Can we live in a baby universe formed by a delayed first-order phase transition?

TL;DR

This paper explores the possibility that our universe originated as a baby universe formed by a delayed first-order phase transition within a specific particle physics model, linking early universe cosmology with collider physics.

Contribution

It introduces a novel measure for the probability of residing in a baby universe and demonstrates its high likelihood within a gauged $U(1)_{B-L}$ extension of the Standard Model.

Findings

Probability measure can be close to 1 in significant parameter regions.

Model is consistent with current cosmological observations.

Predicts a detectable heavy neutral gauge boson at colliders.

Abstract

We examine the idea that our universe began as a baby universe and show that this is feasible in a gauged $U(1)_{B-L}$ extension of the Standard Model with the classically conformal principle. For the first time, we define a measure to describe the probability that we reside in a baby universe, and find that it can be close to 1 in a considerable portion of the parameter space. The framework is consistent with current cosmological data, and it predicts the existence of a heavy neutral gauge boson, which could be detected at colliders, thereby offering a direct link between early-universe dynamics and experimentally testable signatures at the TeV scale.