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Debastiani, V. R., Sakai, S., & Oset, E. (2019). Considerations on the Schmid theorem for triangle singularities. Eur. Phys. J. C, 79(1), 69–13pp.
Abstract: We investigate the Schmid theorem, which states that if one has a tree level mechanism with a particle decaying to two particles and one of them decaying posteriorly to two other particles, the possible triangle singularity developed by the mechanism of elastic rescattering of two of the three decay particles does not change the cross section provided by the tree level. We investigate the process in terms of the width of the unstable particle produced in the first decay and determine the limits of validity and violation of the theorem. One of the conclusions is that the theorem holds in the strict limit of zero width of that resonance, in which case the strength of the triangle diagram becomes negligible compared to the tree level. Another conclusion, on the practical side, is that for realistic values of the width, the triangle singularity can provide a strength comparable or even bigger than the tree level, which indicates that invoking the Schmid theorem to neglect the triangle diagram stemming from elastic rescattering of the tree level should not be done. Even then, we observe that the realistic case keeps some memory of the Schmid theorem, which is visible in a peculiar interference pattern with the tree level.
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Murgui, C., Peñuelas, A., Jung, M., & Pich, A. (2019). Global fit to b -> c tau nu transitions. J. High Energy Phys., 09(9), 103–45pp.
Abstract: We perform a general model-independent analysis of b -> c tau(nu) over bar (tau) transitions, including measurements of R-D, R-D*, their q(2) differential distributions, the recently measured longitudinal D* polarization F-L(D)*, and constraints from the B-c -> tau(nu) over bar (tau) lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected b -> c tau(nu) over bar (tau) observables, such as the baryonic transition Lambda(b) -> Lambda(c)tau(nu) over bar (tau), the ratio R-J/psi, the forward-backward asymmetries A(FB)(D()*()), the tau polarization asymmetries P-tau(D()*()), and the longitudinal D* polarization fraction F-L(D)*. The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary R-D(*) measurement by the Belle collaboration.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Fernandez, P., Izmaylov, A., & Novella, P. (2019). Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km. Phys. Rev. D, 99(7), 071103–10pp.
Abstract: We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6) x 10(20) protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3 + 1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin(2)theta(24 )for the sterile neutrino mass splitting Delta m(41)(2 )< 3 x 10(-3 )eV(2)/c(4).
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Jiang, S. J., Sakai, S., Liang, W. H., & Oset, E. (2019). The chi c J decay to phi K*(K)over-bar, phi h(1)(1380) testing the nature of axial vector meson resonances. Phys. Lett. B, 797, 134831–5pp.
Abstract: We perform a theoretical study of the chi(cJ) -> phi K*(K) over bar -> phi K pi(K) over bar reaction taking into account the K*(K) over bar final state interaction, which in the chiral unitary approach is responsible, together with its coupled channels, for the formation of the low lying axial vector mesons, in this case the h(1)(1380) given the selection of quantum numbers. Based on this picture we can easily explain why in the chi(c0) decay the h(1)(1380) resonance is not produced, and, in the case of chi(c1) and chi(c2) decay, why a dip in the K+ pi K-0(-) mass distribution appears in the 1550-1600 MeV region, that in our picture comes from a destructive interference between the tree level mechanism and the rescattering that generates the h(1)(1380) state. Such a dip is not reproduced in pictures where the nominal h(1)(1380) signal is added incoherently to a background, which provides support to the picture where the resonance appears from rescattering of vector-pseudoscalar components.
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Hernandez, P., Pena, C., & Romero-Lopez, F. (2019). Large Nc scaling of meson masses and decay constants. Eur. Phys. J. C, 79(10), 865–13pp.
Abstract: We perform an ab initio calculation of the Nc scaling of the low-energy couplings of the chiral Lagrangian of low-energy strong interactions, extracted from the mass dependence of meson masses and decay constants. We compute these observables on the lattice with four degenerate fermions, Nf=4, and varying number of colours, Nc=3-6, at a lattice spacing of a similar or equal to 0.075 fm. We find good agreement with the expected Nc scaling and measure the coefficients of the leading and subleading terms in the large Nc expansion. From the subleading Nc corrections, we can also infer the Nf dependence, that we use to extract the value of the low-energy couplings for different values of Nf. We find agreement with previous determinations at Nc=3 and Nf=2,3 and also, our results support a strong paramagnetic suppression of the chiral condensate in moving from Nf=2 to Nf=3.
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Mandal, R., & Pich, A. (2019). Constraints on scalar leptoquarks from lepton and kaon physics. J. High Energy Phys., 12(12), 089–40pp.
Abstract: We present a comprehensive analysis of low-energy signals of hypothetical scalar leptoquark interactions in lepton and kaon transitions. We derive the most general effective four-fermion Lagrangian induced by tree-level scalar leptoquark exchange and identify the Wilson coefficients predicted by the five possible types of scalar leptoquarks. The current constraints on the leptoquark Yukawa couplings arising from lepton and kaon processes are worked out, including also loop-induced transitions with only leptons (or quarks) as external states. In the presence of scalar leptoquark interactions, we also derive the differential distributions for flavour-changing neutral-current transitions in semileptonic kaon modes, including all known effects within the Standard Model. Their interference with the new physics contributions could play a significant role in future improvements of those constraints that are currently hampered by poorly-determined non-perturbative parameters.
