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Alvarez-Castillo, D. E., Blaschke, D. B., Grunfeld, A. G., & Pagura, V. P. (2019). Third family of compact stars within a nonlocal chiral quark model equation of state. Phys. Rev. D, 99(6), 063010–19pp.
Abstract: A class of hybrid compact star equations of state is investigated that joins by a Maxwell construction a low-density phase of hadronic matter, modeled by a relativistic mean-field approach with excluded nucleon volume, with a high-density phase of color superconducting two-flavor quark matter, described within a nonlocal covariant chiral quark model. It is found that the occurrence of a stable branch of hybrid compact stars requires a nonvanishing vector meson coupling in the quark model that exceeds a minimal value which depends on the presence of a diquark condensate. It is shown that these hybrid stars do not form a third family disconnected from the second family of ordinary neutron stars unless additional (de) confining effects are introduced with a density-dependent bag pressure. A suitably chosen density dependence of the vector meson coupling assures that at the same time the 2M(circle dot) maximum mass constraint is fulfilled on the hybrid star branch. A twofold interpolation method is realized which implements both the density dependence of a confining bag pressure at the onset of the hadron-to-quark matter transition and the stiffening of quark matter at higher densities by a density-dependent vector meson coupling. For three parametrizations of this class of hybrid equation of state the properties of corresponding compact star sequences are presented, including mass twins of neutron and hybrid stars at 2.00, 1.39 and 1.20 M-circle dot, respectively, and the hybrid compact star (third) families. The sensitivity of the hybrid equation of state and the corresponding compact star sequences to variations of the interpolation parameters at the 10% level is investigated and it is found that the feature of third family solutions for compact stars is robust against such a variation. This advanced description of hybrid star matter allows us to interpret GW170817 as a merger not only of two neutron stars but also of a neutron star with a hybrid star or of two hybrid stars.
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Alvarez-Ortega, D., Olmo, G. J., Rubiera-Garcia, D., & Saez-Chillon Gomez, D. (2022). Eternal versus singular observers in interacting dark-energy-dark-matter models. Phys. Rev. D, 106(2), 023523–14pp.
Abstract: Interacting dark-energy-dark-matter models have been widely analyzed in the literature in an attempt to find traces of new physics beyond the usual cosmological (Lambda CDM) models. Such a coupling between both dark components is usually introduced in a phenomenological way through a flux in the continuity equation. However, models with a Lagrangian formulation are also possible. A class of the latter assumes a conformal/disformal coupling that leads to a fifth force on the dark-matter component, which consequently does not follow the same geodesics as the other (baryonic, radiation, and dark-energy) matter sources. Here we analyze how the usual cosmological singularities of the standard matter frame are seen from the dark-matter one, concluding that by choosing an appropriate coupling, dark-matter observers will see no singularities but a non beginning, non ending universe. By considering two simple phenomenological models we show that such a type of coupling can fit observational data as well as the usual Lambda CDM model.
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Alvarez-Ruso, L. et al, & Nieves, J. (2018). NuSTEC White Paper: Status and challenges of neutrino-nucleus scattering. Prog. Part. Nucl. Phys., 100, 1–68.
Abstract: The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments require a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result. In this White Paper we discuss in detail the impact of neutrino-nucleus interactions, especially the nuclear effects, on the measurement of neutrino properties using the determination of oscillation parameters as a central example. After an Executive Summary and a concise Overview of the issues, we explain how the neutrino event generators work, what can be learned from electron-nucleus interactions and how each underlying physics process – from quasi-elastic to deep inelastic scattering – is understood today. We then emphasize how our understanding must improve to meet the demands of future experiments. With every topic we find that the challenges can be met only with the active support and collaboration among specialists in strong interactions and electroweak physics that include theorists and experimentalists from both the nuclear and high energy physics communities.
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Alvarez-Ruso, L., Graczyk, K. M., & Saul-Sala, E. (2019). Nucleon axial form factor from a Bayesian neural-network analysis of neutrino-scattering data. Phys. Rev. C, 99(2), 025204–14pp.
Abstract: The Bayesian approach for feedforward neural networks has been applied to the extraction of the nucleon axial form factor from the neutrino-deuteron-scattering data measured by the Argonne National Laboratory bubble-chamber experiment. This framework allows to perform a model-independent determination of the axial form factor from data. When the low 0.05 < Q(2) < 0.10-GeV2 data are included in the analysis, the resulting axial radius disagrees with available determinations. Furthermore, a large sensitivity to the corrections from the deuteron structure is obtained. In turn, when the low-Q(2) region is not taken into account with or without deuteron corrections, no significant deviations from previous determinations have been observed. A more accurate determination of the nucleon axial form factor requires new precise measurements of neutrino-induced quasielastic scattering on hydrogen and deuterium.
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Alvarez-Ruso, L., & Saul-Sala, E. (2021). Neutrino interactions with matter and the MiniBooNE anomaly. Eur. Phys. J.-Spec. Top., 230, 4373–4389.
Abstract: The excess of electron-like events measured by MiniBooNE challenges our understanding of neutrinos and their interactions. We review the status of this open problem and ongoing efforts to resolve it. After introducing the experiment and its results, we consider the main experimental backgrounds and the related physics of neutrino interactions with matter, such as quasielastic-like scattering and weak pion production on nucleons and nuclei. Special attention is paid to single photon emission in neutral current interactions and, in particular, its coherent channel. The difficulties to reconcile the MiniBooNE anomaly with global oscillation analysis is then highlighted. We finally outline some of the proposed solutions of the puzzle involving unconventional neutrino-interaction mechanisms.
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