arXiv subjects

Alberto García Martín-Caro

Publications and source records attributed to Alberto García Martín-Caro.

At least 19 recordsLinked to original sources

arXiv2026

Electroweak form factors of large nuclei as BPS skyrmions

We employ the Bogomolnyi-Prasad-Sommerfield (BPS) Skyrme model within the framework of semi-classical quantization as an effective model to compute both the electromagnetic and neutral current form factors for heavy nuclei. Our results show excellent agreement with the experimental data for low- to moderate momentum transfer. Further, we present an analytic expression of the neutral current form factor for generic nuclei, expressed as a power series in the momentum transfer. Our method provides an alternative to existing phenomenological approaches which, after fitting just one global radial parameter, allows for a surprisingly precise determination of the electroweak form factors at low momentum transfer for all heavy nuclei. Such a simple and robust description is particularly relevant for precision neutrino experiments, because it allows for a certain control over model-dependent systematics, which is essential for probing physics beyond the Standard Model.

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arXiv2026

Quantization of Brane-Skyrmions via Physics-Informed Neural Networks

In this work, we investigate the canonical quantization of topological solitons appearing in braneworld scenarios. In particular, we focus on Brane-Skyrmions, topological field configurations analogous to standard Skyrmions, which emerge as solutions of the Dirac-Nambu-Goto action supplemented by an induced curvature term. By quantizing the (iso)spin collective coordinates of the Brane-Skyrmion, we obtain a Hamiltonian that we solve perturbatively via an expansion in powers of $J^2$, in contrast to the standard Skyrme model. Furthermore, we implement a Physics-Informed Neural Network (PINN) to determine the soliton profile that minimizes the energy, consistently incorporating the backreaction from the quantized spin degrees of freedom. We conclude with a discussion of the potential applications of this framework to the description of hadronic spectra. Our results highlight both the theoretical potential of brane-defect models and the growing role of neural network methods in theoretical physics.

hep-th↗

arXiv2026

Cuspidal Singularities in Collapsing Domain Walls

Domain wall networks have attracted renewed interest, particularly in relation to the dynamics of network collapse. Accurately describing this process is challenging and typically requires large scale numerical simulations. Here we adopt a complementary approach by studying the collapse of individual closed domain walls, extending previous thin wall analyses and comparing them with adaptive mesh refinement field theory simulations. Firstly, we show that collapsing domain walls generically develop worldvolume singularities of two types: cuspidal edge singularities, consisting of one dimensional singular edges that propagate along the wall surface at the speed of light for a finite time, and cuspidal vertex singularities, which are spike like and instantaneous events where the wall moves momentarily at the speed of light. Both types of features arise generically from smooth initial conditions, and their formation and evolution follow the universal patterns of singularity theory. We show that these structures are captured both by the Nambu-Goto equations and by an eikonal like approximation valid in the relativistic regime. Furthermore, we demonstrate that the same singular structures are reproduced qualitatively in full field theory simulations, establishing that they are not artifacts of the thin wall approximation but robust features of realistic domain wall dynamics. Naturally, such focusing effects in the field theory simulations result in localized regions of high energy density. We briefly discuss possible phenomenological implications.

hep-th↗

arXiv2026

On curvature corrections for field theory cosmic strings

We present a combined analytical and numerical study of the effective action of field theory cosmic strings in the Abelian-Higgs model in flat space. Starting directly from the underlying solitonic field theory description, we provide a systematic derivation of the low energy effective action and present evidence for the absence of nontrivial curvature correction terms when only the translational Goldstone modes are retained. Using this framework, we extend the effective theory to include higher energy fluctuations of the soliton profile, which map to massive degrees of freedom propagating on the worldsheet. We show that the leading curvature contribution enters only through the coupling between these massive modes and the worldsheet Ricci scalar. We validate the resulting effective theory via lattice simulations of the full field theory equations of motion in flat space, implemented with Adaptive Mesh Refinement to capture the string dynamics across different scales. The numerical simulations confirm the dynamics obtained using the effective action in its validity range. Furthermore, they also demonstrate the existence of the predicted parametric instability of excited strings that drives the transfer of energy from massive excitations to the Goldstone sector.

hep-th↗

arXiv2025

Quantum fermion emission from excited kinks

The amplitude of an excited shape mode in a kink is expected to decay with a well-known power law via scalar radiation emission due to the nonlinear self-coupling of the scalar field. In this work we propose an alternative decay mechanism via pair production of fermions in a simple extension of the $ϕ^4$ model in which the scalar field is coupled to a (quantum) fermionic field through a Yukawa-like interaction term. We study the power emitted through fermions as a function of the coupling constant in the semi-classical limit (without backreaction) and compare it to the case of purely scalar radiation emission.

