# Lectures on Bulk Reconstruction

### Submission summary

 As Contributors: Nirmalya Kajuri Arxiv Link: https://arxiv.org/abs/2003.00587v4 (pdf) Date submitted: 2020-07-14 02:00 Submitted by: Kajuri, Nirmalya Submitted to: SciPost Physics Lecture Notes Academic field: Physics Specialties: Gravitation, Cosmology and Astroparticle Physics High-Energy Physics - Theory Approach: Theoretical

### Abstract

If the AdS/CFT conjecture holds, every question about bulk physics can be answered by the boundary CFT. But we still don't know how to translate all the questions about bulk physics to questions about the boundary CFT. Completing this bulk-boundary dictionary is the aim of the bulk reconstruction program, which we review in these lectures. We cover the HKLL contruction, bulk reconstruction in AdS/Rindler, mirror operator construction of Papadodimas and Raju and the Marolf-Wall paradox. These notes are based on lectures given at ST4 2018.

###### Current status:
Editor-in-charge assigned

### Submission & Refereeing History

Resubmission 2003.00587v4 on 14 July 2020
Submission 2003.00587v3 on 16 March 2020

## Reports on this Submission

### Report

This is my second round of refereeing of this manuscript (reflecting arXiv v4). While I am largely satisfied with the author's responses and corrections, there are still some lingering issues.

p.5 Eq. 6: If the gravitational action has not been expanded, then the question remains why there isn't a $O(N)$ term, as one would expect from a generic expansion in $N$. If the answer is that there cannot be such a term so that the CFT is in correspondence with an action that describes pure Einstein gravity plus a scalar field, then is this an assumption? Can you check this in examples? The example that I'm aware of is the partition function of 2D QCD (hep-th/9301068), but I would ask that the author comment further on this consideration.

p.9 below Eq. 30: I think it should read "We can see from (14) that modes between $-\Delta$ and $\Delta$ do not appear..."

p.9 above Eq. 31: Open bracket, incorrect capitalization, "too"

p. 18 penultimate parag.: incorrect spacing, capitalization in parentheses

p.20 above Eq. 62: \times instead of $X$, should read $\mathbb{R}$ instead of $R$ throughout paragraph.

p.26 footnote 8: "rRemember"

p. 28 below Eq. 90: My comment 7.10 has not been satisfactorily addressed. The sentence still contains typos and grammar issues.

p.28 parag. above Eq. 91: "equiilibrium"

p. 29 below Eq. 92: "how doe", again use \times instead of $X$

I again urge the author to carefully go through the manuscript and fix presentation issues, as I requested in my original report. In particular, the author should pay close attention to typos, punctuation, italicization, and indentation.

### Requested changes

1- Itemized comments in report
2- Fix typos, presentation, and formatting issues throughout

• validity: good
• significance: -
• originality: -
• clarity: high
• formatting: below threshold
• grammar: reasonable

### Report

This article provides a well-written, accessible and coherent perspective on bulk reconstruction. The strengths, weaknesses and my overall summary remain as before. But the current version has been corrected and improved in many small ways. It will be particularly useful for readers who are new to the field or are looking for an entry to the literature.

• validity: -
• significance: -
• originality: -
• clarity: -
• formatting: -
• grammar: -