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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General framework of Supersymmetry [on hold]

Even the people who are skeptical about SUSY are happy with the SUSY searches going on at LHC because they recognize that SUSY's general framework is quite flexible and the search strategy used in ...
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2answers
108 views

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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1answer
77 views

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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0answers
127 views

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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0answers
174 views

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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1answer
110 views

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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0answers
26 views

Correct Yukawa Term with a SU(2) Higgs Triplet?

Given $SU(2)$ doublet fermions $\Psi^1$ and $\Psi^2$ and a $SU(2)$ triplet Higgs $H$, how does the correct Yukawa term look like in tensor notation? Schematically, we have $$ 2 \otimes 2 \otimes 3 ...
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0answers
20 views

Package for flavour physics computation? [closed]

Which softwares one usually uses for flavour physics related calculations? I saw one called SUSY_FLAVOR. I haven't used it yet though. What in case of other BSM models other than SUSY? Is there any ...
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0answers
143 views

One-Loop Yukawa RGEs

I'm currently trying to understand how one can write the one-loop RGEs for the Yukawa couplings using the general formula: One example I'm interested in is how the author derives, using this ...
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2answers
60 views

Is there any stable hadron?

Neutron can decay into proton and I think some hypothesis claim that proton can also undergoes decay into subatomic particles... Is there any hadron that never decays?
3
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1answer
67 views

Supersymmetry as a solution of hierarchy problem

Hierarchy problem is the statement of why the weak force is much stronger than gravity. In terms of coupling constant, weak force (Fermi coupling) is much larger than gravity (Newton's constant). I ...
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54 views

Symmetry of interaction lagrangian and symmetry of full lagrangian

Suppose we have lagrangian $$ \tag 1 L = \frac{\theta}{f_{\gamma}}F_{EM}\tilde{F}_{EM} +\frac{1}{2}(\partial_{\mu}\theta)^2 - \frac{1}{2}m_{\theta}^2\theta^2 + L_{SM}, $$ where $\tilde{F}_{EM}$ ...
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1answer
93 views
+50

Soft SUSY breaking fermion mass terms in MSSM for matter fields

In the Minimal Supersymmetric Standard Model, the chiral fermion fields (the Higgsinos) don't have any soft SUSY breaking mass terms and soft SUSY breaking trilinear interactions while their scalar ...
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0answers
55 views

Is there a model of the universe with the transfinite (space)time?

In mathematics there is a concept of ordinal numbers where one can count to infinity and beyond. For example the least number that is greater than all the finite numbers is denoted by $\omega$. Such ...
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28 views

Anomalies, neutrino condensate and neutrino masses

Is neutrino number conservation not affected by the U(1) QCD and QED anomalies due its zero U(1) charge? Is this the reason why the neutrino should be massless and there should be no lepton family ...
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1answer
60 views

Fundamentals for predicting the standard model? [closed]

. Now, the question(s). What must a theory include to be consistent with the standard model? What concepts/ fields must be predicted?(such as predicting a Higgs field, gauge groups, particles being ...
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3answers
157 views

Are field theories special?

Our best descriptions of the microscopic world, that satisfy many fundamental requirements (as we know them today), are field theories. Is there something fundamental about field interactions, or are ...
3
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1answer
102 views

Quark mixing vs neutrino mixing, mass eigenstates, weak states and detection

I have some doubts regarding the CKM matrix in the quark sector and PMNS matrix in the leptonic sector. Let us call $(d^\prime, s^\prime, b^\prime)$ the weak basis for quarks and $(d,s,b)$ the mass ...
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0answers
9 views

How can we reduce the number of necessary parameter to 19 in phenomenological Minimal Supersymmetric Standard Model (pMSSM)?

I am very new in SUSY and I heard something about pMSSM. Question is that how we can reduce the number of necessary parameter to 19 in pMSSM. If you have any suggestion as a brief introduction or any ...
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0answers
46 views

Why are there only two linearly independet quartic Higgs terms for the adjoint $24$ in $SU(5)$ GUTs?

I've read the statement in countless papers, for example, here Eq. 4.2 or here Eq. 2.1 without any further explanation or reference, that the "most general renormalizable Higgs potential" for an ...
3
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0answers
39 views

Why do we need any model beyond SM to fine-tune the Higgs mass?

