It’s been a while, and this post will likely be updated tomorrow to include more.

Here’s what I found of interest in gr-qc over the past couple days:

Relativistic Cosmological Perturbation Theory and the Evolution of Small-Scale Inhomogeneities. (arXiv:1106.0627v4 [gr-qc] UPDATED)

http://arxiv.org/abs/1106.0627

The title is so ridiculous I had to save it and read the abstract. I know there is a mathematical basis for it, but “Cosmological Perturbation Theory” is the kind of thing that makes me think “Good luck; have fun”

Updated constraints from the PLANCK experiment on modified gravity. (arXiv:1307.2002v1 [astro-ph.CO])

http://arxiv.org/abs/1307.2002

Contraints are good. This sets specific limits on the length-scale parameter B0 in f(R) gravity.

note: f(R) gravity is a family of theories in which we have different functions of the Ricci scalar appear in the Einstein-Hilbert action.

Impacts of Generalized Uncertainty Principle on Black Hole Thermodynamics and Salecker-Wigner Inequalities. (arXiv:1307.1894v1 [gr-qc])

http://arxiv.org/abs/1307.1894

Saved because I was curious what some of the things involved are. Apparently you can relate the mess of generalized uncertainty principles to the lifetime of BHs among other things.

note: The Generalized Uncertainty Principle is denoted dp * dx = hbar/2 [ 1 + b0 (Lp/hbar)^2 (dp)^2 ]

b0? seems to allow for a minimum length slightly above the planck length if you take the Plank momentum as a maximum, I guess?

I should mention that Doubly Special Relativity [should investigate later] apparently uses a different Heisenberg relationship and the relation shown is typical in BH physics and applies in Str Theory. Similarly, a quadratic form has been used recently, it seems.

note: Salecker-Wigner Ineqs -the first appear to relate the uncertainty in position in one frame to the next, dx’ = dx + hbar*t/2m (dx)^-1…this is complicated from what I can tell and involves some concept of “coherence” in quantum gravity with respect to proper time [also not really an ineq?]; the second deals with the minimum mass of a quantum clock m >= k t_max/t_min^2 where k is some constant.

Universal Landau Pole. (arXiv:1302.4321v3 [hep-th] UPDATED)

http://arxiv.org/abs/1302.4321

Starts off the bat with big assumptions in the abstract… “Our understanding of quantum gravity suggests that at the Planck scale the usual geometry loses its meaning.”

But let’s go with that for now…

They suppose a unified fundamental interaction at Planck scale at the Universal Landau Pole where *all* couplings diverge, right, except QCD? I am too lazy to read this right now, but last I checked alpha_s fit the bill for a “gauge coupling”

Wait “at which all gauge couplings diverge. The Higgs quartic coupling also diverges while the Yukawa couplings vanish” what? maybe I need to see what the difference between a gauge and a Yukawa coupling is…

On the plus side, this supposedly fixes any instabilities in the SM vacuum, woo?

A Note on (No) Firewalls: The Entropy Argument. (arXiv:1211.7033v4 [hep-th] UPDATED)

http://arxiv.org/abs/1211.7033

“An argument for firewalls based on entropy relations is refuted.”

Clean & Simple. Not reading at the moment, but half-glad this is still going on.

A new limit on local Lorentz invariance violation of gravity from solitary pulsars. (arXiv:1307.2552v1 [gr-qc])

http://arxiv.org/abs/1307.2552

I’m not crazy about limit papers, but they’re important so I need to at least read the abstracts. Apparently, there are three parameters you can use to quantify local Lorentz violation in PN form. Going to strong-field we have alpha_2 which induces precession of pulsar spin around its direction of motion in the preferred frame. They contrained alpha_2. Limit is ~10^-9 which is better than the ~10^-7 Solar system limits, limit on alpha_3 is 10^-20 and alpha_1 is 10^-5 though I haven’t investigated why; in GR these numbers are zero.

A formal introduction to Horndeski and Galileon theories and their generalizations. (arXiv:1307.2450v1 [hep-th])

http://arxiv.org/abs/1307.2450

Curious what the things in the title are. Requirements for Galileons are outlined as: scalar field in flat space with field eq that are polynomial in second order derivatives of the field only. No higher or lower order derivatives…weird.

note: Galileons theories are a subset of Horndeski theories.

note on note: Horndeski action is given by

S = S_GG [gmunu, phi] + S_m [gmunu, psi]

SGG is over a mess of Lagrangians…it’s so ugly I don’t see the motivation. It’s sort of a generalization of Galileons in that it appears to stop at second order derivatives, but you have plenty of first order derivative terms.

Yuck.

more to come on this, then probably a quick run of my top papers from astro-ph and maybe hep-ph.

I guess we’ll see?