The main difference that I was trying to make from the version of Michael and Chip was to avoid the impression that I got from their version that naturalness is not a legitimate concept. I was trying to emphasize that it is something we actually do every day when we are faced with a scientific problem, namely dimensional analysis. I felt that the current version made it seem something mysterious. Since there seems to be no consensus among the conveners that the different approach in my version is preferred, I agree with Michael that the original version remains the default. I would then request the following small changes: Line 164: Please remove the phrase "slippery principle." This is unnecessarily florid and makes it sound like naturalness is not something to be taken seriously. I would suggest no adjective at all: We do have a hint from the principle of "naturalness." The fact that it says "hint" makes it clear that this is not a precise concept. Lines 184-185: "The corresponding naturalness bounds are" > "The corresponding bounds suggested by naturalness are" Line 188: "This gives the bound" > "This suggests the bound" The idea is to make it clear that naturalness "bounds" are not not sharp boundaries. Markus Luty ============================================ Physics Department University of California, Davis One Shields Avenue Davis, CA 95616 Phone: +1 530 554 1280 Skype: markus_luty On Mon, Oct 14, 2013 at 7:46 AM, Ashutosh Kotwal <[log in to unmask]>wrote: > hi all, > Its clear we all agree there are no guarantees. Its hard > to make an incisive argument for the slope of the prior distribution for > the amount of fine tuning, But its not unreasonable that there is some > slope (i.e. all else being the same, less fine tuning is preferred over > more fine tuning). In the end, this is a decision-making criterion, not a > prediction. Its a reason to bet a certain way. The past is a guide: people > thought SU(5)-motivated proton decay was a good bet, and people thought the > top quark should be 30 GeV and tristan (or even Petra before that) had a > good chance to see it. So these projects were done. > > As Chip said, at 1 TeV we are in the game and there is a > good chance we will win. > > I will add one comment about the bet placed on the Higgs > for the LHC (SSC). In the absence of Higgs, we always say "unitarity would > be violated in longitudinal Vector boson scattering". But as an > experimentalist who is not motivated by quantum mechanics arguments, I > would say that observing this "unitarity violating" cross section is > actually very hard. All it says is that the amplitude A has a condition > that Im(A) > |A|^2 (factor of 2 somewhere maybe). But A is pretty small > and its really hard to see this rising cross section at high VV mass… > > In other words, the Higgs was again a bet on nature > choosing the easy solution and not the hard solution to find. And we won > this bet. > > I am ok with betting on ~ 1 TeV new particles. Especially > when the LHC is already on the field…we just have to step up to the plate. > Are we really going to turn our back on this game (might I add "again?') ? > > regards, > Ashutosh > > On Oct 13, 2013, at 4:21 PM, "Peskin, Michael E." < > [log in to unmask]> wrote: > > > Dear Colleagues, > > > > Sally has a very nice analysis of the difference between the naturalness > sections of the long report > > (section 1.2.2) proposed by me and by Markus. The current draft was > agreed upon between Chip > > and me before we sent it to you, but I will take responsibility for its > attitude. Sally's reply to my > > email yesterday is pasted in below. I sent Markus' version yesterday, > and it appears again below. > > > > Anyone who wants to weigh in on this -- especially to object to what is > in the current draft -- should write > > back by Monday morning if possible. My attitude is that if I have an > honest difference of opinion with one > > of the conveners, I should win, but if I have an honest difference of > opinion with most of the conveners, > > their (your) opinion should win. So, let us all know your opinion by > replying to snowmass-ef. > > > > I do think it is important to say that it is more likely to find the > first new particles at 1 TeV than at 5 TeV. > > Otherwise, why is LHC so highly motivated? > > > > Thanks, > > > > Michael > > > > > ------------------------------------------------------------------------------- > > > > > > The naturalness sections that Michael and Marcus wrote reflect honest > > differences of scientific opinion. Michael is trying to quantify > naturalness > > and Marcus is arguing that this isn't really well defined. From what > Marcus > > wrote, the reader would infer that 5 TeV is just as likely as 1 TeV for > new > > particles so we should look at as high an energy as possible. From what > Michael > > wrote, you would take home that 1 TeV new particles are much more likely > > than 5 TeV. > > > > I subscribe to Marcus's view, but as long as the naturalness section > which > > Michael wrote refrains from saying that there must be particles at 1 TeV, > > I'm ok. > > > > Sally > > > > > ------------------------------------------------------------------------------------ > > > ------------------------------------------------------------------------------------------- > > Michael E. Peskin [log in to unmask] > > HEP Theory Group, MS 81 ------- > > SLAC National Accelerator Lab. phone: 1-(650)-926-3250 > > 2575 Sand Hill Road fax: 1-(650)-926-2525 > > Menlo Park, CA 94025 USA www.slac.stanford.edu/~mpeskin/ > > > --------------------------------------------------------------------------------------------- > > ________________________________________ > > > > from Markus: > > > > > > Lines 152-196. I do not think that naturalness is a "bothersome hint" or > a "slippery principle." I think it can be explained in very basic physical > terms. I suggest the following: > > > > "Naturalness" is at bottom the use of dimensional analysis to estimate > unknown parameters. If a quantity such as the Higgs mass is sensitive to a > physics associated with a mass $M$, then dimensional analysis suggests that > the Higgs mass should be of order $M$. Of course, this does not take into > account the possibility that this dependence is absent, in which case we > expect to have a good reason why this sensitivity is absent, such as a > symmetry or some kind of decoupling. > > > > Decades of theoretical work in quantum field theory has shown that > elementary scalar masses are generically sensitive to physics at higher > scales, and only three mechanisms have been established that can avoid this > sensitivity. These are supersymmetry, (SUSY), Higgs compositeness, and > extra dimensions. Each of these predict a rich spectrum of new states at > the scale where the new structure becomes apparent. In SUSY, these consist > of the superpartners of all known particles, while in both composite and > extra-dimensional models we expect towers of massive resonances. (The fact > that the phenomenology is qualitatively similar is the first sign that > extra-dimensional models are in fact a realization of Higgs compositeness, > a fascinating and deep equivalence that was discovered in string theory and > has propagated to particle phenomenology and back again to fundamental > theory.) > > > > These mechanisms allow the Higgs mass to be calculated from other more > fundamental parameters, and they confirm the expectations of naturalness in > the sense that the Higgs mass is indeed sensitive to the new particles > associated with SUSY or compositeness. The Higgs mass therefore cannot be > much smaller than the scale $M$ of new particles predicted in these models. > The Higgs mass can be much smaller than $M$ only if there is an unexplained > accidental cancellation, or "fine tuning." > > > > We can see the naturalness problem even without knowing what the new > fundamental physics is. If we simply assume that there is *some* new > physics at a scale $M$ we can estimate the sensitivity of the Higgs mass to > new physics at the scale $M$ by computing quantum loops in the standard > model with a cutoff of order $M$. The parameter in the Higgs potential then > receives corrections of order > > > > Eq. (1.4) with $M$ instead of $\Lambda$ > > > > where $g_{Htt}$ is the same Yukawa coupling as in (1.2), $\alpha_w$ and > $\lambda$ are the couplings of these particles, and $\theta_w$ is the weak > mixing angle. Note that all terms are proportional to $M^2$, simply as a > result of the fact that it is the Higgs mass squared that appears in the > Lagrangian. Experience with many specific models teaches us that if there > is new physics at the scale $M$, (1.4) gives a reasonable estimate of the > contribution of new physics at the scale $M$ to the Higgs mass. The > suppression factors in (1.4) mean that the natural expectation for the > scale $M$ is that it cannot exceed the Higgs mass by about a factor of 10. > > > > Although there is no general agreement on how to quantitatively measure > the (un)naturalness of a given model, it is clear that the degree of tuning > required to obtain $m_h \ll M$ grows quadratically with $M$. This means > that if we increase the sensitivity to heavy particle masses by a factor of > 10, we increase our probing of naturalness by a factor of 100. This > provides a very strong motivation to for searches at the largest possible > energies. > > > > > > ######################################################################## > > Use REPLY-ALL to reply to list > > > > To unsubscribe from the SNOWMASS-EF list, click the following link: > > https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-EF&A=1 > > > > ######################################################################## > > Use REPLY-ALL to reply to list > > > > To unsubscribe from the SNOWMASS-EF list, click the following link: > > https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-EF&A=1 > ######################################################################## > Use REPLY-ALL to reply to list > > To unsubscribe from the SNOWMASS-EF list, click the following link: > https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-EF&A=1 > ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the SNOWMASS-EF list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=SNOWMASS-EF&A=1