Kåre Fridell
Theoretical particle physicist working on physics beyond the Standard Model — why the Universe contains matter but no antimatter, what neutrinos can tell us, and how dark matter would show up in experiments.
About
Kåre studied physics at the University of Gothenburg and worked on direct detection of dark matter as a project assistant at Chalmers University of Technology. He did his PhD at the Technical University of Munich with Prof. Julia Harz, then spent 2022–2025 as a postdoctoral researcher at KEK in Tsukuba, Japan, with visits to Fermilab and Florida State University. He is now a postdoc at Charles University in Prague.
His research connects theory with the experiments that can test it: rare meson decays, neutrino scattering, neutron–antineutron oscillation searches, and the LHC and future colliders. This site collects plain-language summaries of his publications. Most of the papers are freely readable in full, and every page links to the original.
The research in one minute
Dark matter 🌑
How hypothetical dark-matter particles would scatter off atomic nuclei, and how polarised targets or spin-1 dark matter change the signals that direct-detection experiments should look for.
Baryogenesis ⚖
Why the Universe contains matter but almost no antimatter. These papers explore baryon-number violation — above all neutron–antineutron oscillations and the bound states of heavy particles — and what the next generation of experiments can reveal.
Neutrinos & lepton number 👻
The tiny masses of neutrinos suggest that lepton number is violated by nature. This thread maps the possible new interactions and how rare B and K meson decays, neutrinoless double beta decay and cosmology constrain them.
Colliders & experiments ⚡
Testing new physics with real data: LHC searches for photophobic axions, a muon collider's reach for lepton-flavour violation, the Belle II B → Kνν excess, and CEνNS experiments probing neutrino magnetic moments.
Publications
22 publications, newest work listed last within each theme. The year is the year of publication; every title links to a plain-language page, and the full text is free wherever it exists (arXiv, open-access journals, Proceedings of Science, or mediaTUM).
Dark matter 2 papers
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2018
Direct detection of fermionic and vector dark matter with polarised targets
Dark matter scattering off spin-polarised nuclei leaves a polarisation-dependent signal that could in principle reveal whether the dark matter particle is a fermion or a vector boson.
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2019
Non-relativistic Effective Interactions of Spin 1 Dark Matter
Working out how spin-1 (vector) dark matter scatters off nuclei reveals two interaction operators specific to vector dark matter that can change predicted direct-detection rates by up to a factor of ten.
Baryogenesis 5 works
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2021
Probing baryogenesis with neutron-antineutron oscillations
Whether a future neutron–antineutron oscillation signal can be tied to the matter–antimatter asymmetry depends on the mass hierarchy of the new particles: a small hierarchy means washout kills it, a large one leaves baryogenesis possible over a broad, testable range.
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2021
Probing Baryogenesis using Neutron-Anti-Neutron Oscillation conference proceedings
The ICHEP 2020 proceedings version: how the same baryon-number-violating interaction would wash out a matter–antimatter asymmetry, and the scales future experiments probe.
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2022
Neutron-antineutron oscillations as a probe of baryogenesis conference proceedings
The TAUP 2021 proceedings version: how a future oscillation signal would reveal the strength of baryon-asymmetry washout, probing high- and low-scale baryogenesis alongside collider searches.
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2022
New Ideas in Baryogenesis: A Snowmass White Paper
A community white paper surveying thirteen new baryogenesis mechanisms and seven ways experiments — colliders, neutrino and neutron-oscillation searches, gravitational waves — can test them.
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2024
Impact of Bound State Formation on Baryogenesis
Bound states of heavy particles can erase more than 90% of a predicted baryon asymmetry, or boost it by a factor of a few — so baryogenesis models must include them.
Neutrinos & lepton number 7 papers
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2020
Constraining lepton number violating interactions in rare kaon decays
Rare kaon decays can probe lepton-number-violating new physics above about 11 TeV through a distinctive scalar-current signature, using E949, NA62 and KOTO data.