hep-th↗

arXiv2025

Robustness of analogue Hawking radiation in cavities with moving boundaries

In this work we explore the limitations and robustness of thermal radiation in dynamical Casimir systems serving as analogs for Hawking radiation. Through detailed numerical analysis, we characterize particle production spectra in cavities with moving boundaries under various configurations, including expanding, collapsing, and rigidly accelerating scenarios. We find that thermal signatures emerge in specific expanding cavity configurations but are highly dependent on frequency bands and acceleration parameters. In those configurations of the cavity where there is thermal production, we derive fitting expressions that quantify deviations from idealized thermal spectra through gray-body factors, revealing oscillatory behaviors tied to acceleration duration. Our results identify which experimental setups can reliably simulate gravitationally-induced phenomena and quantify how finite-size effects and transient dynamics modify the expected thermal distributions, providing a comprehensive framework for distinguishing genuine Hawking-like radiation from experimental artifacts.

quant-ph↗

arXiv2025

Spinning boson stars in nonlinear sigma models and Universal Relations

Boson stars are hypothetical compact objects derived from solutions of a self-gravitating complex scalar field. In this study, we extend the traditional models by generalizing the kinetic term of the scalar field to that of a nonlinear sigma model. Concretely, we obtain spinning boson star solutions for a family of models parametrized by the curvature of their two-dimensional target manifold, as well as for various self-interaction potentials. We derive the global properties and multipolar structure of these solutions as a function of both the curvature of the target space and the strength of self-interactions. Our results suggest that a nonzero curvature in the target manifold can have a significant impact on the structure of the solutions, allowing for a range of notably different masses and degrees of compactness. However, we find that the relations between different multipoles are consistent with those for the standard complex scalar stars, and hence the universality of such relations is extended to curved target spaces.

gr-qc↗

arXiv2025

Effective Actions for Domain Wall Dynamics

We introduce a systematic method to derive the effective action for domain walls directly from the scalar field theory that gives rise to their solitonic solutions. The effective action for the Goldstone mode, which characterizes the soliton's position, is shown to consist of the Nambu-Goto action supplemented by higher-order curvature invariants associated to its worldvolume metric. Our approach constrains the corrections to a finite set of Galileon terms, specifying both their functional forms and the procedure to compute their coefficients. We do a collection of tests across various models in $2+1$ and $3+1$ dimensions that confirm the validity of this framework. Additionally, the method is extended to include bound scalar fields living on the worldsheet, along with their couplings to the Goldstone mode. These interactions reveal a universal non-minimal coupling of these scalar fields to the Ricci scalar on the worldsheet. A significant consequence of this coupling is the emergence of a parametric instability, driven by interactions between the bound states and the Goldstone mode.

hep-th↗

arXiv2025

Feshbach resonances and dynamics of BPS solitons

We demonstrate that the geodesic dynamics of BPS solitons can be modified by the excitation of Feshbach resonances, or quasi-bound modes, in a toy model of two scalar fields. A mode-generated force emerges, with a strength determined by the spectral flow of the frequency on the moduli space, and weakened by the coupling between the bound and scattering components of the resonance. Notably, spectral walls persist unaffected by the resonant mode's exponential decay, as the decay constant vanishes at the spectral wall. Our motivation comes from the 't Hooft-Polyakov monopoles, which do not present true bound states but long lived semi-bound excitations. Our findings suggest the existence of spectral walls in the scattering of excited monopoles in three dimensions, whose trajectories may significantly deviate from the geodesic motion in the moduli space of unexcited monopoles.

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arXiv2025

Instanton Corrections to the MSTB Kink Mass

The Montonen-Sarker-Trullinger-Bishop (MSTB) model enjoys two classically degenerate kink solutions in the same topological sector. We construct the instanton that interpolates between them and argue that the two lowest lying Hamiltonian eigenstates in the kink sector of the corresponding quantum theory correspond to symmetric and antisymmetric combinations of coherent states localized at these two solutions. We use the instanton gas approximation to provide a simple, analytic formula for the leading contribution to the mass splitting between these two states.

hep-th↗

arXiv2024

Classical and quantum field theory in a box with moving boundaries: A numerical study of the Dynamical Casimir Effect

We present a detailed description of a quantum scalar field theory within a flat spacetime confined to a cavity with perfectly reflecting moving boundaries. Moreover, we establish an equivalence between this time-dependent setting and a field theory on an acoustic metric with static Dirichlet boundary conditions. We discuss the classical and quantum aspects of the theory from the latter perspective, accompanied by the introduction of novel numerical techniques designed for the (nonperturbative) computation of particle production attributed to the Dynamical Casimir effect, applicable to arbitrary boundary trajectories. As an illustrative example of these methodologies, we compute the particle production for a massless field in 1+1 dimensions. Notably, our approaches readily extend to encompass scenarios involving massive fields and higher dimensions

quant-ph↗

arXiv2024

Hawking radiation from an analogue bouncing geometry

We propose a setting that simulates Hawking radiation from an analogue bouncing geometry, i.e., a collapsing geometry that reverts its collapse after a finite time, in a setup consisting of a coplanar waveguide terminated in superconducting quantum-interference devices at both ends. We demonstrate experimental feasibility of the proposed setup within the current technology. Our analysis illustrates the resilience of Hawking radiation under changes in the physics at energy scales much larger than the temperature, supporting the idea that regular alternatives to black holes would also emit Hawking radiation.

