tag:blogger.com,1999:blog-8666091.post4916142694080845618..comments2020-03-13T03:28:45.250+01:00Comments on The Reference Frame: Why stringy enhanced symmetries are natural, important, and coolLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger41125tag:blogger.com,1999:blog-8666091.post-48830244379430890722012-08-10T19:17:23.371+02:002012-08-10T19:17:23.371+02:00Dear Dilaton, I see your comment on TRF just like ...Dear Dilaton, I see your comment on TRF just like if it were a normal message. However, in the moderation panel, it appears in the "pending [waiting for moderation]" with a flag icon. It also appears in the approved ones with a flag icon.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-29378636429166170062012-08-10T18:45:19.573+02:002012-08-10T18:45:19.573+02:00This is a test if Lumo can see it if I flag my com...This is a test if Lumo can see it if I flag my comment ...Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-28440553163707594572012-08-10T18:23:07.345+02:002012-08-10T18:23:07.345+02:00That was strange, I just saw it in my inbox about ...That was strange, I just saw it in my inbox about an hour ago but Cliff had posted it 3 or 4 days before ... And as I followed the link in my inbox it said Abuse Report etc ...<br />Anyway thanks for looking at it Lumo :-).<br />Maybe Cliff comes along again and sees that I have lost his comment. If not, I blame the jerk that I have to read *** something else at the weekend :-PDilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-91795121364911437232012-08-10T17:54:01.906+02:002012-08-10T17:54:01.906+02:00If true, that's terrible. As a moderator, I wa...If true, that's terrible. As a moderator, I wasn't informed about it in any way - it just disappears because someone mysterious labels it in some way? Scary.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-90247086778785858942012-08-10T17:28:24.217+02:002012-08-10T17:28:24.217+02:00Cliffs comment was below the comment above where I...Cliffs comment was below the comment above where I said "Thanks for these additional helpful comments" etc ... I had to expand it to read what Cliff said and as I tried to answer Cliffs hidden comment and my answer to it disappeared ...Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-69475451949651427692012-08-10T17:21:05.250+02:002012-08-10T17:21:05.250+02:00Dear Dilaton, was it retroactively made disappeare...Dear Dilaton, was it retroactively made disappeared on Disqus? I didn't think it was possible. Where was it?<br /><br /><br />Note that "Abuse report" is the faulty message displayed instead of all new users' "this comment awaits moderation".Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-32267657307610191162012-08-10T17:17:57.831+02:002012-08-10T17:17:57.831+02:00Cliff ...?!
I`ve just seen that you gave me addit...Cliff ...?!<br /><br />I`ve just seen that you gave me additional links about the different branes in string/M-theory, but your comment was hidden because of an "Abuse report" by some jerk (WTF?) ... Now as I wanted to say thank you both of our comments have gone :-(((<br /><br />So could you repost this comment, I liked it :-)? Or maybe Lumo can recover it ... ;-)Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-20699117466373872272012-08-07T02:41:06.286+02:002012-08-07T02:41:06.286+02:00When I saw the rule mentioned, I thought of it as ...When I saw the rule mentioned, I thought of it as following naturally from the equivalent rule in geometric / Clifford algebra; the number of independent measurements you can make is always half the number of generators of the group (round up for an odd number of generators). I.e. spin-1/2 dimension 2, two generators suffice, sigma_x and sigma_y, and get 2/2 = 1 measurement. Clifford algebra on 4 generators you get Dirac matrices and 4/2 = 2 measurements, say spin and charge or handedness and spin etc. In Clifford algebra theory this number is the "maximum number of independent commuting [square] roots of unity", if I recall correctly. For the Dirac matrices, a maximal set of such roots is { D(1,1,-1,-1), D(1,-1,1,-1) } where D means diagonal matrix.