arXiv subjects

Thomas Rink

Publications and source records attributed to Thomas Rink.

8 recordsLinked to original sources

arXiv2026

Neutrino mass limits and decaying dark matter: background evolution versus perturbations

We revisit cosmological neutrino mass bounds when a fraction of dark matter is allowed to decay to massless dark radiation. By compensating the late-time increase in the matter density induced by neutrinos becoming non-relativistic, decaying dark matter (DDM) can render datasets solely sensitive to the background density effectively insensitive to neutrino masses. Using data from baryonic acoustic oscillations (BAO) and Type Ia supernovae together with a distance prior from the cosmic microwave background (CMB), we find that neutrino masses as large as ${\cal O}(1\,\mathrm{eV})$ are allowed without degrading the fit. Moreover, the combination of BAO data with the CMB distance prior yields a preference for a non-zero DDM fraction, and alleviates the need for dynamical dark energy with phantom crossing. However, the degeneracy introduced by DDM is decisively broken once perturbation observables are included. Incorporating the full $\textit{Planck}$ CMB likelihood, and in particular CMB lensing, restores strong constraints on the neutrino mass in the DDM scenario, $\sum m_\nu \lesssim 0.079\,\mathrm{eV}$. In contrast, neutrino mass constraints in a smooth dark energy model described by the Chevallier-Polarski-Linder parametrization become merely $\sim 25\%$ stronger compared to background-only analyses. Our results highlight the essential role of structure-growth measurements in assessing extensions of the dark sector and to obtain robust cosmological neutrino mass bounds.

astro-ph.CO↗

arXiv2025

Testing lepton non-unitarity with the next generation of Germanium-based CE$\nu$NS reactor experiments

Coherent elastic neutrino-nucleus scattering (CE$\nu$NS) has been experimentally confirmed using neutrinos from pion decay at rest, solar neutrinos and reactor antineutrinos. Future CE$\nu$NS experiments will foreseeable lead to precision measurements which will be a powerful tool to search for new physics beyond the Standard Model. In this work, we investigate possible deviations from unitarity in the $3\times3$ leptonic mixing matrix that controls the propagation of active neutrinos. Such deviations may originate from the mixing with additional gauge singlet fermions and depending on their mass scale and mixing, the resulting phenomenology can differ substantially. We explore two well-motivated regimes: the \textit{seesaw limit}, where the new fermions are heavy and kinematically inaccessible, leading to effective deviations from unitarity in the active sector; and the \textit{light sterile limit}, where they are light enough to be produced and participate in neutrino propagation and scattering processes. We show how these scenarios modify both CE$\nu$NS and elastic neutrino--electron scattering (E$\nu e$S), and we present the corresponding sensitivity projections for a future CE$\nu$NS reactor experiment obtained by upscaling the CONUS+ experiment, which reported the first observation of reactor CE$\nu$NS. We identify the leading experimental systematics relevant for such an upscaling and demonstrate the resulting capability to probe TeV-scale new physics. Our results highlight the strong potential of CE$\nu$NS to test the structure of the lepton sector and to search for physics beyond the Standard Model.

hep-ph↗

arXiv2024

Light vector bosons and the weak mixing angle in the light of future germanium-based reactor CE$\nu$NS experiments

In this work, the sensitivity of future germanium-based reactor neutrino experiments to the weak mixing angle $\sin^{2}\theta_{W}$, and to the presence of new light vector bosons is investigated. By taking into account key experimental features with their uncertainties and the application of a data-driven and state-of-the-art reactor antineutrino spectrum, the impact of detection threshold and experimental exposure is assessed in detail for an experiment relying on germanium semiconductor detectors. With the established analysis framework, the precision on the Weinberg angle, and capability of probing the parameter space of a universally coupled mediator model, as well as a U(1)$_{\rm B-L}$-symmetric model are quantified. Our investigation finds the next-generation of germanium-based reactor neutrino experiments in good shape to determine the Weinberg angle $\sin^{2}\theta_{W}$ with $<10$ % precision using the low-energetic neutrino channel of CE$\nu$NS. In addition, the current limits on new light vector bosons determined by reactor experiments can be lowered by about an order of magnitude via the combination of both CE$\nu$NS and E$\nu$eS. Consequently, our findings provide strong phenomenological support for future experimental endeavours close to a reactor site.

hep-ph↗

arXiv2022

Constraints on pseudo-Dirac neutrinos using high-energy neutrinos from NGC 1068

Neutrinos can be pseudo-Dirac in Nature - they can be Majorana fermions while behaving effectively as Dirac fermions. Such scenarios predict active-sterile neutrino oscillations driven by a tiny mass-squared difference $(\delta m^2)$, which is an outcome of soft lepton number violation. Oscillations due to tiny $\delta m^2$ can only take place over astrophysical baselines and hence are not accessible in terrestrial neutrino oscillation experiments. This implies that high-energy neutrinos coming from large distances can be naturally used to test this scenario. We use the recent observation of high-energy neutrinos from the active galactic nuclei NGC 1068 by the IceCube collaboration to rule out $\delta m^2$ in the region $[1.4 \times 10^{-18}, 10^{-17}]\, {\rm eV}^2$ at more than $90\%$ confidence level - one of the strongest limits to date on the values of $\delta m^2$. We also discuss possible uncertainties which can reduce the sensitivity of these results.

