tag:blogger.com,1999:blog-2381900080106522441.comments2018-04-16T20:13:13.025+02:00relatively quantumNorberthttp://www.blogger.com/profile/04965554394207041308noreply@blogger.comBlogger30125tag:blogger.com,1999:blog-2381900080106522441.post-17570837974167670082018-04-16T20:13:13.025+02:002018-04-16T20:13:13.025+02:00i look forward to this. I used to visit physics fo...i look forward to this. I used to visit physics forum and read Marcus summary of the latest results in LQG, but sadly he has passed away several years ago.<br />if you have the time and interest, since you are the only LQG blog i know of, and this is a LQG blog, could you summarize recent research directions and papers and results in LQG and spinfoam similar to what Marcus did back on PF. <br /><br />is there a merger coming for string theory and LQG?neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-50243217607153851922018-04-16T10:51:54.570+02:002018-04-16T10:51:54.570+02:00The known dual models in the papers above are stat...The known dual models in the papers above are statistical model. They often have a CFT description at the critical point, but not necessarily away from it. So the framework seems more general so far. About slides, I hope to upload a talk soon. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-39772485863318784092018-04-16T04:14:31.226+02:002018-04-16T04:14:31.226+02:00thanks
do you have any powerpoint slides that sum...thanks<br /><br />do you have any powerpoint slides that summarize gauge/gravity dualities in LQG that you can share now?<br /><br />is the gauge theory in gauge/gravity dualities in LQG also a CFT?<br /><br />neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-50718558597373049662018-04-15T07:48:42.704+02:002018-04-15T07:48:42.704+02:00Hi Neo.
is there a gauge/gravity dualities where ...Hi Neo.<br /><br />is there a gauge/gravity dualities where gravity side is described by LQG?<br /><br />So far, duals have been found for 3d LQG with vanishing cosmological constant:<br />https://arxiv.org/abs/1504.02822<br />https://arxiv.org/abs/1710.04202<br />https://arxiv.org/abs/1710.04237<br /><br />any papers and research on this topic?<br /><br />on top of the above:<br />https://arxiv.org/abs/1610.02134<br />https://arxiv.org/abs/1705.01964<br />https://arxiv.org/abs/1612.06679<br />https://arxiv.org/abs/1804.01387Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-77826924744297512332018-04-15T04:32:24.402+02:002018-04-15T04:32:24.402+02:00" In addition, more general scenarios for gau..." In addition, more general scenarios for gauge/gravity dualities have been studied, extending beyond the realms of AdS, CFT, and string theory."<br /><br />is there a gauge/gravity dualities where gravity side is described by LQG?<br /><br />"In addition, there is an increased recent interest within loop quantum gravity in holographic computations"<br /><br />any papers and research on this topic?neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-3061907701809373332017-11-29T10:57:25.257+01:002017-11-29T10:57:25.257+01:00This comment has been removed by a blog administrator.William B. Wrighthttps://www.blogger.com/profile/15582613695997982381noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-51961839721242598772017-11-07T13:32:59.193+01:002017-11-07T13:32:59.193+01:00nice post
nice post<br /> Love Abakumovahttps://www.blogger.com/profile/05855229033239366297noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-65704919269321232432017-11-06T10:39:49.415+01:002017-11-06T10:39:49.415+01:00nice post
nice post<br /> Walter D. Sikeshttps://www.blogger.com/profile/05855229033239366297noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-29763471726659500662017-10-31T12:53:44.646+01:002017-10-31T12:53:44.646+01:00As I’ve not been a good student of physics I don’t...As I’ve not been a good student of physics I don’t have much idea regarding this post, but at least being good in my basic, I think the idea given in this post is much helpful.<a href="http://www.rushmypapers.me/">paper writer service</a>https://www.blogger.com/profile/14692066396687335496noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-92039497580191988292017-10-25T17:37:55.666+02:002017-10-25T17:37:55.666+02:00hmmmmmhmmmmmJeCksOnhttps://www.blogger.com/profile/12087778649552689484noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-21919324563684380192017-09-27T08:35:04.457+02:002017-09-27T08:35:04.457+02:00Yes, all currently open positions have been filled...Yes, all currently open positions have been filled. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-29246732133542584352017-09-26T22:03:07.572+02:002017-09-26T22:03:07.572+02:00Hello,
Have PhD positions been filled? The deadli...Hello, <br />Have PhD positions been filled? The deadline to apply is in December, right?<br /><br />Sergio Patiño Lópezhttps://www.blogger.com/profile/10812899636350499988noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-70996111797231351522017-04-07T09:25:41.946+02:002017-04-07T09:25:41.946+02:00Excellent advice, I know about this not by hearsay...Excellent advice, I know about this not by hearsay, it's a real experience of many years of work. I have been making presentations on various topics and products for a long time. Especially useful for beginners, who do not fully understand why this is done so scrupulously and accurately. If you like to work with Google tools, this will help you <a href="https://poweredtemplate.com/google-slides-themes/" rel="nofollow">https://poweredtemplate.com/google-slides-themes/</a> to diversify your work and add unique features.Kenneth Franzhttps://www.blogger.com/profile/05888858156254081041noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-46172755204989392982016-06-24T10:49:14.408+02:002016-06-24T10:49:14.408+02:00In order to establish a connection between LQG and...In order to establish a connection between LQG and string theory one needs an effective field theory approximation to LQG whith matter, where the matter is represented by special loops embedded in a spin network.