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PTOLEMY Collaboration(Betti, M. G. et al), de Salas, P. F., Gariazzo, S., & Pastor, S. (2019). A design for an electromagnetic filter for precision energy measurements at the tritium endpoint. Prog. Part. Nucl. Phys., 106, 120–131.
Abstract: We present a detailed description of the electromagnetic filter for the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Starting with an initial estimate for the orbital magnetic moment, the higher-order drift process of E x B is configured to balance the gradient-B drift motion of the electron in such a way as to guide the trajectory into the standing voltage potential along the mid-plane of the filter. As a function of drift distance along the length of the filter, the filter zooms in with exponentially increasing precision on the transverse velocity component of the electron kinetic energy. This yields a linear dimension for the total filter length that is exceptionally compact compared to previous techniques for electromagnetic filtering. The parallel velocity component of the electron kinetic energy oscillates in an electrostatic harmonic trap as the electron drifts along the length of the filter. An analysis of the phase-space volume conservation validates the expected behavior of the filter from the adiabatic invariance of the orbital magnetic moment and energy conservation following Liouville's theorem for Hamiltonian systems. (C) 2019 Elsevier B.V. All rights reserved.
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Elor, G., Escudero, M., & Nelson, A. E. (2019). Baryogenesis and dark matter from B mesons. Phys. Rev. D, 99(3), 035031–18pp.
Abstract: We present a new mechanism of baryogenesis and dark matter production in which both the dark matter relic abundance and the baryon asymmetry arise from neutral B meson oscillations and subsequent decays. This setup is testable at hadron colliders and B factories. In the early universe, decays of a long lived particle produce B mesons and antimesons out of thermal equilibrium. These mesons/antimesons then undergo CP violating oscillations before quickly decaying into visible and dark sector particles. Dark matter will be charged under the baryon number so that the visible sector baryon asymmetry is produced without violating the total baryon number of the Universe. The produced baryon asymmetry will be directly related to the leptonic charge asymmetry in neutral B decays: an experimental observable. Dark matter is stabilized by an unbroken discrete symmetry, and proton decay is simply evaded by kinematics. We will illustrate this mechanism with a model that is unconstrained by dinucleon decay, does not require a high reheat temperature, and would have unique experimental signals-a positive leptonic asymmetry in B meson decays, a new decay of B mesons into a baryon and missing energy, and a new decay of b-flavored baryons into mesons and missing energy. These three observables are testable at current and upcoming collider experiments, allowing for a distinct probe of this mechanism.
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Aguilar, A. C., Ferreira, M. N., Figueiredo, C. T., & Papavassiliou, J. (2019). Gluon mass scale through nonlinearities and vertex interplay. Phys. Rev. D, 100(9), 094039–19pp.
Abstract: We present a novel analysis of the gluon gap equation, where its full nonlinear structure is duly taken into account. In particular, while in previous treatments the linearization of this homogeneous integral equation introduced an indeterminacy in the scale of the corresponding mass, the current approach determines it uniquely, once the value of the gauge coupling at a given renormalization point is used as input. A crucial ingredient for this construction is the “kinetic term” of the gluon propagator, whose form is not obtained from the complicated equation governing its evolution, but is rather approximated by suitable initial Ansatze, which are subsequently improved by means of a systematic iterative procedure. The multiplicative renormalization of the central equation is carried out following an approximate method, which is extensively employed in the studies of the standard quark gap equation. This approach amounts to the effective substitution of the vertex renormalization constants by kinematically simplified form factors of the three- and four-gluon vertices. The resulting numerical interplay, exemplified by the infrared suppression of the three-gluon vertex and the mild enhancement of the four-gluon vertex, is instrumental for obtaining positive-definite and monotonically decreasing running gluon masses. The resulting gluon propagators, put together from the gluon masses and kinetic terms obtained with this method, match rather accurately the data obtained from large-volume lattice simulations.
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Cepedello, R., Deppisch, F. F., Gonzalez, L., Hati, C., & Hirsch, M. (2019). Neutrinoless Double-Beta Decay with Nonstandard Majoron Emission. Phys. Rev. Lett., 122(18), 181801–6pp.
Abstract: We present a novel mode of neutrinoless double-beta decay with emission of a light Majoron-like scalar particle phi. We assume it couples via an effective seven-dimensional operator with a (V + A) lepton current and (V +/- A) quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass. We calculate the total double-beta decay rate and determine the fully differential shape for this mode. We find that future double-beta decay searches are sensitive to scales of the order Lambda(NP) approximate to 1 TeV for the effective operator and a light scalar m(phi) < 0.2 MeV, based on ordinary double-beta decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double-beta decay, which is the main background. We point out possible ultraviolet completions where such an effective operator can emerge.
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