A model of the basic particles and forces featuring six quarks, three charged leptons, three massless neutral leptons and four fundamental force carrying bosons. The twelve fermions are arranged into three generations, while the bosons serve to explain the electromagnetic interaction plus the strong ...

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627 views

“Space” in General Relativity and “vacuum” in Standard Model, is it the same thing?

And expansion of space is equal to expansion of vacuum?
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301 views

Pion decay in particle physics

I'm taking a particle physics course and we're using Perkins Introduction to High Energy Physics as the text. I am looking at problem 1.7. It asks whether $$\pi^0\rightarrow e^- + e^+$$ is allowed or ...
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341 views

Do I need to study the “Standard Model” before studying String Theory?

After this semester, I'll have a background up to a first course in QFT (first 5 or 6 chapters of Peskin and Schroeder). The next step in QFT will be something specific to the Standard Model ...
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1answer
323 views

Relation of Higgs couplings to masses of fundamental particles

The standard model has 12 massive leptons and 2 massive bosons other than the Higgs. My understanding of the Higgs mechanism is at about the level of this article, which goes as follows. Start with ...
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2answers
410 views

Why is there a linear relationship between charge and isospin?

So the title basically says it all. Something that's really bothering me is the fact that the Gell-Mann Nishijima relationship can be extended to provide a linear relationship between charge and all ...
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1answer
447 views

Labelling representations using isospin and hypercharge

Can someone explain how isospin and hypercharge can be used to label representations? What is the meaning of the term singlet, doublet etc in this context? In particular how can I use it to label ...
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1answer
235 views

Weak isospin confinement?

According to the Wikipedia article on color confinement: The current theory is that confinement is due to the force-carrying gluons having color charge [...], i.e. because the gauge group is ...
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2answers
552 views

Is the Higgs a quantum field or a particle?

The Higgs is not detected in the asymptotic data, so it is possible that there is no particle interpretation for the Higgs quantum field. Indeed, the Higgs potential is only positive definite if the ...
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1answer
880 views

Introduction to Physical Content from Adjoint Representations

In particle Physics it's usual to write the physical content of a Theory in adjoint representations of the Gauge group. For example: $24\rightarrow (8,1)_0\oplus (1,3)_0\oplus (1,1)_0\oplus ...
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962 views

What's the Standard Model width of a 125 GeV Higgs?

There's a fairly broad mass spread in the new results out of Atlas and CMS. I'm curious how this fits with the expected SM width.
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1answer
509 views

Why does the Higgs field only couple to opposite-chiralities fermions?

According to the Wikipedia page on the Standard Model, the Higgs field interact with fermions through a Yukawa interaction coupling only left to right chiralities. What is the reason for that? Is that ...
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2answers
104 views

What is it exactly that conflicts when trying to unify all 4 fundamental forces?

Everyone knows that there are 4 fundamental forces: Gravity Electromagnetic Weak Strong At school and university you're taught that no one has been able to unify these 4 fources. However, not a ...
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98 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 ...
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1answer
280 views

Hypercharge of the complex Higgs doublet

I was wondering how one can see that the hypercharge of the complex Higgs doublet is $Y=\frac{1}{2}$. Complex Higgs doublet. $$ \Phi(x) = \begin{pmatrix}\ \Phi^{+}(x)\\ \Phi^{0}(x) \end{pmatrix} $$ ...
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169 views

What is the exact relation between $\mathrm{SU(3)}$ flavour symmetry and the Gell-Mann–Nishijima relation

I'm trying to understand how the Gell-Mann–Nishijima relation has been derived: \begin{equation} Q = I_3 + \frac{Y}{2} \end{equation} where $Q$ is the electric charge of the quarks, $I_3$ is the ...
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1answer
139 views

What sorts of complications do massive neutrinos bring to the Standard Model?

Naively, I'd just think of considering them as any other massive fermions (but without electric charge), including the appropriate chiralities (and neutrino-higgs coupling when necessary). ...
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2answers
322 views

Do all the particles acquire mass in the Standard Model due to the Higgs mechanism only?

