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K2K Collaboration(Mariani, C. et al), Cervera-Villanueva, A., Tornero-Lopez, A., Burguet-Castell, J., Catala, J., Gomez-Cadenas, J. J., et al. (2011). Measurement of inclusive pi(0) production in the charged-current interactions of neutrinos in a 1.3-GeV wide band beam. Phys. Rev. D, 83(5), 054023–17pp.
Abstract: In this paper, we report on the measurement of the rate of inclusive pi(0) production induced by charged-current neutrino interactions in a C8H8 target at a mean energy of 1.3 GeV in the K2K near detector. Out of a sample of 11 606 charged- current neutrino interactions, we select 479 pi(0) events with two reconstructed photons. We find that the cross section for the inclusive pi(0) production relative to the charged-current quasielastic cross section is (CC)-C-sigma pi(0)/sigma CCQE = 0.426 +/- 0.032 (stat) +/- 0.035 (syst). The energy-dependent cross section ratio is also measured. The results are consistent with previous experiments for exclusive channels on different targets.
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Alexandre, J., Mavromatos, N. E., Mitsou, V. A., & Musumeci, E. (2024). Resummation schemes for high-electric-charge objects leading to improved experimental mass limits. Phys. Rev. D, 109(3), 036026–20pp.
Abstract: High-electric-charge compact objects (HECOs) appear in several theoretical particle physics models beyond the Standard Model, and are actively searched for in current colliders, such as the Large Hadron Collider at CERN. In such searches, mass bounds of these objects have been placed, using Drell-Yan and photon-fusion processes at tree level so far. However, such mass-bound estimates are not reliable, given that, as a result of the large values of the electric charge of the HECO, perturbative quantum electrodynamics calculations break down. In this work, we perform a Dyson-Schwinger resummation scheme (as opposed to lattice strong-coupling approach), which makes the computation of the pertinent HECO-production cross sections reliable, thus allowing us to extract improved mass bounds for such objects from ATLAS and MoEDAL searches.
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Alicki, R., Barenboim, G., & Jenkins, A. (2023). Quantum thermodynamics of de Sitter space. Phys. Rev. D, 108(12), 123530–13pp.
Abstract: We consider the local physics of an open quantum system embedded in an expanding three-dimensional space x, evolving in cosmological time t, weakly coupled to a massless quantum field. We derive the corresponding Markovian master equation for the system's nonunitary evolution and show that, for a de Sitter space with Hubble parameter h 1/4 const, the background fields act as a physical heat bath with temperature TdS 1/4 h/2z. The energy density of this bath obeys the Stefan-Boltzmann law pdS proportional to h4. We comment on how these results clarify the thermodynamics of de Sitter space and support previous arguments for its instability in the infrared. The cosmological implications are considered in an accompanying Letter.
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Alvarado, F., An, D., Alvarez-Ruso, L., & Leupold, S. (2023). Light quark mass dependence of nucleon electromagnetic form factors in dispersively modified chiral perturbation theory. Phys. Rev. D, 108(11), 114021–23pp.
Abstract: The nucleon isovector electromagnetic form factors are calculated up to next-to-next-to-leading order by combining relativistic chiral perturbation theory (ChPT) of pion, nucleon, and Delta o1232 thorn with dispersion theory. We specifically address the light-quark mass dependence of the form factors, achieving a good description of recent lattice QCD results over a range of Q2 less than or similar to 0.6 GeV2 and M pi less than or similar to 350 MeV. For the Dirac form factor, the combination of ChPT and dispersion theory outperforms the pure dispersive and pure ChPT descriptions. For the Pauli form factor, the combined calculation leads to results comparable to the purely dispersive ones. The anomalous magnetic moment and the Dirac and Pauli radii are extracted.
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Alvarado, F., & Alvarez-Ruso, L. (2022). Light-quark mass dependence of the nucleon axial charge and pion-nucleon scattering phenomenology. Phys. Rev. D, 105(7), 074001–13pp.
Abstract: The light-quark mass dependence of the nucleon axial isovector charge (gA) has been studied up to nextto-next-to-leading order, O(p4), in relativistic chiral perturbation theory using extended-on-mass-shell renormalization, without and with explicit Delta(1232) degrees of freedom. We show that in the Delta-less case, at this order, the flat trend of gA(MN) exhibited by state-of-the-art lattice QCD (LQCD) results cannot be reproduced using low energy constants extracted from pion-nucleon elastic and inelastic scattering. A satisfactory description of these LQCD data is only achieved in the theory with Delta. From this fit, we report gA(MN(phys)) = 1.260 1 0.012, close to the experimental result, and d16 = -0.88 1 0.88 GeV-2, in agreement with its empirical value. The large uncertainties are of theoretical origin, reflecting the difference between O(p3) and O(p4) that still persists at large MN in presence of the Delta.
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Alvarez, A., Cepedello, R., Hirsch, M., & Porod, W. (2022). Temperature effects on the Z(2) symmetry breaking in the scotogenic model. Phys. Rev. D, 105(3), 035013–8pp.
Abstract: It is well known that the scotogenic model for neutrino mass generation can explain correctly the relic abundance of cold dark matter. There have been claims in the literature that an important part of the parameter space of the simplest scotogentic model can be constrained by the requirement that no Z(2)-breaking must occur in the early universe. Here we show that this requirement does not give any constraints on the underlying parameter space at least in those parts, where we can trust perturbation theory. To demonstrate this, we have taken into account the proper decoupling of heavy degrees of freedom in both the thermal potential and in the RGE evolution.
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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., Hernandez, E., Nieves, J., & Vicente Vacas, M. J. (2016). Watson's theorem and the N Delta(1232) axial transition. Phys. Rev. D, 93(1), 014016–16pp.
Abstract: We present a new determination of the N Delta axial form factors from neutrino induced pion production data. For this purpose, the model of Hernandez et al. [Phys. Rev. D 76, 033005 (2007)] is improved by partially restoring unitarity. This is accomplished by imposing Watson's theorem on the dominant vector and axial multipoles. As a consequence, a larger C-5(A) (0), in good agreement with the prediction from the off-diagonal Goldberger-Treiman relation, is now obtained.
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Alvarez-Ruso, L., Ledwig, T., Martin Camalich, J., & Vicente Vacas, M. J. (2013). Nucleon mass and pion-nucleon sigma term from a chiral analysis of lattice QCD data. Phys. Rev. D, 88(5), 054507–20pp.
Abstract: The pion mass dependence of the nucleon mass within the covariant SU(2) baryon chiral perturbation theory both without and with explicit Delta(1232) degrees of freedom up to order p(4) is investigated. By fitting to a comprehensive set of lattice QCD data in 2 and 2 + 1 flavors from several collaborations, for pion masses M-pi < 420 MeV, we obtain low energy constants of natural size that are compatible with pion-nucleon scattering data. Our results are consistent with the rather linear pion mass dependence showed by lattice QCD. In the 2 flavor case we have also performed simultaneous fits to nucleon mass and sigma(pi N) data. As a result of our analysis, which encompasses the study of finite volume corrections and discretization effects, we report a value of sigma(pi N) = 41(5)(4) MeV in the 2 flavor case and sigma(pi N) = 52(3)(8) MeV for 2 + 1 flavors, where the inclusion of the Delta(1232) resonance changes the results by around 9 MeV. In the 2 flavor case we are able to set independently the scale for lattice QCD data, given by a Sommer scale of r(0) = 0.493(23) fm.
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