Martin Hirsch

A bstract: The observed baryon asymmetry (BAU) of the universe puts strong constraints on any ( B − L )-violating interaction. An observation of a ( B − L )-violating nucleon decay channel would therefore have profound implications for our understanding of the BAU. Here we point out that the observation of the final state with a kaon and a charged lepton in a future nucleon decay experiment would hint at ( B − L ) violation even if the charge of the lepton is not determined experimentally. In SMEFT, this follows from the fact that n → K ⁺ ℓ ⁻ arises already at dimension seven, while the ( B − L )-conserving decay n → K ⁻ ℓ ⁺ requires dimension-ten operators that, in addition, would be accompanied by lower-dimensional ( B + L )-violating decay modes. An observation of n → Kℓ in the absence of other modes such as p → π ⁰ ℓ ⁺ , would then strongly suggest that ( B − L ) is violated.

A bstract: Heavy neutral leptons (HNLs) and axion-like particles (ALPs) are both considered well-motivated candidates for beyond the standard model (BSM) physics. If ALPs with sizable couplings to gluons exist, they will be abundantly produced at the LHC. Therefore, HNLs produced via the ALP portal may provide unprecedented sensitivities to HNL parameters. Here, we study the prospects for the high-luminosity LHC to search for long-lived HNLs. We consider future far detectors as well as ATLAS in our simulations. In the limit where the ALP mass is above the TeV scale, HNLs are effectively produced by a dimension-8 operator connecting HNL pairs to gluons. For completeness, we therefore also calculate future LHC sensitivities for HNLs produced via N _R SMEFT operators with gluons.

In Standard Model (SM) effective field theory, invisible neutron decay arises from d = 12 operators. Adding new, light particles to the field content of the SM, such as right-handed neutrinos, allows to construct operators for invisible neutron decay at much lower dimensions. Observing invisible neutron decay, if nucleon decays with charged leptons remain absent, would therefore point towards the existence of new neutral degrees of freedom. Here, we discuss four cases: (i) Adding right-handed neutrinos to the SM; (ii) a right-handed neutrino and an axionlike particle; (iii) a right-handed neutrino and a (nearly) massless singlet scalar; and (iv) a right-handed neutrino and a light Z ′ . We give the general tree-level decomposition for the resulting d = ( 7 – 9 ) operators for invisible neutron decay. We also briefly discuss LHC searches related to the exotic states found in these UV completions.

We present a novel strategy to uncover indirect signs of new physics in collider data using the standard model effective field theory (SMEFT) framework, offering notably improved sensitivity compared to traditional global analyses. Our approach leverages genetic algorithms to efficiently navigate the high-dimensional space of operator subsets, identifying deformations that improve agreement with data without relying on prior ultraviolet (UV) assumptions. This enables the systematic detection of SMEFT scenarios that outperform the standard model in explaining observed deviations. We validate the approach on current large hadron collider and large electron-positron collider measurements, perform closure tests with injected UV signals, and assess performance under high-luminosity projections. The algorithm successfully recovers relevant operator subsets and highlights directions in parameter space where deviations are most likely to emerge. Our results demonstrate the potential of SMEFT-based discovery searches driven by model selection, providing a scalable framework for future data analyses.

A correction to this paper has been published: https://doi.org/10.1007/JHEP05(2025)238

Motivated by the recent Year-2 data release of the DESI collaboration, we update our results on time-varying dark energy models driven by the Cohen-Kaplan-Nelson bound. The previously found preference of time-dependent dark energy models compared to ΛCDM is further strengthend by the new data release. For our particular models, we find that this preference increases up to ≈ 2.6 σ depending on the used supernova dataset.

We study the phenomenology of heavy neutral leptons (HNLs) at the LHC in effective field theory, concentrating on d = 6 operators with top quarks. Depending on the operator choice and HNL mass, the HNLs will be produced either from proton-proton collisions in association with a single top, or via non-standard decays of top quarks. For long-lived HNLs we estimate the sensitivity reach of different detectors to various operators with top quarks and the HNLs for the high-luminosity phase of the LHC. For certain operators, ATLAS and some far detectors (MATHUSLA and ANUBIS) will be able to probe the associated new-physics scale as large as 12 TeV and 4.5 TeV, respectively, covering complementary HNL-mass ranges.

We discuss an extension of the standard model with a real scalar triplet, T, including non-renormalizable operators (NROs) up to d = 6. If T is odd under a Z ₂ symmetry, the neutral component of T is a good candidate for the dark matter (DM) of the universe. We calculate the relic density and constraints from direct and indirect detection on such a setup, concentrating on the differences with respect to the simple model for a DM T with only renormalizable interactions. Bosonic operators can change the relic density of the triplet drastically, opening up new parameter space for the model. Indirect detection constraints, on the other hand, rule out an interesting part of the allowed parameter space already today and future CTA data will, very likely, provide a decisive test for this setup.

Neutrino masses and dark matter (DM) might have a common origin. The scotogenic model can be considered the proto-type model realizing this idea, but many other variants exist. In this paper we explore the phenomemology of a particular DM neutrino mass model, containing a triplet scalar. We calculate the relic density and check for constraints from direct detection experiments. The parameter space of the model, allowed by these constraints, contains typically a long-lived or quasi-stable doubly charged scalar, that can be searched for at the LHC. We reinterpret existing searches to derive limits on the masses of the scalars of the model and estimate future sensitivities in the high-luminosity phase of the LHC. The searches we discuss can serve to constrain also many other 1-loop neutrino mass models.