211 research outputs found
Impact of sterile neutrinos on nuclear-assisted cLFV processes
We discuss charged lepton flavour violating processes occurring in the
presence of muonic atoms, such as muon-electron conversion in nuclei
, the (Coulomb enhanced) decay of muonic atoms
into a pair of electrons BR(, N), as well as Muonium
conversion and decay, and .
Any experimental signal of these observables calls for scenarios of physics
beyond the Standard Model. In this work, we consider minimal extensions of the
Standard Model via the addition of sterile fermions, providing the
corresponding complete analytical expressions for all the considered
observables. We first consider an "ad hoc" extension with a single sterile
fermion state, and investigate its impact on the above observables. Two well
motivated mechanisms of neutrino mass generation are then considered: the
Inverse Seesaw embedded into the Standard Model, and the MSM. Our study
reveals that, depending on their mass range and on the active-sterile mixing
angles, sterile neutrinos can give significant contributions to the above
mentioned observables, some of them even lying within present and future
sensitivity of dedicated cLFV experiments. We complete the analysis by
confronting our results to other (direct and indirect) searches for sterile
fermions.Comment: 32 pages, 11 figures. v2: minor revision, matches published version
on JHE
Effect of steriles states on lepton magnetic moments and neutrinoless double beta decay
We address the impact of sterile fermion states on the anomalous magnetic
moment of charged leptons, as well as their contribution to neutrinoless double
beta decays. We illustrate our results in a minimal, effective extension of the
Standard Model by one sterile fermion state, and in a well-motivated framework
of neutrino mass generation, embedding the Inverse Seesaw into the Standard
Model. The simple "3+1" effective case succeeds in alleviating the tension
related to the muon anomalous magnetic moment, albeit only at the 3
level, and for light sterile states (corresponding to a }cosmologically
disfavoured regime). Interestingly, our analysis shows that a future observation does not necessarily imply an inverted hierarchy for the
active neutrinos in this simple extension. Although the Inverse Seesaw
realisation here addressed could indeed ease the tension in , bounds
from lepton universality in kaon decays mostly preclude this from happening.
However, these scenarios can also have a strong impact on the interpretation of
a future signal regarding the hierarchy of the active neutrino
mass spectrum.Comment: 25 pages, 19 figure
Charged lepton flavour violation from low scale seesaw neutrinos
In the work presented here, we have studied the impact of right handed
neutrinos, which are introduced to account for the evidence of neutrino masses,
on charged lepton flavour violating observables. In particular, we have focused
on the loop induced decays of the Z boson into two leptons of different
flavour. We have performed a numerical study of the rates predicted for these
processes within the Inverse Seesaw model, specifically considering scenarios
where transitions are suppressed. Our conclusion, after comparison
with the most relevant experimental constraints, is that branching ratios as
large as can be predicted in the or
channels, together with heavy neutrinos having masses of the TeV order. Such
rates could be accessible at next generation colliders.Comment: 13 pages, 5 figures, 3 tables. Proceedings of the Corfu Summer
Institute 2016 "School and Workshops on Elementary Particle Physics and
Gravity", 31 August - 23 September 2016, Corfu, Greec
Consequences of the Dresden-II reactor data for the weak mixing angle and new physics
The Dresden-II reactor experiment has recently reported a suggestive evidence
for the observation of coherent elastic neutrino-nucleus scattering, using a
germanium detector. Given the low recoil energy threshold, these data are
particularly interesting for a low-energy determination of the weak mixing
angle and for the study of new physics leading to spectral distortions at low
momentum transfer. Using two hypotheses for the quenching factor, we study the
impact of the data on: (i) The weak mixing angle at a renormalization scale of
, (ii) neutrino generalized interactions with light
mediators, (iii) the sterile neutrino dipole portal. The results for the weak
mixing angle show a strong dependence on the quenching factor choice. Although
still with large uncertainties, the Dresden-II data provide for the first time
a determination of at such scale using coherent elastic
neutrino-nucleus scattering data. Tight upper limits are placed on the light
vector, scalar and tensor mediator scenarios. Kinematic constraints implied by
the reactor anti-neutrino flux and the ionization energy threshold allow the
sterile neutrino dipole portal to produce up-scattering events with sterile
neutrino masses up to MeV. In this context, we find that limits are
also sensitive to the quenching factor choice, but in both cases competitive
with those derived from XENON1T data and more stringent that those derived with
COHERENT data, in the same sterile neutrino mass range.Comment: 11 pages, 5 figures. Statistical analysis improved; V3: matches
published version in JHE
Light vector mediators facing XENON1T data
Recently the XENON1T collaboration has released new results on searches for
new physics in low-energy electronic recoils. The data shows an excess over
background in the low-energy tail, particularly pronounced at about keV.
