arXiv subjects

Tomás Ferreira Chase

Publications and source records attributed to Tomás Ferreira Chase.

5 recordsLinked to original sources

arXiv2026

Cosmological Gravitational Waves from Ultralight Vector Dark Matter

We compute the abundance of cosmological gravitational waves produced during the evolution of an ultralight vector (spin-1) dark matter field. A homogeneous background vector field breaks spatial isotropy, requiring a Bianchi I geometry and inducing a mixing between the scalar, vector, and tensor perturbation sectors. We derive the perturbation equations in this background and show that, as a consequence of this mixing, scalar perturbations act as a source of tensor modes, generating a stochastic GW background. The production and cosmological evolution of these gravitational waves are implemented in \texttt{class.VFDM}, a modified version of \texttt{CLASS}, from which we obtain the present-day spectrum.

astro-ph.CO↗

arXiv2025

Gravitational waves of quasi-circular, inspiraling black hole binaries in an ultralight vector dark-matter environment

The gravitational waves emitted by massive black hole binaries can be affected by a variety of environmental effects, which, if detected, could inform astrophysics and cosmology. We here study how gravitational waves emitted by black holes in quasi-circular orbits are affected by the presence of an ultra-light, vector-field, dark-matter environment that is minimally coupled to the binary. This dark-matter environment induces oscillatory gravitational potentials that perturb the orbit of the binary, leaving an imprint in the binary's binding energy, and thus, on the gravitational waves emitted. We here compute the effect of this environment on the gravitational-wave phase using the stationary-phase approximation within the post-Newtonian formalism. We then perform a Fisher analysis to estimate the detectability of this environmental effect with a four-year LISA observation, focusing on vector fields with ultra-light masses in the $(10^{-19}, 10^{-16}) \; \rm{eV}$ range. We conclude that the observation of such gravitational waves with space-borne interferometers, like LISA, could yield a measurement or constraint on local, vector dark-matter environments, provided the dark-matter density is larger than roughly $10^{14} \rm{M}_\odot/{\rm{pc}}^3$.

astro-ph.CO↗

arXiv2025

Cosmological perturbations with ultralight vector dark matter fields: numerical implementation in CLASS

In this work we consider a dark matter candidate described by an ultralight vector field, whose mass is in principle in the range $H_{\rm{eq}}\sim 10^{-28}\rm{eV}\ll m< \rm{eV}$. The homogeneous background vector field is assumed to point in a given direction. We present a numerical implementation of cosmological perturbations in a Bianchi type I geometry with vector field dark matter in a modified version of the Cosmic Linear Anisotropy Solving System (CLASS). We study the evolution of large-scale cosmological perturbations in the linear regime. We compute the matter power spectrums defined for Fourier modes pointing in a given direction. We obtain interesting features in the power spectrums whose observational significance depends on the field mass. We compare the results with the standard $\rm{ΛCDM}$ and with the corresponding well-studied ultralight scalar field dark matter case. As for the scalar case we obtain a suppression in the power spectrums at small scales characterized by the same scale, namely the Jeans scale. The main characteristic feature of the vector field model we notice here for first time is that the amplitude of the suppression effect depends on the direction of the Fourier modes with respect to the background vector field, leaving eventually a possible anisotropic imprint in structure formation at small scales.

astro-ph.CO↗

arXiv2024

Ultralight vector dark matter, anisotropies and cosmological adiabatic modes

In this work we study the early time behavior and the background evolution of ultralight vector dark matter. We present a model for vector dark matter in an anisotropic Bianchi type I universe. Vector fields source anisotropies in the early universe characterized by a shear tensor which rapidly decays once the fields start oscillating, making them viable dark matter candidates. We present the set of equations needed to evolve scalar cosmological perturbations in the linear regime, both in synchronous gauge and Newtonian gauge. We show that the shear tensor has to be taken into account in the calculation of adiabatic initial conditions.

astro-ph.CO↗

arXiv2021

Rényi entropies of the massless Dirac field on the torus

We compute the Rényi entropies of the massless Dirac field on the Euclidean torus (the Lorentzian cylinder at non-zero temperature) for arbitrary spatial regions. We do it by the resolvent method, i.e., we express the entropies in terms of the resolvent of a certain operator and then use the explicit form of that resolvent, which was obtained recently. Our results are different in appearance from those already existing in the literature (obtained via the replica trick), but they agree perfectly, as we show numerically for non-integer order and analytically for integer order. We also compute the Rényi mutual information, and find that, for appropriate choices of the parameters, it is non-positive and non-monotonic. This behavior is expected, but it cannot be seen with the simplest known Rényi entropies in quantum field theory because they are proportional to the entanglement entropy.

hep-th↗