Tagged Questions

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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Supersymmetry and grand unification

I came across this diagram in my introductory particle physics class. Given the fact that SUSY can make the plot look suspiciously nice, what can we do with it? Also, electromagnetism has been ...
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Why is $\sqrt{v_1+v_2+\ldots} =246$ GeV in multi-Higgs models?

Where does the condition come from that in models with several electroweak breaking doublets the square root of the squared sum of the VEVs should yield $246$ GeV?
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Can a symmetry breaking VEV lie far above the “symmetry breaking scale?”

The scale where some symmetry gets broken can be computed using the renormalization group equations for the gauge couplings. If there is only one Higgs VEV responsible for some breaking, can this VEV ...
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Where does the matching condition for $U(1)$ subgroups come from in unified models?

The matching conditions for a breaking $G \rightarrow \prod_i G_i$ are $$\omega_G-\frac{C_2(G)(\mu)}{12 \pi}=\omega_{G_i}-\frac{C_2(G_i)(\mu)}{12 \pi} ,$$ where $C_2(g)$ denotes the quadratic ...
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Scalar dark matter

I was going through a minimal standrad model which included a real scalar singlet particle that can act as a candidate for dark matter.In that model,It was emphasized that such a scalar particle can ...
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Construct an effective field theory of neutrino mass

This is the problem I am trying to solve. I kinda write down the Lagrangian as $$L = \frac{1}{2}m_L \bar{v}_L^Cv_L$$ but I don't know how to continue. Can anyone help me?
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What is the meaning of SU(2) triplet scalar field? [closed]

The following is an about a Left-Right Symmetric model. $SU(2)\otimes SU(2)$ $(2\otimes 2=3\oplus 1)$ will generate a triplet, which in Left-Right Symmetric model is ...
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What would happen if there was a fifth fundamental force? [closed]

Preceding this question, as a student of physics, my knowledge of theoretical physics is somewhat limited. So I came across this article, which posited what the universe would be like if three ...
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Shouldn't there be 6 fundamental forces? [closed]

I'm listening to Leonard Susskind's The Black Hole War. In it he states (paraphrased) that a string wrapped around a compact dimension once imparts one unit of charge. Wrapped one way, it's a ...
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Few questions regarding String-Net theory and the Standard Model

A friend today showed me this post and after reading Prof. Wen's answer, few questions came to my mind. Prof. Wen says: all fermions (elementary or composite) must carry gauge charges (see ...
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1-Loop Mass Splitting of vector-like Fermions

In this paper the author argues that for a vector-like fermion doublet, with degenerate mass $M$ at tree level, we always have a mass splitting between the charged component of the doublet $L$ and the ...
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Mass of an imaginative stable top quark at low energies? [duplicate]

Masses are not fixed quantities, but change with energy because of the renormalization group running. These can be calculated in a given renormalization scheme, for example, the MS scheme: Imagine ...
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What physics does the Super Proton Proton Collider intend to explore in the $\lesssim 100\:\mathrm{TeV}$ range?

Chinese scientists have completed an initial conceptual design of a super giant particle collider which will be bigger and more powerful than any particle accelerator on Earth. With a circumference of ...
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Hierarchy problem and quadratic corrections in the Standard Model

In this paper, the third paragraph of the “Introduction” says that the Standard Model by itself is a natural theory. As I understand, they say there is no quadratic divergence in the Standard Model ...
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What are the remaining obstacles to low-energy quantum gravity?

In a 2003 review Burgess outlined how the QFT perturbative methodology is being extended to gravity, and described some effective quantum gravity expansions that reproduce general relativity in the ...
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750 GeV diphoton resonance: KK graviton?

As everybody of you may know at LHC they found this probable resonance (https://cds.cern.ch/record/2114808, https://cds.cern.ch/record/2114853?ln=en). It may be a scalar or a KK graviton mode. Now, ...
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SU(2) confinement picture

Preamble: In section 2 of these lecture notes (Gerard 't Hooft, 1998) an alternative interpretation of the weak interaction is presented, in which the weak force is confined, much like the strong ...
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Why standard model particles cannot be dark matter particles

I'm interested if any of the particles in the standard model could be potential candidates for dark matter? I know that we do not see dark matter, therefore dark matter does not interact ...
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Given a VEV how can I compute which generators remain unbroken using tensor methods?

This is a follow up to this question. A generator $T_a$ of a given gauge group $G$ remains unbroken after some Higgs field $\Phi$ gets a vev if $$T_a \langle\Phi\rangle =0$$ I'm trying to ...
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How to find the remaining subgroup after some linear combination of Higgs fields gets a VEV?

This is a follow-up question to this question. How can I compute which generators remain unbroken when a linear combination of Higgs fields $a \Phi_1+ b\Phi_2$ get a vev? If I compute the unbroken ...
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Massless bosons but not massless fermions?

I noticed some article on massless Weyl fermions and it got me thinking. I'm wondering if there is any explanation for why bosons (specifically gauge bosons) can be massless (photon and gluon) but we ...
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Symmetry breaking to a special subalgebra?

This is a follow-up to my question here. For regular subalgebras of some group's Lie algebra the root system of the subalgebra is a subset of the root system of the original's group algebra. In ...
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Why should the modes of the linearized metric perturbation be “wavefunctions” of gravitons (in the Randall-Sundrum model)?

In "An Alternative to Compactification" by Randall and Sundrum, they discuss the localization of "graviton modes" around the Planck brane in the Randall-Sundrum model where we have a compact fifth ...
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How to find the remaining subgroup after some Higgs field gets a VEV?

Say we have a group $G$ and a set of Higgs fields in a representation $R$ of $G$. One of the Higgs fields in $R$ gets a VEV, how can I determine the remaining subgroup after this symmetry breaking? ...
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What's the significance of neutrino oscillations? [duplicate]

I read some about neutrino oscillations and flavour changing between three types of neutrinos. The question is, what is the significance of that observation? So far, we did not expect them to ...
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Signs of supersymmetry and thus dark matter at CERN

The Large Hadron Collider at CERN has just re-started after a two year pause and is now running at unprecedented levels of 6.5 TeV, with collisions that will release up to 13.5 TeV. With this increase ...
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With the LHC about to restart as max energy, are there absolutely no hints or tantalizing signs of Supersymmetry in previous data?

Over the last couple of years I've seen several articles talk about hints or bumps in the data that might point to Supersymmetry. An article in NewScientist from Summer 2012 discussed the discovery of ...
Significance of $U(1)$ extensions of SM [closed]
Let's assume $U(1)$ extensions of SM with some detalizations: 1) Fermion sector of SM is extended by adding new very massive fermions; 2) Gauge group of SM is extended by adding new spontaneously ...