hep-ph↗

arXiv2022

Coherent elastic neutrino-nucleus scattering -- First constraints/observations and future potential

The detection of coherent elastic neutrino-nucleus scattering (CE$\nu$NS) opens new possibilities for neutrino physics within and beyond the Standard Model. Following the initial discovery in 2017, several experimental attempts have emerged allowing this reaction channel to be studied with the full repertoire of modern detection technologies. As one of several reactor experiments, CONUS aims for an observation with antineutrinos emitted from the powerful $3.9$ GW$_{th}$ reactor of the nuclear power plant in Brokdorf (Germany). In particular, the application of ultra-low threshold, high-purity germanium detectors within a sophisticated shield design in close proximity to a nuclear reactor core represents an important step towards high-statistics neutrino detection with small-scale detectors. In addition to the conventional interaction, typical extensions of the Standard Model neutrino sector can be investigated with data provided from different neutrino sources and several target materials. Among these, new neutrino interactions as well as electromagnetic neutrino properties are of particular interest. This talk gives an overview of existing CE$\nu$NS results and highlights the advantage of using different neutrino sources and target materials. The example of CONUS is used to demonstrate the various capabilities of recent and future CE$\nu$NS measurements.

hep-ph↗

arXiv2020

Leptogenesis and low-energy CP violation in a type-II-dominated left-right seesaw model

We consider leptogenesis in a left-right-symmetric seesaw scenario in which neutrino mass generation and leptogenesis are dominated by the type-II seesaw term. Motivated by grand unification, we assume that the neutrino Dirac mass matrix is dominated by a single entry of the order of the top-quark mass, which leaves the low-energy phases of the lepton mixing matrix as the only sources of CP violation. Working in a regime where the triplet scalar predominantly decays into leptons, this results in a predictive scenario based on a minimal number of parameters. We perform a detailed analysis of the flavored Boltzmann equations within a revised density matrix framework and demonstrate that the observed baryon asymmetry can be successfully generated in this simple model. We point out that the significance of flavor effects is limited, and we discuss the implications for low-energy observables such as the Dirac CP phase and neutrinoless double beta decay.

hep-ph↗

arXiv2017

Perturbed Yukawa Textures in the Minimal Seesaw Model

\noindent We revisit the \textit{minimal seesaw model}, i.e., the type-I seesaw mechanism involving only two right-handed neutrinos. % This model represents an important minimal benchmark scenario for future experimental updates on neutrino oscillations. % It features four real parameters that cannot be fixed by the current data: two $CP$-violating phases, $δ$ and $σ$, as well as one complex parameter, $z$, that is experimentally inaccessible at low energies. % The parameter $z$ controls the structure of the neutrino Yukawa matrix at high energies, which is why it may be regarded as a label or index for all UV completions of the minimal seesaw model. % The fact that $z$ encompasses only two real degrees of freedom allows us to systematically scan the minimal seesaw model over all of its possible UV completions. % In doing so, we address the following question: Suppose $δ$ and $σ$ should be measured at particular values in the future---to what extent is one then still able to realize approximate textures in the neutrino Yukawa matrix? % Our analysis, thus, generalizes previous studies of the minimal seesaw model based on the assumption of exact texture zeros. % In particular, our study allows us to assess the theoretical uncertainty inherent to the common texture ansatz. % One of our main results is that a normal light-neutrino mass hierarchy is, in fact, still consistent with a two-zero Yukawa texture, provided that the two texture zeros receive corrections at the level of $\mathcal{O}\left(\textrm{10}\,\%\right)$. % While our numerical results pertain to the minimal seesaw model only, our general procedure appears to be applicable to other neutrino mass models as well.

hep-ph↗

arXiv2016

Minimal Seesaw Model with a Discrete Heavy-Neutrino Exchange Symmetry

We present a Froggatt-Nielsen flavor model that yields a minimal realization of the type-I seesaw mechanism. This seesaw model is minimal for three reasons: (i) It features only two rather than three right-handed sterile neutrinos: N_1 and N_2, which form a pair of pseudo-Dirac neutrinos; (ii) the neutrino Yukawa matrix exhibits flavor alignment, i.e., modulo small perturbations, it contains only three independent parameters; and (iii) the N_1,2 coupling to the electron flavor is parametrically suppressed compared to the muon and tau flavors, i.e., the neutrino Yukawa matrix exhibits an approximate two-zero texture. Crucial ingredients of our model are (a) Froggatt-Nielsen flavor charges consistent with the charged-lepton masses as well as (b) an approximate, discrete exchange symmetry that manifests itself as N_1 <--> i N_2 in the heavy-neutrino Yukawa interactions and as N_1 <--> N_2 in the heavy-neutrino mass terms. This model predicts a normal light-neutrino mass hierarchy, a close-to-maximal CP-violating phase in the lepton mixing matrix, δ~3/2π, as well as resonant leptogenesis in accord with arguments from naturalness, vacuum stability, perturbativity and lepton flavor violation.

hep-ph↗