gr-qc↗

arXiv2024

Nuclear mass radius and pressure in the Skyrme model

We compute the mass radius, scalar radius, tensor radius, baryon number radius and mechanical radius of nuclei with baryon number $B=1,2,3,4,5,6,7,8,32,108$ in the Skyrme model. The relations between these radii and the nuclear gravitational form factors are investigated. We also compute the `pressure' distribution and find that it is negative in the core region for all the nuclei with $B>1$. This suggests that the way mechanical stability is achieved in nuclei is qualitatively different than in the nucleon.

hep-ph↗

arXiv2023

The charge density and neutron skin thickness of Skyrmions

Motivated by recent parity violating electron scattering experiments, we compute the Neutron Skin Thickness (NST) of nuclei modelled as (quantized) Skyrmions, the topological solitons of the Skyrme model. We show how in a certain approximation, the result for the NST is oblivious to the fine details of the (generally very complicated) quantum state of the soliton and only depends on the total baryon number and the isospin number. Moreover, in the leading order, the linear dependence on the asymmetry parameter is recovered, as expected both from experimental data and other models of nuclei such as the liquid drop model.

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arXiv2023

Gravitational form factors of nuclei in the Skyrme model

We compute the gravitational form factor $D(t)$ of various nuclei in the generalized Skyrme model where nuclei are described as solitonic field configurations each with a definite baryon number $B$. We separately discuss the cases $B=1$ (nucleons), $B=2$ (deuteron), $B=3$ (helium-3 and tritium) and extrapolate to larger $B$-values. Configurations with $B>1$ are in general not spherically symmetric, and we demonstrate how group theory helps to extract the form factor. Numerical results are presented for the configurations with $B=1,2,3,4,5,6,7,8,32,108$. We find that the $B$-dependence is consistent with a power-law $D(0)\propto B^β$ with $β=1.7\sim 1.8$. Other gravitational form factors can be calculated in the same framework, and we show the result for the $J(t)$ form factor associated with angular momentum for the $B=3$ solution.

nucl-th↗

arXiv2023

Effective no-hair relations for spinning Boson Stars

Boson Stars are, at present, hypothetical compact stellar objects whose existence, however, could resolve several enigmas of current astrophysics. If they exist, either as independent astrophysical entities or as a matter admixture of more standard compact stars, then their imprints can probably be observed in the not-too-distant future from the gravitational signal of coalescing binaries in current and future GW detectors. Here we show that the multipole moments of rotating boson stars obey certain universal relations, valid for a broad set of models and various states in terms of the \textit{harmonic indices}. These universal relations are equivalent to a kind of no-hair theorem for this exotic matter, allowing to map these universal (i.e. model independent) multipoles to an equally universal gravitational field around the stellar object. Further, the multipole moments can be related to observable astrophysical quantities.

gr-qc↗

arXiv2023

Universal relations for rotating Boson Stars

Boson stars represent a hypothetical exotic type of compact stellar object that may be observed from the gravitational signal of coalescing binaries in current and future GW detectors. In this work we show that the moment of inertia $I$, the (dimensionless) angular momentum $χ$ and the quadrupole moment $Q$ of rotating boson stars obey a universal relation, valid for a wide set of boson star models. Further, the obtained $I-χ-Q~$ relation clearly differs from its famous neutron star counterpart, providing us with an unequivocal diagnostic tool to distinguish boson stars from ordinary compact stars or other celestial bodies in GW observations. Such universal (i.e. model-independent) relations also provide a useful tool to probe the strong gravity regime of general relativity and to constrain the equation of state of matter inside compact stars.

gr-qc↗

arXiv2022

Kaon condensation in skyrmion matter and compact stars

We address the possibility of the appearance of a charged kaon condensate in neutron star cores described within a generalized Skyrme model. Our treatment of strange degrees of freedom is based on the Bound State Approach by Callan and Klebanov, which allows to obtain an in-medium effective potential for the $s$-wave kaon condensate. We predict the onset of kaon condensation at a certain threshold density - whose value depends on the parameters of the model, and ranges between 1.5 and 2.5 times saturation density -, and obtain both the particle fractions and equation of state for dense matter in the kaon condensed phase. Finally, we discuss the effect of such condensates on the mass-radius curves and other observable properties of neutron stars with kaon condensed cores.

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