<br /><br />Then Alexander's counterexamples are natural, they're just the extra independent measurement you get from an odd number of generators.Carl Brannennoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-62220376309811274202012-08-06T14:38:44.928+02:002012-08-06T14:38:44.928+02:00Hey Dilaton, in addition to Lumo's answer, thi...Hey Dilaton, in addition to Lumo's answer, this presentation by Clifford Johnson can be a useful "quick n dirty" type summary of the roles of different branes, including the NS branes:<br />http://arxiv.org/html/hep-th/9802001v1/page1.html<br /><br />There's also a handy table and some other info over here:http://ncatlab.org/nlab/show/brane#worldvolume_theories_20<br /><br /><br /><br />Good luck in your studies ;]Cliffnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-74988849379468946742012-08-06T12:34:45.268+02:002012-08-06T12:34:45.268+02:00Thanks for these helpful additional comments Lumo!...Thanks for these helpful additional comments Lumo!<br />Assuming that you have written the 2005 article not only for the Trollmaster ... :-P, ;-) , I`ll read that too since it is probably what I was looking for :-)Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-66428315077106976932012-08-06T07:06:21.615+02:002012-08-06T07:06:21.615+02:00Dear Dilaton, danke for your excitement! In genera...Dear Dilaton, danke for your excitement! In general, different vacua contain various extended objects - various branes. In M-theory, you inevitably find M2- and M5-branes because there is a 3-form potential C_{mnp}, a field related to the metric tensor (gravity) by the 11-dimensional supersymmetry, and it is ready to be integrated over 3-dimensional surfaces in the spacetime, the world volumes of M2-branes (3-1=2).<br /><br /><br />This 3-form C potential has a 4-form field strength - analogue of the electromagnetic fields E,B in four dimensions - and they may be translated to a 7-form by multiplying it by the 11-index epsilon Levi-Civitta symbol (11-4=7). This dual electromagnetic field 7-form is locally the derivative of a 6-form and the 6-form may be integrated over 6D surfaces, the world volumes of M5-branes (6-1=5). There are no strings in 11D M-theory but the branes exist, anyway, and in some sense, M2 and M5 branes are the fundamental branes playing the role of strings and D-branes in perturbative string theory.<br /><br /><br />If you compactify one dimension of M-theory on a circle, M2-branes become D2-branes in the resulting type IIA string theory. Wrapped M2-branes become the fundamental strings, F1-branes. Wrapped M5-branes (on the circle) become D4-branes and unwrapped ones are the NS5-branes. In every vacuum, one may check what extended objects of this kind exist and determine their couplings - what they do. At some moment, your question is way too general because "what the fundamental branes do" is like asking "tell me everything about string/M-theory" because everything that ever occurs or has ever occurred is, according to string/M-theory, something that the strings or branes do. ;-) So let me better stop.<br /><br /><br />See also http://motls.blogspot.cz/2005/01/types-and-meaning-of-branes.html?m=1Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-80875050169202458962012-08-05T23:58:06.258+02:002012-08-05T23:58:06.258+02:00Dear Lumo,
from all of the branes floating around...Dear Lumo,<br /><br />from all of the branes floating around in M-theory, only the D-branes are good friends to me (I know a little bit about them from Lenny Susskind :-) ...). So I`m always wondering what the other extended or brany objects (such as the M2 branes mentioned in this text for example) are or why they are there and what they do?<br />Wikipedia gives no useful answer so I`d appreciate a better explanation ;-)<br /><br />I like this whole article a lot, 3 000 000 thanks for this Lumo :-). Large parts of it are almost exactly at my level, others (towards the end) are a bit more "challenging" but most things are on the right side of my cosmological horizon (not completely unreachable) I think :-D<br /><br />CheersDilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-31300096161100119082012-08-05T21:41:59.161+02:002012-08-05T21:41:59.161+02:00Dear George, I don't think that there is any d...Dear George, I don't think that there is any difference between your second question and the first one and I have already answered it. Why are you posting it again? There is absolutely nothing "contrived" about the self-duality of the tori in the heterotic string and one can't perturb the tori away from the self-duality at all. There are no moduli or other parameters in the heterotic string that would allow you to do so. There isn't any heterotic theory away from the self-dual radius and in the blog entry, I have actually