Jure Zupan

A bstract: We perform an initial study of DUNE’s sensitivity to enhanced neutrino polarizability within models of light scalar mediators. We identify two possible signatures of polarizability due to neutrino scattering on electrons and due to coherent scattering on argon nuclei. These result in either one or two separated electromagnetic showers, respectively, with no associated hadronic activity. For each signature we compute the signal rates and the relevant backgrounds, obtaining the projected reach of the DUNE near detector. We then compare this with the current astrophysical and terrestrial bounds on light scalar models coupling to neutrinos and/or photons.

We chart new-physics models that produce exotic, high-multiplicity muon decays featuring prompt or displaced e + e − pairs and/or photons, with or without missing energy, such as μ → 5 e , μ → 7 e , etc. Starting from an effective-field-theory perspective, we estimate the reach on the ultraviolet scale and identify conditions under which lower-multiplicity modes are suppressed or occur at comparable rates. We then construct explicit realizations in minimal dark-sector models with light, feebly interacting particles, such as flavor-protected scalars, dark photons, inelastic dark matter, and axionlike particles. The predicted novel signatures can be probed at MEG II and Mu3e, as well as during calibration runs of COMET and Mu2e. A future discovery would provide valuable insights into short-distance dynamics and the mechanism of lepton-flavor symmetry breaking.

We present iHOMER, an iterative version of the HOMER method to extract Lund fragmentation functions from experimental data. Through iterations, we address the information gap between latent and observable phase spaces and systematically remove bias. To quantify uncertainties on the inferred weights, we use a combination of Bayesian neural networks and uncertainty-aware regression. We find that the combination of iterations and uncertainty quantification produces well-calibrated weights that accurately reproduce the data distribution. A parametric closure test shows that the iteratively learned fragmentation function is compatible with the true fragmentation function.

We review observational, experimental and theoretical results related to Dark Matter.

Axionlike particles (ALPs) are well-motivated examples of light, weakly coupled particles in theories beyond the Standard Model. In this work, we study long-lived ALPs coupled exclusively to leptons in the mass range between 2 m e and m τ − m e . For anarchic flavor structure the leptophilic ALP production in tau decays or from ALP-tau bremsstrahlung is enhanced thanks to derivative couplings of the ALP and can surpass production from electron and muon channels, especially for ALPs heavier than m μ . Using past data from high-energy fixed-target experiments such as CHARM and BEBC we place new constraints on the ALP decay constant f a , reaching scales as high as O ( 10 8 ) GeV in lepton-flavor-violating channels and f a ∼ O ( 10 2 ) GeV in lepton-flavor-conserving ones. We also present projections for the event-rate sensitivity of current and future detectors to ALPs produced at the Fermilab Main Injector, the CERN SPS, and in the forward direction of the LHC. We show that SHiP will be sensitive to f a values that are over an order of magnitude above the existing constraints.

We update the HOMER method, a technique to solve a restricted version of the inverse problem of hadronization – extracting the Lund string fragmentation function f(z) f ( z ) from data using only observable information. Here, we demonstrate its utility by extracting f(z) f ( z ) from synthetic Pythia simulations using high-level observables constructed on an event-by-event basis, such as multiplicities and shape variables. Four cases of increasing complexity are considered, corresponding to e^+e^- e + e − collisions at a center-of-mass energy of 90≥v 90 ≥ v producing either a string stretched between a q q and \bar{q} q ‾ containing no gluons; the same string containing one gluon g g with fixed kinematics; the same but the gluon has varying kinematics; and the most realistic case, strings with an unrestricted number of gluons that is the end-result of a parton shower. We demonstrate the extraction of f(z) f ( z ) in each case, with the result of only a relatively modest degradation in performance of the HOMER method with the increased complexity of the string system.

A bstract: We explore the possibility that the interactions of a light scalar singlet, which mixes with the Standard Model (SM) Higgs, also receive other UV contributions of comparable size. We focus, in particular, on the flavor aligned limit, where couplings of the light scalar to the SM are almost flavor diagonal, but not necessarily proportional to the Higgs Yukawa couplings. The phenomenology of such a general flavor aligned light scalar differs from both the Higgs-mixed scalar, as well as from a general axion-like particle. We explore this for light scalar masses below a few hundred MeV, such that they can be produced in kaon decays, and in decays of η and η ^′ mesons, and the transitions described using chiral perturbation theory. We then derive constraints on the light scalar interactions, assuming that light scalar decays are either just into photons or are invisible. We also discuss several UV examples of such light scalar models: a two-Higgs doublet model extended by a light scalar, a light dilaton from the dark sector, and a SM extended by heavy vector-like quarks and a light scalar. For the latter we also performed matching onto low energy theory at one-loop.

A bstract: Part of the energy created in deuterium-tritium fusion reactors is carried away from plasma by a high-intensity neutron flux, which is then absorbed by the reactor’s inner walls. The neutron flux can be used to sustain the reaction by the following mechanism: the walls are coated with lithium-rich breeding blankets , in which a fraction of neutrons interacts with lithium, creating tritium, which can be, in turn, used a fuel for the main reaction. The interactions of neutrons with the materials within the breeding blanket can also result in the production of dark sector particles, feebly interacting light scalars or pseudoscalars, via nuclear transitions. We estimate the potential size of such dark sector flux outside the reactor and consider possible detection methods at current and future thermonuclear fusion reactors. In our analysis, we take into account all other current bounds, recasting also the SNO axion bound for a CP even scalar. We find that year-long searches at current and future reactors can set leading constraints on dark scalar- and dark pseudoscalar-nucleon couplings.