Casals, M., Fabbri, A., Martinez, C., & Zanelli, J. (2016). Quantum dress for a naked singularity. Phys. Lett. B, 760, 244–248.
Abstract: We investigate semiclassical backreaction on a conical naked singularity space-time with a negative cosmological constant in (2 + 1)-dimensions. In particular, we calculate the renormalized quantum stress-energy tensor for a conformally coupled scalar field on such naked singularity space-time. We then obtain the backreacted metric via the semiclassical Einstein equations. We show that, in the regime where the semiclassical approximation can be trusted, backreaction dresses the naked singularity with an event horizon, thus enforcing (weak) cosmic censorship.
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Das, D., Dey, U. K., & Pal, P. B. (2016). S-3 symmetry and the quark mixing matrix. Phys. Lett. B, 753, 315–318.
Abstract: We impose an S-3 symmetry on the quark fields under which two of three quarks transform like a doublet and the remaining one as singlet, and use a scalar sector with the same structure of SU(2) doublets. After gauge symmetry breaking, a Z(2) subgroup of the S-3 remains unbroken. We show that this unbroken subgroup can explain the approximate block structure of the CKM matrix. By allowing soft breaking of the S-3 symmetry in the scalar sector, we show that one can generate the small elements, of quadratic or higher order in the Wolfenstein parametrization of the CKM matrix. We also predict the existence of exotic new scalars, with unconventional decay properties, which can be used to test our model experimentally.
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Xiao, C. W., Nieves, J., & Oset, E. (2019). Prediction of hidden charm strange molecular baryon states with heavy quark spin symmetry. Phys. Lett. B, 799, 135051–10pp.
Abstract: We have studied the meson-baryon S-wave interaction in the isoscalar hidden-charm strange sector with the coupled-channels, eta(c)Lambda, J/psi Lambda, (D) over bar Xi(c), (D) over bar (s)Lambda(c), (D) over bar Xi(c)', (D) over bar*Lambda(c), (D) over bar*Xi(c)', (D) over bar*Xi*(c) in J(p) = 1/2(-), J/psi Lambda, (D) over bar*Xi(c), (D) over bar (s)*Lambda(c), (D) over bar*Xi(c)', (D) over bar Xi(c)*, (D) over bar*Xi(c)* in 3/2(-) and (D) over bar*Xi(c)* in 5/2(-). We impose constraints of heavy quark spin symmetry in the interaction and obtain the non vanishing matrix elements from an extension of the local hidden gauge approach to the charm sector. The ultraviolet divergences are renormalized using the same meson-baryon-loops regulator previously employed in the non-strange hidden charm sector, where a good reproduction of the properties of the newly discovered pentaquark states is obtained. We obtain five states of 1/2(-), four of 3/2(-) and one of 5/2(-), which could be compared in the near future with forthcoming LHCb experiments. The 5/2(-), three of the 3/2(-) and another three of the 1/2(-) resonances are originated from isoscalar (D) over bar (()*())Xi(c)' and (D) over bar (()*()) Xi(c)* interactions. They should be located just few MeV below the corresponding thresholds (4446, 4513, 4588 and 4655 MeV), and would be SU(3)-siblings of the isospin 1/2 (D) over bar (()*())Sigma(()(c)*()) quasi-bound states previously found, and that provided a robust theoretical description of the P-c(4440), P-c(4457) and P-c(4312) LHCb exotic states. The another two 1/2(-) and 3/2(-) states obtained in this work are result of the (D) over bar (()*())Xi(c)- D-s(()*()) Lambda(c) coupled-channels isoscalar interaction, are significantly broader than the others, with widths of the order of 15 MeV, being (D) over bar (()(s)*())Lambda(c) the dominant decay channel.
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Feijoo, A., Valcarce Cadenas, V., & Magas, V. K. (2023). The Xi(1620) and Xi(1690) molecular states from S =-2 meson-baryon interaction up to next-to-leading order. Phys. Lett. B, 841, 137927–6pp.
Abstract: We have studied the meson-baryon interaction in the neutral S = -2 sector using an extended Unitarized Chiral Perturbation Theory, which takes into account not only the leading Weinberg-Tomozawa term (as all the previous studies in S = -2 sector), but also the Born terms and next-to-leading order contribution. Based on the SU(3) symmetry of the chiral Lagrangian we took most of the model parameters from the BCN model [1], where these were fitted to a large amount of experimental data in the neutral S = -1 sector. We have shown that our approach is able to generate dynamically both Xi(1620) and Xi(1690) states in very reasonable agreement with the data, and can naturally explain the puzzle with the decay branching ratios of Xi(1690). Our results clearly illustrate the reliability of chiral models implementing unitarization in coupled channels and the importance of considering Born and NLO contributions for precise calculations.
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Ramos, A., & Oset, E. (2013). The role of vector-baryon channels and resonances in the gamma p -> K-0 Sigma(+) and gamma n -> K-0 Sigma(0) reactions near the K*Lambda threshold. Phys. Lett. B, 727(1-3), 287–292.
Abstract: We have studied the gamma p -> K-0 Sigma(+) reaction in the energy region around the K*Lambda and K*Sigma thresholds, where the CBELSA/TAPS cross section shows a sudden drop and the differential cross section experiences a transition from a forward-peaked distribution to a flat one. Our coupled-channel model incorporates the dynamics of the vector meson-baryon interaction which is obtained from the hidden gauge formalism. We find that the cross section in this energy region results from a delicate interference between amplitudes having K*Lambda and K*Sigma intermediate states. The sharp downfall is dictated by the presence of a nearby N* resonance produced by our model, a feature that we have employed to predict its properties. We also show results for the complementary gamma n -> K-0 Sigma(0) reaction, the measurement of which would test the mechanism proposed in this work.
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