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We present a detailed analysis of the rare exclusive Higgs boson decays into a single vector meson and a photon and investigate the possibility of using these processes to probe the light-quark Yukawa couplings. We work with an effective Lagrangian with modified Higgs couplings to account for possible new-physics effects in a model-independent way. The h → V γ decay rate is governed by the destructive interference of two amplitudes, one of which involves the Higgs coupling to the quark anti-quark pair inside the vector meson. We derive this amplitude at next-to-leading order in α s using QCD factorization, including the resummation of large logarithmic corrections and accounting for the effects of flavor mixing. The high factorization scale µ ∼ m h ensures that our results are rather insensitive to the hadronic parameters characterizing the light-cone distribution amplitude of the vector meson. The second amplitude arises from the loop-induced effective hγγ * and hγZ * couplings, where the off-shell gauge boson converts into the vector meson. We devise a strategy to eliminate theoretical uncertainties related to this amplitude to almost arbitrary precision. This opens up the possibility to probe for O(1) modifications of the c-and b-quark Yukawa couplings and O(30) modifications of the s-quark Yukawa coupling in the high-luminosity LHC run. In particular, we show that measurements of the ratios Br(h → Υ(nS) γ)/Br(h → γγ) and Br(h → bb)/Br(h → γγ) can provide complementary information on the real and imaginary parts of the b-quark Yukawa coupling. More accurate measurements would be possible at a future 100 TeV proton-proton collider.

We present a detailed theoretical analysis of very rare, exclusive hadronic decays of the electroweak gauge bosons V = W, Z from first principles of QCD. Our main focus is on the radiative decays V → M γ, in which M is a pseudoscalar or vector meson. At leading order in an expansion in powers of Λ QCD /m V the decay amplitudes can be factorized into convolutions of calculable hard-scattering coefficients with the leading-twist light-cone distribution amplitude of the meson M . Power corrections to the decay rates arise first at order (Λ QCD /m V ) 2 . They can be estimated in terms of highertwist distribution amplitudes and are predicted to be tiny. We include one-loop O(α s ) radiative corrections to the hard-scattering coefficients and perform the resummation of large logarithms α s ln(m 2 V /µ 2 0 ) n (with µ 0 ∼ 1 GeV a typical hadronic scale) to all orders in perturbation theory. Evolution effects have an important impact both numerically and conceptually, since they reduce the sensitivity to poorly determined hadronic parameters. We present detailed numerical predictions and error estimates, which can serve as benchmarks for future precision measurements. We also present an exploratory study of the weak radiative decays Z → M W . Some of the decay modes studied here have branching ratios large enough to be accessible in the high-luminosity run of the LHC. Many of them can be measured with high accuracy at a future lepton collider. This will provide stringent tests of the QCD factorization formalism and enable novel searches for new physics.One of the main challenges to particle physics is to obtain a rigorous control of stronginteraction phenomena in a regime where QCD is strongly coupled. Over the years, lattice QCD has made much progress in computing the static properties of hadrons from first principles. The concept of quark-hadron duality has enabled us to make systematic predictions for inclusive decay processes with a large energy release, such as e + e − → hadrons at large √ s, or inclusive weak decays like B → Xlν. In these cases, non-perturbative aspects of the strong interactions can be accounted for using a local operator-product expansion. A conceptually more difficult problem is to control strong-interaction effects in exclusive hadronic processes at large energy. For deep-inelastic scattering a factorization theorem can be derived, in which all non-perturbative physics associated with the initial-state nucleon can be described in terms of parton distribution functions (PDFs), up to power corrections suppressed by Λ QCD / √ s. The same framework is routinely used to calculate cross sections at hadron colliders such as the LHC in terms of convolutions of calculable partonic cross sections with PDFs, even though the underlying factorization formula can only be proved for the simplest such processes.The QCD factorization approach developed by Brodsky and Lepage [1, 2], Efremov and Radyushkin [3,4] and others [5] provides a theoretical basis for controlling strong-interaction effects in exclusive p...

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We present a detailed analysis of the collider signatures of TeV-scale massive vector bosons motivated by the hints of lepton flavour non-universality observed in Bmeson decays. We analyse three representations that necessarily appear together in a large class of ultraviolet-complete models: a colour-singlet (Z), a colour-triplet (the U 1 leptoquark), and a colour octet (G). Under general assumptions for the interactions of these exotic states with Standard Model fields, including in particular possible right-handed and flavour off-diagonal couplings for the U 1 , we derive a series of stringent bounds on masses and couplings that constrain a wide range of explicit new-physics models.