# I Implications of no proton decay, simplest GUT ruled out

1. Dec 15, 2016

### kodama

Search for Proton Decay via p→e+π0 and p→μ+π0 in 0.31 megaton⋅years exposure of the Super-Kamiokande Water Cherenkov Detector
M. Miura (The Super-Kamiokande Collaboration)
(Submitted on 12 Oct 2016)
We have searched for proton decay via p→e+π0 and p→μ+π0 using Super-Kamiokande data from April 1996 to March 2015, 0.306 megaton⋅years exposure in total. The atmospheric neutrino background rate in Super-Kamiokande IV is reduced to almost half that of phase I-III by tagging neutrons associated with neutrino interactions. The reach of the proton lifetime is further enhanced by introducing new signal criteria that select the decay of a proton in a hydrogen atom. No candidates were seen in the p→e+π0 search. Two candidates that passed all of the selection criteria for p→μ+π0 have been observed, but these are consistent with the expected number of background events of 0.87. Lower limits on the proton lifetime are set at τ/B(p→e+π0)>1.6×1034 years and τ/B(p→μ+π0)>7.7×1033 years at 90% confidence level.
Subjects: High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:1610.03597 [hep-ex]

experiments put proton lifetime past 1.6 10^34 years, which rules out the simplest GUT's SU(5) and SO(10) GUT

what are the implications to unification, including string unification, that the simplest models have been now ruled out?

larger and more complicated GUT seem to imply more particles and forces and seems less parsimonious than just plain SM with no GUT

What are the implications of an idea there is no GUT, only SM but no GUT or GUT-scale, which the results seem to imply?

2. Dec 16, 2016

### MrRobotoToo

The famous paper by Shaposhnikov and Wetterich where they use asymptotic safety to predict that the Higgs boson should have a mass of 126 GeV to within a few GeV uncertainty looms large in my mind. They assumed that there’s a desert separating the electroweak and Planck scales, i.e. no grand unification and no low-energy supersymmetry. There’s also a series of papers by Roberto Percacci and his collaborators where they investigate the effect of matter fields on the asymptotic safety of gravity. The gist of their work is that too many matter fields fouls up asymptotic safety, and go on to show that most grand unified and supersymmetric models are ruled out by this criterion. So this null result further bolsters these speculations of a desert.

3. Dec 16, 2016

### kodama

is this the paper you are alluding to?

Consistency of matter models with asymptotically safe quantum gravity
P. Donà, Astrid Eichhorn, Roberto Percacci
(Submitted on 16 Oct 2014)
We discuss the compatibility of quantum gravity with dynamical matter degrees of freedom. Specifically, we present bounds we obtained in [1] on the allowed number and type of matter fields within asymptotically safe quantum gravity. As a novel result, we show bounds on the allowed number of spin-3/2 (Rarita-Schwinger) fields, e.g., the gravitino. These bounds, obtained within truncated Renormalization Group flows, indicate the compatibility of asymptotic safety with the matter fields of the standard model. Further, they suggest that extensions of the matter content of the standard model are severely restricted in asymptotic safety. This means that searches for new particles at colliders could provide experimental tests for this particular approach to quantum gravity.
Comments: prepared for the proceedings of Theory Canada 9; new results on the gravitino, 8 pages, 1 figure, 1 table
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Cite as: arXiv:1410.4411 [gr-qc]

it also seems both non-detection of dark matter and electron and neutron EDM seems to support this.
does this imply dark matter should be light weight? i.e keV or ueV

Last edited: Dec 16, 2016
4. Dec 16, 2016

### MrRobotoToo

Yes, I believe that’s their most recent paper on the subject. If Percacci et al. are correct, then even Planck-scale supersymmetry is ruled out. But as you may have noticed from Table I of their paper, it’s still possible to add sterile neutrinos and perhaps a scalar or two. There are several $\nu MSM$ models that predict the lightest sterile neutrino will have a mass in the keV region, so that’s what I’m keeping an eye out for.

