arXiv subjects

A. Ramos

Publications and source records attributed to A. Ramos.

At least 19 recordsLinked to original sources

arXiv2026

Comprehensive study of hidden charm pentaquarks with an improved unitarization method

This work investigates dynamically generated hidden-charm baryon resonances arising from meson-baryon interactions. Using the local hidden gauge formalism, we model the interaction via t-channel vector meson exchange and unitarize the amplitude using the Bethe-Salpeter equation. To address regularization issues, we propose a novel ``hybrid loop function'' scheme that eliminates the unphysical poles -- common artifacts in cutoff or dimensional regularization -- while keeping the predictions of physical states. Consequently, the model successfully reproduces six experimentally known hidden-charm pentaquarks as well as earlier theoretical results, and predicts new states in the S=-1, I=1 sector.

hep-ph↗

arXiv2025

Dynamical Systems Perspective for a Real-Time Response to a Marine Oil Spill

This paper discusses the combined use of tools from dynamical systems theory and remote sensing techniques and shows how they are effective instruments which may greatly contribute to the decision making protocols of the emergency services for the real-time management of oil spills. This work presents the successful interplay of these techniques for a recent situation, the sinking of the Oleg Naydenov fishing ship that took place in Spain, close to the Canary Islands, in April 2015.

physics.ao-ph↗

arXiv2025

The SHMS 11 GeV/c Spectrometer in Hall C at Jefferson Lab

The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnetic spectrometer comprised of a series of new superconducting magnets which transport charged particles through an array of triggering, tracking, and particle-identification detectors that measure momentum, energy, angle and position in order to allow kinematic reconstruction of the events back to their origin at the scattering target. The detector system is protected from background radiation by a sophisticated shielding enclosure. The entire spectrometer is mounted on a rotating support structure which permits measurements to be taken with a large acceptance over laboratory scattering angles from 5.5 to 40 degrees, thus allowing a wide range of low cross-section experiments to be conducted. These experiments complement and extend the previous Hall C research program to higher energies.

physics.ins-det↗

arXiv2024

Femtoscopic study of the $S=-1$ meson-baryon interaction: $K^-p$, $\pi^-\Lambda$ and $K^+\Xi^-$ correlations

We study the femtoscopic correlation functions of meson-baryon pairs in the strangeness $S=-1$ sector, employing unitarized s-wave scattering amplitudes derived from the chiral Lagrangian up to next-to-leading order. For the first time, we deliver predictions on the $\pi^-\Lambda$ and $K^+\Xi^-$ correlation functions which are feasible to be measured at the Large Hadron Collider. We also demonstrate that the employed model is perfectly capable of reproducing the $K^-p$ correlation function data measured by the same collaboration, without the need to modify the coupling strength to the $\bar{K}^0n$ channel, as has been recently suggested. In all cases, the effects of the source size on the correlation are tested. In addition, we present detailed analysis of the different coupled-channel contributions, together with the quantification of the relative relevance of the different terms in the interaction. These calculations require the knowledge of the so-called production weights, for which we present two novel methods to compute them.

hep-ph↗

arXiv2024

FLAG Review 2024

We review lattice results related to pion, kaon, $D$-meson, $B$-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More specifically, we report on the determination of the light-quark masses, the form factor $f_+(0)$ arising in the semileptonic $K \to \pi$ transition at zero momentum transfer, as well as the decay-constant ratio $f_K/f_\pi$ and its consequences for the CKM matrix elements $V_{us}$ and $V_{ud}$. We review the determination of the $B_K$ parameter of neutral kaon mixing as well as the additional four $B$ parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for $m_c$ and $m_b$ as well as those for the decay constants, form factors, and mixing parameters of charmed and bottom mesons and baryons. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant $\alpha_s$. We review the determinations of nucleon charges from the matrix elements of both isovector and flavour-diagonal axial, scalar and tensor local quark bilinears, and momentum fraction, helicity moment and the transversity moment from one-link quark bilinears. We also review determinations of scale-setting quantities. Finally, in this review we have added a new section on the general definition of the low-energy limit of the Standard Model.

