tag:blogger.com,1999:blog-2846514233477399562.post4932364536369466533..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: Thoughts on RK Jesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger18125tag:blogger.com,1999:blog-2846514233477399562.post-15098484341472880102021-04-24T12:08:01.995+01:002021-04-24T12:08:01.995+01:00Yes, this is subjective to a large extent. But the...Yes, this is subjective to a large extent. But there is one objective point here. Once you add right-handed neutrinos, the local symmetries of the SM allow you to write down the Majorana mass term for them. So pure Dirac neutrinos are not natural from the theoretical point of view, unless you do more gymnastics, for example declare that the global symmetry L or B-L is exact. In this sense Dirac neutrinos are uglier. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-3537904418098628252021-04-23T06:32:59.222+01:002021-04-23T06:32:59.222+01:00"the other option - Dirac neutrinos - is much..."the other option - Dirac neutrinos - is much uglier theoretically"<br /><br />Uglier in which sense? To me, the SM looks prettier with Dirac neutrinos than without. Is this an eye-of-the-beholder thing?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-56920934090139435972021-04-12T11:27:58.427+01:002021-04-12T11:27:58.427+01:00I actually agree that one should entertain the pos...I actually agree that one should entertain the possibility that the SM is more fundamental than we think. However, neutrino oscillations strongly suggest that at least dimension-5 non-renormalizable operators should be added to the SM Lagrangian (the other option - Dirac neutrinos - is much uglier theoretically). My "we know" is mostly based on this insight, plus some circumstantial evidence from dark matter and baryogenesis. Note that I'm not saying that the true fundamental theory is non-renormalizable - my statement refers to the effective theory at the electroweak scale. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-21030930492306600242021-04-12T10:55:36.926+01:002021-04-12T10:55:36.926+01:00"But we know that the Standard Model is just ..."But we know that the Standard Model is just an effective theory, and that non-renormalizable interactions must exist in nature, even if they are very suppressed so as to be unobservable most of the time."<br /><br />How can you be so sure? QCD seems to work on all scales, for example. Even if you find some perturbatively non-renormalizable interaction, you could still get away with it if there's a non-trivial fixed point of the RG flow. I'm not saying that the latter possibility is more plausible, and I'm an expert in neither. But after decades of not finding any clear signs of New Physics, maybe we should re-entertain the notion that the Standard Model is in fact fundamental, and that we just don't understand yet how it all comes about.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-66992959702475387412021-04-02T22:09:35.790+01:002021-04-02T22:09:35.790+01:00There are significant backgrounds in the nonresona...There are significant backgrounds in the nonresonant ee channel. I wonder if the 'experimental screwup' could be mismodelled backgrounds / signal shape rather than bad efficiencies for which I find the cross-checks quite convincing.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-24338371904636453042021-04-02T16:56:54.098+01:002021-04-02T16:56:54.098+01:00You're totally right: the type-1 see-saw is a ...You're totally right: the type-1 see-saw is a renormalizable UV completion of the SM. What I meant in this passage is an alternative viewpoint, which is however equivalent for all practical purpose. At the electroweak scale, 100-1000 GeV, the only available degrees of freedom are, most likely, those of the SM. The additional neutrinos that come with the see-saw are heavy (again, most likely), maybe even as heavy as 10^15 GeV. Therefore we cannot produce them in our colliders. All the effects of these heavy neutrinos that we can see are adequately described by the said dimension-5 operators. The is the effective theory thinking, where we get rid of all heavy unavailable degrees of freedom in the theory, at the price of losing renormalizability. This is practical and theoretically ok, until one day we reach the scale where we can produce the new particles from beyond the SM, be it the see-saw neutrinos or something else. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-10507084501884911792021-04-02T07:11:43.967+01:002021-04-02T07:11:43.967+01:00Nice to see new posts here. This is an excellent p...Nice to see new posts here. This is an excellent post.<br /><br />I have a comment/question.<br /><br />You write about neutrino oscillations being best described by dimension-5 non-renormalizable interaction. My understanding is that when such an operator is used and non-zero Dirac terms are allowed, eg type 1 Seesaw mechanism, then the theory is then renormalizable. I'm not a neutrino physicist but I've found the seesaw mechanism to be the most plausible extension of the SM, not least since it seems to keep the renormalisability criteria used to build the SM in the first place. <br /><br />Am I wrong about a type 1 seesaw theory being renormalisable ? Rogernoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-32926977481328188532021-03-31T19:31:42.197+01:002021-03-31T19:31:42.197+01:00I don't disagree, which BSM model appears more...I don't disagree, which BSM model appears more contrived at this point is clearly a matter of subjective bias.