Scuola Normale Superiore di Pisa

## Talks by Alberto Salvio

## Quadratic Gravity

Alberto Salvio
Scuola Normale Superiore di Pisa

An extension of general relativity (GR) obtained by adding local quadratic terms to the action will be considered. Such theory can be a viable UV completion of GR. The additional terms soften gravity above a certain energy scale and render gravity renormalizable. The presence of 4 derivatives implies via the Ostrogradsky theorem that the *classical* Hamiltonian is unbounded from below.

## UV-complete relativistic field theories and softened gravity

Alberto Salvio
Scuola Normale Superiore di Pisa

A field theory is fundamental if it features a UV fixed point (either trivial or interacting). Gravity may not change drastically the UV behavior if the Einstein gravitational interactions are softened above a critical sub-Planckian energy scale. A concrete implementation of this softened gravity can be obtained by adding terms quadratic in the curvature to the Einstein-Hilbert action. One way to implement this scenario consists in requiring that all matter couplings flow to zero at infinite energy (total asymptotic freedom).

## Magnetic Properties of (Holographic) Superconductors

Alberto Salvio
Scuola Normale Superiore di Pisa

I will discuss magnetic properties of superconductors, first in a model independent way and then by using holographic models. This approach has the advantage of highlighting the generic features of superconducting materials and, at the same time, the predictions of specific models. I will start with the Meissner effect and the vortices. Given the importance of the magnetic field dynamics in these phenomena, I will describe how to introduce a dynamical gauge field in holography. Then I will show that the holographic superconductor, like all known high-temperature superconductors, is Type II.