1. Dec 20, 2017

star apple

You were assuming fresh and blood fairies and goblins in other "multiverse"? Even in physics.. we need to use the right definition to avoid confusion.. in our universe.. "fairies" and "goblins" are words to reserve creatures that are anything but flesh and blood. In my country, we mostly have so much reports of bad goblins possessing school children. This occurs elsewhere in other parts of the world too:

https://www.dailystar.co.uk/news/la...ession-priest-goblin-woman-scream-philippines

All right. You may think they are all simply deluded as this is what our physics can give us at this point in time. But note of this. Even if they are delusions, "fairies" and "goblins' were not flesh and blood in our universe. So we mustn't use the terms to refer to them as scientists in other multiverses.

This is just to illustrate semantics is important when comparisons are made or this or other multiverses (therefore this post is to clarify semantics and i'm not violating any forum rule).

Speaking of multiverses. What are good books related to string landscapes and multiverses, are they same? how do they differ?

To be scientific. Let's avoid talking about the fairies and golbins and narrow it down to multiverses and high scale supersymmetry. If there were high scale supersymmetry.. does it mean supersymmetry is still not dead?

2. Jan 1, 2018

gdixon

Every failure to find evidence is viewed optimistically,
giving rise to a clamor for more funding and higher
energies. It was never a beautiful idea; not even pretty.
Like GUTs, it arose out of nothing more fundamental
than a desire to extend an idea (standard symmetry
gauge groups) that was at the time novel, and giving
rise to multiple Nobel prizes. As a graduate student
I was pushed very hard to commit to SUSY. I saw
absolutely nothing elegant or beautiful in the idea,
so in the end disappointed my mentors by looking
elsewhere for Dirac’s mathematical beauty.

Want to assess its value accurately? Take a vote, but
take each yes vote and divide by some measure of how
much that person’s funding and reputation will be hurt
if it fails (and how many fruitless years (nay, decades)
they’ve committed to the idea).

3. Jan 23, 2018

Quotidian

I am not well educated in physics, but read articles about it in the popular press, New Scientist and the like. It seems that there has been no confirmation of the so-called SUSY model by the LHC since the announcement of the discovery of the Higgs Boson (although I note above that some say it's still 'out there' but we don't have/will never have enough power to detect it).

But at least some are saying that the model should be abandoned. So the question I have is this. SUSY was originally devised to solve a whole set of issues in fundamental physics, and apparently did so in a mathematically elegant manner. But if SUSY is regarded as being disconfirmed, then the issues that SUSY was supposed to be the solution for, remain as outstanding problems. What kinds of problems are they?

4. Jan 24, 2018

Urs Schreiber

Yes, supergravity KK-models predict axions (the "B-field") generically. While standard cold WIMP dark matter models work excellently on cosmological scales, they have severe problems on galactic scales (whence "MOND"). But ultralight axions are getting much attention these days (under various names, such as BEC/superfluid/fuzzy dark matter ) since they would naturally explain a phase shift of behaviour that dark matter (if any) needs to exhibit at around the scale of galaxies.

See Hui-Tremaine-Ostriker-Witten 16 between equations (3) and (5).

5. Feb 15, 2018

Martin0001

Nothing new up to 10^16 GeV, maybe up to 10^19 GeV. So new physics might be there but under event horizons.
OK, we are not building any particle accelelators size of Solar System (to get 10^16 GeV) or hundreds of light years across to get 10^19 GeV anytime soon.
Boys, time to pack your toys and go home on dinner. Mama is calling. Nothing to see here.

6. Feb 15, 2018

bluecap

In 1 Billion A.D. Can we already reach 10^16 GeV or say 3 Billion A.D.? How many billions of years later before we can probe the planck scale?

Anyway. A hundred years from now.. when building more accelerators would no longer be viable due to financial, environment, political or military catastrophe. Can we at least do one last experiment never before tried (at least officially)...

