arXiv subjects

Benjamin Koch

Publications and source records attributed to Benjamin Koch.

At least 19 recordsLinked to original sources

arXiv2026

Starobinsky-inflation in asymptotically safe shift-symmetric scalar-tensor theory

We investigate the constraining power of scalaron-driven inflation on asymptotically safe scalar-tensor theories. Starting from a Horndeski-type theory and applying a renormalization group improvement procedure generates higher-derivative couplings which are fixed in terms of the microscopic parameters - a structure that is expected to occur also within first principle computations based on the asymptotic safety mechanism. The latter are taken to be the free parameters appearing at the Gaussian fixed point. We find that the free parameter initially associated with the non-minimal gravity-matter coupling is not confined to the gravity-matter sector of the theory and also enters the effective higher-derivative couplings in the gravitational sector. We review the setting of multi-field inflationary models which is appropriate to analyze the inflationary dynamics in this context and illustrate their applicability by working out the explicit bounds on the non-minimal gravity-matter coupling resulting from cosmological observations. Given the fixed point structure of asymptotically safe scalar-tensor theories, the results indicate that UV-completions by two of the three available non-Gaussian fixed points can be ruled out while pinpointing phenomenologically viable RG trajectories emanating from the third fixed point.

gr-qc↗

arXiv2025

Equivalence of scalar-tensor theories and scale-dependent gravity

We present a novel equivalence between scale-dependent gravity and scalar-tensor theories that have only a single scalar field with a canonical kinetic term in the Einstein frame and a conformal coupling to the metric tensor. In particular, we show that the set of well-behaved scale-dependent gravity theories can be fully embedded into scalar-tensor theories in a unique way. Conversely, there are multiple ways to write a scalar-tensor theory as a scale-dependent theory. This equivalence is established both on the level of the actions and on the level of field equations. We find that, in the context of this equivalence, the scale-setting relation $k(x)$ is naturally promoted to a dynamical field, which is made manifest by including a corresponding kinetic term in the scale-dependent action. In addition, we demonstrate that the new equivalence fits well into the framework of existing equivalences involving the aforementioned theories and $f(R)$-gravity. Finally, we apply the equivalence relations to explicit examples from both scale-dependent gravity and scalar-tensor theories.

gr-qc↗

arXiv2025

Generalized Boundary Conditions for the qBounce Experiment

Discrepancies between theory and recent qBounce data have prompted renewed scrutiny of how boundary conditions are implemented for ultracold neutrons bouncing above a mirror in Earth's gravity. We apply the theory of self-adjoint extensions to the linear gravitational potential on the half-line and derive the most general boundary condition that renders the Hamiltonian self-adjoint. This introduces a single real self-adjoint parameter $\lambda$ that continuously interpolates between the Dirichlet case and more general (Robin-type) reflecting surfaces. Building on this framework, we provide analytical expressions for the energy spectrum, eigenfunctions, relevant matrix elements, and a set of sum rules valid for arbitrary $\lambda$. We show how nontrivial boundary conditions can bias measurements of $g$ and can mimic or mask putative short-range ''fifth-force''. Our results emphasize that enforcing self-adjointness-and modeling the correct boundary physics-is essential for quantitative predictions in gravitational quantum states. Beyond neutron quantum bounces, the approach is broadly applicable to systems where boundaries and self-adjointness govern the observable spectra and dynamics.

quant-ph↗

arXiv2025

Geodesics in Quantum Gravity

We investigate the motion of test particles in quantum-gravitational backgrounds by introducing the concept of q--desics, quantum-corrected analogs of classical geodesics. Unlike standard approaches that rely solely on the expectation value of the spacetime metric, our formulation is based on the expectation value of quantum operators, such as the the affine connection-operator. This allows us to capture richer geometric information. We derive the q--desic equation using both Lagrangian and Hamiltonian methods and apply it to spherically symmetric static backgrounds obtained from canonical quantum gravity. Exemplary results include, light-like radial motion and circular motion with quantum gravitational corrections far above the Planck scale. This framework provides a refined description of motion in quantum spacetimes and opens new directions for probing the interface between quantum gravity and classical general relativity.

gr-qc↗

arXiv2025

Quantum Uncertainties of Static Spherically Symmetric Spacetimes

We present a canonical quantization framework for static spherically symmetric spacetimes described by the Einstein-Hilbert action with a cosmological constant. In addition to recovering the classical Schwarzschild-(Anti)-de Sitter solutions via the Ehrenfest theorem, we investigate the quantum uncertainty relations that arise among the geometric operators in this setup. Our analysis uncovers an intriguing relation to black hole thermodynamics and opens a new angle towards generalized uncertainty relations. We further obtain an upper and a lower limit of the mass that is allowed in our model, for a given value of the cosmological constant. Both limits, when evaluated for the known value of the cosmological constant, have a stunning relation to observed bounds. These findings open a promising avenue for deeper insights into how quantum effects manifest in spacetime geometry and gravitational systems.

