arXiv subjects

Simon Langenscheidt

Publications and source records attributed to Simon Langenscheidt.

9 recordsLinked to original sources

arXiv2026

Chern-Simons corner phase spaces in BF-BB theories

We investigate an approach to determine corner Poisson brackets of fields restricted to codimension 2 and 3 surfaces in 4D theories, without making use of boundary conditions. Instead, within the example of BF-BB type theories, we show that the constraint/generator algebra on a partial Cauchy slice is enough to determine the Poisson brackets and a corner symplectic form, useful in extended phase space constructions or holography. The codimension 2 phase space turns out to be of Chern-Simons type, but lacking a flatness constraint. In a setting with codimension 3 surfaces, there is also a further Wess-Zumino-type current algebra. We apply this approach also to a specific formulation of full 4D gravity, based on the Maxwell algebra $\gfrak=\mathfrak{so}(1,3)\ltimes(\rbb^{1,3}\tilde\oplus \mathfrak{so}(1,3)^\ast)$. This realises the corner Poisson bracket of the spin connection for the first time and shows it is off-shell commutative, while the corner metric is noncommutative.

hep-th↗

arXiv2026

A Covariant Formulation of Logarithmic Supertranslations at Spatial Infinity

We investigate the asymptotic symmetries of asymptotically flat spacetimes at spatial infinity. We propose a new symplectic structure and conservative boundary conditions in a polyhomogeneous Beig-Schmidt expansion. The asymptotic symmetries extend the BMS algebra by abelian sectors, notably incorporating regular log-translations and log-supertranslations. The associated charges are finite and conserved, and we show that their algebra admits a central extension between supertranslations and log-supertranslations, and between the singular translations and regular log-translations. Our analysis is compatible with, and extends, both the work of arXiv:1106.4045 and arXiv:2211.10941 : it extends the former by incorporating log-supertranslations, and the latter by allowing both parities of the log-supertranslations in the same phase space. These newly identified symmetries at spatial infinity encode novel physical information that has not been revealed in other regions of asymptotically flat spacetimes, thereby opening the door to new observables to consider at null and timelike infinity.

hep-th↗

arXiv2025

Edge modes of tetrad gravity: Unlike diffeomorphisms, all shifts are integrable

We present an improved notion of internal tetrad shifts in 4 dimensions which is always integrable in the presence of corners. This allows us to study the fully extended corner symmetry algebra of gauge charges, which is a deformation of $ISO(1,3)^S$ involving spacetime curvature. We argue this implies corner noncommutativity of the spin connection $ω$. The latter in particular hints that an extended BF theory might be a better way understand the dynamics of tetrad gravity. This result presents us with an integrable, complete set of edge modes for gravity in 4D, with potential ramifications for asymptotic symmetries and quantisation.

hep-th↗

arXiv2025

Boundaries, frames and the issue of physical covariance

We focus on three distinct lines of recent developments: edge modes and boundary charges in gravitational physics, relational dynamics in classical and quantum gravity, and quantum reference frames. We argue that these research directions are in fact linked in multiple ways, and can be seen as different aspects of the same research programme. This research programme has two main physical goals and one general focus, as well as broader conceptual implications. The physical goals are to move beyond the two idealizations/approximations of asymptotic or closed boundary conditions in gravitational physics and of ideal reference frames (coded in coordinate frames or gauge fixings), thus achieving a more realistic modelling of (quantum) gravitational physical phenomena. These two goals combine to identify a key open issue: a proper characterization of physical covariance, i.e. covariance across fully physical (as opposed to idealized) reference frames. The broader conceptual implications concern the influence of observers in physics and possible physical limits to objectivity.

