Physics seminar:Dr. Yavuz Eksi,Today, 12 May 2010, FENS L035, 13:40

Constraints on Perturbative f(R) Gravity via Neutron Stars
                                 Dr. Yavuz Ekşi (ITU)
Abstract:
Neutron stars, with their super-nuclear densities are sufficiently extreme objects that allow us to test two important
aspects of fundamental physics: the equation of state of cold nuclear matter i.e. the ultimate ground state of matter,
and gravity in the strong field-high curvature limit. This talk will emphasize the importance of neutron stars in testing
alternative theories of gravity. We then will specialize on perturbative f(R) gravity models of the form
f(R)=R+alpha R^n  where R is the Ricci scalar and the case alpha=0 corresponds to the general relativity of Einstein.
I will discuss the structure of neutron stars in these toy model of gravity, obtain the hydrostatic equilibrium equations
and solve them to find the mass-radius relation. I will present our recent constraint on the value
of alpha by using the recent observational constraints on the mass-radius relation. For n=2 we find that
|alpha| lesssim 10^{10} cm^{2} which is 5 orders of magnitude smaller than the recent constraint obtained from
solar system tests. This implies, for such gravity models, that deviations from Einstein's general relativity in the strong
gravity regime should be below a curvature scale of 10^{-10} cm^{-2}.    
K. Yavuz Ekşi,
Istanbul Technical University
Collaborators: Savaş Arapoğlu, Cemsinan Deliduman (Mimar Sinan University)                    
Wednesday, 12 May 2010,  FENS L035,  13:40