# Horava Gravity talks now available on line

1. Nov 8, 2009

### MTd2

http://pirsa.org/C09026

You can consider Petr Horava talk as both the last talk of Asymptotic safety conference or the first of Horava Gravity, since he tries to tie both of them to a common origin. Nice! :)

2. Nov 9, 2009

### atyy

He says that Horava-Lifgarbagez does NOT break Lorentz invariance!

Because it was never there in the first place :rofl:

Apparently he's working with Cenke Xu - who's a condensed matter guy who's worked on emergent gravitons before - http://arxiv.org/abs/cond-mat/0602443.

Last edited: Nov 9, 2009
3. Nov 9, 2009

### MTd2

http://pirsa.org/09110131/

CDT and Horava-Lifgarbagez gravity
Speaker(s): Jan Ambjorn

4. Nov 9, 2009

### MTd2

http://pirsa.org/09110060/
Horava-Lifgarbagez gravity: What's the matter?
Speaker(s): Gianluca Calcagni

I didn't quite understood the dialogue between Horava and the other guy, but Gianluca looked a bit embarrased :S

5. Nov 10, 2009

### MTd2

Now all talks are available online, check that out!

6. Nov 10, 2009

### atyy

So what's the update on the scalar mode? Has it been gotten rid off or turned into a feature?

7. Nov 10, 2009

### MTd2

No one knows for sure. Check Shiji talk (im sorry, there was indeed a talk abot the scalar mode) and Ted Jacobson`s sumary of the conference. For me, it seems feature a feature.

8. Nov 10, 2009

### marcus

I took your advice and watched both Shinji and Ted Jacobson. Especially enjoyed Jacobson. Absolutely wonderful. His own impromptu insightful comment, and also the wide open discussion with many people excited and speaking up----Petr Horava, Niayesh Afshordi, Lee Smolin, Shinji, Diego Blas, Robert Brandenberger.
http://pirsa.org/09110066/

9. Nov 10, 2009

### MTd2

Shinji uploaded today a new paper. I dare to say it is the best one until this date on Horava gravity. He goes way beyond the title. He does short but extraordinarily didadic expositions of the problems and prove solutions that help solve them. Along the way, he shows amazing things, like there is no real horizon on a black hole, but the speed of light goes to infinity at when one approaches where it should be the singularity. It is an amazing read.

http://arxiv.org/abs/0911.1814

Stellar center is dynamical in Horava-Lifgarbagez gravity

Keisuke Izumi, Shinji Mukohyama
(Submitted on 10 Nov 2009)
In Horava-Lifgarbagez gravity, regularity of a solution requires smoothness of not only the spacetime geometry but also the foliation. As a result, the regularity condition at the center of a star is more restrictive than in general relativity. Assuming that the energy density is a piecewise-continuous, non-negative function of the pressure and that the pressure at the center is positive, we prove that the momentum conservation law is incompatible with the regularity at the center for any spherically-symmetric, static configurations. The proof is totally insensitive to the structure of higher spatial curvature terms and, thus, holds for any values of the dynamical critical exponent $z$. Therefore, we conclude that a spherically-symmetric star should include a time-dependent region near the center. We also comment on the condition under which linear instability of the scalar graviton does not show up.