<br /><br />With no clear direction in sight, we may soon see "ambulance chasing" being turned on again and mirroring the case of the 750 GeV anomaly.Ervin Goldfainhttps://www.blogger.com/profile/07585008304556273617noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-47678860394262731862021-03-31T16:49:39.842+01:002021-03-31T16:49:39.842+01:00No. Simplest models with a single Z' or a sing...No. Simplest models with a single Z' or a single leptoquark do not predict LFU violation in W decays. So there is no need for any conspiracy to avoid signals in W decays. More complicated models, where there is also a W' partner to Z', may affect W decays. But these are more contrived imo, although that is of course subjective. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-59270920046650183282021-03-31T15:57:13.505+01:002021-03-31T15:57:13.505+01:00"... it's easy to cook up a model where t..."... it's easy to cook up a model where the B-meson decays are affected while the W boson decays look SM-like"<br /><br />But isn't such a cooked up model a contrived attempt to "force" BSM physics at the LHC?Ervin Goldfainhttps://www.blogger.com/profile/07585008304556273617noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-18336015312221992942021-03-31T15:44:13.546+01:002021-03-31T15:44:13.546+01:00The two are not directly related. The LHCb sees le...The two are not directly related. The LHCb sees lepton flavor universality violation in B-meson decays. LEP saw lepton flavor universality violation in W boson decays, but this is now ruled out by more precise measurements at the LHC and the Tevatron. In the past, some theorists tried to connect the two anomalies, and those models are now disfavored. But it's easy to cook up a model where the B-meson decays are affected while the W boson decays look SM-like. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-84094166785869231652021-03-31T14:46:48.889+01:002021-03-31T14:46:48.889+01:00Jester,
Is the LHCb anomaly in conflict with the ...Jester,<br /><br />Is the LHCb anomaly in conflict with the previous report by the ATLAS collaboration?<br /><br />http://resonaances.blogspot.com/2020/08/death-of-forgotten-anomaly.html<br /><br />ErvinErvin Goldfainhttps://www.blogger.com/profile/07585008304556273617noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-8979031108492545682021-03-31T09:24:57.559+01:002021-03-31T09:24:57.559+01:00That is the question. The two main proposals on th...That is the question. The two main proposals on the market are Z' bosons and leptoquarks, but all models so far are ugly to the point of being offensive. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-57029908970120692622021-03-31T01:28:34.619+01:002021-03-31T01:28:34.619+01:00Been a looooooong time, but isn’t the coefficient ...Been a looooooong time, but isn’t the coefficient of the dimension five operator that gives rise to neutrino masses roughly the reciprocal of th GUT scale, which makes a fair bit of sense. What are you integrating out at 40 TeV?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-54684075920155353842021-03-30T11:39:07.408+01:002021-03-30T11:39:07.408+01:00" But we know that the Standard Model is just..." But we know that the Standard Model is just an effective theory, and that non-renormalizable interactions must exist in nature"<br />You could even state that a non renormalizable theory is the root to a deeper understanding, of v-course Fermi ->qed<br />Thanks for your thoughts!NoSiVahttps://www.blogger.com/profile/00143816761345128485noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-14499822541043566352021-03-30T10:27:38.080+01:002021-03-30T10:27:38.080+01:00Bertie, I would still bet against new physics, but...Bertie, I would still bet against new physics, but with much less convictions than e.g. during SUSY bets :) If I had to put a number on the odd, it would be 10-20% for new physics.<br />Anon, some of these observables in tension are not "clean", and the apparent deviations could be just due to wrong theoretical predictions. As for the clean ones, like RK* or RpK, I don't know the nuts and bolts of the analyses enough, but naively it seems possible that an unknown "screw-up" in RK also feeds into those other analyses.Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-68661429156242350152021-03-30T10:13:49.898+01:002021-03-30T10:13:49.898+01:00Nice post.
May I ask which side of the 'even m...Nice post.<br />May I ask which side of the 'even money' bet you currently fall, Jester? bertiehttps://www.blogger.com/profile/01726915977622567280noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-88435949456312137942021-03-30T07:09:14.798+01:002021-03-30T07:09:14.798+01:00Nice thoughts! about "some other 1-3 sigma te...Nice thoughts! about "some other 1-3 sigma tensions in the data": could some of them suffer from similar "possible Experimental screw-ups"? in this case, would we expect seeing a consistent pattern of deviations? Is there any "possible Experimental screw-up" you would highlight?Anonymousnoreply@blogger.com