There may be a Particle Desert where nothing occurs below 10^16 GeV and above those already explored. So let the last final experiment be about testing non-thermal based symmetry breaking. Perhaps all those missing particles would suddenly popping up. In many unofficial experiments now. They detected exotic particles even monopoles by initiating non-thermal phase transition but no other scientists want to even try duplicating any of it. So before we dismantle the last particle accelerator on earth and before the last particle physicists get into other fields like banking or telecommunications industry.. can we at least try this one last experiment? Perhaps we would see results the world has never seen before..

7. Feb 16, 2018

Urs Schreiber

Interesting to read Gordon Kane, who keeps going all in with yesterday's

Exciting implications of LHC Higgs Boson Data
(arXiv:1802.05199)

The content is not entirely new, in itself it seems to be a (somewhat hasty) writeup of a talk given already in January 2017 on occasion of Kane receiving the Sakurai prize 2017 "For instrumental contributions to the theory of the properties, reactions, and signatures of the Higgs boson."

The prize announcement knows that "Dr. Kane made important early contributions to the study of the Higgs Bosons, including an upper limit on the Higgs boson mass..." (this refers to his bold claim of a Higgs mass prediction via the $G_2$-MSSM in Kane 11, a useful informed comment is here), "...to the study of dark matter and its detection and to string theory phenomenology. His more recent work has been in the development of testable models based on string theory, in particular those based on $G_2$ compactifications of M-theory, a predictive approach that explains the hierarchy between the weak scale and the Planck scale. Dr. Kane has argued that these ideas form a consistent framework with a non-thermal cosmological history of the universe."

The article discusses four "clues" obtained from the LHC data and argued to be clues for the presence of low-scale supersymmetry. The third clue claims that some model of low scale susy is still consistent with observation, the first clue recalls that the observed Higgs mass is close to the upper limit constrained by low-scale susy, while the fourth clue claims that the observed Higgs potential is inconsistent without low-scale susy, which would cure the apparent vacuum instability.

I suppose that whether or not low-scale susy is the answer, there is a point to be made, re the fourth clue, that the apparent vacuum instability of the experimentally observed Higgs potential is in contrast to the often heard claim that "nothing new or interesting" for HEP has come out of the observation of the Higgs at LHC.

8. Feb 16, 2018

bluecap

Very hopeful and encouraging.
Just a question Urs. Is there no existing work or papers about non-thermal symmetry breaking or phase transition whether in the quantum fields, quantum vacuum, spacetime or other stuff? If there is. What is the technical words used for non-thermal symmetry breaking. To illustrate the point. For the electroweak. We need very high temperature to put the symmetry back into place just like what we are doing at particle accelerating by colliding particles and reproducing the high temperature. Is there any concept where you can put the symmetry back into place for other particles by non-thermal means? If none. Why is it not possible?

9. Feb 16, 2018

Urs Schreiber

By the way, the text has a bit of overlap with that of his book
where it corresponds to sections 5.1 and 6.4.

Hm, it seems to me that the bulk of the literature is about supersymmetry breaking in non-thermal contexts. A few authors discuss thermal supersymmetry breaking, for brief exposition see for instance
• Claudio Lucchesi,
"Symmetries at finite temperature"
in F. Gieres et. al (eds.)
"Symmetries in physics"
Edition Frontieres (1997)
There is maybe some care advised regarding the difference between invoking high tempterature to argue that a system has high energy and having a genuinely thermal description, usually referred to as "QFT at finite temperature". The latter requires more work and is considered by fewer authors.

10. Feb 17, 2018

bluecap

I was asking whether you can have a new gauge-like field or fundamental force (not electroweak or strong) that has similar symmetry breaking as SUSY breaking not dependent on spontaneous symmetry breaking (or Big Bang scale gauge fields) but could be for instance gravity or anomaly mediated (as applied to SUSY symmtry breaking see https://arxiv.org/pdf/hep-th/0601076.pdf) ... or in other words, are soft gauge-like forces possible also by some SUSY-like vacua dynamics?

