Loopy Ryu-Takayanagi?

 A paper that came to my attention from a Twitter feud on LQG is this paper by Smolin, resulting in me adding a new category to this blog, called ``Loops":

[1608.02932] Holographic relations in loop quantum gravity

This is interesting for two reasons. Firstly, it invokes categorial holography as Smolin terms it, which was introduced by Crane in his paper called Categorial Physics, and secondly, it uses spin networks in an interesting way. The idea is to use punctured 2-surfaces and attribute to them a Hilbert space, and eventually attributing to quantum spinnet a ``bulk" by extending from the punctures. Essentially, stating that there is a map $\mathcal{T}^{p}: \mathcal{H}_{\mathcal{B};j, i}\to \mathcal{H}_{\Sigma ; j, i}$ as noted in the paper. However, I must say something here; one may not need to invoke these constructions in the first place and instead approach a deformation perspective, such as Cauchy slice holography or in general, holography of information if canonical quantum gravity is all we wanted. The feud seems to be very unnecessary and for that matter I don't think there is any need to point fingers saying ``string theory is just conjecture" or ``LQG is just conjecture". If such holography is emergent (as it seems above, but I am no expert) in LQG, then it is very fascinating. Calumny is a dangerous thing and as is the nature of politicising quantum gravity. 

Horowitz-Myers AdS soliton conjecture

A ``new" positive energy conjecture was conjectured back in 1999 by Horowitz and Myers [arXiv:hep-th/9808079], which somehow escaped my attention till Steve McCormick mentioned it to me in a tweet (X-post? sounds weird though). I will briefly outline what it is, but the technicalities will be left to the reader as an exercise. The idea is essentially to take the near-extremal p-brane solution and double Wick rotate it, so as to obtain the AdS soliton with periodicity. The interest then would be to work with metrics that look like 

\[g_{\mu \nu }=\tilde{g}_{\mu \nu }+h_{\mu \nu }\]

and fall-off conditions w.r.t $r$, where $\tilde{g}_{\mu \nu }$ is the AdS soliton metric. Horowitz and Myers go on to propose two conjectures, which are as follows:

1. SUGRA solutions: $g_{\mu \nu }=\tilde{g}_{\mu \nu }$ is the only solution to $D=10$ type IIB SUGRA, taking $\tilde{g}_{\mu \nu }\times S^{5}_{l}$ for which $\mathcal{E}= 0$, and $\mathcal{E}\geq 0$ in general.
2. Geometric solutions: $g_{\mu \nu }=\tilde{g}_{\mu \nu }$ is the only solution to $D=5$ field equations with $\Lambda = -6/l^{2}$ so that $\mathcal{E}=0$, and $\mathcal{E}\geq 0$ in general.

Seemingly, these are still open problems. However, I believe that resolving at least some aspects of these conjectures will go a long way in making sense of the geometric description of AdS/CFT. 

Papers to Read

 I was asked what papers I have on my library so far. Since I found it hard to try and point out each paper, I have uploaded a part of the library to the github repository. Hopefully, these papers are the significant advances that one just beginning to work in hep-th can refer to, and other papers that I have not included will be mentioned later. I do not mean any copyright infringement if such a thing happens. If there is the possibility of that, I will instead replace the directory with arXiv links, which should be better. For now, enjoy :)

Papers in high energy physics Theory