Does any parameter window of white-noise CSL remain viable?
In plain words
The best-studied collapse model, continuous spontaneous localization (CSL), has two numbers: how often collapse happens and over what distance. In 2025 a dark-matter detector excluded the originally proposed values; the question is whether any values remain that still collapse visible objects fast enough.
Precise statement
Markovian (white-noise) CSL has collapse rate $\lambda$ and correlation length $r_{C}$. X-ray spontaneous emission in XENONnT gives $\lambda / r_{C}^{2} < 3.0e-7\,\mathrm{s}^{-1}\,\mathrm{cm}^{-2}$ (90 percent C.L.) for $r_{C}$ below about $1e-3\,\mathrm{cm}$; mechanical and interferometric bounds cover larger $r_{C}$. Theoretical lower bounds require collapse of a barely visible object within about $1e-2\,\mathrm{s}$. Determine whether the region between experimental upper bounds and theoretical lower bounds is empty for all $r_{C}$.
What would settle it
Spontaneous-radiation, heating and interferometric bounds that, with an agreed macroscopic-collapse criterion, exclude or leave open a region of the $(\lambda, r_C)$ plane.
Status in the literature
Unverified note
XENONnT (Phys. Rev. Lett. 136, 120201, 2026) excluded the GRW values $\lambda = 1e-16\ \mathrm{s}^{-1}$, $r_{C} = 1e-5\ \mathrm{cm}$ at $9.1\sigma$, improving the previous X-ray bound about 135-fold.
Related problems
- More general than Can massive superpositions exclude the GRW collapse rate?