Bernlochner, F. U., Fedele, M., Kretz, T., Nierste, U., & Prim, M. T. (2025). Model independent bounds on heavy sterile neutrinos from the angular distribution of B → D*ℓν decays. J. High Energy Phys., 01(1), 040–23pp.
Abstract: In this paper we study the bounds that can be inferred on New Physics couplings to heavy sterile neutrinos N from the recent measurements performed by the Belle collaboration of the angular analysis of B -> D l nu l decays, with l = e, mu. Indeed, a sterile neutrino N may lead to competing B -> D & lowast;& ell;N<overline> decays and Belle might have measured an incoherent sum of these two independent channels. After reviewing the theoretical formalism required to describe this phenomenon in full generality, we first perform a bump hunt in the Mmiss2 Belle distribution to search for evidences of an additional massive neutrino. We found in such a way a small hint at Mmiss2 similar to (354 MeV)2. However, the Belle angular analysis is sensitive to N masses up to O(50 MeV), preventing us to further inspect this hint. Nevertheless, we study the potential impact of this additional channel in the allowed mass range on the measured angular distributions and extract model-independent bounds on the new-physics couplings which could mediate such an interaction. In particular, in the mass window here inspected, we obtain the most stringent bounds for vector and left-handed scalar operators to date.
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de Blas, J., Chowdhury, D., Ciuchini, M., Coutinho, A. M., Eberhardt, O., Fedele, M., et al. (2020). HEPfit: a code for the combination of indirect and direct constraints on high energy physics models. Eur. Phys. J. C, 80(5), 456–31pp.
Abstract: HEPfit is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to (i) fit the model parameters to a given set of experimental observables; (ii) obtain predictions for observables. HEPfit can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing HEPfit to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.
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