arXiv subjects

Sergio Sevillano Muñoz

Publications and source records attributed to Sergio Sevillano Muñoz.

13 recordsLinked to original sources

arXiv2026

Supernova microlensing as a probe of ultracompact minihalos and primordial cosmology

We propose using supernova microlensing to search for ultracompact minihalos and other extended dark structures seeded by enhanced primordial small-scale power. Unlike conventional microlensing searches, which are often optimized for primordial black holes, cosmological supernovae are sensitive to lenses with physical sizes comparable to their Einstein radii (up to $\sim {\rm pc}\left(M/10^4M_\odot\right)^{1/2}$ scale), opening a qualitatively different region of dark object parameter space. We compute the extended object detection efficiency relative to point lenses. We then show how projected limits on the abundance of ultracompact minihalos can be mapped, in benchmark formation scenarios, onto constraints on the primordial power spectrum. With the Vera C. Rubin Observatory expected to deliver an unprecedented LSST supernova sample, supernova microlensing is poised to become a timely and complementary probe of small-scale structure and the physics of the early Universe.

astro-ph.CO↗

arXiv2026

Misalignment from kicks: the impact of particle interactions on ultra-light dark matter

Oscillating ultra-light scalar fields are a natural explanation for the dark matter in our universe, as long as a mechanism, often called a misalignment mechanism, exists to explain the amplitude of the scalar oscillations. If the dark matter scalar couples to the Standard Model, then the dynamics of ordinary matter can influence the behaviour of dark matter in the early universe. In this work we show how this changes the expected value of the scalar field and the resulting amplitude of late time scalar oscillations, and therefore the abundance of dark matter at late times. For dark matter scalars that interact quadratically with Standard Model fields we derive estimates of the size of this effect as a function of the strength of the coupling, and for axion-like fields we show that interactions with dark sector matter can temporarily destabilize the field, leading to large field displacements.

hep-ph↗

arXiv2026

Updated constraints on the primordial power spectrum at sub-Mpc scales

The primordial power spectrum of matter density perturbations contains highly valuable information about new fundamental physics, in particular cosmological inflation, but is only very weakly constrained observationally for small cosmological scales $k\gtrsim 3\,{\rm Mpc}^{-1}$. We derive novel constraints, $\mathcal{P}_\mathcal{R}(k)\lesssim 5\cdot10^{-6}$ over a large range of such scales, from the formation of ultracompact minihalos in the early universe. Unlike most existing constraints of this type, our results do not rest on the assumption that dark matter can annihilate into ordinary matter.

astro-ph.CO↗

arXiv2026

Unified dark sector approaches to cosmological tensions

We present an analytical study of minimal mass-varying dark matter models, in which a single scalar field controls the dark matter mass, focusing on their utility in simultaneously addressing multiple cosmological tensions. We show that such minimal models can naturally become relevant at two critical epochs in the history of the Universe; matter-radiation equality and the present day, generating an early dark energy-like energy injection, as motivated by the Hubble tension, and an apparent phantom crossing, as suggested by baryon acoustic oscillation data from the DESI project. Crucially, the characteristic timing of these effects is tied to the cosmological background evolution itself, rather than specific energy scales. In addition, the intermediate evolution reduces the clustering matter density and can therefore lower $S_8$, in the direction preferred by data, while avoiding new long-range interactions. We derive analytic arguments to understand the conditions for these effects to arise in the same model and assess whether they can occur without introducing additional fine-tuning. This provides a simple framework for identifying which potentials and couplings to dark matter can simultaneously affect early- and late-time cosmological tensions.

