Bondi-Metzner-Sachs Particles.

Area of Science:

• Theoretical Physics
• Quantum Gravity
• Mathematical Physics

Background:

• The Bondi-Metzner-Sachs (BMS) group describes symmetries of spacetime at null infinity.
• Understanding representations of the BMS group is crucial for quantum gravity.
• Previous classifications of BMS group representations lacked a unique decomposition.

Purpose of the Study:

• To construct wave functions for unitary irreducible representations (UIRs) of the BMS group.
• To demonstrate that these UIRs describe quantum superpositions of particles on different gravity vacua.
• To introduce a new method for decomposing supermomenta.

Main Methods:

• Construction of wave functions for BMS group UIRs.
• Reconsideration of McCarthy's classification of BMS group UIRs.
• A unique, Lorentz-invariant, nonlinear decomposition of supermomenta into hard and soft components.

Main Results:

• Wave functions for BMS particles have been successfully constructed.
• These wave functions represent quantum superpositions of (Poincaré) particles.
• The particles propagate on inequivalent gravity vacua.
• A novel decomposition of supermomenta was employed.

Conclusions:

• The constructed wave functions provide a new perspective on BMS particles.
• The findings link particle behavior to different gravity vacua.
• The nonlinear decomposition offers a unique way to analyze supermomenta.