# The Null Energy Condition and its violation

## TL;DR

This paper reviews scalar field theories with second-derivative Lagrangians that can violate the Null Energy Condition without obvious problems, exploring their applications in cosmology and universe creation experiments.

## Contribution

It provides a concise overview of theories violating the Null Energy Condition and discusses their potential use in cosmology and laboratory universe creation.

## Key findings

- Some scalar theories admit NEC violations without pathologies
- Examples of these theories applied in cosmology
- Potential for universe creation in laboratory settings

## Abstract

We give a mini-review of scalar field theories with second-derivative Lagrangians, whose field equations are second order. Some of these theories admit solutions violating the Null Energy Condition and having no obvious pathologies. We give a few examples of using these theories in cosmological setting and also in the context of the creation of a universe in the laboratory.