I'm aware of the difference between gauge and susy symmetry breaking from http://people.sissa.it/~bertmat/lect7.pdf

Can you design a fundamental force of nature that has same symmetry breaking mechanism as proposed for SUSY and can initiate symmetry breaking far below the weak scale or even low energy?

11. Feb 17, 2018

Urs Schreiber

The fact that positive vacuum energy reflects spontaneous supersymmetry breaking is a direct consequence of the fact that local supersymmetry is an extension of local Poincaré symmetry, hence of gravity. Technically, this is because the stress-energy tensor $(T_{\mu \nu})$ in supersymmetric field theories is the image of the supersymmetry Noether's conserved current $(S_{\nu \beta})$ under the super-Poisson-bracket with the supercharge $(Q_\alpha)$

$$T_{\mu \nu} \;=\; \gamma_\mu^{\alpha \beta} \{Q_\alpha, S_{\nu,\beta}\}$$

so that the vacuum expectation value of the stress-energy tensor is

$$\langle vac \vert T_{\mu \nu} \vert vac \rangle = \gamma_\mu^{\alpha \beta} \langle vac \vert \{Q_\alpha, S_{\nu,\beta}\} \vert vac \rangle$$

which hence vanishes if the vacuum state is supersymmetric, hence if supersymmetry is not spontaneously broken.

So the specific nature of spontaneous supersymmetry-breaking is a reflection of the special fact that (local) supersymmetry is an odd-graded extension of (local) Poincaré-symmetry, hence of gravity. Symmetries not related to gravity in such a way cannot show this effect.

I recommend going to the original articles, such as Witten 81, section 2. The graphics that you reproduce above originates in Fayet-Ferrara 77, Fig. 1 on p. 286 (38 of 86).

12. Feb 17, 2018

bluecap

What range of energy in TeV do you think the Superpartners can be lurking?

Also is there a possibility or mechanism (complex as it may be) for the supersymmetry be between normal matter and mirror matter (these being direct counterpart of all our baryonic particles but only right handed and form perhaps 5% of the dark matter sector? See a thesis about cosmology and mirror universe... https://arxiv.org/abs/astro-ph/0312607

Perhaps each is in different vacuum or spacetime boundary or the thousands of mechanisms or possibilities or variants of models physicists can easily write such as for example in ArXiv?

13. Feb 18, 2018

Urs Schreiber

This I am really not the right one to ask or answer.

I do take interest supergravity, on the grounds that it has excellent theoretical motivation, and I appreciate the curious fact that KK-compactifications to 4d that preserve global $N=1$ supersymmetry happen to be those that are mathematically rich (CY-geometry, $G_2$-geometry), whatever that may be telling us; but I notice that there seems to be no theoretical reason why these compactifications should be dynamically preferred, and that the folklore of their phenomenological motivations (hierarchy problem, gauge coupling unification, naturalness) is based on an essentially numerological attitude only.

This makes me want to recall that:

"The alternative to naturalness, often neglected as an alternative, is having a theory."

which is a great sentence that one finds in Kane 17, p. 56 (6-10).

Now Kane of course does assume $G_2$-compactification, which, while certainly interesting in itself, seems to be lacking a dynamical explanation from within the theory; but that granted then the great achievement of him and his collaborators is that, based on this single assumption, they first of all try to and then to a remarkable extent succeed with working out the theoretical consequences systematically, by analysis of the theory. Even if the result eventually disagrees with experiment, we will have learned what the generic predictions of this model are, hence will have learned something tangible about 11d supergravity and its UV completion, while from much of the unsystematic by-hand susy model building entertained elsewhere we will possibly have to conclude in 50 years time to have learned little, besides the lesson that physics unconstrained by theoretical framework becomes arbitrary.

One of the theoretical insights that Kane and collaborators have been amplifying is that in this model the gravitino mass after susy-breaking sets the scale for the moduli and the superpartners, such that, in the words of Kane 17, p. 43 (5-1), the upshot is this:

"When supersymmetry is broken the gravitino becomes massive — the splitting between the graviton (always massless) and the gravitino is a measure of the strength of the supersymmetry breaking, and it sets the scale for all the superpartner masses.

