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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Electroweak symmetry breaking with additional gauge group(s)

Is it possible that rather than the electroweak splitting into SU(2)xU(1), that there could instead of another gauge group in the dark sector? Suppose SU(2)xU(1)xSU(N)_d. Is that ruled out by the full ...
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1answer
36 views

Is the $\nu_e$ massive?

Neutrino oscillations imply that the $\nu_\tau$ is more massive than the $\nu_\mu$, and the $\nu_\mu$ is more massive than the $\nu_e$, so it's inferred that the $\nu_\mu$ and $\nu_\tau$ have mass. ...
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How can family symmetries explain the 3 generations and their mixing?

I recently read several papers (e.q. this one http://arxiv.org/abs/1301.1340 ) about the usage of discrete, additional symmetries that can be used to explain the PMNS and/or CKM matrices. ...
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Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants?

Do any, all, or no adjustments to standard model change the Weinberg angle or it’s relation to masses or coupling constants? If any, which (types of) ones? For the ones that do, what are the relations ...
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1answer
80 views

Viability of a Fayet Iliopoulos term in the MSSM

Why is a Fayet Iliopoulos term $-kD$ in the MSSM (Minimal Susy Standard Model) not relevant (or subdominant to an F-term)? According to Martin (A Supersymmetry Primer, p.70) it's because squarks and ...
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1answer
133 views

Statistical significance in Z boson excess paper

In a recent ATLAS paper, a excess of $3\sigma$ was reported from the Standard Model prediction in a search looking for a same-sign dilepton signal with an invariant mass around the Z peak. For brevity ...
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44 views

Futility of developing new fundamental models of physics? [closed]

I know that this site is meant for physics professionals to discuss physics as it is accepted and very well established today, so I will keep this as brief and vague as I can. As I learn physics, I ...
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0answers
22 views

Cosmological and astrophysical bounds on physics beyond SM [closed]

There are many cases when cosmological and astrophysical observations make restrictions on particle physics models. For example, some axion models are rejected by white dwarf luminocity functions, ...
5
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1answer
89 views

Current knowledge of Higgs

What is the current knowledge about the Higgs field after its discovery in the LHC? Does it exactly mimic the standard model Higgs? Does this knowledge rules out the possibility of other Higgs ...
2
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0answers
36 views

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 ...
2
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1answer
75 views

Why is a tensor times its dual a derivative?

Why is a term like $$F \tilde{F}$$ or $$G \tilde{G}$$ considered to be a derivative? Where are the derivatives? This is said in a PRD article. Check section IV page 5.
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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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20 views

Introducing inert superfield in R-symmetry model in extended MSSM

Some papers, e.g, Chakraborty et al, Frugiuele and Gregoire introduce inert superfield doublet $\hat{R}_d$ and $\hat{R}_u$. I have a question, what is the role of these inert superfields?
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1answer
109 views

String Theory: Why should(n't) the string snap?

My question is related to a comment in the margin of the popularising site The Official String Theory Web Site. There are two basic types of string theories: those with closed string loops that ...
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1answer
64 views

How experimentalists put bounds on new physics at the LHC?

I would like to understand how experimentalists search for new physics at the LHC. Lets imagine I want to use the LHC data to put a bound on the coupling of some new physics effective operator, say, ...
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5answers
2k views

Why don't we have a theory of everything?

What is currently stopping us from having a theory of everything? i.e. what mathematical barriers, or others, are stopping us from unifying GR and QM? I have read that string theory is a means to ...
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0answers
28 views

Real representations of chiral fields

Why we can´t have real representations of chiral fields, i.e. why does a multiplet of chiral field (Weyl spinors) under a real representaiton of a Lie Group transforms as a "vector". It is easy to see ...
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2answers
116 views

Does String Theory Predict more than Four Forces?

String theory literature tells us that ST predicts the four forces: weak, strong, EM, and gravity. What it fails to tell us is if that's all the forces it predicts. Might there be a fifth force that ...
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0answers
85 views

Evaluation of the anomalous dimensions of fields in SUSY $SU(5)$

The general formula for the anomalous dimension can be found in Martin΄s review article (hep-ph/9709356), on page 62 relation (6.5.4). In the case of $SU(5)$ and especially in the paper of Kobayashi, ...
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0answers
41 views

Mass generation for Z' and W' bosons

I read that some Beyond the Standard Model theories require the existence of additional gauge bosons such as $Z'$ and $W'$. As far as I understood, an extension of the $SU(2)_L$ symmetry is required, ...
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2answers
52 views

Sakharov condition of departure from equilibrium

I have a doubt with the third Sakharov condition which demands a departure from equilibrium. But why is that necessary when both baryon violating interactions and well as CP violation is present in a ...
2
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1answer
67 views

Leptogenesis with singlet neutrinos

(i) The Lagrangian of electroweak model extended with right-chiral singlet neutrinos $N_{iR}$ contains the Yukawa coupling term+ the bare Majorana mass term $$f_{\alpha ...
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1answer
423 views

How can the mass of Higgs give preference to SUSY vs multiverse?

According to the documentary Particle Fever, the precise value of the Higgs boson's mass could give more credence to either SUSY or multiverse theories. If the mass had been 115 GeV or below SUSY ...
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1answer
92 views

What's inside a quark? [duplicate]

What particles make up a quark? We all know quarks (3, uud) make up a proton. I read on Wikipedia they are called "hadrons" ,but how do they work? Is the collection wave functions of the components ...
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0answers
64 views

How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim ...
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47 views

How could we find preons?

If I understand correctly, scientists were able to find strong evidence for the existence of quarks by using deep inelastic scattering. If quarks (hypothetically) are composed of preons, could we use ...
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0answers
28 views

What are hadronic uncertainties?