proven this point. Could you please try to read it again and avoid posting the same question-non-question for the third time? Thanks, LMLuboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-90316780316313037602012-08-05T21:37:54.113+02:002012-08-05T21:37:54.113+02:00I am aware that heterotic string doesnot exist un...I am aware that heterotic string doesnot exist unless radii<br /> are self dual . but the geometrical picture seems contrived then . <br />what type of extra 16 dimensions are those?can you perturb them ? if so what happens?bushjr2noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-65712115475081130102012-08-05T20:48:06.325+02:002012-08-05T20:48:06.325+02:00Dear George, it's not tuning at all! The heter...Dear George, it's not tuning at all! The heterotic theory would be inconsistent at tori that are not self-dual. There is really no theory in which the torus wouldn't be self-dual. So there's no assumption going on into the determination of the self-duality property. The self-duality is a mathematical necessity, something you may derive. You may say that the self-duality follows from the laws of physics.<br /><br /><br />Saying that the self-duality is "fine-tuning" would be the same like saying that p=sqrt(2) is exactly fine-tuned so that p^4 - 4 =0. Well, it's not fine-tuned; it's an identity one may actually prove. "Fine-tuning" is a completely different situation in which the value of a parameter could a priori be different but we experimentally find out that Nature seems to prefer a particular value with special properties. But non-self-dual tori of the heterotic string aren't allowed even *a priori* so it's not fine-tuning.Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-26055810816183942392012-08-05T20:42:23.623+02:002012-08-05T20:42:23.623+02:00thank you for your nice presentation of gauge symm...thank you for your nice presentation of gauge symmetries. <br /><br />how<br /> natural ( and likely) is for those extra 16 dimensions to be <br />compactified exactly at self dual radius? isnt this a fine tuning?bushjrnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-52257621046479141402012-08-05T18:06:35.290+02:002012-08-05T18:06:35.290+02:00Ok, these symmetries are cool, important and natur...Ok, these symmetries are cool, important and natural... but they are most probably the flavour structure. Somehow string theory, not allowing ungauged symmetries, promotes flavour to SO(32) and kins. Of course flavour is related to force, but it is mostly because of self consistency; such as we could say that flavour SU(2) isospin is related to weak isospin<br /><br />Metodologically, it is absurd to have the force group just there, around the corner in KK, and try to extract it from other place. The only nuissance to get the force structure out from D=11 was the lack of chirality, and lately (textbook and some articles) Schwartz was arguing that chirality was not a problem anymore because it was possible to extract it from the branes. And even if it were not, we could still have other ways to evade the non-go.<br /><br />The only excuse I can think is a "self-conspiracy theory" to train yourselves to do not see it, in order to win time to explore fully all the theory without distraction, nor input, from the phenomenology.Alejandro Riverohttp://www.facebook.com/alejandro.riveronoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-27884522141303518552012-08-05T12:10:35.104+02:002012-08-05T12:10:35.104+02:00Yeah, I think from such very nice pedagogical art...Yeah, I think from such very nice pedagogical articles everybody can <br />learn and take out something :-). <br />Seing them appear on TRF they always tease me and I can never resist <br />since I`m so fascinated and intrigued by nice funny colorful yarn balls <br />:-D<br /><br />http://junipertreehouse.files.wordpress.com/2010/11/yarn.jpg<br /><br />How I`d like it to be able to play with and have fun with them ... !!!