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2020
Implications of Rare Kaon Decays on Lepton Number Violating Interactions conference proceedings
The ICHEP 2020 proceedings version: rare kaon data already require lepton-number-violating new physics above a multi-TeV scale — and a signal would pressure high-scale leptogenesis while hinting at radiatively generated neutrino masses.
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2024
Probing lepton number violation: a comprehensive survey of dimension-7 SMEFT
A comprehensive survey of all twelve dimension-7 lepton-number-violating SMEFT operators, weighing low-energy bounds (neutrinoless double beta decay, meson decays, neutrino data) against LHC and FCC collider limits.
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2024
Simplified models of d=7 lepton number violation conference proceedings
The ICHEP 2024 proceedings version: how the observed neutrino mass arises at one loop in every two-field completion of a dimension-7 operator, and why LHC data constrains them most.
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2025
Radiative neutrino masses from dim-7 SMEFT: a simplified multi-scale approach
Catalogues the minimal UV completions of dimension-7 lepton-number-violating operators and shows how a simple multi-scale method fixes loop-neutrino-mass estimates that can otherwise be wildly wrong.
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2025
Leptogenesis and neutrino mass with scalar leptoquarks
A scalar-leptoquark model can generate both the observed neutrino mass scale and the Universe's matter–antimatter asymmetry at once, without clashing with existing experiments.
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2026
Feasibility study of lepton number violation in rare B and K meson decays
Lepton-number violation could explain future excesses in rare B and K meson decays, but only if the new interaction nearly ignores at least one type of lepton — or the new-physics scale sits very close to the electroweak scale.
Colliders & experiments 7 works
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2022
Probing active-sterile neutrino transition magnetic moments with photon emission from CEνNS
CEνNS experiments could spot a nuclear recoil plus a photon from a decaying sterile neutrino — a nearly background-free probe of neutrino transition magnetic moments and of the Dirac or Majorana nature of neutrinos.
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2022
Distinguishing Dirac vs Majorana Neutrinos at CEνNS experiments conference proceedings
The EPS-HEP 2021 proceedings version: recoil-plus-photon coincidences at CEνNS experiments can probe neutrino transition magnetic moments and distinguish Dirac from Majorana sterile neutrinos.
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2022
Transition neutrino magnetic moments in CEνNS conference proceedings
The TAUP 2021 proceedings version: NUCLEUS photon-plus-recoil coincidences could reveal the properties of a sterile neutrino while the recoil search itself reaches new ground.
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2023
Lepton flavor physics at μ⁺μ⁺ colliders
A 2 TeV μ⁺μ⁺ collider with 1 ab⁻¹ could discover lepton-flavour violation in μ⁺μ⁺ → μ⁺τ⁺ with over a hundred events while respecting rare-decay bounds.
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2024
Decoding the B⁺ → K⁺ νν excess at Belle II: Kinematics, operators, and masses
Fitting the Belle II event shape, a vector-current decay into two invisible 0.6 GeV particles — possibly dark matter — fits the excess best, with a 2 GeV particle a close second.
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2024
Noncanonical nucleon decays as window into light new physics
Nucleon decays into light new particles such as sterile neutrinos, dark photons, ALPs or dark scalars would leave unusually slow visible debris, opening a decades-wide probe of new physics below a few GeV.
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2024
Heavy photophobic ALP at the LHC
LHC multi-boson data already constrain photophobic axion-like particles up to masses of about 3.4 TeV — a region where the usual diphoton searches are blind.
PhD thesis 1 work
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2022
Phenomenology of Baryogenesis and Neutrino Physics: From Effective Field Theory to Simplified Models
A guided tour of the thesis: how lepton- and baryon-number violation can be probed by rare kaon decays, CEνNS and neutron–antineutron experiments, and how such models could explain the matter–antimatter asymmetry.
About this site
Every page linked here is a plain-language summary written for this family website. The summaries aim to be accurate, but they simplify — for the real thing, follow the links to the papers. Figures are reproduced from the original publications; the papers and their free versions are linked on each page. Publication data follows the INSPIRE-HEP record.