ATLAS and CMS combined their results recently and it shows that higgs mass is ~125 GeV. Theoretical physicists try to figure out the "low mass" of the Higgs which causes hierarchy problem at high ...
2
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1answer
55 views

Evidence for standard model description of neutrons

as I don't know too much about experiments I have the following question concerning the evidence about the quark constituents in neutrons. After a quick google investigation I found some sentences ...
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22 views

How to compute remnant discrete charges?

When a $U(1)$ gauge symmetry is broken by Higgs field with $U(1)$ charge $g$, we have a remnant $\mathbb{Z}_q$ symmetry. How can I compute the corresponding charges under this remnant group for ...
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0answers
49 views

What does complexification mean for our particles in physics

As gauge group let's consider the popular $SO(10)$ group. The fundamental representation $\pi$ of the corresponding Lie algebra $\mathfrak{so}(10)$ is $10$ dimensional $$ \pi: \mathfrak{so}(10) ...
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1answer
104 views

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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0answers
49 views

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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45 views

Why is the tensor product $n \otimes n = 1$ for $SO(n)$ not the usual scalar product?

For concreteness let's consider $SO(4)$. The quantum numbers for the four states in the fundamental representations are (schematically) $$ (1, 1) ,(-1, 1) ,(1, -1) ,(-1, -1 )$$ thus $$ 4= ...
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0answers
72 views

What do people mean with a vev=diag( -2,-2,-2,-2,-2,-2,3,3,3,3)?

For example, in this paper on page 21 the authors write the vev that breaks $SO(10)$ to $SU(4)\times SU(2) \times SU(2)$ $$ <54>= 1/5 \cdot diag( -2,-2,-2,-2,-2,-2,3,3,3,3) \omega_s$$ where ...
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0answers
54 views

Explicit Matrix Representation for 54 Higgs rerpesentation for $SO(10)\rightarrow$ Pati-Salam Breaking

Which Higgs field or linear combination of Higgs fields gets a vev if we want to break $$ SO(10) \rightarrow SU(4) \times SU(2) \times SU(2) ? $$ Formulated a bit differently, I'm looking for an ...
2
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0answers
27 views

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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2answers
104 views

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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43 views

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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163 views

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 ...
2
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1answer
97 views

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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1answer
133 views

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 ...
2
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1answer
203 views

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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1answer
143 views

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 ...
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1answer
141 views

Why do decompositons like $16 \otimes 16 = 10 \oplus 120 \oplus 126$ tell us which Higgs representations we can use?

EDIT: I found an answer, which I do not understand: In Gürsey - Symmetry breaking patterns in E6 he writes: " Because of Fermi-Dirac statistics of fermions they must occur in the symmetric part of ...
3
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1answer
76 views

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 ...
2
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1answer
182 views

Why does the electromagnetic and weak coupling strength do not meet at the electroweak scale?

The running of the coupling strengths is usually visualized on a logarithmic scale like here What surprises me is that the weak and the electromagnetic coupling strength do not meet before the GUT ...
3
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291 views

Effective field theories and gauge anomalies cancellation

Lets assume some theory which concludes sets of generations of fermions (lets call them $A$ and $B$). Fermions $A$ have some gauge group $G_{A}$ (for example, SM), while fermions $B$ are charged under ...
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66 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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1answer
231 views

Scale invariance in QFT?

About scale invariance in "beyond the standard model". At the base of the analysis is the principle of scale invariance. So what is being said: what if there were another sector of the theory that ...
17
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1answer
528 views

Why do we need complex representations in Grand Unified Theories?

EDIT4: I think I was now able to track down where this dogma originally came from. Howard Georgi wrote in TOWARDS A GRAND UNIFIED THEORY OF FLAVOR There is a deeper reason to require ...
5
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1answer
113 views

Where would the dark matter particle fit inside a picture of the standard model of particle physics?

Where would the dark matter particle fit inside a picture of the standard model of particle physics? While I am particularly fond of the Sterile Neutrino, I have not been able to find any example of ...
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159 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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27 views

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 ...
5
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1answer
63 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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29 views

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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28 views

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 ...