hep-lat↗

arXiv2024

Double strangeness pentaquarks and other exotic hadrons in the $\Xi_b \to \Xi\ J/\Psi\ \phi$ decay

We study the possibility that four $\Xi$ resonances $(\Xi(1620)$, $\Xi(1690)$, $\Xi(1820)$, $\Xi(1950))$ could correspond to pentaquark states, in the form of meson-baryon bound systems. We also explore the possible existence of doubly strange pentaquarks with hidden charm $(P_{css})$ and find two candidates structured in a similar form, at energies of $4493~{\rm MeV}$ and $4630~{\rm MeV}$. The meson-baryon interaction is built from t-channel meson exchange processes which are evaluated using effective Lagrangians. Moreover we analyse the $\Xi_b\to\Xi~J/\psi~\phi$ decay process, which permits exploring the existence of the heavy double strange pentaquark, as well as other exotic hadrons, in the three different two-body invariant mass spectra of the emitted particles. In the $J/\psi\phi$ mass spectrum, we analyse the nature of the $X(4140)$ and $X(4160)$ resonances. In the $J/\psi\Xi$ invariant mass spectrum, we study the signal produced by the doubly strange pentaquark, where we conclude that it has a good chance to be detected in this reaction if its mass is around $4580-4680~{\rm MeV}$. Finally, in the $\phi\Xi$ spectrum we study the likelihood to detect the $\Xi(2500)$ state.

hep-ph↗

arXiv2023

Constraining the low-energy S=-2 meson-baryon interaction with two-particle correlations

The two-particle correlation technique applied to $K^-\Lambda$ pairs in pp collisions at LHC recently provided the most precise data on the strangeness $S=-2$ meson-baryon interaction. In this letter, we use for the first time femtoscopic data to constrain the parameters of a low-energy effective QCD Lagrangian. The tuned model delivers new insights on the molecular nature of the $\Xi(1620)$ and $\Xi(1690)$ states. This procedure opens the possibility to determine higher order corrections, directly constraining QCD effective models particularly in the multi-strange and charm sectors.

hep-ph↗

arXiv2022

Double strangeness molecular-type pentaquarks from coupled channel dynamics

The existence of pentaquarks with strangeness content zero and one are major discoveries of the latest years in hadron physics. Most of these states can be understood as hadronic molecules and were predicted prior to their discovery within a model based on unitarized meson-baryon amplitudes obtained from vector meson exchange interactions. Contrary to earlier statements, we show this model to also predict the existence of pentaquarks with double strangeness, at about 4500 MeV and 4600 MeV, which are generated in a very specific and unique mechanism, via an attraction induced by a strong coupling between the two heaviest meson-baryon states.

hep-ph↗

arXiv2022

Anisotropic star models in the context of vanishing complexity

We use the definition of complexity for static and self--gravitating objects to build up three physical general relativistic anisotropic models fulfilling the vanishing complexity condition which serves to provide the extra information needed to close the system of Einstein field equations. We evaluate the physical acceptability of these models by testing some of the conditions that the geometric and material sector must satisfy in order to be considered as reasonable realistic models. We present the results of this analysis by asserting that the studied cases demonstrate to be feasible and stable under the chosen set of parameters. Furthermore, the $P_{\perp}=0$ and the Consenza's anisotropy models that seem not satisfying the expect conditions are also discussed.

gr-qc↗

arXiv2022

An optimal investment strategy aimed at maximizing the expected utility across all intermediate capital levels

This study investigates an optimal investment problem for an insurance company operating under the Cramer-Lundberg risk model, where investments are made in both a risky asset and a risk-free asset. In contrast to other literature that focuses on optimal investment and/or reinsurance strategies to maximize the expected utility of terminal wealth within a given time horizon, this work considers the expected value of utility accumulation across all intermediate capital levels of the insurer. By employing the Dynamic Programming Principle, we prove a verification theorem, in order to show that any solution to the Hamilton-Jacobi-Bellman (HJB) equation solves our optimization problem. Subject to some regularity conditions on the solution of the HJB equation, we establish the existence of the optimal investment strategy. Finally, to illustrate the applicability of the theoretical findings, we present numerical examples.

