- About Us
- People
- Undergrad
- Graduate
- Research
- News & Events
-
News by Year
- 2022
- Physics Professors named Canada Research Chairs
- Physics Faculty and Graduate Student Win Teaching Awards
- SFU Physics Professor wins 2021 Buchalter Cosmology Prize
- Dr. Hayden's Research in SFU Scholarly Impact
- Karen Kavanagh selected as a Fellow of the MRS
- Applied Physics undergrad wins AMPP Poster Competition
- Physics BSc Grad Gives Convocation Address
- Dr. Simmons Appointed to Quantum Tech Expert Panel
- Physics Undergrad wins SFU Service Award
- Meet the Canada Research Chair in Silicon Quantum Tech
- Dr. Sivak's Research Featured on NSERC Impact Story
- Physics Grad Wins Dean's Convocation Medal
- First-year Physics major wins John Pearson Prize
- Higgs Boson turns 10!
- SFU Physics BSc graduate wins 2nd prize in the CAP Congress Competition
- Physics members win ATLAS Outstanding Achievement Award
- SFU Physics Research featured in Quanta Magazine
- Silicon Quantum Lab Publishes Major Breakthrough
- Biophysics Research Featured on Scholarly Impact
- Levon Pogosian wins BC Sugar Achievement Award
- Dr. Simmons on SFU's Quantum Computing Breakthrough
- John Bechhoefer named Distinguished SFU Professor
- 2021
- Simmons wins Women of Distinction Award
- Pogosian's Research in SFU Scholarly Impact
- PhD Graduate Awarded Convocation Medal
- Convocation Speaker Aidan Wright
- Nancy Forde Elected BSC President
- Bechhoefer named Royal Society of Canada Fellow
- Jeff Sonier Named American Physical Society Fellow
- SFU undergrads receive quantum grant award
- 2020
- 2019
- 2018
- 2022
- Events by Year
- Events By Category
-
News by Year
- Outreach
- _how-to
- Congratulations to our Class of 2021
- Archive
- Atlas Tier 1 Data Centre
Cosmology Seminar
Alternatives to General Relativity: Counting the degrees of freedom in "Horndeski-like" theories
Daniele Steer
APC, Paris 7
Alternatives to General Relativity: Counting the degrees of freedom in "Horndeski-like" theories
Jan 24, 2017 at 12PM
Synopsis
Scalar-tensor theories of gravity are widely used in cosmology and extensions of general relativity, with applications ranging from inflation to the late-time observed acceleration of the Universe, and tests of gravitation. In this talk we focus on so-called "Horndeski-like" theories - scalar-tensor theories in 4 dimensions having field equations (both for the metric and the scalar) with derivatives of order less than or equal to two - as well as some extensions of these which have been proposed recently. As we will discuss, having covariant second-order field equations is a priori enough, once diffeomorphism invariance is taken into account, to have just 3 propagating degrees of freedom in vacuum (counting 2 for the metric and 1 for the scalar), and to put the theory on the safe side as far as Ostrogradski’s type of instability is concerned. But there seem to be exceptions: indeed the extensions mentioned above appear to have higher order equations of motion and yet propagate 3 degrees of freedom. We will try to clarify these different points, all of which are relevant for the applications of these theories.
http://www.sfu.ca/physics-archive/cosmology/seminars/