"It is important to understand that there are two measures relevant to understanding supersymmetry breaking, one the scale at which it is broken (about $10^{14}$ GeV as described above), and the other the resulting gravitino mass. In the compactified M-theory case the gravitino mass is calculated, and comes out to be about 40 TeV (40 000 GeV). Sometimes even experts confuse these two scales if they are speculating about supersymmetry breaking without a real theory to calculate.

"Thus 40 TeV is the natural scale for superpartner masses. That is not a surprising number in a theory starting with everything at the Planck scale, but it is surprising if one expects the superpartner masses to be near the particle masses (all well below 1 TeV). The squarks and other masses are indeed predicted to be at the gravitino scale, tens of tera-electronvolts."

"The theory has formulas (‘supergravity formulas’) for all the masses. When one calculates carefully the masses of the superpartners of the gauge bosons that mediate the Standard Model forces they turn out to get no contribution from one large source, and the resulting value for the superpartners of the gauge bosons (gauginos) is about 1 TeV, rather than about 40 TeV. They are the gluino, photino, zino, and wino. The strong force gluino is heavier, about 1.5 TeV or somewhat more, and the electroweak ones (photino, zino, wino) are somewhat lighter, about half a tera-electronvolt. The lightest superpartner, which is important for how to detect the signals at the LHC and for understanding dark `matter, will be a combination of the electroweak ones, and thus about half a tera-electronvolt in mass. All of these are observable at the LHC in the run underway through 2018. That run is supposed to collect an amount of data measured in units called inverse femtobarns ($fb^{-1}$). At the time of writing (December 2016) it has collected about $40 fb^{-1}$, and is into the region where we can hope for signals of gauginos. The goal for the LHC is to collect $300 fb^{-1}$ through 2018. Without a detailed theory to calculate with, we would not have had serious predictions for masses."

(from Kane 17, chapter 5).

14. Feb 18, 2018

ISamson

My father used to study and research Supersymmetry.
We were talking, and he was saying that the field is dying out. Now, he studies dark matter and energy with another professor.
Just what he told me.

15. Feb 18, 2018

Urs Schreiber

Sure, that's a truism after the LHC results did rule out most of what people in the field had claimed would be seen.

On the other hand, just as an idea being fashionable does not make it true, so an idea being unfashionable alone does not make it false. The truth is more subtle than the common sport-event-like attitude towards it may indicate.

16. Feb 18, 2018

Martin0001

I don't know what we could reach within 1 billion od years. First we should concentrate on surviving here on Earth for next thousand of years because our current actions may well result in an extinction much earlier than that.
Personally I believe that Planck accelerator could be built by Kardashev 3 civillization, eg one which could summon to intelligent use most of energy of entire galaxy.
IMO such civillizations dont exist and probably cannot exist.
Testing Planck energy interactions faces 2 major hurdles. First one and already an enormous challenge to accelerate particles to said energy is dwarfed by really unsurmonable problem of adequate *luminosity* of said accelerator.
Just think about hopelessly small effective crossections for collisions at Planck energy. After all you are probing distances in range of 10^-35cm. It have been calculated that one attempting to collect data from 10 such collisions (to get statistically significant results) would need to accelerate *lunar mass* of leptons or 0.01-0.1 of solar mass of hadrons to said energy, all in a reasonable time. That assuming that he could keep a beam 1um (!) wide.
So it is rather out of question. The best chance for such a device to be built is perhaps as a result of some sort of military arms race between 2 advanced Kardashev 3 civilizations. One could evaporate a planet by pressing a button over million of light years distance. Supermassive BH would be a power source, constellations of orbiting it neutron stars would be deflecting and beaming magnets/masses etc.
Mind you, the risk of causing quantum vacuum phase transition (and destruction of entire Universe within Hubble radius) would be substantial during such experiments, so a large degree of recklessness is a prerequisite for those attempting it. So reckless civillization would probably finish itself off long before getting there.

