# Born-Infeld Gravity Theories

## İbrahim Güllü

Ortadoğu Teknik Üniversitesi

**Özet :** The BI gravity, in some sense, is the most natural, minimal generalization

of Einstein’s gravity with a better UV behavior, and hence, is a potentially

viable proposal for low energy quantum gravity. We develop techniques of

analyzing the unitarity of general Born-Infeld gravity actions in D-dimensional

spacetimes. The determinantal form of the action allows us to find a compact

expression quadratic in the metric fluctuations around constant curvature

backgrounds. This is highly nontrivial since for the Born-Infeld actions,

in principle, infinitely many terms in the curvature expansion should contribute

to the quadratic action in the metric fluctuations around constant curvature

backgrounds, which would render the unitarity analysis intractable.

By using the developed techniques we construct Born-Infeld (BI) type gravity

theories which describe tree-level unitary (nonghost and nontachyonic)

massless spin-2 modes around their maximally symmetric vacua in four dimensions.

Building unitary BI actions around flat vacuum is straightforward, but this is

a complicated task around (anti)-de Sitter backgrounds. We solve the issue and

give details of constructing perturbatively viable determinantal BI theories.

It is interesting that the Gauss-Bonnet combination, which is a total derivative

in four dimensions, plays an important role in the construction of viable

BI theories.

We also construct an n-dimensional Born-Infeld type gravity theory that has

the same properties as Einstein’s gravity in terms of the vacuum and particle

content: Namely, the theory has a unique viable vacuum (maximally symmetric

solution) and a single massless unitary spin-2 graviton about this vacuum.

The Gauss-Bonnet combination again plays a non-trivial role in the construction

of the theory. As an extreme example, we consider the infinite dimensional

limit where an interesting exponential gravity arises.

**Tarih :** 29 Eylül 2016 Perşembe, Saat: 15:00

**Yer :** MSGSÜ Bomonti Yerleşkesi, Fizik Bölümü

**Ayrıntılı bilgi :** Cemsinan Deliduman (cemsinan@msgsu.edu.tr)