String Theory Background

• String theory invented 1970s, popular 1980s-90s
• Requires 9 dimensions of space (we live in 3)
• String theorists assume 6 extra dimensions rolled up to small sizes (~10^-35 m, Planck length)
• Named after Max Planck who said "science progresses one funeral at a time"

Large Extra Dimensions Evolution

• Late 1990s: Idea that some dimensions much larger than Planck length
• Called "large extra dimensions" - could be measurable with next generation experiments
• 20 years ago: Multiple experiments searched (particle colliders, astrophysics, tabletop)
• Results: No evidence found

Dark Dimensions Research Program

• Revival began 2022 around Cumrun Vafa (Harvard string theorist)
• Focus: One extra dimension particularly large (~1 micrometer)
• Other 5 dimensions ignored as too small to measure
• Current experimental constraints: ~52 micrometers
• Justification: Related to cosmological constant and "swamp conjecture"

Dark Matter Connection

• Dark matter: 80% of universe matter, only detected via gravitational effects
• Alternative theory: Gravity laws wrong (not preferred explanation)
• Normal matter confined to 3D "brane" (from membrane)
• Atomic nuclei smaller than micrometer extra dimension
• Nuclear physics requires confinement to 3D space

Gravitational Mechanism

• Gravity experiences large extra dimensions
• Rolled-up dimensions create standing waves
• Standing waves = gravitons (gravity field quanta)
• Graviton masses depend on wavelengths fitting in extra dimension
• Massive gravitons proposed as dark matter particles

Dark Dimensions Novelty

• Extra dimension radius varies spatially
• Variable radius creates gravitons with different masses
• Heavier gravitons decay into lighter ones
• Decay process heats up lower-mass gravitons
• Heating changes dark matter behavior
• Effects predicted on large-scale galactic filament structure

Scientific Criticism

• "Naturalness" arguments used to justify parameters
• Naturalness predictions not scientific, can be shifted
• Pattern: Always "next experiment" will test ideas
• Same concept attempted 25 years ago
• LHC searched for this previously, found nothing
• Current work uses parameter ranges not yet excluded