SciPost Physics

SciPost Physics Vol. 20 issue 2 (February 2026)

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• Tachyonic and parametric instabilities in an extended bosonic Josephson junction

  Laura Batini, Sebastian Erne, Jörg Schmiedmayer, Jürgen Berges

  SciPost Phys. 20, 026 (2026) · published 2 February 2026 | Toggle abstract · pdf

  We study the decay of phase coherence in an extended bosonic Josephson junction realized via two tunnel-coupled Bose-Einstein condensates. Specifically, we focus on the $\pi$-trapped state of large population and phase imbalance, which, similar to the breakdown of macroscopic quantum self-trapping, becomes dynamically unstable due to the amplification of quantum fluctuations. We analytically identify early tachyonic and parametric instabilities connected to the excitation of atom pairs from the condensate to higher momentum modes along the extended direction. Furthermore, we perform Truncated Wigner numerical simulations to observe the build-up of non-linearities at later times and explore realistic experimental parameters.

• Asymptotic safety, quantum gravity, and the swampland: A conceptual assessment

  Ivano Basile, Benjamin Knorr, Alessia Platania, Marc Schiffer

  SciPost Phys. 20, 027 (2026) · published 2 February 2026 | Toggle abstract · pdf

  We provide a conceptual assessment of some aspects of fundamental quantum field theories of gravity in light of foundational aspects of the swampland program. On the one hand, asymptotically safe quantum gravity may provide a simple and predictive framework, thanks to a finite number of relevant parameters. On the other hand, a (sub-)set of intertwined swampland conjectures on the consistency of quantum gravity can be argued to be universal via effective field theory considerations. We answer whether some foundational features of these frameworks are compatible. This involves revisiting and refining several arguments (and loopholes) concerning the relation between field-theoretic descriptions of gravity and general swampland ideas. We identify the thermodynamics of black holes, spacetime topology change, and holography as the core aspects of this relation. We draw lessons on the features that a field theoretic description of gravity must (not) have to be consistent with fundamental principles underlying the swampland program, and on the universality of the latter.