[JHEP 2026] The Menagerie of Wormholes: A New Holographic Origin for Our Inflating Universe

TL;DR

Theoretical physicists have mapped out a "menagerie" of gravitational solutions in the Euclidean path integral, discovering that "wineglass-shaped" wormholes might be the true progenitors of our universe. Unlike the famous but troubled Hartle-Hawking "No-Boundary" state, these AdS-anchored wormholes naturally explain why our universe started with a period of rapid inflation.

Context: Beyond the "No-Boundary" Paradox

For decades, the No-Boundary Proposal by Hartle and Hawking was the gold standard for describing the "beginning" of time. However, it harbors a nasty secret: it statistically prefers a universe with no inflation, which contradicts everything we see in the Cosmic Microwave Background (CMB).

The authors of this paper shift the coordinate system. By assuming Asymptotically Anti-de Sitter (AdS) boundary conditions, they leverage the power of Holography (AdS/CFT) to define a much richer and more predictable Hilbert space for the universe. In this framework, the "birth" of the universe isn't a point, but a transition between different gravitational "saddles" or shapes.

The Menagerie: Categorizing Spacetime Shapes

The paper meticulously classifies four types of Euclidean geometries that compete to be the "dominant" origin story:

1. Disconnected Geometries: Two separate AdS "caps." These represent a non-cosmological outcome where the universe never truly "begins."
2. Simple Wormholes: A tube connecting two boundaries. These continue into "crunching" universes—short-lived and doomed.
3. Wineglass Wormholes: A more complex tube that expands, then narrows, then expands again. These are the "Holy Grail"—they continue into inflating FLRW universes.
4. Oscillatory Wormholes: Exotic shapes where the "throat" bounces multiple times, suggesting a more complex multi-stage early universe.

Figure 1: Comparison of the different Euclidean AdS gravitational saddles. Note how the "Wineglass" geometry (third from left) provides the bridge to an expanding, inflationary cosmology.

Methodology: How to Build a Wormhole

To make these shapes mathematically tractable, the authors use an Einstein-Scalar-Maxwell model. The secret sauce is the $U(1{)}^3$ gauge field. In Euclidean signature, a dominant magnetic field creates a negative energy density (${\rho }_{rad}^E<0$).

This negative density acts as a "support" for the wormhole throat, preventing it from collapsing. By using a piecewise analytic ansatz, the team was able to solve the Equations of Motion (EOM) across different regions (AdS-like vs. dS-like) and ensure a smooth join up to the third derivative ($O(a^{\prime \prime \prime })$).

The Discovery: Phase Transitions in the Path Integral

The most striking part of the paper is the "battle" between these shapes. Using Background Subtraction—a technique to cancel out the infinite volume of AdS boundaries—the authors calculated which shape is the "cheapest" in terms of Action ($S_E$).

• Dirichlet vs. Neumann: The choice of Boundary Conditions (BCs) for the scalar field changes everything.
• Inflation Emergent: Under "Neumann" conditions for the scalar field, wineglass wormholes actually dominate when the electromagnetic source is small.
• Physical Insight: This means that in a specific regime of quantum gravity, an inflating universe isn't just possible—it is the most probable outcome.

Figure 2: The on-shell action differences. The "jumps" in these lines represent phase transitions where the universe shifts from a "dead" state to a "cosmological" wormhole state.

Deep Insight: The "Initial State" Problem Resolved

One of the biggest headaches in cosmology is the Initial Condition. Why did the inflaton field start high up on its potential plateau?

This paper provides a geometric answer: For the wineglass wormhole to exist, the scalar field must explore the positive region of the potential. The wormhole geometry itself "selects" the high-energy state required for inflation.

Limitations and Future Work

While the piecewise ansatz is a brilliant tool for analytic control, it is an approximation of a single, smooth (but unknown) scalar potential. Future research will likely focus on:

• Numerical verification with more "natural" Higgs-like potentials.
• Cosmological Correlators: Calculating the actual CMB signatures these wormholes would leave behind.
• Centaur Geometries: Exploring if the universe could "smoothly cap off" without a second boundary.

Conclusion

By treating the early universe as a "Menagerie" of competing wormholes, this research brings us closer to a version of quantum cosmology that is both mathematically rigorous (holographic) and phenomenologically successful (inflationary). The universe didn't just happen; it was the winner of a geometric high-stakes competition.