arXiv subjects

Fuensanta Vilches

Publications and source records attributed to Fuensanta Vilches.

4 recordsLinked to original sources

arXiv2026

How well can the QCD axion hide?

Motivated UV frameworks generically predict the existence of multiple axion fields. Their interplay gives rise to novel collective phenomena - including level crossings and the formation of string bundles - which modify the predicted mass and couplings of the QCD axion as a solution to both the strong CP problem and the observed dark matter abundance. Among these effects, the domain wall number is determined by the full anomaly structure of the theory: in the single axion case, the absence of long-lived domain walls imposes $E/N \geq 8/3$ as a theoretical bound on the QCD axion photon coupling, assuming the global structure of the Standard Model gauge group is minimal. We show that this bound can be relaxed in the multi-axion framework. Combined with the fact that the QCD axion can become a subdominant dark matter component, this might render multi-axion scenarios experimentally challenging. Nevertheless, a careful analysis of the parameter space reveals that in most regions where the QCD axion evades detection, an axion-like particle remains visible to next-generation experiments. When all signals fall below future projections, we identify the most promising regions of parameter space to probe in an illustrative two-axion setup.

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arXiv2025

Reconstructing a Heavy Neutral Lepton at the LHC

Heavy lepton singlets $N$ slightly mixed with a standard neutrino $ν_\ell$ are usually searched for at the LHC in the trilepton plus $p_{\rm T}^{\rm miss}$ channel: $pp \to W^+ \to \ell^+ N$ with $N\to \ell^- W^+ \to \ell^- \ell'^+ ν$. We show that, although the longitudinal momentum of the final $ν$ escapes detection, the mass of the heavy lepton can be reconstructed. While this possibility has not been considered in recent LHC searches, we find that the search for a mass peak could systematically improve the current collider bounds on the mixing $|V_{\ell N}|^2$ for any mass $m_N\ge M_W$.

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arXiv2025

Automation of a Matching On-Shell Calculator

We introduce $\texttt{mosca}$, a $\texttt{Mathematica}$ package designed to facilitate on-shell calculations in effective field theories (EFTs). This initial release focuses on the reduction of Green's bases to physical bases, as well as transformations between arbitrary operator bases. The core of the package is based on a diagrammatic on-shell matching procedure, grounded in the equivalence of physical observables derived from both redundant and non-redundant Lagrangians. $\texttt{mosca}$ offers a complete set of tools for performing basis transformations, diagram isomorphism detection, numerical substitution of kinematic configurations, and symbolic manipulation of algebraic expressions. Planned future developments include extension to one-loop computations, thus providing support for EFT renormalization directly in a physical basis and automated computation of one-loop finite matching, including contributions from evanescent operators. The package, along with example notebooks and documentation, is available at: https://gitlab.com/matchingonshell/mosca.

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arXiv2024

Efficient on-shell matching

We propose an efficient method to perform on-shell matching calculations in effective field theories. The standard off-shell approach to matching requires the use of a Green's basis that includes redundant and evanescent operators. The reduction of such a basis to a physical one is often highly non-trivial, difficult to automate and error prone. Our proposal is based on a numerical solution of the corresponding on-shell matching equations, which automatically implements in a trivial way the delicate cancellation between the non-local terms in the full theory and those in the effective one. The use of rational on-shell kinematics ensures an exact analytic solution despite the numerical procedure. In this way we only need a physical basis to perform the matching. Our procedure can be used to reduce any Green's basis to an arbitrary physical one, or to translate between physical bases; to renormalize arbitrary effective Lagrangians, directly in terms of a physical basis; and to perform finite matching, including evanescent contributions, as we discuss with explicit examples.

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