arXiv subjects

Benjamin Muntz

Publications and source records attributed to Benjamin Muntz.

7 recordsLinked to original sources

arXiv2026

A Lapse in the Cosmological Constant Problem with Bulk Dynamics

We have previously proposed a new approach to the cosmological constant problem based on anisotropic scaling in a compact extra dimension. In the ultra-local $z=0$ limit, the interplay between a projectable lapse, foliation-preserving diffeomorphisms, and higher-form fluxes renders the gravitational field equations insensitive to radiative corrections to the matter vacuum energy. Here we extend this framework beyond the ultra-local limit by introducing $z=1$ deformations that restore dynamics along the compact direction. We show that vacuum-energy cancellation persists at the level of the background equations, while generic extrinsic-curvature couplings propagate an additional scalar ghost. A healthy quadratic spectrum selects the Fierz-Pauli relation between these couplings. This motivates a particularly simple realization in terms of five-dimensional Einstein gravity, a top-form flux, and a spacelike khoron scalar field that dynamically defines a preferred projectable foliation. In this covariant formulation, the global constraint arises from an auxiliary einbein on the space of khoron leaves, and constant shifts of the renormalized matter vacuum energy cancel algebraically from the intrinsic Einstein equations. Finally, allowing matter to propagate around the compact dimension generates finite, topology-sensitive Casimir contributions that are not automatically removed by the mechanism. Suppressing these contributions requires additional spectral conditions on the propagating bulk degrees of freedom.

hep-th↗

arXiv2026

Dimensional Analysis is a Gauge Theory

I argue that dimensional analysis can appropriately be thought of as a gauge theory. This picture naturally leads to the usual quantity calculus through inherent properties of Lie groups, Lie algebras, and representation theory. The gauge theory interpretation is perhaps strongest for non-constant units. I explain how Stevens's classification of scales of measurement can be understood by choices of different gauge groups. Finally, I reinterpret and rephrase the Buckingham-{\Pi} Theorem in a way that also applies to typical gauge theories. Counting the number of ''{\Pi}''s becomes a well-known problem of invariant theory.

physics.hist-ph↗

arXiv2026

A Lapse in the Cosmological Constant Problem

We present a new mechanism for addressing the cosmological constant problem based on global constraints arising from a lapse function in a higher-dimensional gravitational theory. Inspired by Horava-Lifshitz gravity, we consider a 5d spacetime with anisotropic scaling along a compact extra dimension, while preserving Lorentz invariance in four dimensions. In the deep infrared limit, variation with respect to the lapse generates a global constraint on the 4d geometry, closely analogous to that of vacuum energy sequestering. Although the resulting effective gravitational equations differ from standard sequestering, radiative contributions to the Standard Model vacuum energy are nevertheless cancelled at all orders.

hep-th↗

arXiv2025

From Frame Covariance to the Swampland Distance Conjecture

Field space geometry plays a central role within the Swampland Programme, most notably in the various Distance Conjectures. However, for gravitational EFTs, this geometry is not uniquely defined: one can cast the action in many synonymous descriptions related by Weyl transformations, in which the field space metric transforms non-trivially across conformal frames. This raises a crucial question of how we are meant to think of the field space metric in view of employing the Swampland Conjectures. In this work we resolve this ambiguity by developing a fully frame-covariant framework for studying gravitational EFTs. We show that all conformal frames arise as distinct foliations of a singular higher-dimensional auxiliary geometry. Applying ADM formalism to the augmented field space, it is clear how Weyl- and unit transformations can be understood from a geometric point of view. Using this framework, we revisit the Species Scale Distance Conjecture and Sharpened Distance Conjecture, and show how the bounds derive from universal properties of gravitational EFTs under Weyl transformations. This strongly suggests that aspects of these conjectures apply to a much broader class of scalar-tensor theories and are consequences of frame covariance, rather than constraints imposed by quantum gravity.

hep-th↗

arXiv2024

Do we live on the End of the World?

We propose a scenario of a de Sitter universe living on an End-of-the-World brane. Motivated by the Swampland programme and in particular the Cobordism Conjecture, we consider a compact region of AdS$_5$ nucleating from nothing, with a dS$_4$ living on its boundary. We show that it can equivalently be interpreted as an up-tunnelling from AdS$_5$ with cosmological constant $\Lambda\to -\infty$, following Brown and Dahlen's proposal for 'nothing'. Their picture naively leads to the conclusion that the brane has infinite negative tension. But we show that it becomes finite and positive once we employ holographic renormalization, recovering the Bubble of Something where the domain wall becomes a boundary of spacetime. The same holds true in any number of dimensions and, moreover, at the level of metric perturbations. This provides motivation for alternative routes of obtaining cosmology from quantum gravity or string theory using domain walls, departing from conventional vacuum approaches.

hep-th↗

arXiv2024

Horndeski speed tests with scalar-photon couplings

We revisit multi-messenger constraints from neutron star mergers on the speed of propagation of gravitational and electromagnetic waves in Horndeski and beyond Horndeski theories. By considering non-trivial couplings between the dark energy field and the electromagnetic sector, the electromagnetic wave can propagate through the cosmological background at non-unit speed, altering the phenomenological constraints on its gravitational counterpart. In particular, we show that recent models derived from a Kaluza-Klein compactification of higher dimensional Horndeski models fall into a broader class of theories disformally related to those whose gravitational waves propagate with unit speed. This disformal equivalence can, however, be broken by the gravitational couplings to other sectors with interesting phenomenological consequences. We also consider higher order couplings between the scalar and the photon with second order field equations, and show that they are not compatible with constraints coming from multi-messenger speed tests and the decay of the gravitational wave.

gr-qc↗

arXiv2023

Starobinsky Inflation in the Swampland

We argue that the Starobinsky model of inflation, realised via an $R^2$ term in the Lagrangian, can originate from quantum effects due to a tower of light species. By means of two separate arguments, we show how this implies that the scale of the $R^2$ term must be of order of the species scale $\Lambda_s$, namely the energy at which gravity becomes strongly coupled. We discuss the implications and challenges of this scenario for inflation, inflationary reheating, and string theory embeddings. In this context, we collect strong evidence to conclude that Starobinsky inflation lies in the Swampland.

hep-th↗