physics.hist-ph↗

arXiv2024

Channel-State duality with centers

We study extensions of the mappings arising in usual channel-state duality to the case of Hilbert spaces with a direct sum structure. This setting arises in representations of algebras with centers, which are commonly associated with constraints, and it has many physical applications from quantum many-body theory to holography and quantum gravity. We establish that there is a general relationship between non-separability of the state and the isometric properties of the induced channel. We also provide a generalisation of our approach to algebras of trace-class operators on infinite dimensional Hilbert spaces.

quant-ph↗

arXiv2024

New edge modes and corner charges for first-order symmetries of 4D gravity

We present a set of noncommuting frame-translation symmetries in 4D gravity in tetrad-connection variables, which allow expressing diffeomorphisms as composite transformations. Working on the phase space level for finite regions, we pay close attention to the corner piece of the generators, discuss various possible charge brackets, relative definitions of the charges, coupling to spinors and relations to other charges. What emerges is a picture of the symmetries and edge modes of gravity that bears local resemblance to a Poincare group $SO(1,3)\ltimes \mathbb{R}^{1,3}$, but possesses structure functions. In particular, we argue that the symmetries and charges presented here are more amenable to discretisation, and sketch a strategy for this charge algebra, geared toward quantum gravity applications.

gr-qc↗

arXiv2024

Holographic properties of superposed quantum geometries

We study the holographic properties of a class of quantum geometry states characterized by a superposition of discrete geometric data, in the form of generalised tensor networks. This class specifically includes spin networks, the kinematic states of lattice gauge theory and discrete quantum gravity. We employ an algebraic, operatorial definition of holography based on quantum information channels, an approach which is particularly valuable in settings, such as the one we consider, where the relevant Hilbert space of states does not factorize into subsystem Hilbert spaces due to gauge invariance. We apply random tensor network techniques (successfully used in the AdS/CFT context) to analyse information transport properties of the bulk-to-boundary and boundary-to-boundary maps associated with this superposition of quantum geometries, and produce typicality results about the average over the geometric data colouring the fixed graph structure. In this context, one naturally obtains a nontrivial area operator encoding the dominant contribution to entropy calculations. Among our main results is the requirement that one can only isometrically map a bulk region onto boundaries with fixed total area. We furthermore inquire about similar state-induced mappings between segments of the boundary, and discuss related conditions for isometric behaviour. These generalisations make further steps towards quantum gravity implementations of tensor network holography.

quant-ph↗

arXiv2022

Superposed Random Spin Tensor Networks and their Holographic Properties

We study criteria for and properties of boundary-to-boundary holography in a class of spin network states defined by analogy to projected entangled pair states (PEPS). In particular, we consider superpositions of states corresponding to well-defined, discrete geometries on a graph. By applying random tensor averaging techniques, we map entropy calculations to a random Ising model on the same graph, with distribution of couplings determined by the relative sizes of the involved geometries. The superposition of tensor network states with variable bond dimension used here presents a picture of a genuine quantum sum over geometric backgrounds. We find that, whenever each individual geometry produces an isometric mapping of a fixed boundary region C to its complement, then their superposition does so iff the relative weight going into each geometry is inversely proportional to its size. Additionally, we calculate average and variance of the area of the given boundary region and find that the average is bounded from below and above by the mean and sum of the individual areas, respectively. Finally, we give an outlook on possible extensions to our program and highlight conceptual limitations to implementing these.

quant-ph↗

arXiv2019

Interactions in MacDowell-Mansouri Gravitation

In this bachelor thesis, possible kinetic terms and couplings of standard fields in MacDowell-Mansouri-Stelle-West gravity are studied with some aspects of group theory in mind. Possible obstructions to these couplings are considered and used to make statements about the validity of the theory when coupled to matter. While interactions themselves turn out to be mostly unaffected except for scalar fields, the theory fails at its goal of putting gravity on equal footing with Yang-Mills theories. This happens with the kinetic term for spin-1 gauge fields and spin-0 ones, as one needs auxiliary fields to ensure manifest covariance with respect to the internal group $ SO(2,3) $.

hep-th↗