arXiv subjects

Mattias Blennow

Publications and source records attributed to Mattias Blennow.

At least 19 recordsLinked to original sources

arXiv2026

Gauged Flavour for Asymmetric Dark Matter

We propose a framework that links the origin of the Standard Model flavour hierarchies to the generation of asymmetric dark matter via leptogenesis. The key new ingredient is a gauged $SO(3)$ flavour symmetry acting on both the visible and dark sectors, whose spontaneous breaking generates fermion mass hierarchies. Right-handed neutrino decays produce a primordial lepton asymmetry, which is redistributed into baryon and dark matter asymmetries by electroweak and flavour sphalerons respectively. Dark matter arises as baryon-like bound states of a confining $SU(3)$, providing a natural rationale for the similar mass scales of visible and dark matter. We analyze flavour, collider, electroweak, and cosmological constraints. Anomaly cancellation requires the presence of mirror fermions, inducing a seesaw-like suppression of new physics effects in the lighter generations, such that different observables are sensitive to different flavour-breaking scales. Meson oscillations provide the dominant constraints, with $K$ and $B_s$ observables constraining the highest and intermediate scales, while the lowest scale may place some mirror fermions potentially within reach of future collider searches and is currently probed by flavour violating $B_s$ decays and electroweak observables. Flavour interactions are also bounded from below by the requirement of a sufficiently fast decay of the symmetric dark matter component, leading to a tightly constrained and predictive scenario testable through several complementary probes.

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arXiv2025

Misconceptions in Neutrino Oscillations in presence of a non-Unitary Mixing

Deviations from unitarity of the CKM matrix in the quark sector are considered excellent windows to probe physics beyond the Standard Model. In its leptonic counterpart, the PMNS matrix, these searches are particularly motivated, as the new physics needed to generate neutrino masses often leads to non-unitary mixing among the standard neutrinos. It is then interesting to consider how neutrino oscillations are affected in such scenario. This simple question is, however, subject to several subtleties: What is the correct way to define oscillation probabilities for a non-unitary mixing matrix? Do these probabilities add up to one? Does a non-unitary mixing matrix lead to observable flavor transitions at zero distance? What is the interplay between unitarity constraints obtained from neutrino oscillations and from electroweak precision data? This work aims to shed light on these issues and to clarify the corresponding misconceptions commonly found in the literature. We also compile updated bounds from neutrino oscillation searches to compare with those from flavour and electroweak precision observables.

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arXiv2023

Bounds on lepton non-unitarity and heavy neutrino mixing

We present an updated and improved global fit analysis of current flavor and electroweak precision observables to derive bounds on unitarity deviations of the leptonic mixing matrix and on the mixing of heavy neutrinos with the active flavours. This new analysis is motivated by new and updated experimental results on key observables such as $V_{ud}$, the invisible decay width of the $Z$ boson and the $W$ boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistic, which may present significant deviations from a $χ^2$ distribution. The results are provided for three different Type-I seesaw scenarios: the minimal scenario with only two additional right-handed neutrinos, the next to minimal one with three extra neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrize via a generic deviation from a unitary leptonic mixing matrix. Additionally, we also analyze the case of generic deviations from unitarity of the leptonic mixing matrix, not necessarily induced by the presence of additional neutrinos. This last case relaxes some correlations among the parameters and is able to provide a better fit to the data. Nevertheless, inducing only leptonic unitarity deviations avoiding both the correlations implied by the right-handed neutrino extension as well as more strongly constrained operators is challenging and would imply significantly more complex UV completions.

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arXiv2022

Right-handed neutrinos and the CDF II anomaly

We point out that right-handed neutrinos can resolve the tension between the latest CDF II measurement of the $W$-boson mass, $M_W$, and the standard model. Integrating out the new states yields a single $d=6$ operator, which induces a deviation from unitarity in the PMNS matrix. This alters the extraction of the Fermi constant from muon decay and increases the prediction for $M_W$, in line with the CDF II result. Non-unitarity of the PMNS matrix would also affect beta, meson, and tau decays. We find that the CDF II value for $M_W$ can be explained without conflicting with lepton flavour universality constraints or the invisible decay width of the $Z$. However, the so-called Cabibbo angle anomaly is worsened if right-handed neutrinos are the origin of the $d=6$ operator. The situation improves if the operator coefficient is left unconstrained, implying additional sources of new physics, but a common explanation of both anomalies is in tension with universality bounds.

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arXiv2020

Probing Lepton Flavor Models at Future Neutrino Experiments

Non-Abelian discrete symmetries provide an interesting opportunity to address the flavor puzzle in the lepton sector. However, the number of currently viable models based on such symmetries is rather large. High-precision measurements of the leptonic mixing parameters by future neutrino experiments, including ESSnuSB, T2HK, DUNE, and JUNO, will be crucial to test such models. We show that the complementarity among these experiments offers a powerful tool for narrowing down this broad class of lepton flavor models.

