24 research outputs found

### Non-Unitarity vs sterile neutrinos at DUNE

Neutrino masses are one of the most promising open windows to physics beyond
the Standard Model (SM). Several extensions of the SM which accommodate
neutrino masses require the addition of right-handed neutrinos to its particle
content. These extra fermions will either be kinematically accessible (sterile
neutrinos) or not (deviations from Unitarity of the PMNS matrix) but at some
point they will impact neutrino oscillation searches. We explore the
differences and similitudes between the two cases and compare their present
bounds with the expected sensitivities of DUNE. We conclude that Non-Unitarity
(NU) 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.Comment: Talk and poster presented at NuPhys2016 (London, 12-14 December
2016). 8 pages, LaTeX, 4 eps figures. Based on arXiv:1609.0863

### Decoherence in neutrino propagation through matter, and bounds from IceCube/DeepCore

We revisit neutrino oscillations in matter considering the open quantum
system framework which allows to introduce possible decoherence effects
generated by New Physics in a phenomenological manner. We assume that the
decoherence parameters $\gamma_{ij}$ may depend on the neutrino energy, as
$\gamma_{ij}=\gamma_{ij}^{0}(E/\text{GeV})^n$ $(n = 0,\pm1,\pm2)$. The case of
non-uniform matter is studied in detail, both within the adiabatic
approximation and in the more general non-adiabatic case. In particular, we
develop a consistent formalism to study the non-adiabatic case dividing the
matter profile into an arbitrary number of layers of constant densities. This
formalism is then applied to explore the sensitivity of IceCube and DeepCore to
this type of effects. Our study is the first atmospheric neutrino analysis
where a consistent treatment of the matter effects in the three-neutrino case
is performed in presence of decoherence. We show that matter effects are indeed
extremely relevant in this context. We find that IceCube is able to
considerably improve over current bounds in the solar sector ($\gamma_{21}$)
and in the atmospheric sector ($\gamma_{31}$ and $\gamma_{32}$) for $n=0,1,2$
and, in particular, by several orders of magnitude (between 3 and 9) for the
$n=1,2$ cases. For $n=0$ we find $\gamma_{32},\gamma_{31}< 4.0\cdot10^{-24}
(1.3\cdot10^{-24})$ GeV and $\gamma_{21}<1.3\cdot10^{-24} (4.1\cdot10^{-24})$
GeV, for normal (inverted) mass ordering.Comment: 31 pages, 8 figure

### Neutrino Observables from a U(2) Flavor Symmetry

We study the predictions for CP phases and absolute neutrino mass scale for
broad classes of models with a U(2) flavor symmetry. For this purpose we
consider the same special textures in neutrino and charged lepton mass matrices
that are succesful in the quark sector. While in the neutrino sector the U(2)
structure enforces two texture zeros, the contribution of the charged lepton
sector to the PMNS matrix can be parametrized by two rotation angles.
Restricting to the cases where at least one of these angles is small, we obtain
three representative scenarios. In all scenarios we obtain a narrow prediction
for the sum of neutrino masses in the range of 60$-$75 meV, possibly in the
reach of upcoming galaxy survey experiments. All scenarios can be excluded if
near-future experimental date provide evidence for either neutrinoless
double-beta decay or inverted neutrino mass ordering.Comment: 8 pages, 4 figure

### Neutrino observables from a U(2) flavor symmetry

We study the predictions for CP phases and absolute neutrino mass scale for broad classes of models with a U(2)-like flavor symmetry. For this purpose we consider the same special textures in neutrino and charged lepton mass matrices that are successful in the quark sector. While in the neutrino sector the U(2) structure enforces two texture zeros, the contribution of the charged lepton sector to the Pontecorvo-Maki–Nakagawa–Sakata (PMNS) matrix can be parametrized by two rotation angles. Restricting to the cases where at least one of these angles is small, we obtain three representative scenarios. In all scenarios we obtain a narrow prediction for the sum of neutrino masses in the range of 60–75 meV, possibly in the reach of upcoming galaxy survey experiments. All scenarios can be excluded if near-future experimental date provide evidence for either neutrinoless double-beta decay or inverted neutrino mass ordering

### 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.Comment: 19 pages, 2 figures: minor changes and references added, version
published in JHE

