Abstract: For a general H-b -> Hc tau nu <overbar></mml:mover>tau decay we analyze the role of the tau polarization vector P μin the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes, in addition to the Standard Model (SM) contribution, vector, axial, scalar, pseudoscalar and tensor new physics (NP) terms which strength is governed by, complex in general, Wilson coefficients. We show that both in the laboratory frame, where the initial hadron is at rest, and in the center of mass of the two final leptons, a P -></mml:mover> component perpendicular to the plane defined by the three-momenta of the final hadron and the tau lepton is only possible for complex Wilson coefficients, being a clear signal for physics beyond the SM as well as time reversal (or CP-symmetry) violation. We make specific evaluations of the different polarization vector components for the Lambda (b) -> Lambda (c), <mml:mover accent=“true”>B<mml:mo stretchy=“true”><overbar></mml:mover>c -> eta (c), J/psi and <mml:mover accent=“true”>B<mml:mo stretchy=“true”><overbar></mml:mover> -> D-(*) semileptonic decays, and describe NP effects in the complete two-dimensional space associated with the independent kinematic variables on which the polarization vector depends. We find that the detailed study of P μhas great potential to discriminate between different NP scenarios for 0(-) -> 0(-) decays, but also for Lambda (b) -> Lambda (c) transitions. For this latter reaction, we pay special attention to corrections to the SM predictions derived from complex Wilson coefficients contributions.

Abstract: For nearly a century, studying cosmic-ray air showers has driven progress in our understanding of elementary particle physics. In this work, we revisit the production of millicharged particles in these atmospheric showers and provide new constraints for XENON1T and Super-Kamiokande and new sensitivity estimates of current and future detectors, such as JUNO. We discuss distinct search strategies, specifically studies of single-energy-deposition events, where one electron in the detector receives a relatively large energy transfer, as well as multiple-scattering events consisting of (at least) two relatively small energy depositions. We demonstrate that these atmospheric search strategies especially the multiple-scattering signature – provide significant room for improvement beyond existing searches, in a way that is complementary to anthropogenic, beam-based searches for MeV-GeV millicharged particles. Finally, we also discuss the implementation of a Monte Carlo simulation for millicharged particle detection in large-volume neutrino detectors, such as IceCube.

Abstract: Four decay modes of the B-c(+) meson into a J/psi meson and multiple charged kaons or pions are studied using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13TeV and corresponding to an integrated luminosity of 9 fb(-1). The decay B-c(+) -> J/psi K+ K- pi(+)pi(+)pi(-) is observed for the first time, and evidence for the B-c(+) -> J/psi 4 pi(+)3 pi(-) decay is found. The decay B-c(+) -> J/psi 3 pi(+)2 pi(-) is observed and the previous observation of the B-c(+) -> psi(2S)pi(+)pi(+)pi(-) decay is confirmed using the psi(2S) -> J/psi pi(+)pi(-) decay mode. Ratios of the branching fractions of these four B-c(+) decay channels are measured.

Abstract: Hadronic matrix elements of local four-quark operators play a central role in non-leptonic kaon decays, while vacuum matrix elements involving the same kind of operators appear in inclusive dispersion relations, such as those relevant in tau -decay analyses. Using an SU(3)(L) circle times SU(3)(R) decomposition of the operators, we derive generic relations between these matrix elements, extending well-known results that link observables in the two different sectors. Two relevant phenomenological applications are presented. First, we determine the electroweak-penguin contribution to the kaon CP-violating ratio epsilon '/epsilon, using the measured hadronic spectral functions in tau decay. Second, we fit our SU(3) dynamical parameters to the most recent lattice data on K -> pi pi matrix elements. The comparison of this numerical fit with results from previous analytical approaches provides an interesting anatomy of the Delta I = 1/2 enhancement, confirming old suggestions about its underlying dynamical origin.

Abstract: Haloscopes are resonant cavities that serve as detectors of dark matter axions when they are immersed in a strong static magnetic field. In order to increase the volume and improve space compatibility with dipole or solenoid magnets for axion searches, various haloscope design techniques for rectangular geometries are discussed in this study. The volume limits of two types of haloscopes are explored: those based on single cavities and those based on multicavities. In both cases, possibilities for increasing the volume of long and/or tall structures are presented. For multicavities, 1D geometries are explored to optimise the space in the magnets. Also, 2D and 3D geometries are introduced as a first step in laying the foundations for the development of these kinds of topologies. The results prove the usefulness of the developed methods, evidencing the ample room for improvement in rectangular haloscope designs nowadays. A factor of three orders of magnitude improvement in volume compared with a single cavity based on the WR-90 standard waveguide is obtained with the design of a long and tall single cavity. Similar procedures have been applied for long and tall multicavities. Experimental measurements are shown for prototypes based on tall multicavities and 2D structures, demonstrating the feasibility of using these types of geometries to increase the volume of real haloscopes.