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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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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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$\mathbb{Z}_6$ 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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601 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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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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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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380 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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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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23 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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142 views

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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38 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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62 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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46 views

Thought Experiments to Corroborate Unification

Apart from beauty, is there reason to believe the known forces to be parts of one "superforce?" The response to a similar question seems incomplete in that it does not address unification; there is ...
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81 views

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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80 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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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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39 views

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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36 views

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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134 views

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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87 views

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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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. ...
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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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Can $E_8 \times E_8$ contain the standard model?

I know $E_8$ by itself can't be gauge group because it has no complex representation and so would not be chiral. But assuming the existence of mirror matter which also would have $E_8$ gauge group ...
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The strong CP problem in Grand Unified Theories

The strong CP problem could, in principle, be solved by a massless up quark. Can this solution be embedded in Grand Unified Theories, such as $SO(10)$ (or $SU(5)$)? These theories, in particular $SO(...
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105 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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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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106 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 ...