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arXiv2020

Testing Lepton Flavor Models at ESSnuSB

We review and investigate lepton flavor models, stemming from discrete non-Abelian flavor symmetries, described by one or two free model parameters. First, we confront eleven one- and seven two-parameter models with current results on leptonic mixing angles from global fits to neutrino oscillation data. We find that five of the one- and five of the two-parameter models survive the confrontation test at $3σ$. Second, we investigate how these ten one- and two-parameter lepton flavor models may be discriminated at the proposed ESSnuSB experiment in Sweden. We show that the three one-parameter models that predict $\sinδ_{\rm CP}=0$ can be distinguished from those two that predict $|\sinδ_{\rm CP}|=1$ by at least $7σ$. Finally, we find that three of the five one-parameter models can be excluded by at least $5σ$ and two of the one-parameter as well as at most two of the five two-parameter models can be excluded by at least $3σ$ with ESSnuSB if the true values of the leptonic mixing parameters remain close to the present best-fit values.

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arXiv2019

The distribution of inelastic dark matter in the Sun

If dark matter is composed of new particles, these may become captured after scattering with nuclei in the Sun, thermalise through additional scattering, and finally annihilate into neutrinos that can be detected on Earth. If dark matter scatters inelastically into a slightly heavier ($\mathcal{O} (10-100)$ keV) state it is unclear whether thermalisation occurs. One issue is that up-scattering from the lower mass state may be kinematically forbidden, at which point the thermalisation process effectively stops. A larger evaporation rate is also expected due to down-scattering. In this work, we perform a numerical simulation of the capture and thermalisation process in order to study the evolution of the dark matter distribution. We then calculate and compare the annihilation rate with that of the often assumed Maxwell--Boltzmann distribution. We also check if equilibrium between capture and annihilation is reached and find that this assumption definitely breaks down in a part of the explored parameter space. We also find that evaporation induced by down-scattering is not effective in reducing the total dark matter abundance.

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arXiv2018

IceCube bounds on sterile neutrinos above 10 eV

We study the capabilities of IceCube to search for sterile neutrinos with masses above 10 eV by analyzing its $ν_μ$ disappearance atmospheric neutrino sample. We find that IceCube is not only sensitive to the mixing of sterile neutrinos to muon neutrinos, but also to the more elusive mixing with tau neutrinos through matter effects. The currently released 1-year data shows a mild (around 2$σ$) preference for non-zero sterile mixing, which overlaps with the favoured region for the sterile neutrino interpretation of the ANITA upward shower. Although the null results from CHORUS and NOMAD on $ν_μ$ to $ν_τ$ oscillations in vacuum disfavour the hint from the IceCube 1-year data, the relevant oscillation channel and underlying physics are different. At the $99\%$ C.L. an upper bound is obtained instead that improves over the present Super-Kamiokande and DeepCore constraints in some parts of the parameter space. We also investigate the physics reach of the roughly 8 years of data that is already on tape as well as a forecast of 20 years data to probe the present hint or improve upon current constraints.

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arXiv2017

Non-Unitarity, sterile neutrinos, and Non-Standard neutrino Interactions

The simplest Standard Model extension to explain neutrino masses involves the addition of right-handed neutrinos. At some level, this extension will impact neutrino oscillation searches. In this work we explore the differences and similarities between the case in which these neutrinos are kinematically accessible (sterile neutrinos) or not (mixing matrix non-unitarity). We clarify apparent inconsistencies in the present literature when using different parametrizations to describe these effects and recast both limits in the popular neutrino non-standard interaction (NSI) formalism. We find that, in the limit in which sterile oscillations are averaged out at the near detector, their effects at the far detector coincide with non-unitarity at leading order, even in presence of a matter potential. We also summarize the present bounds existing in both limits and compare them with the expected sensitivities of near future facilities taking the DUNE proposal as a benchmark. We conclude that non-unitarity effects are too constrained to impact present or near future neutrino oscillation facilities but that sterile neutrinos can play an important role at long baseline experiments. The role of the near detector is also discussed in detail.

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arXiv2017

Self-interacting inelastic dark matter: A viable solution to the small scale structure problems

Self-interacting dark matter has been proposed as a solution to the small-scale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schrödinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

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arXiv2016

A combined study of source, detector and matter non-standard neutrino interactions at DUNE

We simultaneously investigate source, detector and matter non-standard neutrino interactions at the proposed DUNE experiment. Our analysis is performed using a Markov Chain Monte Carlo exploring the full parameter space. We find that the sensitivity of DUNE to the standard oscillation parameters is worsened due to the presence of non-standard neutrino interactions. In particular, there are degenerate solutions in the leptonic mixing angle $θ_{23}$ and the Dirac CP-violating phase $δ$. We also compute the expected sensitivities at DUNE to the non-standard interaction parameters. We find that the sensitivities to the matter non-standard interaction parameters are substantially stronger than the current bounds (up to a factor of about 15). Furthermore, we discuss correlations between the source/detector and matter non-standard interaction parameters and find a degenerate solution in $θ_{23}$. Finally, we explore the effect of statistics on our results.

