# QCD-Electroweak First-Order Phase Transition in a Supercooled Universe

## TL;DR

This paper explores a novel cosmological scenario where a first-order QCD phase transition triggers electroweak symmetry breaking in a classically conformal B-L model, with implications for collider physics and early universe phenomena.

## Contribution

It demonstrates a new sequence of phase transitions in a conformal B-L model, where QCD triggers electroweak symmetry breaking, differing from standard cosmological models.

## Key findings

- A first-order QCD phase transition can precede electroweak symmetry breaking.
- Predicted light, weakly coupled particles relevant for collider searches.
- Potential implications for baryogenesis, dark matter, and gravitational waves.

## Abstract

If the electroweak sector of the standard model is described by classically conformal dynamics, the early Universe evolution can be substantially altered. It is already known that---contrarily to the standard model case---a first order electroweak phase transition may occur. Here we show that, depending on the model parameters, a dramatically different scenario may happen: A first-order, six massless quark QCD phase transition occurs first, which then triggers the electroweak symmetry breaking. We derive the necessary conditions for this dynamics to occur, using the specific example of the classically conformal B-L model. In particular, relatively light weakly coupled particles are predicted, with implications for collider searches. This scenario is also potentially rich in cosmological consequences, such as renewed possibilities for electroweak baryogenesis, altered dark matter production, and gravitational wave production, as we briefly comment upon.