gr-qc↗

arXiv2025

Quasi-normal modes and shadows of scale-dependent regular black holes

In this paper we investigate how a regular scale-dependent black hole, characterized by a single extra parameter $\epsilon$, behaves under perturbations by a test field (quasi-normal modes) and under light imaging (shadows) in a four-dimensional space-time background. On the quasi-normal modes side, we study how it responds to scalar and Dirac perturbations. To do this, we implement the well known WKB semi-analytic method of 6th order for obtaining the quasi-normal frequencies. We discuss the behavior of the real and imaginary parts of the quasi-normal modes for different values of the parameter $\epsilon$ and the overtone $n$ and multipole $\ell$ numbers. On the black hole imaging side, we ray-trace the geometry and illuminate it with a thin-accretion disk. Choosing $\epsilon=1.0$ we compute the size of the central brightness depression and generate full images of the black hole. We discuss the features (i.e. luminosity) of successive photon rings through the Lyapunov exponent of nearly-bound, unstable geodesics. Furthermore we use the correspondence (in the limit $\ell \gg n$) between quasi-normal mode frequencies and unstable bound light orbits to infer the numerical values of the latter using the former and find a remarkable accuracy of the correspondence in providing the right numbers. Our results support the usefulness of this correspondence in order to perform cross-tests of black holes using these two messengers.

gr-qc↗

arXiv2025

An Overview of Arithmetic Adaptations for Inference of Convolutional Neural Networks on Re-configurable Hardware

Convolutional Neural Networks (CNNs) have gained high popularity as a tool for computer vision tasks and for that reason are used in various applications. There are many different concepts, like single shot detectors, that have been published for detecting objects in images or video streams. However, CNNs suffer from disadvantages regarding the deployment on embedded platforms such as re-configurable hardware like Field Programmable Gate Arrays (FPGAs). Due to the high computational intensity, memory requirements and arithmetic conditions, a variety of strategies for running CNNs on FPGAs have been developed. The following methods showcase our best practice approaches for a TinyYOLOv3 detector network on a XILINX Artix-7 FPGA using techniques like fusion of batch normalization, filter pruning and post training network quantization.

cs.LG↗

arXiv2025

Very Special Relativity in Accelerated Frames: Non-relativistic Effects in Gravitational Spectroscopy of Ultracold Neutrons

In this paper, we investigate the phenomenology of fermionic systems in uniform gravitational fields within the framework of Very Special Relativity (VSR). We focus on the case of gravitational spectroscopy with ultracold neutrons, explored in experiments like \emph{q}\textsc{Bounce}. Calculating the leading ($c^0$) and next-to-leading ($c^{-1}$) order corrections to the non-relativistic Hamiltonian in an accelerated frame, we obtain the perturbed fermionic energy spectrum. At leading order, we do not find any modifications except for a trivial mass shift, thus preserving the equivalence between inertial and gravitational mass and particle-antiparticle sectors. The next-to-leading order corrections, instead, introduce time-dependent anisotropic contributions depending on the preferred spatial direction in VSR, and can then be used to probe novel Lorentz-violating signatures. Taking \emph{q}\textsc{Bounce} sensitivity as a benchmark, we derive a first rough constraint for the neutron VSR parameter. Finally, we suggest alternative spin-flipping setups to better probe VSR effects and foresee potential future research directions.

hep-ph↗

arXiv2024

Casimir Effect and Gravitational Balance: a Search for Stable Configurations

In this study, we examine the role of the repulsive Casimir force in counteracting the gravitational contraction of a thin spherically symmetric shell. Our main focus is to explore the possibility of achieving a stable balanced configuration within the theoretically reliable weak field limit. To this end, we consider different types of Casimir forces, including those generated by massless scalar fields, massive scalar fields, electromagnetic fields, and temperature-dependent fields.

gr-qc↗

arXiv2024

Padmanabhan's Boundary Variational Principle for Electrodynamics and Yang-Mills Theory

In this note, we revisit a variational principle introduced by Padmanabhan for describing gravitation using a field action composed solely of a boundary term. We demonstrate that this procedure can also be applied to derive Maxwell's and Yang-Mills equations. Additionally, we find that in this boundary approach, $\mathcal{CP}$-violating dual couplings and spontaneous symmetry breaking through gauge boson masses can emerge in a manner analogous to how the cosmological constant appears in the original gravitational context.

physics.gen-ph↗

arXiv2024

An exciting hint towards the solution of the neutron lifetime puzzle?

