5. Theoretical Physics (CSN4)

# An effective theory of quintessence perturbations (by Jorge Norena)

## by Dr Jorge Norena (SISSA-ISAS Trieste)

Europe/Rome
Aula Seminari (Laboratori Nazionali di Frascati)

### Aula Seminari

#### Laboratori Nazionali di Frascati

Description
An appealing alternative to the cosmological constant to explain the accelerated expansion of the universe is quintessence, in which the expansion of the universe becomes dominated at late times by a scalar field. We perform a general analysis in the spirit of effective theories of the perturbations of a quintessence field, thus studying the theoretical constraints on the parameter space. In particular, we argue that an equation of state of the form $p = w\rho$ (where $p$ and $\rho$ are, respectively, the effective pressure and energy density of quintessence) with $w < -1$ can be attained by a single scalar field without the theoretical inconsistencies of the models involving a ghost, and show that it is possible to formulate models that evolve through $w = -1$, differently with what is usually stated in the literature.