q-fin.MF↗

arXiv2022

The strong coupling constant: State of the art and the decade ahead

Theoretical predictions for particle production cross sections and decays at colliders rely heavily on perturbative Quantum Chromodynamics (QCD) calculations, expressed as an expansion in powers of the strong coupling constant $\alpha_s$. The current $\mathcal{O}(1\%)$ uncertainty of the QCD coupling evaluated at the reference Z boson mass, $\alpha_s(m_Z) = 0.1179 \pm 0.0009$, is one of the limiting factors to more precisely describe multiple processes at current and future colliders. A reduction of this uncertainty is thus a prerequisite to perform precision tests of the Standard Model as well as searches for new physics. This report provides a comprehensive summary of the state-of-the-art, challenges, and prospects in the experimental and theoretical study of the strong coupling. The current $\alpha_s(m_Z)$ world average is derived from a combination of seven categories of observables: (i) lattice QCD, (ii) hadronic $\tau$ decays, (iii) deep-inelastic scattering and parton distribution functions fits, (iv) electroweak boson decays, hadronic final-states in (v) $e^+e^-$, (vi) e-p, and (vii) p-p collisions, and (viii) quarkonia decays and masses. We review the current status of each of these seven $\alpha_s(m_Z)$ extraction methods, discuss novel $\alpha_s$ determinations, and examine the averaging method used to obtain the world-average value. Each of the methods discussed provides a ``wish list'' of experimental and theoretical developments required in order to achieve the goal of a per-mille precision on $\alpha_s(m_Z)$ within the next decade.

hep-ph↗

arXiv2021

FLAG Review 2021

We review lattice results related to pion, kaon, $D$-meson, $B$-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More specifically, we report on the determination of the light-quark masses, the form factor $f_+(0)$ arising in the semileptonic $K \to \pi$ transition at zero momentum transfer, as well as the decay constant ratio $f_K/f_\pi$ and its consequences for the CKM matrix elements $V_{us}$ and $V_{ud}$. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of $SU(2)_L\times SU(2)_R$ and $SU(3)_L\times SU(3)_R$ Chiral Perturbation Theory. We review the determination of the $B_K$ parameter of neutral kaon mixing as well as the additional four $B$ parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for $m_c$ and $m_b$ as well as those for the decay constants, form factors, and mixing parameters of charmed and bottom mesons and baryons. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant $\alpha_s$. We consider nucleon matrix elements, and review the determinations of the axial, scalar and tensor bilinears, both isovector and flavor diagonal. Finally, in this review we have added a new section reviewing determinations of scale-setting quantities.

hep-lat↗

arXiv2021

Geodesic motion around hairy black holes

In a recent paper (Phys. Dark Univ. {\bf 31}, 100744 (2021)) it has been obtained new static black hole solutions with primary hairs by the Gravitational Decoupling. In this work we either study the geodesic motion of massive and massless particles around those solutions and restrict the values of the primary hairs by observational data. In particular, we obtain the effective potential, the innermost stable circular orbits, the marginally bounded orbit, and the periastron advance for time--like geodesics. In order to restrict the values taken by the primary hairs we explore their relationship with the rotation parameter of the Kerr black hole giving the same innermost stable circular orbit radius and give the numerical values for the supermassive black holes at Ark 564 and NGC 1365. The photon sphere and the impact parameter associated to null geodesics are also discussed.