<br /><br />As far as the pure LQG is concerned, the first step towards an effective field approximation is an effective action for the corresponding spin-foam model. This formalisam was developed in a series of papers by M. Vojinovic and myself four years ago.A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-29256122970216975282016-04-28T08:51:40.126+02:002016-04-28T08:51:40.126+02:00Matter propagates in a spin foam according to the ...Matter propagates in a spin foam according to the discretized form of the corresponding matter-field action. In the case of fermions there is a problem to formulate such an action because the fermions couple to the tetrads, and the tetrads are not well-defined in a spin-foam geometry. That was the reason to propose a spin-cube formulation, which is a generalization of the spin-foam formulation, based on the substitution of the spin-foam group by a 2-group (in the QG case the Lorentz group is replaced by the Poincare 2-group). The consequence is that the tetrads enter the formalism explicitely, through the edge lengths, so that a spin foam (a colored 2-complex) is replaced by a spin cube, which is a colored 3-complex. Hence in a spin cube the edges carry the 2-group irreps, the triangles carry the corresponding 1-intertwiners and the tetrahedrons carry the corresponding 2-intertwiners as oposed to a spin foam where the triangles carry the group irreps and the tetrahedrons carry the corresponding intertwiners.A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-22811942066855870582016-04-27T11:45:40.255+02:002016-04-27T11:45:40.255+02:00Thank you for the clarification. It still seems to...Thank you for the clarification. It still seems to me that the notion of local Lorentz invariance that you refer to is not what one means when one asks whether LQG is locally Lorentz invariant from a phenomenological point of view. There, the question of how matter propagates, morally from 4-simplex to 4-simplex, is the relevant one. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-7067440309221112032016-04-26T14:52:53.431+02:002016-04-26T14:52:53.431+02:00In canonical LQG the local Lorentz invariance can ...In canonical LQG the local Lorentz invariance can be established by constructing the generators of local Lorentz rotations from holonomy and flux operators (if there is fermionic matter one has to add the matter contributions to the generators) and then verify that the algebra closes. This is a difficult task and anomalies may appear. In the spin-foam case, the analog of the local Lorentz transformations would be the Lorentz transformations that preserve the flat metric in each 4-simplex (provided that such a metric exists in every 4-simplex).A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-35822346223921822432016-04-25T11:38:02.938+02:002016-04-25T11:38:02.938+02:00Thank you for pointing out these differences betwe...Thank you for pointing out these differences between canonical LQG and the spinfoam formulation. I didn’t include them in my post, because I thought that they would distract too much from the core issues. <br /><br />About Lorentz invariance: I am not sure if we speak about the same thing. As emphasised in the post, the notion of “Lorentz invariance” appears in LQG both when choosing the internal gauge group (which can be the Lorentz group), and in the context of the question how the quantum geometry described by your physical state behaves (e.g. how matter fields propagate on it). While there are spinfoam models which are “Lorentz invariant” w.r.t. the the former notion, this is not clear for the second one, and thus for what people usually mean by Lorentz invariance. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-19602610209561224622016-04-24T12:28:04.800+02:002016-04-24T12:28:04.800+02:00In order to better understand the theory called LQ...In order to better understand the theory called LQG, it is necessary to make the distinction between the spin-foam (covariant) and the canonical formulation. Although many people beleive that these two are the same theory, they are really two different theories. In the canonical LQG<br />the spacetime is topologically Sx[a,b] and there are colored graphs (i.e. spin networks) embedded in a smooth 3-manifold S. A physical state is a linear combination of the spin-network states such that it satisfies the hamiltonian constraint. The classical limit in this case is<br />defined by veryfying whether (hbar)Im(log Psi(A)) satisfies the Hamilton-Jacobi equation for the canonical GR in the limit hbar --> 0 and A is the Ashtekar-Barbero connection on S. This is a very difficult task, so that one uses the spin-foam formulation. In the spin-foam formulation, the theory is formulated on a triangulation of Sx[a,b], which is not the same as the smooth manifold Sx[a,b]. Hence obtaining the classical limit requires performing 2 limits, as you point out, i.e. the limit hbar --> 0, or equivalently j(triangle) --> infinity, and the smooth limit, i.e. N --> infinity, where N is the number of 4-simplices in T(Sx[a,b]). The easiest way to study these two limits is to use the effective action formalism. One then obtains that the first limit gives the area-Regge action. This is a problem, because area-Regge theory does not define always a metric geometry, so it is not equivalent to the usual Regge discretization of GR. Hence one needs to modify the usual spin-foam formulation in order to implement the constraints which reduce the area-Regge theory to the length-Regge theory. <br /><br />As far as the Lorentz invariance is concerned, it is not problematic for the spin-foam formulation, because the unitary irreps of the Lorentz group are (j,p) where j is an SU(2) spin and p is a real number. Also one can assume that the area of a triangle in a spacetime triangulation is determined by the flat metric in a 4-simplex which contains that triangle. The Lorentz invariance is more problematic in the canonical case, because it is not manifest.