CWRU Physics Faculty
Claudia de Rham
Baldwin Assistant Professor
Ph. D. Cambridge University, UK (2006)
I am a cosmologist working on very early Universe Cosmology and Dark energy.
More precisely, my
main research interests cover
- Dark Energy and the CC Problem: Particle physics theories typically predict the presence of a vacuum energy, at worst of the order of the Planck mass MPl ~ 1072GeV4, which would cause the Universe to accelerate with a Hubble parameter H ~ 1061km/s Mpc, or at best of the order of the supersymmetry breaking scale Msusy ~ TeV4. Since this is clearly incompatible with observations, physicists have for a long time assumed that some symmetry sets this vacuum energy to zero. However, in 1998, observations of type Ia supernovae measured for the first time the acceleration of the Universe with precision, corresponding to a Hubble parameter of order H ~ 70km/s Mpc, i.e. consistent with a cosmological constant of order 1048GeV4, that is 120 orders of magnitude smaller than predicted from particle physics. This measurement was soon confirmed by many other sources, such as the CMB, matter density and gravitational lensing and is to date arguably the most embarrassing puzzle of modern cosmology.
- Cosmological Perturbations:
The power spectrum and non-gaussianities present in the Cosmic Microwave
provide strong signatures of models of brane inflation.
Click here for a list of papers on the subject.
- Modified / Massive Gravity:
A potential idea to tackle the cosmological constant problem, is to weaken
the effect the vacuum energy has on the geometry by modifying gravity at
large distances (of the order of the Hubble scale today). Effectively this
is possible the graviton was massive or had resonance.
This is the idea behind the degravitation model suggested by N. Arkani-Hamed, S. Dimopoulos, G. Dvali and G. Gabadadze, in 2002 and by G. Dvali, S. Hofmann, and J. Khoury, in 2007
The SLED, or Supersymmetric Large extra dimensions, first proposed by
Y. Aghababaie, C. Burgess, S. Parameswaran
and F. Quevedo in 2003
another potential resolution to the
Naturalness Problem of the Cosmological Constant using two compactified
supersymmetric extra dimensions of submillimeter size, hence potentially
tackling the gauge hierarchy problem.
See Cliff Burgess's review
- EFT of codimension-2 objects: Exploring the effective physics for observers localized on codimension-2 branes or cosmic string and understanding the consequences for the Hierarchy problem and the Cosmological Constant problem.