astro-ph.CO↗

arXiv2026

Neutrino Constraints on Scalar-Tensor Gravity

In this work, we derive novel constraints on scalar-tensor theories from neutrino physics. Spatial variations of the background scalar field effectively generate density and position-dependent Standard Model masses, including neutrinos. Neutrinos are a unicum in the SM due to their ability both to propagate over galactic distances and to traverse dense media such as Earth. This makes them an ideal probe of the background scalar field, which can in turn alter flavour oscillations and supernova time delays. As we enter the era of precision neutrino physics, we are compelled to explore such a scenario. We derive expressions for the relevant observables and obtain new bounds on a broad class of scalar-tensor models. We finally map the bounds to popular screening mechanisms models, such as the Symmetron and Chameleon.

hep-ph↗

arXiv2026

The Revised Evolutionary Volume Tolman Test: Cosmological Constraints from Galaxy Evolution

In this study we adapt a classical cosmology measurement, the volume or number density test, to a modern synthesis of observed galaxy evolution. We do this by using measured galaxy mass functions and the history of galaxy evolution through star formation and galaxy mergers, inspired by the latest results from deep extragalactic surveys. We develop a new framework using measured galaxy volume number densities as a function of redshift and volume to determine cosmological parameters, especially those which alter the volume of the Universe at a given redshift. Whilst this is a classic cosmology test proposed since at least the 1930s, it has largely been abandoned for decades due to uncertainties in galaxy evolution which make it difficult to trace galaxy populations through time. However, recent advances in our understanding of star formation and the merging history of galaxies allow us to revise this method to uncover and measure cosmological parameters, especially those which involve the nature of dark energy. We present a modified version of the volume test, called the revised evolutionary volume Tolman test, using properties of known galaxy evolution as part of the cosmological calculation. We show how this method can successfully be applied and is competitive with other major cosmological measurement methods, including those using supernova and the CMB, when the merger and star formation histories can be measured accurately to between 1 to 10 percent. This accuracy is not yet achievable, but we discuss how future missions will allow these astrophysical quantities to be known at this level. Within this measurement accuracy we can measure the dynamical properties of dark energy, including its evolution through its equation of state. We also give a fuller accounting of the future use of this new method with upcoming galaxy surveys such as Euclid and LSST/Rubin.

astro-ph.CO↗

arXiv2025

A particle's perspective on screening mechanisms

Screening mechanisms are a natural method for suppressing long-range forces in scalar-tensor theories as they link the local background density to their strength. Focusing on Brans-Dicke theories, those including a non-minimal coupling between a scalar degree of freedom and the Ricci scalar, we study the origin of these screening mechanisms from a field theory perspective, considering the influence of the Standard Model on the mechanisms. Additionally, we further consider the role of scale symmetries on screening, demonstrating that only certain sectors, those obtaining their mass via the Higgs mechanism, contribute to screening the fifth forces. This has significant implications for baryons, which obtain most of their mass from the gluon's binding energy. Given that the Planck mass is related to the vacuum expectation value of the non-minimally coupled field, we find an extensive region of the parameter space where screening mechanisms create a spatially dependent gravitational constant. We say that the field over-screens when this effect is more significant than the fifth forces suppressed by screening mechanisms, as we illustrate for the chameleon and symmetron models.

hep-ph↗

arXiv2025

Repository for extended dark matter object constraints

Extended dark matter objects (EDOs) are popular dark matter candidates that interact gravitationally with the Standard Model. These gravitational interactions can be used to constrain their allowed parameter space. However, EDOs can have different formation mechanisms, sizes, and shapes, requiring a case-by-case analysis when studying their impact on different areas of cosmology. We thus present a repository of all available bounds for these objects, with a code that allows plotting user-defined combinations of all up-to-date bounds for a given shape and different radii. We propose a standard for the EDOs' mass profiles so that different sets of bounds are consistent with each other, and provide instructions on using the code and contributing to the repository.

astro-ph.CO↗

arXiv2024

Recasting scalar-tensor theories of gravity for colliders

Diagrammatic approaches to perturbation theory transformed the practicability of calculations in particle physics. In the case of extended theories of gravity, however, obtaining the relevant diagrammatic rules is non-trivial: we must expand in metric perturbations and around (local) minima of the scalar field potentials, make multiple field redefinitions, and diagonalize kinetic and mass mixings. In this note, we will motivate these theories, introduce the package FeynMG -- a Mathematica extension of FeynRules that automates the process described above -- and highlight an application to a model with unique collider phenomenology.

