arXiv subjects

Noelia Sánchez González

Publications and source records attributed to Noelia Sánchez González.

5 recordsLinked to original sources

arXiv2026

Low-energy brane decoupling in AdS flux vacua

We study the decoupling of branes sourcing AdS flux vacua from the asymptotic bulk using scalar-wave absorption probabilities. In a one-modulus truncation, the result depends only on the dimension of the AdS vacuum and on the asymptotic steepness of the scalar potential. We find that for any steepness and for any dimension greater than two the absorption probability vanishes in the low-energy limit, showing that the branes decouple from the bulk. We illustrate the general analysis in several scale-separated AdS vacua. For DGKT we find $P_{\rm abs}\simω^{27/7}$ and an effective transverse dimension $d_{\rm eff}=20/7$. Interestingly, the scalar potential along the brane-induced moduli trajectory agrees with that obtained by compactifying a hypothetical $(4+13/7)$-dimensional gravity theory on a $13/7$-dimensional sphere threaded by flux. We also apply the analysis to scale-separated $\mathrm{AdS}_3$ examples and to the simplest one-modulus KKLT model.

hep-th↗

arXiv2026

Pre-inflationary QCD axion stars after moduli domination

The growth of adiabatic density perturbations during an era of early matter domination induces $\mathcal{O}(1)$ fluctuations in pre-inflationary QCD axion dark matter across a broad, string-theory-motivated parameter space. Remarkably, at $Λ$CDM matter-radiation equality the scale of these perturbations coincides with the quantum Jeans scale, so they collapse to solitonic ``axion stars''. These axion stars have densities up to $10^4\,\mathrm{eV}^4$, and, including their surrounding halos, they contain as much as $50\%$ of dark matter. Direct searches for a smooth axion background can be suppressed, but transient enhancements or indirect astrophysical signals at axion masses $m_a\lesssim 10^{-5}\,{\rm eV}$ would point to a non-standard cosmological history.

hep-ph↗

arXiv2025

High-frequency Gravitational Waves from Superstring Phases in the Early Universe

When moduli roll in the early universe, all physical scales - including string tensions - simultaneously evolve. The dynamics of cosmic string loops with time-varying tension can produce cosmic string loop trackers in which most of the energy density of the universe lies in the form of string loops. This solution can exist as an attractor until the rolling modulus reaches its minimum, when the loops ultimately decay through gravitational wave emission. We explore the spectrum of gravitational waves produced by such string loop trackers. The resulting spectrum is high-frequency and peaks in the GHz regime today. The amplitude of the signal is diluted by any subsequent matter-dominated epochs, and thus the potential observability of the signal crucially depends on the duration of the moduli-dominated epoch that follows once the moduli settle down and oscillate about their minimum.

hep-ph↗

arXiv2025

Dynamical Systems and Superstring Phases in the Early Universe

We study the string theory dynamics of the volume scalar rolling down an exponential potential during the period between inflation and reheating, in a background of cosmic superstring loops. In the context of the LVS potential, we demonstrate the existence of a novel string loop attractor tracker solution, in which 75% of the energy density of the universe is in the form of a gas of fundamental cosmic superstring loops (a configuration preferred over the standard radiation tracker). On this tracker, it is the continual reduction in the string tension as the volume scalar evolves that makes the loops stable against decay. For more general non-LVS potentials, mixed radiation-loop trackers can also occur.

hep-ph↗

arXiv2024

Percolating Cosmic String Networks from Kination

We describe a new mechanism, whose ingredients are realised in string compactifications, for the formation of cosmic (super)string networks. Oscillating string loops grow when their tension $μ$ decreases with time. If $2H + \dotμ/μ< 0$, where $H$ is the Hubble parameter, loops grow faster than the scale factor and an initial population of isolated small loops (for example, produced by nucleation) can grow, percolate and form a network. This condition is satisfied for fundamental strings in the background of a kinating volume modulus rolling towards the asymptotic large volume region of moduli space. Such long kination epochs are motivated in string cosmology by both the electroweak hierarchy problem and the need to solve the overshoot problem. The tension of such a network today is set by the final vacuum; for phenomenologically appealing Large Volume Scenario (LVS) vacua, this would lead to a fundamental string network with $G μ\sim 10^{-10}$.

hep-ph↗