gr-qc↗

arXiv2021

Class I polytropes for anisotropic matter

In this work we study class I interior solutions supported by anisotropic polytropes. The generalized Lane--Emden equation compatible with the embedding condition is obtained and solved for a different set of parameters in both the isothermal and non--isothermal regimes. For completeness, the Tolman mass is computed and analysed to some extend. As a complementary study we consider the impact of the Karmarkar condition on the mass and the Tolman mass functions respectively. Comparison with other results in literature are discussed.

gr-qc↗

arXiv2021

A new formulation of compartmental epidemic modelling for arbitrary distributions of incubation and removal times

The paradigm for compartment models in epidemiology assumes exponentially distributed incubation and removal times, which is not realistic in actual populations. Commonly used variations with multiple exponentially distributed variables are more flexible, yet do not allow for arbitrary distributions. We present a new formulation, focussing on the SEIR concept that allows to include general distributions of incubation and removal times. We compare the solution to two types of agent-based model simulations, a spatially homogeneous one where infection occurs by proximity, and a model on a scale-free network with varying clustering properties, where the infection between any two agents occurs via their link if it exists. We find good agreement in both cases. Furthermore a family of asymptotic solutions of the equations is found in terms of a logistic curve, which after a non-universal time shift, fits extremely well all the microdynamical simulations. The formulation allows for a simple numerical approach; software in Julia and Python is provided.

q-bio.PE↗

arXiv2020

The molecular nature of some exotic hadrons

The exciting discovery by LHCb of the $P_c(4312)^+$ and $P_c(4450)^+$ pentaquarks, or the suggestion of a tetraquark nature for the $Z_c(3900)$ state seen at BESIII and Belle, have triggered a lot of activity in the field of hadron physics, with new experiments planned for searching other exotic mesons and baryons, and many theoretical developments trying to disentangle the true multiquark nature from their possible molecular origin. After a brief review of the present status of these searches, this paper focusses on recently seen or yet to be discovered exotic heavy baryons that may emerge from a conveniently unitarized meson-baryon interaction model in coupled channels. In particular, we will show how interferences between the different coupled-channel amplitudes of the model may reveal the existence of a $N^*$ resonance around 2 GeV having a meson-baryon quasi-bound state nature. We also discuss the possible interpretation of some of the $Ω_c$ states recently discovered at LHCb as being hadron molecules. The model also predicts the existence of doubly-charmed quasibound meson-baryon $Ξ_{cc}$ states, which would be excited states of the ground-state $Ξ_{cc}(3621)$ MeV, whose mass has only been recently established. Extensions of these results to the bottom sector will also be presented.

hep-ph↗

arXiv2020

FLAG Review 2019

We review lattice results related to pion, kaon, $D$-meson, $B$-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More specifically, we report on the determination of the light-quark masses, the form factor $f_+(0)$ arising in the semileptonic $K \to π$ transition at zero momentum transfer, as well as the decay constant ratio $f_K/f_π$ and its consequences for the CKM matrix elements $V_{us}$ and $V_{ud}$. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of $SU(2)_L\times SU(2)_R$ and $SU(3)_L\times SU(3)_R$ Chiral Perturbation Theory. We review the determination of the $B_K$ parameter of neutral kaon mixing as well as the additional four $B$ parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for $m_c$ and $m_b$ as well as those for $D$- and $B$-meson decay constants, form factors, and mixing parameters. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant $α_s$. Finally, in this review we have added a new section reviewing results for nucleon matrix elements of the axial, scalar and tensor bilinears, both isovector and flavor diagonal.

hep-lat↗

arXiv2019

K$^-$ multi-nucleon absorption cross sections and branching ratios in $Λ$p and $Σ^0$p final states

The determination of low-energy cross sections and branching ratios of the K$^-$ multi-nucleon absorption processes in $Λ$p and $Σ^0$p final states performed by the AMADEUS collaboration is presented. Low momentum K$^-$ ($p_\mathrm{K} \simeq$ 127 MeV/c) produced at the DA$Φ$NE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The $Λ$p spectra are interpreted in terms of K$^-$ multi-nucleon absorption processes; the possible contribution of a K$^-$pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.

nucl-ex↗