I know that a mass term for an intermediate boson is not compatible with the gauge symmetry. But in principle a mass term for the electron field does not violate a gauge symmetry. However to build an ...
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2answers
623 views

Feynman rules for SUSY

This might be an incredibly naive question, but I'm wondering if there are a set of rules for "translating" between Standard Model and SUSY. For instance, if I want want to go from a Standard Model ...
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190 views

Width of the decay of Higgs boson into dimuon

According to Standard model, the partial width of the decay of Higgs into dimuon (up to tree level) is: $$\Gamma\approx\frac{m_H}{8\pi} \left(\frac{m_{\mu}}{\nu}\right)^2$$ with the Higgs mass ...
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307 views

How do physicists know that mass of possible Higgs particle is limited between two values?

How do physicists know that mass of possible Higgs particle is limited between two values 90 GeV/c$^2$ and 145 GeV/c$^2$?
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1answer
264 views

Why are WW gg ττ branching ratios so similar for a 115 GeV SM Higgs?

In a previous question on Higgs branching ratios, I find this image (originally from page 15 here). I am VERY intrigued by the fact that decays to WW, gg, and ττ are almost equally probable, for ...
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0answers
211 views

Effective Field Theory (EFT) decoupling top

The decoupling theorem of Appelquist-Carazzone says that if you want to decouple a particle, the low energy resulting theory need to be renormalizable. You can't do that for the top, because you break ...
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147 views

How many orders of magnitude in energy spans the Standard Model phenomenological spectrum?

I am wondering if it makes sense to state that the upper limit is roughly 1012 eV (up to know the physics probed by the LHC seems to be pretty consistent with the SM) and the lower one is ... the ...
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875 views

Does every elementary particle have its own separate field?

Higgs field is pretty simple for me to understand, you have one field that creates one particle (Higgs boson). So I continue to assume one field one particle. Up field creates a up quark. Down field ...
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4k views

The Higgs field a new Luminiferous aether?

As of this writing it has been made clear to me that classical physics' Luminiferous aether was a terriblly poor discriptor of space. With the advent of Special Relativity and General Relativity, that ...
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2answers
428 views

Is the Higgs 3/4 detected already?

Can someone provide an expanded explanation on the statement that the Higgs field is already 3/4 detected? Link to ref (@nic, sorry I left it off, do a quick search on Higgs to find the right ...
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158 views

Is there a table that sums up the parameters, the assumptions/symmetries, and the predictions of the standard model?

The title says it all: is there a table that sums up the parameters, the assumptions/symmetries, and the (most important) predictions of the standard model?
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1k views

“Periodic Table” of Particles of the Standard Model?

What is a good, single, "periodic table" of all the particles of the Standard Model? I thought Particle Data Group would have a single-page PDF of this, but I couldn't find a single table listing all ...
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351 views

Does Standard Model confirm that mass assigned by Higgs Mechanism creates gravitational field?

I am not comparing passive gravitational mass with rest inertial mass. Is there an evidence in Standard Model which says that active gravitational mass is essentially mass assigned by Higgs mechanism. ...
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3answers
515 views

Does the Standard Model require neutrinos to be massless?

I am an undergraduate student in Physics, I have a basic understanding of Particle Physics and Quantum Mechanics but none whatsoever of Quantum Field Theory. I know that Neutrino mixing requires ...
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2answers
1k views

What is the Standard Model equation which unified Strong, Weak, and Electromagnetism?

I always heard that three atomic force in small scale structure (Strong, weak and electromagnetic) are unified through the standard model, but I've never seen its unified equation. What is single ...
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2answers
195 views

Do any good theories exist on why the weak interaction is so profoundly chiral?

I find the profound asymmetry in the sensitivity of left and right chiral particles to be one of the most remarkable analytical observations captured in the Standard Model. Yet for some, I've not ...
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2answers
349 views

Can special/general relativity be derived from the standard model?

