arXiv subjects

Moira Venegas

Publications and source records attributed to Moira Venegas.

8 recordsLinked to original sources

arXiv2026

CMB Birefringence from Axion String Networks Calibrated to an AMR Simulation

A cosmological network of axion strings may exist in the Universe today. If axion-like particles couple to electromagnetism, such a network induces spatially varying birefringence in the polarization of the cosmic microwave background (CMB), which can be probed by current and next-generation CMB experiments. We calibrate a loop-crossing model against a large-scale adaptive-mesh-refinement (AMR) simulation of axion-string network dynamics in the early Universe and use the calibrated model to predict CMB birefringence from recombination to today. We find that the non-detection of anisotropic birefringence in CMB observations places a strong upper bound on the electromagnetic anomaly coefficient $\mathcal{A}$ that enters the axion-photon coupling $g_{aγγ} = - \mathcal{A} α_\mathrm{em} / πf_a$. A joint analysis of available anisotropic birefringence measurements constrains $|\mathcal{A}| < 0.24$ at 95% C.L., which is independent of the Peccei-Quinn scale $f_a$, assuming that the axions are hyperlight so that the network survives until today. This limit strongly restricts the high-energy embedding of hyperlight axions, excluding the minimal Grand Unified Theory prediction for the electromagnetic anomaly coefficient at high significance. In addition, we discuss the implications of an axion-string origin for the recently reported evidence of isotropic birefringence.

astro-ph.CO↗

arXiv2026

Dipole Radiation and Kinetic Mixing from Dark Photon Solitons

Wave-like dark matter composed of spin-1 particles, known as dark photons, is theorized to form clumps called "vector solitons". These solitons are compact astrophysical objects that exhibit coherent oscillations and a high concentration relative to the local dark matter density. A significant portion of dark matter in galactic halos today may consist of these solitons. This study explores how photons can be produced from these vector solitons by the influence of external electromagnetic fields or charge densities, via a dimension-6 dark photon-photon coupling and a kinetic mixing, respectively. We further explore the astrophysical implications of these phenomena, highlighting a novel avenue for dark matter discovery that our research provides.

hep-ph↗

arXiv2025

Free streaming of warm wave dark matter in modified expansion histories

In models of warm dark matter, there is an appreciable population of high momentum particles in the early universe, which free stream out of primordial over/under densities, thereby prohibiting the growth of structure on small length scales. The distance that a dark matter particle travels without obstruction, known as the free streaming length, depends on the particle's mass and momentum, but also on the cosmological expansion rate. In this way, measurements of the linear matter power spectrum serve to probe warm dark matter as well as the cosmological expansion history. In this work, we focus on ultra-light wave wave dark matter (WWDM) characterized by a typical comoving momentum $q_\ast$ and mass $m$. We first derive constraints on the WWDM parameter space $(q_\ast, m)$ using Lyman-$α$ forest observations due to a combination of the free-streaming effect and the white-noise effect. We next assess how the free streaming of WWDM is affected by three modified expansion histories: early matter domination, early dark energy, and very early dark energy.

astro-ph.CO↗

arXiv2025

Setting up stasis with gravitational interactions

An epoch known as cosmological stasis may have taken place in the early Universe. During matter-radiation stasis, a population of non-relativistic particles with different masses gradually decay into relativistic particles, and the effective equation of state $w$ remains approximately constant at a value between that of matter ($w=0$) and that of radiation ($w=1/3$). In this work, we investigate how to set up the appropriate initial conditions for stasis using gravitational interactions. We consider two scenarios: that the tower of non-relativistic particles is populated by the evaporation of primordial black holes (PBHs) and that the tower is populated by cosmological gravitational particle production (CGPP) during inflation. We calculate the abundance of particles on different levels of the tower to assess whether stasis is viable. We find that both scenarios can provide the needed initial conditions for stasis, and that they predict distinctive scaling exponents $Ω_l \propto m_l^α$ with mass $m_l$.

hep-ph↗

arXiv2024

Revisiting signatures of thermal axions in nonstandard cosmologies

We revisit the formation of a thermal population of hadronic axions in nonstandard cosmologies, in light of the recent developments in obtaining continuous and smooth interaction rates for both the gluon and photon couplings. For certain cosmological histories, such as low-temperature reheating (LTR) and kination-like scenarios, the thermalization of the axion can be severely delayed to higher masses. In the case that thermal equilibrium is achieved, we improve the constraints on LTR for axion masses around the eV scale with respect to previous works and we constrain for the first time early matter-dominated (EMD) cosmologies. We also point out the possibility of having the co-existence of cold and warm dark matter populations of axions in kination-like scenarios in the eV mass range.

hep-ph↗

arXiv2022

Vortex solutions in the presence of Dark Portals

The existence of hidden sectors weakly coupled to the visible one has been extensively studied as a way to extend the Standard Model (SM) and to provide a good dark matter candidate. In this work we analyze two models in which gauge and scalar hidden fields interact with the visible sector which, for simplicity we take as an Abelian Higgs model. In one of them, the hidden sector consists of an uncharged scalar. The connection with the visible Abelian Higgs sector is in this case provided by the interaction between the scalars in the two sectors and also by the coupling between the hidden scalar and the visible squared field strength. This model can be seen as an extension of previously studied ones both in high energy and in condensed matter physics and the solutions that we find indicate that it could be relevant in connection to establishing the dark matter relic density. In the second model, both sectors correspond to spontaneously broken gauge theories and hence they feature classical vortex solutions. Introducing three different portals between the two sectors, we analyze the dependence of the model dynamics on the portal parameters and discuss the physical implications in connection with dark matter and gravitational radiation issues.

hep-th↗

arXiv2021

New opportunities for axion dark matter searches in nonstandard cosmological models

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology. Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $ϕ$ described by a general equation of state $ω$. The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window. This is the case for kination, or in general for scenarios with $ω> 1/3$. However, if $ω< 1/3$, as in the case of an early matter domination, the decay of $ϕ$ injects additional entropy relative to the case of the standard model, diluting this way the preexisting axion abundance, and rendering lighter axions viable. For a misalignment angle $0.5 < θ_i < π/\sqrt{3}$, the usual axion window becomes expanded to $4 \times 10^{-9}$ eV $\lesssim m_a \lesssim 2 \times 10^{-5}$ eV for the case of an early matter domination, or to $2 \times 10^{-6}$ eV $\lesssim m_a \lesssim 10^{-2}$ eV for the case of kination. Interestingly, the coupling axion-photon in such a wider range can be probed with next generation experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN. Axion dark matter searches may therefore provide a unique tool to probe the history of the universe before Big Bang nucleosynthesis.

hep-ph↗

arXiv2021

Relic Density of Axion Dark Matter in Standard and Non-Standard Cosmological Scenarios

In this master's thesis we study the production of axion dark matter through the so-called misalignment mechanism by considering that during that time, the universe was dominated by a new kind of fluid, different than radiation. We perform a very detailed analysis of the oscillation temperature and the relic density today, both analytically and numerically. Our findings show that on the one hand, the oscillation temperature is strongly influenced by the non-standard cosmology, affecting the relic density, and on the other hand, the energy density of the axion gets diluted, because the new fluid eventually decays, injecting entropy into the thermal bath. We find the predicted parameter space of axion dark matter for different non-standard cosmologies and we show its impact on the coupling of axions to two photons.

hep-ph↗