### Relaxing Cosmological Neutrino Mass Bounds with Unstable Neutrinos

At present, cosmological observations set the most stringent bound on the
neutrino mass scale. Within the standard cosmological model ($\Lambda$CDM), the
Planck collaboration reports $\sum m_\nu < 0.12\,\text{eV}$ at 95% CL. This
bound, taken at face value, excludes many neutrino mass models. However,
unstable neutrinos, with lifetimes shorter than the age of the universe
$\tau_\nu \lesssim t_U$, represent a particle physics avenue to relax this
constraint. Motivated by this fact, we present a taxonomy of neutrino decay
modes, categorizing them in terms of particle content and final decay products.
Taking into account the relevant phenomenological bounds, our analysis shows
that 2-body decaying neutrinos into BSM particles are a promising option to
relax cosmological neutrino mass bounds. We then build a simple extension of
the type I seesaw scenario by adding one sterile state $\nu_4$ and a Goldstone
boson $\phi$, in which $\nu_i \to \nu_4 \, \phi$ decays can loosen the neutrino
mass bounds up to $\sum m_\nu \sim 1\,\text{eV}$, without spoiling the light
neutrino mass generation mechanism. Remarkably, this is possible for a large
range of the right-handed neutrino masses, from the electroweak up to the GUT
scale. We successfully implement this idea in the context of minimal neutrino
mass models based on a $U(1)_{\mu-\tau}$ flavor symmetry, which are otherwise
in tension with the current bound on $\sum m_\nu$.Comment: 22 pages, 8 figures, 2 tables, 7 appendices. v2: Matches published
version. Minor upgrades: added appendix on BBN constraints on sterile
neutrinos lighter than active neutrinos, added appendix discussing the
potential amelioration of CMB neutrino decay bounds, refined discussion in
Sec. 3, added discussion on decays within a gauge symmetry in Sec. 4. Results
and conclusions remain unchange

### Summary report of MINSIS workshop in Madrid

Recent developments on tau detection technologies and the construction of
high intensity neutrino beams open the possibility of a high precision search
for non-standard {\mu} - {\tau} flavour transition with neutrinos at short
distances. The MINSIS - Main Injector Non-Standard Interaction Search- is a
proposal under discussion to realize such precision measurement. This document
contains the proceedings of the workshop which took place on 10-11 December
2009 in Madrid to discuss both the physics reach as well as the experimental
requirements for this proposal.Comment: Proceedings of the MINSIS Workshop, Dec 10-11, 2009 in Madrid. 15
pages late

### Neutrinoless double beta decay in seesaw models

We study the general phenomenology of neutrinoless double beta decay in
seesaw models. In particular, we focus on the dependence of the neutrinoless
double beta decay rate on the mass of the extra states introduced to account
for the Majorana masses of light neutrinos. For this purpose, we compute the
nuclear matrix elements as functions of the mass of the mediating fermions and
estimate the associated uncertainties. We then discuss what can be inferred on
the seesaw model parameters in the different mass regimes and clarify how the
contribution of the light neutrinos should always be taken into account when
deriving bounds on the extra parameters. Conversely, the extra states can also
have a significant impact, cancelling the Standard Model neutrino contribution
for masses lighter than the nuclear scale and leading to vanishing neutrinoless
double beta decay amplitudes even if neutrinos are Majorana particles. We also
discuss how seesaw models could reconcile large rates of neutrinoless double
beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published
in JHEP. NME results available in Appendi

### Feebly-Interacting Particles:FIPs 2020 Workshop Report

With the establishment and maturation of the experimental programs searching
for new physics with sizeable couplings at the LHC, there is an increasing
interest in the broader particle and astrophysics community for exploring the
physics of light and feebly-interacting particles as a paradigm complementary
to a New Physics sector at the TeV scale and beyond. FIPs 2020 has been the
first workshop fully dedicated to the physics of feebly-interacting particles
and was held virtually from 31 August to 4 September 2020. The workshop has
gathered together experts from collider, beam dump, fixed target experiments,
as well as from astrophysics, axions/ALPs searches, current/future neutrino
experiments, and dark matter direct detection communities to discuss progress
in experimental searches and underlying theory models for FIPs physics, and to
enhance the cross-fertilisation across different fields. FIPs 2020 has been
complemented by the topical workshop "Physics Beyond Colliders meets theory",
held at CERN from 7 June to 9 June 2020. This document presents the summary of
the talks presented at the workshops and the outcome of the subsequent
discussions held immediately after. It aims to provide a clear picture of this
blooming field and proposes a few recommendations for the next round of
experimental results.Comment: 240 pages, 71 figure