Next-to-leading-order QCD corrections and parton-shower effects for weakino+squark production at the LHC

We present a calculation of the next-to-leading order QCD corrections to weakino+squark production processes at hadron colliders and their implementation in the framework of the POWHEG-BOX, a tool for the matching of fixed-order perturbative calculations with parton-shower programs. Particular care is taken in the subtraction of on-shell resonances in the real-emission corrections that have to be assigned to production processes of a different type. In order to illustrate the capabilities of our code, representative results are shown for selected SUSY parameter points in the pMSSM11. The perturbative stability of the calculation is assessed for the pp →$$ {\tilde{\upchi}}_1^0{\tilde{d}}_L $$ χ ˜ 1 0 d ˜ L process. For the squark+chargino production process pp →$$ {\upchi}_1^{-}{\tilde{u}}_L $$ χ 1 − u ˜ L distributions of the chargino’s decay products are provided with the help of the decay feature of PYTHIA 8.

Removing tadpoles in a soliton sector

It has long been known that perturbative calculations can be performed in a soliton sector of a quantum field theory by using a soliton Hamiltonian, which is constructed from the defining Hamiltonian by shifting the field by the classical soliton solution. It is also known that even if tadpoles are eliminated in the vacuum sector, they remain in the soliton sector. In this note we show, in the case of quantum kinks at two loops, that the soliton sector tadpoles may be removed by adding certain quantum corrections to the classical solution used in this construction. Stated differently, the renormalization condition that the soliton sector tadpoles vanish may be satisfied by renormalizing the soliton solution.

Cuts for two-body decays at colliders

Fixed-order perturbative calculations of fiducial cross sections for two-body decay processes at colliders show disturbing sensitivity to unphysically low momentum scales and, in the case of H → γγ in gluon fusion, poor convergence. Such problems have their origins in an interplay between the behaviour of standard experimental cuts at small transverse momenta (pt) and logarithmic perturbative contributions. We illustrate how this interplay leads to a factorially divergent structure in the perturbative series that sets in already from the first orders. We propose simple modifications of fiducial cuts to eliminate their key incriminating characteristic, a linear dependence of the acceptance on the Higgs or Z-boson pt, replacing it with quadratic dependence. This brings major improvements in the behaviour of the perturbative expansion. More elaborate cuts can achieve an acceptance that is independent of the Higgs pt at low pt, with a variety of consequent advantages.

Renormalization in Combinatorially Non-Local Field Theories: the BPHZ Momentum Scheme

Various combinatorially non-local field theories are known to be renormalizable. Still, explicit calculations of amplitudes are very rare and restricted to matrix field theory. In this contribution I want to demonstrate how the BPHZ momentum scheme in terms of the Connes-Kreimer Hopf algebra applies to any combinatorially non-local field theory which is renormalizable. This algebraic method improves the understanding of known results in noncommutative field theory in its matrix formulation. Furthermore, I use it to provide new explicit perturbative calculations of amplitudes in tensorial field theories of rank r>2.

Hunting for $$B^+\rightarrow K^+ \tau ^+\tau ^-$$ imprints on the $$B^+ \rightarrow K^+ \mu ^+\mu ^-$$ dimuon spectrum

We investigate the possibility of indirectly constraining the $$B^{+}\rightarrow K^{+}\tau ^+\tau ^-$$ B + → K + τ + τ - decay rate using precise data on the $$B^{+}\rightarrow K^{+}\mu ^+\mu ^-$$ B + → K + μ + μ - dimuon spectrum. To this end, we estimate the distortion of the spectrum induced by the $$B^{+}\rightarrow K^{+}\tau ^+\tau ^-\rightarrow K^{+} \mu ^+\mu ^-$$ B + → K + τ + τ - → K + μ + μ - re-scattering process, and propose a method to simultaneously constrain this (non-standard) contribution and the long-distance effects associated to hadronic intermediate states. The latter are constrained using the analytic properties of the amplitude combined with data and perturbative calculations. Finally, we estimate the sensitivity expected at the LHCb experiment with present and future datasets. We find that constraints on the branching fraction of $$O(10^{-3})$$ O ( 10 - 3 ) , competitive with current direct bounds, can be achieved with the current dataset, while bounds of $$O(10^{-4})$$ O ( 10 - 4 ) could be obtained with the LHCb upgrade-II luminosity.

Equation of state of non-relativistic matter from automated perturbation theory and complex Langevin

We calculate the pressure and density of polarized non-relativistic systems of two-component fermions coupled via a contact interaction at finite temperature. For the unpolarized one-dimensional system with an attractive interaction, we perform a thirdorder lattice perturbation theory calculation and assess its convergence by comparing with hybrid Monte Carlo. In that regime, we also demonstrate agreement with real Langevin. For the repulsive unpolarized one-dimensional system, where there is a so-called complex phase problem, we present lattice perturbation theory as well as complex Langevin calculations. For our studies, we employ a Hubbard-Stratonovich transformation to decouple the interaction and automate the application of Wick’s theorem for perturbative calculations, which generates the diagrammatic expansion at any order. We find excellent agreement between the results from our perturbative calculations and stochastic studies in the weakly interacting regime. In addition, we show predictions for the strong coupling regime as well as for the polarized one-dimensional system. Finally, we show a first estimate for the equation of state in three dimensions where we focus on the polarized unitary Fermi gas.

Standard Model and New physics for ε′k/εk

The first result of the lattice simulation and improved perturbative calculations have pointed to a discrepancy between data on ε′k/εk and the standard-model (SM) prediction. Several new physics (NP) models can explain this discrepancy, and such NP models are likely to predict deviations of ℬ(K → πvv) from the SM predictions, which can be probed precisely in the near future by NA62 and KOTO experiments. We present correlations between ε′k/εk and ℬ(K → πvv) in two types of NP scenarios: a box dominated scenario and a Z-penguin dominated one. It is shown that different correlations are predicted and the future precision measurements of K → πvv can distinguish both scenarios.