitting problem, people have developped several mechanisms, such as the Missing Partner, the Missing VEV and the Sliding Singlet mechanism. I couldn't really ...
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70 views

Why does Higgs obtain certain values in SU(5) symmetry breaking?

In the SU(5) GUT model the symmetry is broken by a Higgs field with the element diag(2,2,2,-3,-3) taking a non-zero value. To break it down to SU(3)xSU(2)xU(1) But why exactly this element of all the ...
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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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35 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 $(1,2,-1/2)$: $$ \begin{pmatrix} \nu\\e \end{pmatrix} $$ ...
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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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66 views

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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38 views

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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Invariant linearly independent scalar potential construction for product groups

Lets say one has a gauge group for example SU(n) or SO(n) and has a scalar field which belongs to a certain representation (m-ranked tensor). If one wants to write down the invariant potential for the ...
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391 views

What insights does category theory offer in terms of grand unified theories?

What insights does category theory offer in terms of grand unified theories? Any references to books or papers that give categorical descriptions of any of the common grand unified theories would be ...
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How well theoretically motivated is $R$-parity?

I understand that $R$-parity is empirically necessary in order to avoid proton decay, but theoretically I'm worried that it amounts to a tune or "hack" that spoils the naturalness argument for ...
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108 views

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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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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45 views

$\rm SO(10)$ 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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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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69 views

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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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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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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27 views

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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47 views

Running of gravitational constant versus. other coupling constants, GUT and TOE

Is there any theory that proves convincingly that the gravitational constant runs with energy AND it is like the other coupling constants and converge at a single point at a given energy? Or is that a ...
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69 views

What is the status of SUSY GUTs in 2018?

Grand unification theories (GUTs) generically predict proton decay, and many of them have been under pressure for decades as experiments have failed to see it. I don't think there have been recent ...
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How to decompose E6?

Hi I'm trying to understand decomposition of $E_6\to SO(10)\otimes U(1)_\psi\to SU(5)\otimes U(1)_\psi\otimes U(1)_\chi\to SU(3)_C\otimes SU(2)_L\otimes U(1)_Y\otimes U(1)^\prime$. I believe I mostly ...
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Why does the $\mu^{+}\pi^{0}$ mode in flipped SU(5) becomes more important when compared to simple SU(5)?

I know that the higgs sector of these theories are different and all that. But what is the simple reason of why $p\rightarrow\mu^{+}\pi^{0}$ becomes comparable to $e^{+}\pi^{0}$? One thing I can image ...
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Possible intermediate scales of baryogenesis?

The conventional beyond Standard Model explanation of baryogenesis is that, within Grand Unified Theories (GUT), there exist some new heavy scalar bosons of mass $M_{\rm GUT}\sim10^{15}$ GeV, which ...
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137 views

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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Trinification lepton Yukawa interactions

We have a trinification model of $SU(3)_c\otimes SU(3)_L\otimes SU(3)_R$, where the first is the usual colour group, the second a left $SU(3)$ and the third a right $SU(3)$. As usual, leptons and ...
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What sorts of problems does asymptotically safe gravity face as a potential quantum gravity solution?

I've recently read an article by Ethan Siegel over at Forbes (he also blogs at Starts with a Bang) on asymptotically safe gravity as a possible alternative to string theory. I read the author's blog ...
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Why do the gauge bosons fix the couplings of the SM?

In chapter Chapter 16: Grand Unified Theories in the very first paragraph, the author states Note the SM gauge interactions of quarks and leptons are completely fixed by their gauge charges. Why is ...
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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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27 views

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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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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${\rm SU}(5)$ 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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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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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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$\Delta {b_{L}}$, $\Delta {b_{Y}}$ 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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113 views

Decomposition of the complex conjugate of the fundamental representation of $SU(5)$ in $SU(3)\times SU(2)\times U(1)$

I know I can decompose the fundamental representation (denoted as $5$) of $SU(5)$ as: $$ (3,1)_{-2c/3} \oplus (1,2)_{c} $$ But how do I get the decomposition of the complex conjugate of this ...
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100 views

Which representation do we start with in Grand Unified Theories?

The conventional approach in GUTs is to put all left-chiral fields $F_L$ of the standard model into one representation of the GUT group. For example, the 16 rep for $SO(10)$ GUT: $$ 16_L \rightarrow ...
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117 views

What are the limitations of simulating grand unification theories of elementary particles in condensed matter settings?

What are the limitations of simulating grand unification theories of elementary particles in condensed matter settings? I know that condensed matter systems can be constructed to be described by any ...
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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 ...