arXiv subjects

Matthew Elley

Publications and source records attributed to Matthew Elley.

6 recordsLinked to original sources

arXiv2026

Cuspidal Singularities in Collapsing Domain Walls

Domain wall networks have attracted renewed interest, particularly in relation to the dynamics of network collapse. Accurately describing this process is challenging and typically requires large scale numerical simulations. Here we adopt a complementary approach by studying the collapse of individual closed domain walls, extending previous thin wall analyses and comparing them with adaptive mesh refinement field theory simulations. Firstly, we show that collapsing domain walls generically develop worldvolume singularities of two types: cuspidal edge singularities, consisting of one dimensional singular edges that propagate along the wall surface at the speed of light for a finite time, and cuspidal vertex singularities, which are spike like and instantaneous events where the wall moves momentarily at the speed of light. Both types of features arise generically from smooth initial conditions, and their formation and evolution follow the universal patterns of singularity theory. We show that these structures are captured both by the Nambu-Goto equations and by an eikonal like approximation valid in the relativistic regime. Furthermore, we demonstrate that the same singular structures are reproduced qualitatively in full field theory simulations, establishing that they are not artifacts of the thin wall approximation but robust features of realistic domain wall dynamics. Naturally, such focusing effects in the field theory simulations result in localized regions of high energy density. We briefly discuss possible phenomenological implications.

hep-th↗

arXiv2025

A critical value of the inflationary tensor-to-scalar ratio from inhomogeneous inflation

We show that, for a given fixed value of the number of e-folds of the homogeneous solution, inflation succeeds with order unity inhomogeneities in the initial conditions above a characteristic value of the tensor-to-scalar ratio $r$. In practice, we work with an $\alpha$-attractor $T$-model and vary its characteristic scale $\mu$, keeping the initial inhomogeneities in both gradient and kinetic fields of order unity of the inflationary energy scale. Under these conditions, and assuming 100 e-folds for the homogeneous solution, the requirement for 60 e-folds of inflation occurs at a critical characteristic scale $\mu_{crit} \approx 0.02m_{P}$, corresponding to an $r_{crit} \approx 10^{-6}$. Since increasing the amplitude of the inhomogeneities will make inflation less robust and hence require a higher characteristic scale in order for inflation to succeed, for a given number of e-folds achieved by the homogeneous solution $r_{crit}$ is a lower bound.

astro-ph.CO↗

arXiv2025

GRTresna: An open-source code to solve the initial data constraints in numerical relativity

GRTresna is a multigrid solver designed to solve the constraint equations for the initial data required in numerical relativity simulations. In particular, it is focussed on scenarios with fundamental fields around black holes and inhomogeneous cosmological spacetimes. The code is based on the formalism in Aurrekoetxea, Clough \& Lim arXiv:2207.03125 and can be found at https://github.com/GRTLCollaboration/GRTresna

gr-qc↗

arXiv2024

Robustness of inflation to kinetic inhomogeneities

We investigate the effects of large inhomogeneities in both the inflaton field and its momentum. We find that in general, large kinetic perturbations reduce the number of e-folds of inflation. In particular, we observe that inflationary models with sub-Planckian characteristic scales are not robust even to kinetic energy densities that are sub-dominant to the potential energy density, unless the initial field configuration is sufficiently far from the minimum. This strengthens the results of our previous work. In inflationary models with super-Planckian characteristic scales, despite a reduction in the number of e-folds, inflation is robust even when the potential energy density is initially sub-dominant. For the cases we study, the robustness of inflation strongly depends on whether the inflaton field is driven into the reheating phase by the inhomogeneous scalar dynamics.

astro-ph.CO↗

arXiv2022

Spin-induced dynamical scalarization, de-scalarization and stealthness in scalar-Gauss-Bonnet gravity during black hole coalescence

Particular couplings between a scalar field and the Gauss-Bonnet invariant lead to spontaneous scalarization of black holes. Here we continue our work on simulating this phenomenon in the context of binary black hole systems. We consider a negative coupling for which the black-hole spin plays a major role in the scalarization process. We find two main phenomena: (i) dynamical descalarization, in which initially scalarized black holes form an unscalarized remnant, and (ii) dynamical scalarization, whereby the late merger of initially unscalarized black holes can cause scalar hair to grow. An important consequence of the latter case is that modifications to the gravitational waveform due to the scalar field may only occur post-merger, as its presence is hidden during the entirety of the inspiral. However, with a sufficiently strong coupling, we find that scalarization can occur before the remnant has even formed. We close with a discussion of observational implications for gravitational-wave tests of general relativity.

gr-qc↗

arXiv2020

Dynamical descalarization in binary black hole mergers

Scalar fields coupled to the Gauss-Bonnet invariant can undergo a tachyonic instability, leading to spontaneous scalarization of black holes. Studies of this effect have so far been restricted to single black hole spacetimes. We present the first results on dynamical scalarization in head-on collisions and quasicircular inspirals of black hole binaries with numerical relativity simulations. We show that black hole binaries can either form a scalarized remnant or dynamically descalarize by shedding off its initial scalar hair. The observational implications of these findings are discussed.

gr-qc↗