Can special/general relativity be derived from the standard model? For example the time dilatation in strong gravitation? My feeling is yes, but I am not quite sure.
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1k views

Equation of everything

Is this equation in the image true? Can you give some topics that I can cover the equation? Similar equation from http://www.preposterousuniverse.com:
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221 views

If nature exhibits symmetry, why don't up and down quarks have equal magnitude of electric charge?

I always hear people saying symmetry is beautiful, nature is symmetric intrinsically, physics and math show the inherent symmetry in nature et cetera, et cetera. Today I learned that half of the ...
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3answers
150 views

Are the second and third generations of matter required or optional?

If the second and third matter families (so-called generations: muon, muon neutrino, tau, tau neutrino, ...) didn't exist, would that affect how the universe runs? Are they optional or required?
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1answer
215 views

What if EM or QCD was spontaneously broken?

Suppose that Standard Model Higgs mechanism broke electromagnetism, by e.g. veving the charged component of the doublet, so that the photon was massive with $m_\gamma\sim v$. Could such a Universe ...
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1k views

Does Dark Matter interact with Higgs Field?

Dark matter does have gravitational mass as we know from its discovery. Does it have inertial mass?
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425 views

Sparticles: Relationship to supersymmetry and dark matter?

I was attempting to read this paper after watching a show with Brian Greene. As I understand it, sparticles are a prediction of supersymetry, so I was wondering: Wouldn't the discovery of ...
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2answers
1k views

What is difference between the different 'flavours' of neutrinos?

Moreover, how-come scientist know that muon-neutrino are different from electron-neutrino when they didn't even know what the difference was? Did they interact differently with other particles?
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1answer
207 views

Is the exact form of the Higgs potential known?

Usually the Higgs potential is given as $$ \frac{1}{2}\mu^2\phi^2 - \frac{1}{4}\lambda^2\phi^4 $$ but I never quite understood if this just serves to give us an idea of how symmetry breaking works, or ...
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1answer
143 views

Is there such a thing as red - anti red gluon? Why such gluon posssibilities appear in equations?

Gluon properties have puzzled me for quite a while now. I recently learned that there are 8 kinds of gluons. They are kind of represented by 8 linearly independent SU3 matrices. Matrices represent ...
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2answers
362 views

Why do we have a TeV scale?

When model building we don't want to introduce any new scales into our theory. We usually try to have new particles at the Higgs (TeV) scale (to solve the hierarchy problem), at the GUT scale, or at ...
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1answer
259 views

Why does the pion half-life differ between the charged and uncharged species?

Why does the uncharged pion have much shorter half-life than the charged pion despite the fact that the uncharged pion has a little bit less mass than the charged one, so that according to the ...
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1answer
108 views

Electroweak interaction: From $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ to $W^{\pm},Z_{\mu},A_{\mu}$

EDIT: Additional question at the end I am trying to illuminate how the "unphysical" gauge bosons $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ will be the "physical" $W^{\pm},Z_{\mu},A_{\mu}$ when ...
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1answer
177 views

Fine Tuned Universe

Is the fine tuning that cosmologists talk about (that our Universe is fine tuned for intelligent life) is the same as the fine tuning of the squared mass parameter of the Higgs in the Standard Model? ...
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3answers
399 views

In SUSY why does electroweak symmetry breaking only happen in the SM sector?

This is a difficult question to phrase succinctly, so I hope the title makes sense. What I want to understand is what seems like a lack of symmetry (besides SUSY-breaking) between the SM sector and ...
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2answers
672 views

Predicting Decay Rates via the Standard Model

Question 7584 illustrated a procedure to forecast the decay rates of isotopes with known long average lifetimes. Lifetimes of the many U isotopes vary from micoseconds to gigayears. F has only one ...
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158 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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1answer
989 views

What parity has an electron?

I couldn't find anything about the parity of an electron. Neither in the german, nor in the spanish and nor in the english version of Wikipedia. I only found one sentence in the parity article of ...