Search

Abstract: We present a unified picture of flavor and electroweak symmetry breaking at the TeV scale. Flavor and Higgs bosons arise as pseudo-Goldstone modes in a nonlinear sigma model. Explicit collective symmetry breaking yields stable vacuum expectation values and masses protected at one loop by the little-Higgs mechanism. The coupling to the fermions through a Yukawa Lagrangian with a global flavor symmetry generates well-definite mass textures that correctly reproduce the mass hierarchies and mixings of quarks and leptons. The model is more constrained than usual little-Higgs models because of bounds on weak and flavor physics. The main experimental signatures testable at the LHC are a rather large mass for the (lightest) Higgs boson and a characteristic spectrum of new bosons and fermions with masses around the TeV scale. [Copyright &y& Elsevier]

Correlations between the spins of top-quark pairs produced at a collider can be used to probe quantum entanglement at energies never explored so far. We show how the measurement of a single observable can provide a test of the violation of a Bell inequality at the 98% C.L. with the statistical uncertainty of the data already collected at the Large Hadron Collider, and at the 99.99% C.L. with the higher luminosity of the next run. Detector acceptance, efficiency, and migration effects are taken into account. The test relies on the spin correlations alone and does not require the determination of probabilities--in contrast to all other tests of Bell inequalities. [ABSTRACT FROM AUTHOR]

We study the Z→γγ process in which the Z boson decays into a photon γ and a massless dark photon γ, when the latter couples to standard-model fermions via dipole moments. This is a simple yet nontrivial example of how the Landau-Yang theorem--ruling out the decay of a massive spin-1 particle into two photons--is evaded if the final particles can be distinguished. The striking signature of this process is a resonant monochromatic single photon in the Z-boson center of mass together with missing momentum. LEP experimental bounds allow a branching ratio up to about 10-6 for such a decay. In a simplified model of the dark sector, the dark-photon dipole moments arise from one-loop exchange of heavy dark fermions and scalar messengers. The corresponding prediction for the rare Z→γγ decay width can be explored with the large samples of Z bosons foreseen at future colliders. [ABSTRACT FROM AUTHOR]

If dark photons are massless, they couple to standard-model particles only via higher dimensional operators, while direct (renormalizable) interactions induced by kinetic mixing, which motivates most of the current experimental searches, are absent. We consider the effect of possible flavor-changing magnetic-dipole couplings of massless dark photons in kaon physics. In particular, we study the branching ratio for the process K+→π+π0γ with a simplified-model approach, assuming the chiral quark model to evaluate the hadronic matrix element. Possible effects in the K0-K0 mixing are taken into account. We find that branching ratios up to O(10-7) are allowed--depending on the dark-sector masses and couplings. Such large branching ratios for K+→π+π0γ could be of interest for experiments dedicated to rare K+ decays like NA62 at CERN, where γ can be detected as a massless invisible system. [ABSTRACT FROM AUTHOR]

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors., (© 2022 IOP Publishing Ltd.)

We consider the standard model without the Higgs boson, where the Goldstone modes are described by a nonlinear sigma model. We study the renormalization group flow of the sigma model coupling f and of the electroweak parameters S and T. The condition that the couplings reach a fixed point at high energy leaves the low energy values of f and T arbitrary (to be determined experimentally) and fixes S to a value compatible with electroweak precision data.