Joint cosmology seminar at Tufts:

Tuesday, November 18, 2025, 2:30 pm
574 Boston Ave, Room 316\\
Tufts University
Refreshments at 2:00 outside room 304

Unimodular Henneaux-Teitelboim (HT) Gravity: 4D and 2D applications

Bruno Alexander
Imperial College London

Abstract:

Unimodular Henneaux-Teitelboim (HT) Gravity provides a fully diffeomorphism-invariant route to unimodular gravity by promoting the cosmological constant to a conjugate variable with an associated ``unimodular time''. I will present two complementary applications. In 4D minisuperspace, starting from the connection representation, unimodular Hartle-Hawking wave packets yield a unitary inner product and normalizable states whose peaks track classical FRW dynamics. This work reframes ``creation from nothing'' as the emergence of a semiclassical Universe from interference of incident/reflected packets near the bounce, without invoking Vilenkin's contour. In parallel, I will introduce a 2D cousin obtained via a centrally extended JT/KSY construction. In de Sitter quantum cosmology, superposing Lambda-eigenstates produces unitary evolution in unimodular time, controlled interference near T=0, and sharply separated WKB branches at late times. The same mechanism naturally accommodates transient quantum deformations of global dS and suggests a topology change interpretation in which contracting/expanding branches play the role of Universe/anti-Universe pairs.