Practically I suspect that we might build 1 or 2 more generations of accelerators to get into 0.1 - 1 PeV of hadron energy (or 10-50 TeV for leptons). This will allow to investigate possibility of proton decay by electroweak process mediated by *sphalerons*. If no new physics, eg no new fundamental particles, are found meantime that is it.
Great desert will be considered proven and Standard Model with all its shortcommings will reign for good.

I cannot comment on "unconventional research". There is a slim chance that something worth attention is out there but it will rather go the same way like cold fusion research did. Mind you, conventional physics with string theories, multiverses and inflation is more and more religious like activity and insistence to work on it is a sign of decay of intellect. It is more and more unscientific. Peoples are insisting on beating a dead horse because they simply cannot admit that decades of their work are simply good for nothing. Peter Voit of Columbia University has something to say about it. Read his blog "not even wrong".

Bright part of the picture is that a lot is still to be discovered in *low energy* physics. Who knows, maybe at picokelvins (10^-12K) and below matter starts to behave in such a way that we are not suspecting it even in our wildest dreams. These conditions most unlikely exist *anywhere* in Universe (and never did) if not produced by intelligent beings.
Gravitational wave astronomy is another very promissing avenue.
So even if high energy physics hit its end, there is still a lot to learn.

Last edited: Feb 18, 2018
17. Feb 18, 2018

bluecap

There seems to be 2 main focuses of supersymmetry. In Supergravity and the MSSM (Minimal Supersymmetric Standard Model) where wiki stated that:

"Theoretical motivations
There are three principal motivations for the MSSM over other theoretical extensions of the Standard Model, namely:

Naturalness
Gauge coupling unification
Dark Matter
These motivations come out without much effort and they are the primary reasons why the MSSM is the leading candidate for a new theory to be discovered at collider experiments such as the Tevatron or the LHC."

This seems to differ to Supergravity that also uses Supersymmetry.

1. If the Hierarchy Problem was solved by scale symmetry (see https://www.wired.com/2014/08/multiverse/ ) and dark matter was not caused by the lightest superpartner and the gauge coupling unification meeting at one point is due to hidden forces of nature. Then there is no need for MSSM to be at low energy (slightly above Higgs mass) meaning the Supergravity Supersymmetry could be at say 100 TeV. Is this what you meant?

2. Also if there is no weak scale MSSM and Supersymmetry only occurs above 100 TeV. Can this explain the gauge coupling unification meeting at one point?

3. Lastly. Can any hidden forces of nature mimic the same gauge coupling unification graph meeting at one point? What should be the behavior of the hidden forces of nature?

18. Feb 18, 2018

bluecap

What if axion or any dark matter particle would be undetectable too. Would dark matter die out too like supersymmetry? dark matter is required for cosmos wide gravity dynamics.. but is it not supergravity's Poincare invariance and supersymmetry being local symmetry is also required to exist to make gravity more solvable? or not? I'm interested in this because it seems besides spacetime and quantum fields.. we may need another third theory to combine them.. here supergravity may not even exist.

19. Feb 18, 2018

bluecap

We are still missing something big even at our everyday baryonic energy scale. I'm so curious how physicists could miss them that's why i'm interested in all these questions. Could it be because our particle physics treat particles at isolation and the ensembles would have different behavior. For example we may not detect dark matter using isolated particles but ensembles there may be an effect. Do you know the term for this ensemble approach in physics? Emergence?

