# 10/3 Special Lunch talk: The Cosmological Equation of State

### Non-parametric evolution study of cosmological equation of state with SNeIa, BAO and GRBs.

## Dr. Sergey Postnikov

Nuclear Theory Center, Indiana University

CAS 500

12:30 pm

October 10, 2013

**Abstract:**

We study the dark energy equation of state as a function of redshift $z$ in a non-parametric way, without imposing any {\it a priori} $w(z)$ functional form. As a check of the method, we test our scheme through the use of synthetic data sets produced from a known cosmological model, and having the same relative errors and redshift distribution as the real data. Through proposed luminosity-time $L_{X}-T_{a}$ correlation for GRB X-ray afterglows (the Dainotti et al.), we are able to utilize GRB sample from the {\it Swift} satellite as probes of the expansion history of the Universe out to $z \~ 10$. Within the assumption of a flat FLRW universe and combination of SNeIa data with BAO, relatively probable solutions are close to a constant $w=-1$ solution. If one imposes the restriction of a constant $w$, we obtain $w=-0.99 \pm 0.06$ (consistent with a cosmological constant) and the present day parameters are $H_{0}=70.0 \pm 0.6 \, km \, s^{-1} Mpc^{-1}$ and $\Omega_{\Lambda 0}=0.723 \pm 0.025$. Whereas non-parametric solutions give us probability map which is centered at $H_{0}=70.04 \pm 1 \, km \, s^{-1} Mpc^{-1}$ and $\Omega_{\Lambda 0}=0.724 \pm 0.03$. Our GRB sample allows us to estimate amount and quality of data needed to constrain $w(z)$ in range which extends by an order of magnitude in redshift beyond SNeIa.