hep-ph↗

arXiv2024

Cosmic microwave background constraints on extended dark matter objects

Primordially formed extended dark objects would accrete baryonic matter and impact the ionisation history of the Universe. Insisting on consistency with the anisotropies of the cosmic microwave background, we derive constraints on the dark matter fraction for various classes of objects, of different sizes. We introduce a novel scaling technique to speed up numerical calculations and release our calculation framework in the form of a Mathematica notebook. Conservatively, we focus on spherical accretion and collisional ionisation. We find strong constraints limiting the dark matter fraction to subpercent level for objects of up to $10^4$ AU in size.

astro-ph.CO↗

arXiv2024

Scaling solutions as Early Dark Energy resolutions to the Hubble tension

A wide class of scalar field models including Quintessence and K-essence have the attractive property of tracker regimes, where the energy density stored in the field evolves so as to mimic that of the dominant background component for a period of time. During this evolution, for a brief period of time there is an increase in the energy density of the field as it spirals in towards it's attractor solution. We show that when the peak of this energy density occurs around the epoch of equality, we can address a key requirement of early dark energy (EDE), postulated as a solution to the Hubble tension. In particular we demonstrate how this can occur in a wide class of Quintessence, axion and K-essence models, before showing that the Quintessence models suffer in that they generally lead to sound speeds incompatible with the requirements of EDE, whereas the K-essence and axion models can do a better job of fitting the data.

astro-ph.CO↗

arXiv2023

FeynMG: a FeynRules extension for scalar-tensor theories of gravity

The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics (and elsewhere). Moreover, these rules are readily automated, a process that has catalysed the rise of symbolic algebra packages. However, in the case of extended theories of gravity, such as scalar-tensor theories, it is necessary to precondition the Lagrangian to apply this automation or, at the very least, to take advantage of existing software pipelines. We present a Mathematica code FeynMG, which works in conjunction with the well-known package FeynRules, to do just that: FeynMG takes as inputs the FeynRules model file for a non-gravitational theory and a user-supplied gravitational Lagrangian. FeynMG provides functionality that inserts the minimal gravitational couplings of the degrees of freedom specified in the model file, determines the couplings of the additional tensor and scalar degrees of freedom (the metric and the scalar field from the gravitational sector), and preconditions the resulting Lagrangian so that it can be passed to FeynRules, either directly or by outputting an updated FeynRules model file. The Feynman rules can then be determined and output through FeynRules, using existing universal output formats and interfaces to other analysis packages.

gr-qc↗

arXiv2022

Fifth forces and broken scale symmetries in the Jordan frame

We study the origin of fifth forces in scalar-tensor theories of gravity in the so-called Jordan frame, where the modifications to the gravitational sector are manifest. We focus on theories of Brans-Dicke type in which an additional scalar field is coupled directly to the Ricci scalar of General Relativity. We describe how the necessary diffeomorphism invariance of the modified gravitational sector leads to a modification of the usual gauge fixing term (for the harmonic gauge), as compared to Einstein gravity. This allows us to perform a consistent linearization of the gravitational sector in the weak-field limit, which gives rise to a kinetic mixing between the non-minimally coupled scalar field and the graviton. It is through this mixing that a fifth force can arise between matter fields. We are then able to compute the matrix elements for fifth-force exchanges directly in the Jordan frame, without the need to perform a conformal transformation to the so-called Einstein frame, where the gravitational sector is of Einstein-Hilbert form. We obtain results that are in agreement with the equivalent Einstein-frame calculations and illustrate, still in the Jordan frame, the pivotal role that sources of explicit scale symmetry breaking in the matter sector play in admitting fifth-force couplings.

hep-th↗