Overall, the vista looks rather bleak: nothing new at the LHC; no evidence for WIMPs from astrophysical observations; and now this result about the proton’s lifetime.

5. Dec 16, 2016

### kodama

they do seem bleak, perhaps the most minimal extensions of the SM that address baryogenesis, neutrino masses, dark matter, inflation is what nature has selected out of all possible extensions of the SM.
any idea when LHC will report the 2016 run?

how robust are results from electron and neutron EDM? thus far no EDM has been observed.

6. Dec 17, 2016

### MrRobotoToo

Don’t know about the LHC results: I’m guessing that if they’re not released before Christmas we’ll have to wait until the winter conferences. With regard to the electron and neutron EDMs, the electron one seems to be the most damning, considering that the supersymmetry predictions are literally orders of magnitude larger than the measured upper bound.

I personally think that $\nu MSM$ coupled to asymptotically safe gravity is the best bet right now as to what is going to replace the Standard Model. As you mentioned, it takes down several problems with a single punch, so to speak. The new result regarding the proton got me thinking about how the problem of electric charge quantization (i.e., why the charge of the electron is exactly three times larger than the charge of the down quark) might be addressed in the absence of grand unification. One of the selling points of $SU(5)$, for example, was that it naturally accounted for this odd relationship. I looked around the interwebs, and discovered a little gem. If it’s really true that all there is is the Standard Model (or some minimal extension of it) and gravity, then when calculating something like the gauge anomaly one has to include the contributions from gravity. The requirement of anomaly cancellation sufficiently constrains the quantum numbers such that electric charge is quantized! The calculation is carried out in Section 5 of this paper. This result holds even if there's sterile neutrinos, provided they're Majorana.

7. Dec 17, 2016

### kodama

I personally think that νMSM coupled to asymptotically safe gravity

i infer you are alluding to this paper

The νMSM, Inflation, and Dark Matter
Mikhail Shaposhnikov, Igor Tkachev
(Submitted on 27 Apr 2006 (v1), last revised 3 Aug 2006 (this version, v2))
We show how to enlarge the νMSM (the minimal extension of the standard model by three right-handed neutrinos) to incorporate inflation and provide a common source for electroweak symmetry breaking and for right-handed neutrino masses. In addition to inflation, the resulting theory can explain simultaneously dark matter and the baryon asymmetry of the Universe; it is consistent with experiments on neutrino oscillations and with all astrophysical and cosmological constraints on sterile neutrino as a dark matter candidate. The mass of inflaton can be much smaller than the electroweak scale.
Comments: 9 pages, misprints corrected, final version appeared in Phys. Lett
Subjects: High Energy Physics - Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th)
Journal reference: Phys.Lett.B639:414-417,2006
DOI: https://arxiv.org/ct?url=http%3A%2F%2Fdx.doi.org%2F10%252E1016%2Fj%252Ephysletb%252E2006%252E06%252E063&v=62eaf2e0 [Broken]
Report number: CERN-PH-TH/2006-069
Cite as: arXiv:hep-ph/0604236

νMSM coupled to asymptotically safe gravity in 4d sounds much simpler than string theory

and vMSM and asymptotically safe gravity be embedded or made compatible with string theory or lqg?

Last edited by a moderator: May 8, 2017
8. Dec 18, 2016

### MrRobotoToo

Part of the motivation behind the asymptotic safety scenario is to render ideas like string theory superfluous. After all, if there exists a quantum field theory of gravity that is well behaved in the non-perturbative regime, then what’s the point of string theory? There may also be a tension between AS and LQG. The analyses that have been carried out about the structure of spacetime at sub-Planckian length scales indicate that it has a fractal character, i.e. no evidence of discreteness.

https://arxiv.org/abs/hep-th/0508202
https://arxiv.org/abs/1202.2274
https://arxiv.org/abs/1205.5431

