Comments on: Thou shalt have three generations

By: Matti Pitkänen

Matti Pitkänen — Wed, 30 Sep 2009 13:11:32 +0000

Just the same old boring stuff about p-adic length scale hypothesis predicting the possibility of mass scales coming as half octaves;-).

Primed tops could correspond to p-adic half-octaves of ordinary top rather than higher generations. m= sqrt(2)*m_t with m_t=170 GeV would give m=about 240 GeV and m= 2*m_t gives 340 GeV The lower limit for t’ mass is 280 GeV so that actual mass should be 340 GeV. m= 2*sqrt(2)m_t would give 480 GeV to be compared with 450 GeV mentioned above.

By: dorigo

dorigo — Mon, 07 Apr 2008 09:30:57 +0000

Hi Neil,

sorry – I myself waited too long to answer. Your comment is vague, and I do not remember any real show-stopper against more than three generations from cosmological arguments – but I am probably not well informed. I will try to get back to you after I investigate further.

Cheers,
T.

By: Neil B.

Neil B. — Thu, 03 Apr 2008 01:58:53 +0000

Sorry to come late, but I remember hearing that more than three generations would have left cosmological consequences of a sort we don’t find. Well?

By: island

island — Sun, 30 Mar 2008 19:18:27 +0000

Island, have you seen the cartoon posted by Marco here ?

Ha… that’s pretty funny and right on par with my thinking. Thanks, and thank you to Marco, as well.

By: Eric

Eric — Sat, 29 Mar 2008 22:02:43 +0000

Actually, instead of energy levels of the electron in a bound system such as the hydrogen atom, I would prefer to say that the different generations are just different vibrational modes of the string.

By: dorigo

dorigo — Sat, 29 Mar 2008 21:04:29 +0000

Hi Eric,

I also have a point – an infinite number of generations to me looks quite simple, because they look like the energy levels of an electron in a bound system like an hydrogen atom: infinity takes away one degree of freedom. Not two, nor three, nor four. It can’t be one because of energy considerations, and thus there’s an infinity of replicas.

In any case, I suspect nature did choose, and it chose three. This is however a real mystery – much more mysterious to me than the number of colours, for reasons I mentioned in the post.

Cheers,
T.

By: Eric

Eric — Sat, 29 Mar 2008 20:17:36 +0000

Hi Tommaso,
Yes, I know but my point being that there are already two superfluous generations for which we have no explanation for, and so it doesn’t make any sense to prefer three, four, five, or an infinite number of generations. Of course, your other post on the Higgs mass suggesting that a signal may be emerging in the range 114-130 GeV also suggest only three generations of MSSM fermions, if true.

By: dorigo

dorigo — Sat, 29 Mar 2008 19:34:47 +0000

Ok Alejandro, but three colors have been established, while evidence against N fermion families is still sketchy… Or am I wrong ?

Island, have you seen the cartoon posted by Marco here ?

Eric, one cannot prefer something which is ruled out by experiment. One can only choose between theories we have not yet killed!

Cheers,
T.

By: Eric

Eric — Sat, 29 Mar 2008 18:35:38 +0000

Why not just prefer one generation rather than an infinite number. The structures in the universe as we know it don’t depend on the existence of more than one generation.

By: island

island — Sat, 29 Mar 2008 09:04:03 +0000

Island, I do not think I’d be shocked – a non-find comes in very slowly, as opposed to a find.

Yeah, “GITMO” has nothing on you guys… In fact, this whole last year is like one long water-boarding session, before the real torture starts…

So we’d all have time to get accustomed to it, come to terms with it, and accept it.

Maybe you experimentalists would, but theorists will be in-line with the beam dump…

By: Alejandro Rivero

Alejandro Rivero — Sat, 29 Mar 2008 00:09:09 +0000

Well, the practicioners of Maldacena’s conjecture would think more natural if there were an infinite number of colours.

But yes, I still should prefer an infinite number of generations (thus of flavour) than exactly 4 generations.

By: dorigo

dorigo — Fri, 28 Mar 2008 22:39:29 +0000

Hi Alejandro,

I actually do think there is nothing magical in three generations. I would think it much more natural if there were an infinite number… But then we’d have to part with asymptotic freedom

Island, I do not think I’d be shocked – a non-find comes in very slowly, as opposed to a find. So we’d all have time to get accustomed to it, come to terms with it, and accept it.

Cheers,
T.

By: island

island — Fri, 28 Mar 2008 16:16:32 +0000

Surely not finding the Higgs would make us pause

Probably because you’ll be so shocked that it is actually possible to hear me cheering from the other side of the Atlantic…

By: Alejandro Rivero

Alejandro Rivero — Fri, 28 Mar 2008 00:24:01 +0000

A 4th generation sounds too cheap even as a trick: 128 degrees of freedom in total, an exact power of two? C’mon.

By: dorigo

dorigo — Thu, 27 Mar 2008 12:57:24 +0000

Hi Tripitaka, thank you…

Surely not finding the Higgs would make us pause. As would the discovery of a fourth generation of chiral matter… If there were infinite generations, I think a 120 GeV Higgs might well be unobservable even at the LHC (I should be able to do the computation but I am too lazy…), due to the asymptotic behavior of the H->gg branching fraction.

Cheers,
T.

By: Tripitaka

Tripitaka — Thu, 27 Mar 2008 12:16:58 +0000

Fantastic post!
Goodness me, you do raise some worrying questions about the nature of discovery in this age of advanced research, worst case scenario being that the chosen assumptions may eliminate the possibility of detecting a real signal I guess!
One thing about nature is that it seems to have no problem with redundancy, why not 10 generations, or a hundred for that matter (though I must on the subject of redundancy that I recoil in horror at multiverse theories which really DO seem too wasteful!)
Anyway, we punters are cheering on the sidelines in the hope of some absurd exerimental result emerging that will set all the theorist on their asses… null Higs should do the trick?

By: dorigo

dorigo — Wed, 26 Mar 2008 07:08:00 +0000

Yep Kea, I did… Jester links to an enthusiastic CP-violation talk which is all about four generations, and which even mentions the “need” for a 400 GeVish new quark pair.

Anon, I will ask John about b-tags. But you must realize that we are talking about a handful of events. Whether they survive b-tagging or not says very little. For instance, if these were the decay of a real t’ quark, b-tagging would probably reduce them, although not just as much as if they were W+jet events (who knows what the fourth column of the CKM is ?). Since backgrounds at 400 GeV are half top and half W+jets, any result is possible.

Cheers,
T.

By: Anonymous

Anonymous — Wed, 26 Mar 2008 04:36:34 +0000

If one restricts to b tags, does the bump go away?

Looking at the public web page, it is not possible to tell — and the “public” note requires a CDF password to access!

By: Kea

Kea — Wed, 26 Mar 2008 04:25:05 +0000

Hmm. Interesting. I see you mentioned the 400GeV bump on the Resonaances post about new physics.