<br /><br />But I get scared if they do something strange, unexpected, and attack me<br /> ... <br />This makes me jump high into the air and after five sumersaults <br />backward hide behind a thick pile of QFT books :-P<br /><br />http://wallpaper.goodfon.com/image/259319-5616x3744.jpg<br /><br />(Reading on now below the two prehistories; the explanations how gauge <br />groups can be obtained from Kaluza-Klein are very nice :-) !)Dilatonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-43693169618163571092012-08-05T08:52:48.956+02:002012-08-05T08:52:48.956+02:00Thanks Dilaton and PeterF :-) Exactly the encourag...Thanks Dilaton and PeterF :-) Exactly the encouragement I need. What I like about this Physics blog is that, beside a complicated technical and mathematical paragraph, Lubos always explains it with words too... internet helps with the jargon, and you guys with a new angle of understanding. Precious to me. That's where and when I get my eurêka moments... and all this while keeping real :-)Shannonnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-88283844445749497602012-08-05T04:19:22.429+02:002012-08-05T04:19:22.429+02:00About how it is possible that algebraic and other ...About how it is possible that algebraic and other math can be appreciated without being completely absorbed:<br /><br /><br />I once (especially on one occasion that sticks in my mind) deeply disappointed Lubos by posting a pessimistically put metaphorical comment about how I my appreciation of mathematical physics (or maths generally) was limited. <br />In hindsight I should have (or would have saved Lubos some pain had I) described my limitations in a 'positive' or optimistc (or glass half-full rather than half-empty) way. For example I could have said that how I perceive and appreciate the greatness of string/M-theory and the actual and potential potency of mathematical thinking generally can be likened to that someone who enjoy the final product of what good composers/arrangers and players (of music) produces but who can not produce or even write down or perform something even remotely similar (partly because their talent or training is not sufficient for them to be clear about how the music is written on the score and which and how instruments are used to achieve all the tonal and timbral qualities that adds up to a subjectively nicely stimulating musical experience).<br /><br /><br />My mathematical background is in reality limited to a longstanding curiosity about how most things work/are, and to an in highschool suddenly flared feverish interest and enjoyment of simple algebra, simple vector matrixes, simple statistics and simple probability theory (a long way from the by Lubos pioneered Matrix String Theory ;>). Anyway my interest and absorbtion was so strong that I once woke up in the middle of the night full of joy for having understood how some of this simple mathematical stuff worked! %}Peter F.noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-66042391980932382702012-08-05T00:31:57.328+02:002012-08-05T00:31:57.328+02:00From my listing of examples it can be understood t...From my listing of examples it can be understood that I sympathetise with the desire (I can not tell about the motivations) of this "TRF Reader". Remember that the SM has not a pure gauge group but a broken gauge group. The low energy SM has the symmetries SU(3)xU(1), which can be produced from D=9. The high energy SM has SU(3)xSU(2)xU(1), which can happen in D=11. So perhaps the SM lives in the middle, in D=10 --string theory would be the ultimate higgs mechanism!--, or perhaps it is best analysed using a network of dualities between 9 and 11.eeeeeeAlejandro Riverohttp://profiles.google.com/al.riveronoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-55914327092850505732012-08-05T00:22:10.825+02:002012-08-05T00:22:10.825+02:00Well after the first counterexample I thought that...Well after the first counterexample I thought that perhaps it was a good argument for simple group, and them I noticed the second one.Alejandro Riverohttp://profiles.google.com/al.riveronoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-40093403850997676332012-08-04T20:35:08.381+02:002012-08-04T20:35:08.381+02:00Air is Hippocratian. Lubos used it- In Chinese ele...Air is Hippocratian. Lubos used it- In Chinese elements are metal and wood. Hippocrates had fire, water, air, earth and ether.menoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-71792788753146178252012-08-04T20:02:47.625+02:002012-08-04T20:02:47.625+02:00When I look at the examples, the thumb rule of min...When I look at the examples, the thumb rule of mine looks pretty stupid. ;-)Luboš Motlhttp://motls.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-89399736660384347182012-08-04T19:56:56.882+02:002012-08-04T19:56:56.882+02:00Nah, come on Shannon ;-)
You have no cop-outs ......Nah, come on Shannon ;-)<br /><br />You have no cop-outs ... ;-P :-D :-)Dilatonnoreply@blogger.com