• Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.


PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback


(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,075 questions , 2,226 unanswered
5,347 answers , 22,743 comments
1,470 users with positive rep
818 active unimported users
More ...

  Why Can't $AdS_5$ SUSY Extremal Black Holes be Large?

+ 2 like - 0 dislike

When we put the BPS condition and the extremality condition together on the most general black hole solution in $AdS_5$ (with minimally gauged supergravity), we get that the relation between the horizon radius and a parameter $a$ (that can be varied from $0$ to $1$) is the following: $$r_+^2=a(a+2)\tag{1}$$ I work in the units where the $AdS$ radius is set to unity - this sets the $g$ of the linked paper to unity. Also, I should mention that I have taken both the angular momenta to be identical - reducing two parameters $a,b$ of the linked paper to a single parameter $a=b$.

The equation $(1)$ clearly suggests that the radius of a SUSY extremal black hole can not be larger than $1$ by orders of magnitude. On the other hand, both the large extremal and large SUSY black holes individually seem to enjoy the status of valid solutions as one can easily verify from the general expressions in the linked (or any other similar) paper.

Mathematically, I find no inconsistency with these results (nor do I hope/wish to find) but I can't understand in a qualitative sense why the large black holes can't accommodate SUSY and extremality at the same time. In other words, no matter what combination of mass, charge and angular momenta you provide a large SUSY black hole with (that are consistent with the BPS condition), its temperature will always be non-zero. Is there any heuristic explanation for this?

PS: Moreover, as explained in the linked paper, the only way for a SUSY black hole to be free of naked CTCs is to be extremal (or to be a topological soliton). So, in other words, all the large SUSY black holes in $AdS_5$ will always suffer from naked CTCs as they can't be extremal.

This post imported from StackExchange Physics at 2017-07-25 21:38 (UTC), posted by SE-user Dvij

asked Jul 8, 2017 in Theoretical Physics by Dvij D.C. (40 points) [ revision history ]
edited Jul 25, 2017 by Dilaton

As far as it is explained in the linked paper and it follows from calculations (including some sort of restrictions), then why do you pose this "Why? question?

Besides, this subject is so exotic and speculative even for this forum that I am not sure you will get more clarifications than you have already got.

@VladimirKalitvianski the topic is legitimate theoretical physics and therefore just  fine for PhysicsOverflow. We also do have experts in the subject who can potentially answer, so lets hope for the best.

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
Please complete the anti-spam verification

user contributions licensed under cc by-sa 3.0 with attribution required

Your rights