9. Dec 18, 2016

### kodama

How does AS address QG issues like black hole information loss to holography

i did find these 2 papers

Fractal Structure of Loop Quantum Gravity
Leonardo Modesto
(Submitted on 11 Dec 2008)
In this paper we have calculated the spectral dimension of loop quantum gravity (LQG) using simple arguments coming from the area spectrum at different length scales. We have obtained that the spectral dimension of the spatial section runs from 2 to 3, across a 1.5 phase, when the energy of a probe scalar field decrees from high to low energy. We have calculated the spectral dimension of the space-time also using results from spin-foam models, obtaining a 2-dimensional effective manifold at hight energy. Our result is consistent with other two approach to non perturbative quantum gravity: causal dynamical triangulation and asymptotic safety quantum gravity.
Subjects: General Relativity and Quantum Cosmology (gr-qc)
Journal reference: Class.Quant.Grav.26:242002,2009
DOI: 10.1088/0264-9381/26/24/242002
Cite as: arXiv:0812.2214 [gr-qc]

Fractal Quantum Space-Time
Leonardo Modesto
(Submitted on 11 May 2009)
In this paper we calculated the spectral dimension of loop quantum gravity (LQG) using the scaling property of the area operator spectrum on spin-network states and using the scaling property of the volume and length operators on Gaussian states. We obtained that the spectral dimension of the spatial section runs from 1.5 to 3, and under particular assumptions from 2 to 3 across a 1.5 phase when the energy of a probe scalar field decreases from high to low energy in a fictitious time T. We calculated also the spectral dimension of space-time using the scaling of the area spectrum operator calculated on spin-foam models. The main result is that the effective dimension is 2 at the Planck scale and 4 at low energy. This result is consistent with two other approaches to non perturbative quantum gravity: "causal dynamical triangulation" and "asymptotically safe quantum gravity". We studied the scaling properties of all the possible curvature invariants and we have shown that the singularity problem seems to be solved in the covariant formulation of quantum gravity in terms of spin-foam models. For a particular form of the scaling (or for a particular area operator spectrum) all the curvature invariants are regular also in the Trans-Planckian regime.
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Cite as: arXiv:0905.1665 [gr-qc]

10. Dec 19, 2016

### MrRobotoToo

That’s very interesting and rather encouraging. I suppose the main difference is that in the asymptotic safety scenario this fractal structure continues at arbitrarily short length scales, whereas in LQG the Planck scale is a ‘hard bottom’.

11. Dec 19, 2016

### kodama

what would happen if you attempt to express loop gravity as a quantum field theory and take a
Renormalization group flow?

12. Dec 20, 2016

### MrRobotoToo

If any prospective PhD candidates are reading this thread, you've just gave them a great idea for a research topic.

13. Dec 20, 2016

### kodama

i was thinking, doesn't LQG imply a nontrivial UV fixed point? if LQG could be expressed as a QFT, how would it differ from As gravity?

14. Dec 20, 2016

### MrRobotoToo

LQG purports to be a quantization of the ordinary Einstein-Hilbert field theory of gravity. A renormalization group flow analysis of that particular truncation of gravity’s effective action has already been performed by several people, and it does reveal an ultraviolet fixed point. If the asymptotic safety scenario is correct about spacetime having a fractal structure at sub-Planckian scales, then it means that observables like volume and surface area can only be well defined over some coarse-graining of space. Perhaps LQG’s results of quantized volume and surface area are merely pointing at the finest coarse-graining over which these observables can be defined, and not some ‘hard bottom’ to space as is usually supposed.