<br />A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-26351971533305893282016-04-15T12:14:41.739+02:002016-04-15T12:14:41.739+02:00Nice review! I would like to point out that the de...Nice review! I would like to point out that the described approaches are all based on the assumption that the short-distance topological structure of the spacetime is given by a smooth manifold. This is a logical possibility, but somehow I find it difficult to believe. Note that the approaches you refer to as "smaller" are precisely those where the smooth manifold structure is abandoned and one uses a non-commutative manifold, or a discrete set, or a piecewise linear manifold, etc ... Even in the case of CDT, although the theory is defined in the picewise linear manifold case (a triangulation), the goal is to obtain the smooth-manifold limit. More than 20 years ago Chris Isham has described this problem in one of his QG reviews: one starts with a smooth manifold M and a metric g, so the simplest thing is to replace (M,g) with (M,g*), where g* is an operator. A more general quantization is to replace (M,g) with (M*,g*) where M* and g* are some quantum generalizations of M and g.A. Mikovichttps://www.blogger.com/profile/03175906801121515444noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-81717218494102153982016-04-13T11:12:50.517+02:002016-04-13T11:12:50.517+02:00Hi Vedran,
thanks a lot for your input. I incorp...Hi Vedran, <br /><br />thanks a lot for your input. I incorporated it in the post. <br />Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-55562607441219592862016-04-12T22:45:45.288+02:002016-04-12T22:45:45.288+02:00Hi,
CDT was misspelled as "casual" DT i...Hi,<br /><br />CDT was misspelled as "casual" DT instead of "causal".<br /><br />Also in asymptotic safety you (almost) always go Euclidean.<br /><br />Finally, in asympt. safety spectral dimension apparently goes to 3/2, and not 2 as previously thought. This was confirmed in CDT and very recently Euclidean Dynamical Triangulations (EDT). Note that this result is relevant as it bypasses one usual apriori counterargument against QFTs of gravity.Vedranhttps://www.blogger.com/profile/02194339965441762137noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-27375307889079912012016-04-12T17:30:05.880+02:002016-04-12T17:30:05.880+02:00Dear Jakob,
thanks a lot for your comment. I fix...Dear Jakob, <br /><br />thanks a lot for your comment. I fixed the typo and added a brief explanation for the origins of the name. It originated in the time before it was realised that one needs to go beyond Wilson-loops to have non-vanishing volumes, i.e. to Wilson-"graphs", but it got stuck. Norberthttps://www.blogger.com/profile/04965554394207041308noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-33796708684607819112016-04-12T17:05:37.183+02:002016-04-12T17:05:37.183+02:00Nice review! In the last section an "of"...Nice review! In the last section an "of" is missing in the sentence "The application the main technical and conceptual ideas". In addition, I think a short explanation is missing on why loop quantum gravity is called LOOP quantum gravity at all.<br /><br />Best wishes,<br /><br />Jakob<br />http://JakobSchwichtenberg.com/Jakob Schwichtenberghttps://www.blogger.com/profile/10458230617292717089noreply@blogger.comtag:blogger.com,1999:blog-2381900080106522441.post-34567936851932301202016-03-29T14:15:08.988+02:002016-03-29T14:15:08.988+02:00In his introductory article, Ashketar asks the que...In his introductory article, Ashketar asks the question, "Can one construct a framework that cures the short-distance difficulties faced by the classical theory near singularities, while maintaining an agreement with it at large scales?”’<br />I have suggested that Einstein’s field equations are slightly wrong (because the equivalence principle is completely false for dark matter and even very slightly wrong for ordinary matter) — I have also suggested that Maxwell's equations are slightly wrong. By correcting Einstein's field equations and Maxwell's equations, most problems with singularities might be resolved.<br />Renormalization in quantum electrodynamics deals with infinite integrals that arise in perturbation theory. Such infinite integral might arise merely because Maxwell’s equations are incorrect at the Planck scale. Assume that leptons have structure at the Planck scale. I conjecture that, EVEN AFTER QUANTUM AVERAGING, Maxwell’s equations might be false at the Planck scale, because leptons have structure at the Planck scale. Let ρ represent the electric charge density (charge per unit volume). I conjecture that, in equation (19b) on page 23 of Einstein’s “The Meaning of Relativity” (5th edition), ρ should be replaced by the expression ρ/ (1 – (ρ^2 / (ρ(max))^2))^(1/2), where ρ(max) is the maximum of the absolute value of the electric charge density in the physical universe.<br />The preceding hypothesis makes the qualitative prediction that electromagnetic radiation emanating from sources near black holes might be unexpectedly large. M82 X-2 might be worth considering in this regard.<br /><a href="https://en.wikipedia.org/wiki/M82_X-2" rel="nofollow">M82 X-2, en.wikipedia</a>David Brownhttps://www.blogger.com/profile/10537922851243581921noreply@blogger.com