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arXiv2016

Pinning down inelastic dark matter in the Sun and in direct detection

We study the solar capture rate of inelastic dark matter with endothermic and/or exothermic interactions. By assuming that an inelastic dark matter signal will be observed in next generation direct detection experiments we can set a lower bound on the capture rate that is independent of the local dark matter density, the velocity distribution, the galactic escape velocity as well as the scattering cross section. In combination with upper limits from neutrino observatories we can place upper bounds on the annihilation channels leading to neutrinos. We find that, while endothermic scattering limits are weak in the isospin-conserving case, strong bounds may be set for exothermic interactions, in particular in the spin-dependent case. Furthermore, we study the implications of observing two direct detection signals, in which case one can halo-independently obtain the dark matter mass and the mass splitting, and disentangle the endothermic/exothermic nature of the scattering. Finally we discuss isospin violation.

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arXiv2016

Global constraints on vector-like WIMP effective interactions

In this work we combine information from relic abundance, direct detection, cosmic microwave background, positron fraction, gamma rays, and colliders to explore the existing constraints on couplings between Dark Matter and Standard Model constituents when no underlying model or correlation is assumed. For definiteness, we include independent vector-like effective interactions for each Standard Model fermion. Our results show that low Dark Matter masses below 20 GeV are disfavoured at the $3 σ$ level with respect to higher masses, due to the tension between the relic abundance requirement and upper constraints on the Dark Matter couplings. Furthermore, large couplings are typically only allowed in combinations which avoid effective couplings to the nuclei used in direct detection experiments.

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arXiv2016

The MOMENT to search for CP violation

In this letter, we analyze for the first time the physics reach in terms of sensitivity to leptonic CP violation of the proposed MuOn-decay MEdium baseline NeuTrino beam (MOMENT) experiment, a novel neutrino oscillation facility that would operate with neutrinos from muon decay. Apart from obtaining a sufficiently intense flux, the bottlenecks to the physics reach of this experiment will be achieving a high enough suppression of the atmospheric background and, particularly, attaining a sufficient level of charge identification. We thus present our results as a function of these two factors. As for the detector, we consider a very massive Gd-doped Water Cherenkov detector. We find that MOMENT will be competitive with other currently planned future oscillation experiments if a charge identification of at least 80 % can be achieved at the same time that the atmospheric background can be suppressed by at least a factor of ten. We also find a large synergy of MOMENT with the current generation of neutrino oscillation experiments, T2K and NOvA, which significantly enhances its final sensitivity.

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arXiv2015

Exploring Source and Detector Non-Standard Neutrino Interactions at ESS$ν$SB

We investigate source and detector non-standard neutrino interactions at the proposed ESS$ν$SB experiment. We analyze the effect of non-standard physics at the probability level, the event-rate level and by a full computation of the ESS$ν$SB setup. We find that the precision measurement of the leptonic mixing angle $θ_{23}$ at ESS$ν$SB is robust in the presence of non-standard interactions, whereas that of the leptonic CP-violating phase $δ$ is worsened at most by a factor of two. We compute sensitivities to all the relevant source and decector non-standard interaction parameters and find that the sensitivities to the parameters $\varepsilon^s_{μe}$ and $\varepsilon^d_{μe}$ are comparable to the existing limits in a realistic scenario, while they improve by a factor of two in an optimistic scenario. Finally, we show that the absence of a near detector compromises the sensitivity of ESS$ν$SB to non-standard interactions.

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arXiv2015

Halo-independent tests of dark matter direct detection signals: local DM density, LHC, and thermal freeze-out

From an assumed signal in a Dark Matter (DM) direct detection experiment a lower bound on the product of the DM--nucleon scattering cross section and the local DM density is derived, which is independent of the local DM velocity distribution. This can be combined with astrophysical determinations of the local DM density. Within a given particle physics model the bound also allows a robust comparison of a direct detection signal with limits from the LHC. Furthermore, the bound can be used to formulate a condition which has to be fulfilled if the particle responsible for the direct detection signal is a thermal relic, regardless of whether it constitutes all DM or only part of it. We illustrate the arguments by adopting a simplified DM model with a Z' mediator and assuming a signal in a future xenon direct detection experiment.

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arXiv2015

Asymmetric capture of Dirac dark matter by the Sun

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

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arXiv2015

A halo-independent lower bound on the dark matter capture rate in the Sun from a direct detection signal

We show that a positive signal in a dark matter (DM) direct detection experiment can be used to place a lower bound on the DM capture rate in the Sun, independent of the DM halo. For a given particle physics model and DM mass we obtain a lower bound on the capture rate independent of the local DM density, velocity distribution, galactic escape velocity, as well as the scattering cross section. We illustrate this lower bound on the capture rate by assuming that upcoming direct detection experiments will soon obtain a significant signal. When comparing the lower bound on the capture rate with limits on the high-energy neutrino flux from the Sun from neutrino telescopes, we can place upper limits on the branching fraction of DM annihilation channels leading to neutrinos. With current data from IceCube and Super-Kamiokande non-trivial limits can be obtained for spin-dependent interactions and direct annihilations into neutrinos. In some cases also annihilations into $ττ$ or $b\bar b$ start getting constrained. For spin-independent interactions current constraints are weak, but they may become interesting for data from future neutrino telescopes.

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