Kaluza-Klein Particle Production Drives Inflation and Potential Dark Matter Candidates

The search for dark matter and an understanding of the universe’s earliest moments drive current cosmological research, and a new model proposes a surprising link between the two. Yusuke Yamada from Waseda Institute for Advanced Study, alongside colleagues at Waseda University, investigates how particles may have formed in the immediate aftermath of the Big Bang, potentially solving both mysteries simultaneously. Their work demonstrates that gauge fields existing in extra, compact dimensions can generate superheavy particles known as Kaluza-Klein particles through a process similar to creating matter from energy. These particles, the researchers show, could account for the universe’s missing dark matter or even come to dominate its overall energy density, offering a compelling new avenue for exploring the fundamental constituents of our cosmos and the forces that shaped it.

Compact dimensions enable the production of Kaluza, Klein (KK) particles charged under the field via the Schwinger effect. The research constructs an extra-natural inflation model within a five-dimensional (5D) quantum electrodynamics (QED) framework coupled to gravity, including matter fields that generate the inflationary one-loop effective potential. Multiple charged fields can exist, and the study demonstrates that KK particle production occurs under these conditions. Because KK momentum is conserved, the produced KK particles may become superheavy dark matter or dominate the universe, depending on the model parameters. Furthermore, the research shows that even when the gauge field does not act as the inflaton, this remains true.

Early Universe Particle Production and Perturbations

Researchers are investigating how particles, particularly those that could constitute dark matter, were created in the very early universe during a period of rapid expansion known as inflation. This process involves understanding how energy was transferred from the field driving inflation to create the particles we observe today. A key focus is on mechanisms that produce massive particles, potentially solving the mystery of dark matter’s composition. The team highlights the importance of comparing theoretical predictions with observational data from the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO), which provide snapshots of the early universe. Discrepancies between measurements of these two phenomena, known as the BAO-CMB tension, are being investigated to refine cosmological models.

Compact Dimensions Drive Inflation and KK Particle Production

Researchers have discovered a novel mechanism for driving inflation, the rapid expansion of the early universe, using gauge fields existing in extra, compact dimensions. This “extra-natural inflation” model proposes that these fields generate an electric field within the compact dimension, leading to the production of particles known as Kaluza-Klein (KK) particles via a process analogous to the Sauter-Schwinger effect. The team’s calculations demonstrate that this process isn’t just theoretical; it naturally produces superheavy KK particles, potentially accounting for a significant portion of the universe’s dark matter. This model differs from standard inflation scenarios by offering a pathway to generate these KK particles without requiring specific conditions on their mass, as long as the gauge fields remain relatively light.

The research reveals that even if the gauge field doesn’t directly drive inflation, its oscillations after inflation can still create these superheavy particles. This suggests that KK particle production is a generic outcome whenever gauge potentials exist in these extra dimensions, broadening the possibilities for understanding the early universe. Importantly, the team found that the energy scale of the produced KK particles is significantly higher than previously considered for cosmological particle production. The study reveals that these KK particles are not merely a byproduct of inflation, but could potentially constitute a significant portion of the universe’s mass, even acting as dark matter. The research further establishes that KK particle production is a generic outcome whenever light gauge fields exist along compact dimensions, even if those fields do not directly drive inflation. The authors acknowledge that the precise fate of these superheavy KK particles, whether they become dark matter or dominate the universe, depends on specific model parameters requiring further investigation.