I am reading articles about recent findings at CERN and the possibility of New Physics contributions, and they keep saying that the discrepancies may be due to hadronic uncertainties... What are ...
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1answer
59 views

Constraints on new unknown stable fermions?

This question is rather speculative, but I would like to ask it anyway. What are the constraints on possibility of discovering new unknown stable fermions of some sort in the future? If I am not ...
2
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1answer
75 views

Why does the $Z$ boson not change quark flavour?

Is it just an observation from Particle Accelerators data? I was trying to understand what is it that mathematically stops the $Z$ boson from changing quark flavour, if it is known?
2
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1answer
92 views

Gauge SU(2) with real triplet

I have come across a model of gauge $SU(2)$ with a real triplet. The covariant derivative for $SU(2)$ complex doublet is written as $$D_\mu=\partial_\mu-igT^aA^a_\mu$$ where $T^a$ are generators of ...
5
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1answer
283 views

Chiral anomalies

Recently I have read that there is contraction of chiral anomalies in SM. But people are working on chiral anomalies theory. So I have the question: what is the importance of development of the theory ...
2
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1answer
71 views

Scalar Particles, Flavor Changing Processes and Gauge Symmetries

Let's consider an extended version of the Standard Model (SM) with a new Yukawa operator of the form $$ \sum_\ell g_\ell\bar{\ell}\ell \phi ,$$ where $\ell$ is any lepton of the SM and $\phi$ is a new ...
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1answer
140 views

Higgs Mechanism

In Higgs mechanism, we take the combination of LH $SU(2)$ doublet and RH singlet along with Higgs doublet so that the overall weak hypercharge and weak isospin is zero to be $SU(2) \times U(1)$ ...
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213 views

What is the meaning of this String Theory Equation from CERN? [closed]

I have recently visited CERN, and in the Globe they showed an equation from string theory. My knowledge about it goes only as far as 'The elegant universe', so no mathematics, but i would say that ...
5
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1answer
9k views

Supersymmetry vs multiverse

I'm a complete noobe in physics and quite honestly need help. My question is simple, based on CERN's tentative findings stating the Higgs boson at a mass of ~125 GeV: Is the physics community leaning ...
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3answers
265 views

Could Dark Matter particles that don't couple to quarks or leptons have been produced?

With what we know about physics, is it possible that when the universe 'began', around when quarks and leptons were produced, another particle, which doesn't couple to either quarks, leptons or ...
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1answer
510 views

What are the alternative theories of dark energy? ($w \neq -1$)

There has been a lot of related questions about dark energy around here but these are usually 2-4 years old and the closest question to mine hasn't really been answered, so I am going to proceed. ...
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2answers
96 views

For what rare events was the LHC built?

I understand that for low cross-section events a very high luminosity is necessary in order to obtain enough data to produce meaningful statistics. That is why the LHC was built. But which are these ...
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3answers
239 views

Why gauge $SU(N)$ and not $SO(N)$?

When building models people typically gauge $SU(N)$ but rarely try to gauge $SO(N)$ (the only example I know about is $SO(10)$, but even that isn't quite $SO(10)$ but actually its double cover). At ...
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0answers
65 views

axion couplings

As I understand it, the axion $a$ originates from the spontaenous symmetry breaking of $U(1)_{PQ}$. This symmetry being anomalous, and because of the QCD vacuum structure, a non vanishing term like ...
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1answer
115 views

Why more than one Higgs?

Since by introducing one Higgs Boson we can give a mass to the leptons and gauge bosons of the weak interaction: Why should we consider more than one Higgs (doublet) once we go beyond the standard ...
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2answers
77 views

Uniqueness of W,Z bosons

What is real reason for considering only ONE unique W and Z bosons, and not of 3 separate flavors, in the Standard Model?
3
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1answer
237 views

Effective theories and dimension six operators

What is the importance of dimension six operators in the study of physics beyond the Standard Model? Are these operators more relevant than dimension five operators like $HHFF$ or operators with ...
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0answers
407 views

Finding the vacuum which breaks a symmetry

I will start with an example. Consider a symmetry breaking pattern like $SU(4)\rightarrow Sp(4)$. We know that in $SU(4)$ there is the Standard Model (SM) symmetry $SU(2)_L\times U(1)_Y$ but depending ...
3
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1answer
165 views

What is the meaning behind the neutrino oscillation parameter?

As far as I can tell, there are 6 parameters that describe how a neutrino oscillates: 2 mass squared differences, 3 mixing angles and another parameter I don't understand at all (delta). Thus I have ...
3
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3answers
533 views

why cannot fermions have non-zero vacuum expectation value?

In quantum field theory, scalar can take non-zero vacuum expectation value(vev). And this way they break symmetry of the Lagrangian. Now my question is what will happen if the fermions in the theory ...
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4answers
144 views

why do the electroweak vacuum have to be charge and color neutral?

My question is why the electroweak vacuum of the Standard Model have to electroweak charge and QCD color neutral? What goes wrong if electroweak vacuum has either non-zero charge or color quantum ...
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0answers
60 views

Can a neutrinos mass oscillate in a similar way to its flavour?

So I've been reading up on neutrino oscillations and I think I'm making some progress in understanding it, but I'm still a long way off. As I understand it, you can 'classify' neutrinos in two ways; ...
2
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1answer
77 views

Mass scales in See-saw mechenism

Are both types of Majorana masses $$\mathcal{L}^L_M=-\frac{m_L}{2}[\overline{(\psi_L)^c}\psi_L + \overline{\psi_L}(\psi_L)^c]$$ and $$\mathcal{L}^R_M=-\frac{m_R}{2}[\overline{(\psi_R)^c}\psi_R + ...