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Akbar, H., Ali, A. T., Olmo, G. J., & Khan, S. (2026). Exploring Spherically Symmetric Static Spacetimes Through Ricci Almost Solitons: Energy Conditions and Matter Profiles. Universe, 12(10), 306–34pp.
Abstract: We investigate Ricci almost solitons (RASs) associated with four-dimensional spherically symmetric static spacetimes. Starting from the general static spherically symmetric metric, the Ricci almost soliton equation is reduced to an overdetermined system of differential equations for the metric functions, the RAS vector field, and the almost soliton factor. By imposing suitable conditions on the resulting differential constraints, several explicit families of non-Einstein metrics admitting RAS structures are obtained. The corresponding RAS vector fields have dimensions ranging from four to fifteen, with a six-dimensional structure in Case (I), fifteen-dimensional structures in Cases (II-A), (II-B), (III-A), (III-B), (IV-A), and (IV-B), and four- and five-dimensional structures for the two particular solutions of Case (V). The sign of the almost soliton factor is analyzed on the admissible radial domains, showing that the obtained geometries may exhibit shrinking, expanding, and steady regions depending on the model parameters and angular variables. The effective energy density, radial pressure, and tangential pressure are reconstructed from the Einstein equations, and the null, weak, strong, and dominant energy conditions are examined. The resulting matter profiles include anisotropic and isotropic fluids, vacuum, cosmological-constant-type configurations, and effective sources with negative energy density. One solution admits a formal finite-radius Schwarzschild junction at its zero radial-pressure surface, although the density is negative there and the solution is therefore not a conventional stellar interior. Another solution has positive constant density but negative pressure throughout its admissible finite radial domain and does not possess a finite pressure-free surface for the considered positive-parameter branch. Other cases exhibit anti-de Sitter asymptotic structures. These results demonstrate that the Ricci almost soliton structure provides a systematic geometric framework for constructing exact static spherically symmetric spacetimes, while the energy conditions and admissible radial domains determine their possible physical interpretation.
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Angles-Castillo, A., Perez, A., & Roldan, E. (2024). Bright and dark solitons in a photonic nonlinear quantum walk: lessons from the continuum. New J. Phys., 26(2), 023004–16pp.
Abstract: We propose a nonlinear quantum walk model inspired in a photonic implementation in which the polarization state of the light field plays the role of the coin-qubit. In particular, we take profit of the nonlinear polarization rotation occurring in optical media with Kerr nonlinearity, which allows to implement a nonlinear coin operator, one that depends on the state of the coin-qubit. We consider the space-time continuum limit of the evolution equation, which takes the form of a nonlinear Dirac equation. The analysis of this continuum limit allows us to gain some insight into the existence of different solitonic structures, such as bright and dark solitons. We illustrate several properties of these solitons with numerical calculations, including the effect on them of an additional phase simulating an external electric field.
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Fuentes-Martin, J., Portoles, J., & Ruiz-Femenia, P. (2015). Instanton-mediated baryon number violation in non-universal gauge extended models. J. High Energy Phys., 01(1), 134–34pp.
Abstract: Instanton solutions of non-abelian Yang-Mills theories generate an effective action that may induce lepton and baryon number violations, namely Delta B = Delta L = nf, being nf the number of families coupled to the gauge group. In this article we study instanton mediated processes in a SU( 2)(l)circle times SU(2)(h)circle times U(1) extension of the Standard Model that breaks universality by singularizing the third family. In the construction of the instanton Green functions we account systematically for the inter-family mixing. This allows us to use the experimental bounds on proton decay in order to constrain the gauge coupling of SU(2)(h). Tau lepton non-leptonic and radiative decays with Delta B = Delta L = 1 are also analysed.
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Mantovani-Sarti, V., Park, B. Y., & Vento, V. (2013). The Soliton-Soliton Interaction in the Chiral Dilaton Model. Int. J. Mod. Phys. A, 28(27), 1350136–19pp.
Abstract: We study the interaction between two B = 1 states in the Chiral Dilaton Model where baryons are described as nontopological solitons arising from the interaction of chiral mesons and quarks. By using the hedgehog solution for B = 1 states we construct, via a product ansatz, three possible B = 2 configurations to analyse the role of the relative orientation of the hedgehog quills in the dynamics of the soliton-soliton interaction and investigate the behavior of these solutions in the range of long/intermediate distance. One of the solutions is quite binding due to the dynamics of the pi and sigma fields at intermediate distance and should be used for nuclear matter studies. Since the product ansatz break down as the two solitons get close, we explore the short range distance regime with a model that describes the interaction via a six-quark bag ansatz. We calculate the interaction energy as a function of the inter-soliton distance and show that for small separations the six quarks bag, assuming a hedgehog structure, provides a stable bound state that at large separations connects with a special configuration coming from the product ansatz.
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