We revisit the neutron lifetime puzzle, a discrepancy between beam and bottle measurements of the weak neutron decay. Since both types of measurements are realized at different times after the nuclear production of free neutrons, we argue that the existence of excited states could be responsible for the different lifetimes. We elaborate on the required properties of such states and under what circumstances it is possible that they have not been experimentally identified yet.

hep-ph↗

arXiv2023

Ultracold Neutrons in the Low Curvature Limit: Remarks on the post-Newtonian effects

Ultracold neutrons are great experimental tools to explore the gravitational interaction in the regime of quantized states. From a theoretical perspective, starting from a Dirac equation in curved spacetime, we applied a perturbative scheme to systematically derive the non-relativistic Schr\"odinger equation that governs the evolution of the neutron's wave function in the Earth's gravitational field. At the lowest order, this procedure reproduces a Schr\"odinger system affected by a linear Newtonian potential, but corrections due to both curvature and relativistic effects are present. Here, we argue that one should be very careful when going one step further in the perturbative expansion. Proceeding methodically with the help of the Foldy-Wouthuysen transformation and a formal post-Newtonian $c^{-2}-$expansion, we derive the non-relativistic Hamiltonian for a generic static spacetime. By employing Fermi coordinates within this framework, we calculate the next-to-leading order corrections to the neutron's energy spectrum. Finally, we evaluate them for typical experimental configurations, such as that of qBOUNCE, and note that, while the current precision for observations of ultracold neutrons may not yet enable to probe them, they could still be relevant in the future or in alternative circumstances.

gr-qc↗

arXiv2023

A Universe from a Lagrangian Fixed Point

In this paper, we investigate the theoretical possibility that a Lagrangian fixed point, when applied to cosmological models, can drive dynamical evolution towards a bouncing universe. We analyze the physics of a Lagrangian fixed point within the context of a gravitational average effective action featuring scale-dependent couplings. To explore this concept, we develop a toy model set in a four-dimensional, spatially flat spacetime, anchored by a Lagrangian fixed point. Solving the cosmological equations of this model analytically, we identify several non-trivial solution branches. These branches are characterized by a modified scale factor and dynamic gravitational couplings, offering new insights into the behavior of cosmological models under these conditions.

gr-qc↗

arXiv2023

Extended BMT equations and the anomalous magnetic moment

We propose a generalized form of the Thomas-Bargmann-Michel-Telegdi equations. These are first-order in both electric and magnetic fields and retain the conventional conserved quantities and constraints. Within this novel phenomenological framework, we delve into an archetypal measurement scenario. Specifically, we scrutinize the contributions to the standard definition of the anomalous magnetic moment observable, highlighting each new correction term.

hep-ph↗

arXiv2023

Earthquake Quantization

In this homage to Einstein's 144th birthday we propose a novel quantization prescription, where the paths of a path-integral are not random, but rather solutions of a geodesic equation in a random background. We show that this change of perspective can be made mathematically equivalent to the usual formulations of non-relativistic quantum mechanics. To conclude, we comment on conceptual issues, such as quantum gravity coupled to matter and the quantum equivalence principle.

quant-ph↗

arXiv2022

The effects of running gravitational coupling on three dimensional black holes

In the present work, we investigate the consequences of running gravitational coupling on the properties of the three-dimensional BTZ black hole. We take as starting point the functional form of gravitational coupling obtained in the context of asymptotic safe gravity theory. By using the standard scale setting relation where $k\sim \xi/r^n$, we compute the solution of the Einstein field equations. We get and analyze the horizon and the thermodynamic properties of this new class of black hole solutions. The impact of the scale--dependent parameter $\xi$ on the cosmological "constant" and metric functions are briefly discussed. We find that the null energy condition is also violated in this setup when scale-dependent gravity and Newton's coupling (coming from the asymptotic safety scenario of gravity) are simultaneously taken into account.

gr-qc↗

arXiv2022

Vacuum energy, the Casimir effect, and Newton's non-constant

We explore two hypotheses. First, the possibility that the quantum vacuum energy density of the Casimir effect contributes to a (local) gravitational vacuum energy density. Second, the possibility that a change in the gravitational coupling implies a change in the cosmological constant. We parametrize these two possibilities in a covariant framework and show that the next generation of Casimir experiments does have a surprisingly good chance of exploring this parameter space.

hep-th↗

arXiv2022

Cosmological constraints on scale-dependent cosmology

This paper examines a cosmological model of scale-dependent gravity. The gravitational action is taken to be the Einstein-Hilbert term supplemented with a cosmological constant, where the couplings, $G_k$ and $\Lambda_k$, run with the energy scale $k$. % Also, notice that, by construction, our formalism recovers general relativity when in the limit of constant Newton's coupling. % Two sub-models based on the scale-dependent cosmological model are confronted with recent observational data from: i) the Hubble parameter $H(z)$, ii) distance modulus $\mu(z)$, and iii) baryon acoustic scale evolution as functions of redshift (BAO). % The viability of the model is discussed, obtaining the best-fit parameters and the maximum likelihood contours for these observables. Finally, a joint analysis is performed for $H(z)$+$\mu(z)$+BAO.

gr-qc↗