Symmetric Superfluids

Abstract

We present a complete classification of symmetric superfluids, namely shift-symmetric and Poincaré invariant scalar field theories that have an enlarged set of classically conserved currents at leading order in derivatives. These theories arise in the decoupling limit of the effective field theory of shift-symmetric, single-clock cosmologies and our results pick out all models with couplings fixed by additional symmetry. Remarkably, in $D\ge 2$ spacetime dimensions there are only two possibilities: the Dirac-Born-Infeld theory and Scaling Superfluids with Lagrangian $(-{\partial }_{\mu }\varphi {\partial }^{\mu }\varphi {)}^{\alpha }$, for some real $\alpha$. The scaling symmetry present for any $\alpha$ is further enhanced to the full conformal group only for $\alpha =D/2$, and to infinitely many additional generators for $\alpha =1/2$. We discuss the stability of Scaling Superfluids and point out that all coupling constants are determined by the speed of sound.

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• Positivity Bounds without Boosts
• Extended Cuscuton as Dark Energy
• Effective Field Theory for Quasicrystals and Phasons Dynamics
• An Algebraic Classification of Exceptional EFTs
• The Cosmological Phonon: Symmetries and Amplitudes on Sub-Horizon Scales
• A Holographic Superfluid Symphony
• Symmetric Scalars
• Scale invariant solids
• Accelerating Universe with a stable extra dimension in cuscuton gravity
• Scale without conformal invariance in membrane theory
• Non-uniqueness of massless transverse-traceless graviton
• Quantum Corrections to Generic Branes: DBI, NLSM, and More
• Soft theorems for boosts and other time symmetries
• Soft Phonon Theorems
• Symmetries for scalarless scalar theories
• Some disquisitions on cosmological 2-form dualities
• Cuscuton Bounce Beyond the Linear Regime: Bispectrum and Strong Coupling Constraints
• An Algebraic Classification of Exceptional EFTs Part II: Supersymmetry
• How Much NEC Breaking Can the Universe Endure?
• K-nonizing
• A new branch of inflationary speed limits
• Horndeski in motion