20. Feb 19, 2018

Urs Schreiber

I had been commenting on this briefly in #38. Naturalness is mostly numerology. Interesting to read Kane 17, about naturalness:

"now the claims are based on calculations in actual theories, while in the past they were based on analogies or ‘naturalness’ arguments" (p. 14 (xii))

"Until recently there were no theories predicting the values of superpartner masses. The arguments based on ‘naturalness’ are basically like saying the weather tomorrow should be the same as today. The opposite of naturalness is having a theory. [...] Claims they [superpartners] should have been seen would be valid given so called naturalness arguments, but are wrong in actual theories. Many of us think that is a misuse of the idea of naturalness, but it is the fashionable use. " (p. 33 (3-2))

"Some arguments (‘naturalness’) can be used to estimate what values they [MSSM parameters] might have. If those arguments were correct some superpartners would already have been discovered at the CERN LHC. It would have been nice if the naturalness arguments had worked, but they did not. Since they were not predictions from a theory it is not clear how to interpret that." (p. 39 (4-3))

"The failure of naïve naturalness to describe the world tells us we should look harder for a theory that does, an ‘ultraviolet completion’. Compactified string/ M-theories appear to be strong candidates for such a theory. The alternative to naturalness, often neglected as an alternative, is having a theory." (p. 57 (6-1-))

Also the lightest superpartner (LSP) as a WIMP dark matter candidate is a model facing drastic constraints from experiment.

If one does actual computations in a theory of supergravity one finds instead (Kane 17, p. 53 (6-7)):

"The dark matter is not the lightest superpartner, but axions or candidates from hidden sectors are strong dark matter candidates."

The supersymmetry of supergravity is local supersymmetry, it need not manifest itself as global symmetry at all. This is just the graded-version of the statement that gravity itself is a theory of local Poincaré-symmetry, and there is no reason to expect to see global Poincaré symmetry. In fact we don't observe global Poincaré symmetry in the universe; one has to work hard to produce, in the laboratory, tiny patches that are approximately globally Poincaré invariant (a vacuum).

Last edited: Feb 20, 2018
21. Feb 19, 2018

haushofer

You can always pull the "not detected YET"-card, of course. Your second question is vague. I don't understand what you mean by "solvable" and how it relates to your former question.

22. Feb 19, 2018

bluecap

I meant in the context of Woit's passage in "Not Even Wrong"'s "This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics." from the paragraph:

"Another reason for being interested in supersymmetry was the hope that it might help with the problem of constructing a quantum field theory for gravity. One of the main principles of general relativity is what is called 'general coordinate invariance', which means that the theory doesn't depend on how one changes the coordinates one uses to label points in space and time. In some sense, general coordinate invariance is a local gauge symmetry corresponding to the global symmetry of space and time translations. One hope for supersymmetry was that one could some make a local symmetry out of it. This would be a gauge theory and might give a new version of general relativity, hopefully one whose quantum field theory would be less problematics."

23. Feb 19, 2018

bluecap

This make sense. Ok. I'll get Gordon Kane book "String Theory and the Real World" https://www.amazon.com/String-Theor...8-1&keywords=string+theory+and+the+real+world

So in short, you agree all particles are superstring/solitonic excitations of the geometry of the space-time continuum? This makes sense too.. and if you consider E8xE8 where the second set is a shadow universe... then it make even more sense as it explains more of the world.. so I guess M-Theory would be a theory about the degrees of freedom to engineer and influence the space-time continuum like composing the music of superstrings such that you can create and uncreate reality as one sees fit. Then this makes perfect sense and the elusive Holy Grail Theory of Everything.

Last edited: Feb 19, 2018
24. Feb 19, 2018

Urs Schreiber

This quote is a weird way to put it. First, supersymmetry is by definition a (graded) extension of spacetime Poincaré symmetry, and second gravity, and hence, supergravity, are induced by this, without need to appeal to any "hopes", by the usual first-order formulation of gravity.

25. Feb 19, 2018

Urs Schreiber

There are various models, inside various theories. By working out the predictions that these models make, we learn which are compatible with observation. I was pointing to Kane's book because it gives an informal exposition of one class of susy models, called the $G_2$-MSSM, which proves wrong much folklore about supersymmetry and which keeps making the worthwhile point that no amount of philosophy (such as naturalness) can supercede the core principle of modern physics: Pick a theory, pick a model inside the theory, then do the computations.