With an exposure of tonne-year, large detection efficiency and energy
resolution, the detector is sensitive as well to solar neutrino backgrounds,
with the most prominent contribution given by neutrinos. We investigate
whether such signal can be explained in terms of new neutrino interactions with
leptons mediated by a light vector particle. We find that the excess is
consistent with this interpretation for vector masses below MeV.
The region of parameter space probed by the XENON1T data is competitive with
constraints from laboratory experiments, in particular GEMMA, Borexino and
TEXONO. However we point out a severe tension with astrophysical bounds and
cosmological observations.Comment: 6 pages, 4 figures. V3: Few typos corrected and one reference added.
Matches version published in PL
Gamma-ray anisotropies from dark matter in the Milky Way: the role of the radial distribution
The annihilation of dark matter particles in the halo of galaxies may end up
into gamma rays, which travel almost unperturbed till to their detection at
Earth. This annihilation signal can exhibit an anisotropic behavior quantified
by the angular power spectrum, whose properties strongly depend on the dark
matter distribution and its clumpiness. We use high resolution pure dark matter
N-body simulations to quantify the contribution of different components (main
halo and satellites) to the global signal as a function of the analytical
profile adopted to describe the numerical results. We find that the smooth main
halo dominates the angular power spectrum of the gamma-ray signal up to quite
large multipoles, where the sub-haloes anisotropy signal starts to emerge, but
the transition multipole strongly depends on the assumed radial profile. The
extrapolation down to radii not resolved by current numerical simulations can
affect both the normalization and the shape of the gamma-ray angular power
spectrum. For the sub-haloes described by an asymptotically cored dark matter
distribution, the angular power spectrum shows an overall smaller normalization
and a flattening at high multipoles. Our results show the criticality of the
dark matter density profile shape in gamma-ray anisotropy searches, and
evaluate quantitatively the intrinsic errors occurring when extrapolating the
dark matter radial profiles down to spatial scales not yet explored by
numerical simulations.Comment: 7 pages, 8 figures. It matches the version published in MNRA
Physics implications of a combined analysis of COHERENT CsI and LAr data
The observation of coherent elastic neutrino nucleus scattering has opened
the window to many physics opportunities. This process has been measured by the
COHERENT Collaboration using two different targets, first CsI and then argon.
Recently, the COHERENT Collaboration has updated the CsI data analysis with a
higher statistics and an improved understanding of systematics. Here we perform
a detailed statistical analysis of the full CsI data and combine it with the
previous argon result. We discuss a vast array of implications, from tests of
the Standard Model to new physics probes. In our analyses we take into account
experimental uncertainties associated to the efficiency as well as the timing
distribution of neutrino fluxes, making our results rather robust. In
particular, we update previous measurements of the weak mixing angle and the
neutron root mean square charge radius for CsI and argon. We also update the
constraints on new physics scenarios including neutrino nonstandard
interactions and the most general case of neutrino generalized interactions, as
well as the possibility of light mediators. Finally, constraints on neutrino
electromagnetic properties are also examined, including the conversion to
sterile neutrino states. In many cases, the inclusion of the recent CsI data
leads to a dramatic improvement of bounds.Comment: 42 pages, 18 Figure
Conservative upper limits on WIMP annihilation cross section from Fermi-LAT -rays
The spectrum of an isotropic extragalactic -ray background (EGB) has
been measured by the Fermi-LAT telescope at high latitudes. Two new models for
the EGB are derived from the subtraction of unresolved point sources and
extragalactic diffuse processes, which could explain from 30% to 70% of the
Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely
due to the annihilation of dark matter (DM) particles in the Galactic halo, we
obtain upper limits on their annihilation cross section \sigmav.
Severe bounds on a possible Sommerfeld enhancement of the annihilation cross
section are set as well. Finally, would {\sigmav} be inversely proportional to
the WIMP velocity, very severe limits are derived for the velocity-independent
part of the annihilation cross section.Comment: Proceedings of XII Taup Conference, Munich, September 201
- …