Publications

Order by: publication date number of citations

• Gluon condensates and effective gluon mass

  Jan Horak, Friederike Ihssen, Joannis Papavassiliou, Jan M. Pawlowski, Axel Weber, Christof Wetterich

  SciPost Phys. 13, 042 (2022) · published 31 August 2022 | Toggle abstract · pdf

  Lattice simulations along with studies in continuum QCD indicate that non-perturbative quantum fluctuations lead to an infrared regularisation of the gluon propagator in covariant gauges in the form of an effective mass-like behaviour. In the present work we propose an analytic understanding of this phenomenon in terms of gluon condensation through a dynamical version of the Higgs mechanism, leading to the emergence of color condensates. Within the functional renormalisation group approach we compute the effective potential of covariantly constant field strengths, whose non-trivial minimum is related to the color condensates. In the physical case of an SU(3) gauge group this is an octet condensate. The value of the gluon mass obtained through this procedure compares very well to lattice results and the mass gap arising from alternative dynamical scenarios.

  14 citations

• Coloring mixed QCD/QED evolution

  Leif Gellersen, Stefan Prestel, Michael Spannowsky

  SciPost Phys. 13, 034 (2022) · published 26 August 2022 | Toggle abstract · pdf

  Parton showers are crucial components of high-energy physics calculations. Improving their modelling of QCD is an active research area since shower approximations are stumbling blocks for precision event generators. Naively, the interference between sub-dominant Standard-Model interactions and QCD can be of similar size to subleading QCD corrections. This article assesses the impact of QCD/QED interference effects in parton showers, by developing a sophisticated shower including QED, QCD at fixed color, and employing complete tree-level matrix element corrections for individual $N_C=3$ color configurations to embed interference. The resulting simulation indicates that QCD/QED interference effects are small for a simple test case and dwarfed by electro-weak resonance effects.

  4 citations

• YFS Resummation for Future Lepton-Lepton Colliders in SHERPA

  Frank Krauss, Alan Price, Marek Schönherr

  SciPost Phys. 13, 026 (2022) · published 18 August 2022 | Toggle abstract · pdf

  We present an implementation of the Yennie-Frautschi-Suura (YFS) scheme for the all-orders resummation of logarithms from the emission of soft real and virtual photons in processes that are critical for future lepton colliders. They include, in particular, $e^-e^+\to f\bar{f}$ and $e^-e^+\to W^-W^+$, where we validate the results of our implementation, improved with fixed-order corrections, with those obtained from the most precise calculations. We also show, for the first time, results for the Higgs-Strahlungs process, $e^-e^+\to ZH$, in YFS resummation including fixed-order improvements up to order $\alpha^3L^3$.

  2 citations

• Jet modifications from colour rope formation in dense systems of non-parallel strings

  Christian Bierlich, Smita Chakraborty, Gösta Gustafson, Leif Lönnblad

  SciPost Phys. 13, 023 (2022) · published 17 August 2022 | Toggle abstract · pdf

  We revisit our rope model for string fragmentation that has been shown to give a reasonable description of strangeness and baryon enhancement in high-multiplicity pp events at the LHC. A key feature of the model is that the enhancement is driven by the increased string tension due to strings overlapping in dense systems. By introducing an improved space-time picture for the overlap between fragmenting strings, where also non-parallel strings are properly taken into account, we are now able to investigate the enhancement both in jets and in the underlying event in a consistent way.

  3 citations

• Fingerprints of freeze-in dark matter in an early matter-dominated era

  Avik Banerjee, Debtosh Chowdhury

  SciPost Phys. 13, 022 (2022) · published 16 August 2022 | Toggle abstract · pdf

  We study the impact of an alternate cosmological history with an early matter-dominated epoch on the freeze-in production of dark matter. Such early matter domination is triggered by a meta-stable matter field dissipating into radiation. In general, the dissipation rate has a non-trivial temperature and scale factor dependence. Compared to the usual case of dark matter production via the freeze-in mechanism in a radiation-dominated universe, in this scenario, orders of magnitude larger coupling between the visible and the dark sector can be accommodated. Finally, as a proof of principle, we consider a specific model where the dark matter is produced by a sub-GeV dark photon having a kinetic mixing with the Standard Model photon. We point out that the parameter space of this model can be probed by the experiments in the presence of an early matter-dominated era.

  8 citations

• Cluster Hadronisation in Sherpa

  Gurpreet Singh Chahal, Frank Krauss

  SciPost Phys. 13, 019 (2022) · published 15 August 2022 | Toggle abstract · pdf

  We present the Sherpa cluster hadronization model and a simple model for non-perturbative colour reconnections. Using two different parton shower implementations we tuned the model to data and we show typical resulting distributions that are sensitive to hadronization effects in $e^+e^-$--annihilations into hadrons.

  7 citations

• Hitting two BSM particles with one lepton-jet: search for a top partner decaying to a dark photon, resulting in a lepton-jet

  K. du Plessis, M. M. Flores, D. Kar, S. Sinha, H. van der Schyf

  SciPost Phys. 13, 018 (2022) · published 15 August 2022 | Toggle abstract · pdf

  A maverick top partner model, decaying to a dark photon was suggested. The dark photon decays to two overlapping electrons for dark photon masses of $\approx 100$ GeV, and results in a so-called lepton-jet. The event includes a top quark as well, which results in events with two boosted objects, one heavy and the other light. We propose a search strategy exploiting the unique signal topology. We show that for a set of kinematic selections, both in hadronic and leptonic decay channel of the SM top quark, almost all background can be eliminated, leaving enough signal events up to top partner mass of about 3 TeV for the search to be viable at the LHC.

  3 citations

• Hamiltonian Truncation Effective Theory

  Timothy Cohen, Kara Farnsworth, Rachel Houtz, Markus A. Luty

  SciPost Phys. 13, 011 (2022) · published 4 August 2022 | Toggle abstract · pdf

  Hamiltonian truncation is a non-perturbative numerical method for calculating observables of a quantum field theory. The starting point for this method is to truncate the interacting Hamiltonian to a finite-dimensional space of states spanned by the eigenvectors of the free Hamiltonian $H_0$ with eigenvalues below some energy cutoff $E_\text{max}$. In this work, we show how to treat Hamiltonian truncation systematically using effective field theory methodology. We define the finite-dimensional effective Hamiltonian by integrating out the states above $E_\text{max}$. The effective Hamiltonian can be computed by matching a transition amplitude to the full theory, and gives corrections order by order as an expansion in powers of $1/E_\text{max}$. The effective Hamiltonian is non-local, with the non-locality controlled in an expansion in powers of $H_0/E_\text{max}$. The effective Hamiltonian is also non-Hermitian, and we discuss whether this is a necessary feature or an artifact of our definition. We apply our formalism to 2D $\lambda \phi^4$ theory, and compute the the leading $1/E_\text{max}^2$ corrections to the effective Hamiltonian. We show that these corrections non-trivially satisfy the crucial property of separation of scales. Numerical diagonalization of the effective Hamiltonian gives residual errors of order $1/E_\text{max}^3$, as expected by our power counting. We also present the power counting for 3D $\lambda \phi^4$ theory and perform calculations that demonstrate the separation of scales in this theory.

  4 citations