# Has proton decay falsified SO(10) GUT?

1. Dec 25, 2009

### ensabah6

I know that proton decay has falsified SU(5) based around 10e30 years.

What proton decay of SO(10)?

Are SUSY SU(5) and SUSY SO(10) still viable?

If the experiment continues with a null result, what models are next in line to be falsified?

Could protons last forever and thus falsfy ALL GUT approaches?

2. Dec 28, 2009

### arivero

ensabah, have you checked the limits in the "particle data group" current review?

3. Dec 28, 2009

### ensabah6

no, do you have a link? thank :)

4. Dec 28, 2009

### blechman

www-pdg.lbl.gov

the particle physicist's almanac!

5. Dec 28, 2009

### Bob S

6. Dec 28, 2009

### arivero

Argh, I forgot to request the 2010 calendar

7. Dec 28, 2009

### hamster143

You need pages 10 and 11. Besides, that's an outdated source.

http://arxiv.org/abs/0903.0676

increases the limit on the observed partial mean life via $p \rightarrow e^+ \pi^0$ channel (the one predicted by common GUTs) by a factor of 5, to 8.8 x $10^{33}$ years.

The original non-supersymmetric SU(5) prediction was, I think, somewhere around $10^{30}$ years, and that has been ruled out.

However, mean life is extremely sensitive to the structure of the unified theory. It scales roughly as the fourth power of the unification energy (or, more accurately, as the fourth power of mass of the massive boson responsible for the decay, which is probably near unification energy). We already know that naive (minimal) non-supersymmetric SU(5) does not result in clean unification, because all three coupling constants fail to meet at the same point. If we allow additional particles beyond those needed to construct minimal SU(5), all hell breaks loose, the unification energy can be anywhere below Planck mass, and proton lifetime can potentially be as high as $10^{42}$ years.

That is, in fact, the way SUSY GUTs "deal" with the problem - contributions from superparticles distort running couplings just enough to raise the unification energy by a couple of orders of magnitude, and lifetime becomes high enough to agree with observations. But that approach is by no means exclusive to SUSY.

Last edited: Dec 28, 2009
8. Dec 28, 2009

### ensabah6

What about non-SUSY SO(10)? I understand that SO(10) is the most highly favored GUT.

That's fascinating. I know there are talks of building Hyper-Kak...
I know that 10^30 protons is doable, and that 10^31 represents a 10x increase.

I'd imagine it'd take well beyond our lifetimes for Super-Kak to get those kind of proton half-lifes.

Isn't the current experimental upper bounds around 10^35 years?

Has there been serious research into the possibility that the absence of proton decay and magnetic monopoles is suggestive evidence that GUT are wrong? The "unified" gauge couplings at 10^16 GEV is just a coincidence? In other words, are GUT are "fact" and only details matter?

9. Dec 28, 2009

### marcus

What about the series of papers by Nicolai and Meissner? They dispense with GUT, also with low-energy SUSY and with extra dimensions. That surely qualifies as serious research.
You can tell from his tone of voice that Nicolai is quite skeptical of GUT
as he says "since the proton so far has refused to decay."

Shaposhnikov is another whose research explores the possibility of dropping GUT.

10. Dec 28, 2009

### ensabah6

Which paper?

The latest paper builds on two earlier Meissner Nicolai papers
3. arXiv:0907.3298 [ps, pdf, other]
Title: Conformal invariance from non-conformal gravity
Authors: Krzysztof A. Meissner, Hermann Nicolai
Journal-ref: Phys.Rev.D80:086005,2009
Subjects: High Energy Physics - Theory (hep-th)

Since string based TOE is predicated on GUT, skepticism of GUT and extra dimensions is skepticism of string theory unification.

11. Dec 29, 2009

### hamster143

There are different ways to break SO(10) down to SM. One way is to go SO(10) -> SU(5) x U(1), in which case there's essentially no difference from SU(5) case. One other way is to go via SU(4) x SU(2) x SU(2) (Pati-Salam), in which case there's more freedom and we can have proton lifetime up to 10^37 years.

12. Dec 29, 2009

### ensabah6

thanks,

does the guage couplings meet in both SUSY SU(5) and SUSY SO(10)?

Can we experimentally test up to 10^37 years? I infer that SUSY-SO(10) increases proton lifetime by order of magnitude.

13. Dec 29, 2009

### marcus

The best exposition of Nicolai and Meissner's work is Nicolai's talk at the July Planck Scale conference. He gives references there. Great talk. He is repeatedly explicit about dispensing with GUT, for the purposes of this program. Doesn't need it and doesn't want it. Anyone who hasn't watched the talk really ought to.
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php [Broken]
This gives the menu of all the talks. both the slides PDF and the video.
Just select Nicolai's talk, which is near the top of the menu.

Does your computer not get videos? I forget. If you have a bandwidth problem let me know and I will suggest an alternative.

Last edited by a moderator: May 4, 2017
14. Dec 29, 2009

### ensabah6

http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf

thx, if true it obviously spells problems for SUSY

Last edited by a moderator: May 4, 2017