15. Dec 20, 2016

### kodama

To what extent can LQG reproduce AS physics, including its success, over a wide range of values up to the planck scale, including prediction higgs mass and possible hiearchy problem. or vice versa, since LQG (supposedly) predicts black hole entropy and hawking radiation, among others, can AS also reproduce these? i.e can LQG and AS be merged?

incidentally in the news feed physics similar to MOND with the intention of doing away dark matter all over the news is this paper and results

First test of Verlinde's theory of Emergent Gravity using Weak Gravitational Lensing measurements
Margot M. Brouwer, Manus R. Visser, Andrej Dvornik, Henk Hoekstra, Konrad Kuijken, Edwin A. Valentijn, Maciej Bilicki, Chris Blake, Sarah Brough, Hugo Buddelmeijer, Thomas Erben, Catherine Heymans, Hendrik Hildebrandt, Benne W. Holwerda, Andrew M. Hopkins, Dominik Klaes, Jochen Liske, Jon Loveday, John McFarland, Reiko Nakajima, Cristóbal Sifón, Edward N. Taylor
(Submitted on 9 Dec 2016 (v1), last revised 19 Dec 2016 (this version, v2))
Verlinde (2016) proposed that the observed excess gravity in galaxies and clusters is the consequence of Emergent Gravity (EG). In this theory the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low redshift galaxies by assuming a background LambdaCDM cosmology. We measure the (apparent) average surface mass density profiles of 33,613 isolated central galaxies, and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end we employ the ~180 square degrees overlap of the Kilo-Degree Survey (KiDS) with the spectroscopic Galaxy And Mass Assembly (GAMA) survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.
Comments: 14 pages, 3 figures. Accepted for publication in MNRAS. Added references for section 1 and 6
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
DOI: 10.1093/mnras/stw3192
Cite as: arXiv:1612.03034 [astro-ph.CO]
(or arXiv:1612.03034v2 [astro-ph.CO] for this version)

16. Dec 22, 2016

### MrRobotoToo

Keep in mind that asymptotic safety by itself doesn’t provide a quantized field theory gravity, but only indicates that such a theory exists, and puts constraints on the running of its couplings. Those constraints are what allowed Shaposhnikov and Wetterich to correctly predict the mass of the Higgs. LQG is one possible quantization of general relativity, and its results on black hole entropy are encouraging. So AS and LQG may complement each other, each making predictions that can’t be extracted from the other. If there does exist a well-behaved quantum field theory of gravity, then it’s important to verify that different quantization procedures be consonant with each other. So one possible line of research is to compare the results of LQG to, for example, those of causal dynamical triangulations.

BTW, in their recent paper on the gauge hierarchy problem, Wetterich and Yamada promise more results to come: “Forthcoming quantum gravity computations will reveal if the required positive value of $A_{\gamma }^{UV}$ is indeed realized.”
Meh, I tend to be skeptical of Verlinde’s ideas. Interferometry experiments on cold, freely falling neutrons indicate that gravity isn’t entropic:

https://arxiv.org/abs/1009.5414
https://arxiv.org/abs/1108.4161

17. Dec 22, 2016

### the_pulp

Sorry I can´t follow that! (most probably because of my ignorance). What I understand is that if I have a Lagrangian with some couplings and we find that they are AS, then that theory is well defined. The only problem is that we cannot calculate the Amplitudes using Perturbation methods. As a consequence, if we find that Standard Model + General Relativity Lagrangian is AS, then that Lagrangian is a quantized field theory that allows the computation of amplitudes taking into account Gravity interactions.

What am I loosing?

18. Dec 22, 2016

### MrRobotoToo

Yes, you’re basically correct. But you’d still have to take that Lagrangian and stick it into the path integral in order to calculate probability amplitudes. Since the couplings for gravity will presumably be large in the ultraviolet regime, one can’t resort to perturbation theory, so one has to calculate the path integral directly with the help of computers, as is done in lattice QCD. That’s the basic idea behind approaches like causal dynamical triangulations.

19. Dec 22, 2016

### the_pulp

So why are you saying that it would not be a quantized theory of gravity? or perhaps you meant that it would not be a perturbative quantum field theory, am I right?

I am no chalenging, I'm just checking if I understand correctly...

Thanks!!

20. Dec 22, 2016

### MrRobotoToo

Just that the RG techniques of asymptotic safety don't help one actually calculate the path integral.