arXiv subjects

Nicolás Loayza

Publications and source records attributed to Nicolás Loayza.

5 recordsLinked to original sources

arXiv2026

CosmoLattice 2.0

This paper introduces $\tt {\mathcal C}osmo{\mathcal L}attice$ $\tt v2.0$, a major upgrade that substantially broadens the physical scope and computational capabilities of the code. It introduces lattice implementations of scalar fields non-minimally coupled to gravity through $ϕ^2R$, as well as axion-like fields coupled to Abelian gauge sectors as $ϕF_{μν}\widetilde F^{μν}$. It also provides new procedures for generating specialized initial conditions, including scaling networks of cosmic defects ($\it e.g.$ strings and domain walls), and fields with arbitrary power spectra. The release also incorporates low-storage Runge-Kutta integrators for non-symplectic systems (suitable $\it e.g.$ for non-minimal scalar kinetic terms as $\mathcal{G}_{ab}\partial_μϕ^a\partial^μϕ^b$), scalar-field simulations on reduced $(1+1)$- and $(2+1)$-dimensional lattices, new optimized gravitational-wave evolution, more flexible field and energy-density outputs, and GPU support that can accelerate simulations by a factor $\mathcal{O}(10)$ relative to CPU execution. Extensive documentation on the use of the code is provided on https://www.cosmolattice.com

astro-ph.CO↗

arXiv2026

The art of simulating the early Universe. Part II. Non-canonical cases & gravitational waves

We present a discussion on lattice techniques for the simulation of non-canonical field theory circumstances, complementing our previous monograph (arXiv:2006.15122) on canonical cases. We begin by reviewing basic aspects of lattice field theory, including symplectic and non-symplectic evolution algorithms. We then introduce lattice implementations of non-canonical interactions, considering scalars with a non-minimal coupling to gravity, $ϕ^2R$, non-minimal scalar kinetic theories, $\mathcal{G}_{ab}(\lbraceϕ_c\rbrace)\partial_μϕ^a\partial^μϕ^b$, and axion-like particle (ALP) interactions with Abelian gauge fields, $ϕF_{μν}\tilde F^{μν}$. Next, we discuss methods to set up special field configurations, including the creation of cosmic defect networks towards scaling (e.g. cosmic strings and domain walls), field configurations based on arbitrary power spectra or spatial profiles, and probabilistic methods as required e.g. for thermal configurations. We further extend the notion of non-canonical theories, discussing the discretization of scalar field dynamics in $d + 1$ dimensions, with $d \neq 3$. Unrelated to non-canonical aspects, we also discuss implementation(s) of gravitational wave (GW) dynamics on the lattice. This document represents the theoretical basis for the non-canonical field theory aspects (interactions, initial conditions, dimensionality) and GW dynamics implemented in ${\mathcal C}$osmo${\mathcal L}$attice v2.0, to be released in 2026.

astro-ph.CO↗

arXiv2026

The non-linear dynamics of axion inflation: a detailed lattice study

We study in detail the fully inhomogeneous non-linear dynamics of axion inflation, identifying three regimes: weak-, mild-, and strong-backreaction, depending on the duration of inflation. We use lattice techniques that explicitly preserve gauge invariance and shift symmetry, and which we validate against other computational methods of the linear dynamics and of the homogeneous backreaction regime. Notably, we demonstrate that the latter fails to accurately describe the truly local dynamics of strong backreaction. We investigate the convergence of simulations of local backreaction, determining the requirements to achieve an accurate description of the dynamics, and providing useful parametrizations of the delay of the end of inflation. Additionally, we identify key features emerging from a proper local treatment of strong backreaction: the dominance of magnetic energy against the electric counterpart, the excitation of the longitudinal mode, and the generation of a scale-dependent chiral (im)balance. Our results underscore the necessity to accurately capture the local nature of the non-linear dynamics of the system, in order to correctly assess phenomenological predictions, such as e.g. the production of gravitational waves and primordial black holes.

astro-ph.CO↗

arXiv2020

Hairy Black-holes in Shift-symmetric Theories

Scalar hair of black holes in theories with a shift symmetry are constrained by the no-hair theorem of Hui and Nicolis, assuming spherical symmetry, time-independence of the scalar field and asymptotic flatness. The most studied counterexample is a linear coupling of the scalar with the Gauss-Bonnet invariant. However, in this case the norm of the shift-symmetry current $J^2$ diverges at the horizon casting doubts on whether the solution is physically sound. We show that this is not an issue since $J^2$ is not a scalar quantity, since $J^μ$ is not a diff-invariant current in the presence of Gauss-Bonnet. The same theory can be written in Horndeski form with a non-analytic function $G_5 \sim \log X$. In this case the shift-symmetry current is diff-invariant, but contains powers of $X$ in the denominator, so that its divergence at the horizon is again immaterial. We confirm that other hairy solutions in the presence of non-analytic Horndeski functions are pathological, featuring divergences of physical quantities as soon as one departs from time-independence and spherical symmetry. We generalise the no-hair theorem to Beyond Horndeski and DHOST theories, showing that the coupling with Gauss-Bonnet is necessary to have hair.

hep-th↗

arXiv2018

Fresnel diffraction of spin waves

The propagation of magnetostatic forward volume waves excited by a constricted coplanar waveguide is studied via inductive spectroscopy techniques. A series of devices consisting of pairs of sub-micrometer size antennae is used to perform a discrete mapping of the spin wave amplitude in the plane of a 30-nm thin YIG film. We found that the spin wave propagation remains well focused in a beam shape of width comparable to the constriction length and that the amplitude within the constriction displays oscillations, two features which are explained in terms of near-field Fresnel diffraction theory.

cond-mat.mes-hall↗