850 research outputs found
Probing nonstandard lepton number violating interactions in neutrino oscillations
We discuss lepton number violating processes in the context of long-baseline
neutrino oscillations. We summarise and compare neutrino flavour oscillations
in quantum mechanics and quantum field theory, both for standard oscillations
and for those that violate lepton number. When the active neutrinos are
Majorana in nature, the required helicity reversal gives a strong suppression
by the neutrino mass over the energy, . Instead, the
presence of non-standard lepton number violating interactions incorporating
right-handed lepton currents at production or detection alleviate the mass
suppression while also factorising the oscillation probability from the total
rate. Such interactions arise from dimension-six operators in the low energy
effective field theory of the Standard Model. We derive general and simplified
expressions for the lepton number violating oscillation probabilities and use
limits from MINOS and KamLAND to place bounds on the interaction strength in
interplay with the unknown Majorana phases in neutrino mixing. We compare the
bounds with those from neutrinoless double beta decay and other microscopic
lepton number violating processes and outline the requirements for future
short- and long-baseline neutrino oscillation experiments to improve on the
existing bounds.Comment: 33 pages, 9 figure
Probing New Physics with Long-Range Neutrino Interactions: An Effective Field Theory Approach
We investigate forces induced by the exchange of two light neutrinos between
Standard Model (SM) fermions in the presence of effective operators
parametrising physics beyond the SM. We first set up a general framework in
which we derive the long-range potential mediated by weakly interacting
neutrinos in the SM, retaining both spin-independent and spin-dependent terms.
We then derive neutrino-mediated potentials when there are vector, scalar and
tensor non-standard interactions present as well as an exotic neutrino magnetic
moment. Examining the phenomenology of such long-range potentials in atomic
scale laboratory experiments, we derive upper bounds on the Wilson coefficients
of the effective operators and compare these to those from processes such as
charged lepton flavour violation.Comment: 60 pages, 6 figure
Neutrinoless double beta decay via light neutralinos in R-parity violating supersymmetry
We perform a study of neutrinoless double beta (0νββ) decay mediated by the lightest neutralino of arbitrary mass in the minimal supersymmetric Standard Model (MSSM) under the presence of R-parity violating trilinear interactions. In this scenario, the exchange of the lightest neutralino can result in 0νββ decay of either long-range or short-range behaviour, depending on the neutralino mass. Using nuclear matrix elements calculated in the interacting boson model, we use an interpolation between the long- and short-range behaviours with an approximate formula. The non-observation of 0νββ decay is then used to place constraints on the supersymmetry parameter space, compatible with constraints from collider experiments. We compare these constraints to bounds from pion decays, CKM unitarity and big bang nucleosynthesis
Probes of Heavy Sterile Neutrinos
We review probes of heavy sterile neutrinos, focusing on direct experimental
searches and neutrinoless double beta decay. Working in a phenomenological
parametrization, we emphasize the importance of the nature of sterile neutrinos
in interpreting neutrinoless double beta decay searches. While current
constraints on the active-sterile neutrino mixing are already stringent, we
highlight planned future efforts that will probe regimes motivated by the
lightness of active neutrinos
Probing active-sterile neutrino transition magnetic moments with photon emission from CEνNS
In the presence of transition magnetic moments between active and sterile neutrinos, the search for a Primakoff upscattering process at coherent elastic neutrino-nucleus scattering (CEνNS) experiments can provide stringent constraints on the neutrino magnetic moment. We show that a radiative upscattering process with an emitted photon in the final state can induce a novel coincidence signal at
CEνNS experiments that can also probe neutrino transition magnetic moments beyond existing limits. Furthermore, the differential distributions for such a radiative mode can also potentially be sensitive to the Dirac vs Majorana nature of the sterile state mediating the process. This can provide valuable insights into the nature and mass generation mechanism of the light active neutrinos
Probing Active-Sterile Neutrino Transition Magnetic Moments with Photon Emission from CENS
In the presence of transition magnetic moments between active and sterile
neutrinos, the search for a Primakoff upscattering process at coherent elastic
neutrino-nucleus scattering (CENS) experiments can provide stringent
constraints on the neutrino magnetic moment. We show that a radiative
upscattering process with an emitted photon in the final state can induce a
novel coincidence signal at CENS experiments that can also probe neutrino
transition magnetic moments beyond existing limits. Furthermore, the
differential distributions for such a radiative mode can also potentially be
sensitive to the Dirac vs. Majorana nature of the sterile state mediating the
process. This can provide valuable insights into the nature and mass generation
mechanism of the light active neutrinos.Comment: 38 pages, 9 figures; expanded discussion of constraints, matches
published versio
Resting-State Neurophysiological Activity Patterns in Young People with ASD, ADHD, and ASD + ADHD
A functional polymorphism of the brain derived neurotrophic factor gene and cortical anatomy in autism spectrum disorder
Autism Spectrum Disorder (ASD) is associated with both (i) post-mortem and neuroimaging evidence of abnormal cortical development, and (ii) altered signalling in Brain Derived Neurotrophic Factor (BDNF) pathways - which regulate neuroproliferative and neuroplastic processes. In healthy controls genotype at a single nucleotide polymorphism that alters BDNF signalling (Val66met) has been related to regional cortical volume. It is not known however if this influence on brain development is intact in ASD. Therefore we compared the relationship between genotype and cortical anatomy (as measured using in vivo Magnetic Resonance Imaging) in 41 people with ASD and 30 healthy controls. We measured cortical volume, and its two sole determinants - cortical thickness and surface area - which reflect differing neurodevelopmental processes. We found “Group-by-Genotype” interactions for cortical volume in medial (caudal anterior cingulate, posterior cingulate) and lateral (rostral middle, lateral orbitofrontal, pars orbitalis and pars triangularis) frontal cortices. Furthermore, within (only) these regions “Group-by-Genotype” interactions were also found for surface area. No effects were found for cortical thickness in any region. Our preliminary findings suggest that people with ASD have differences from controls in the relationship between BDNF val66met genotype and regional (especially frontal) cortical volume and surface area, but not cortical thickness. Therefore alterations in the relationship between BDNF val66met genotype and surface area in ASD may drive the findings for volume. If correct, this suggests ASD is associated with a distorted relationship between BDNF val66met genotype and the determinants of regional cortical surface area – gyrification and/or sulcal positioning
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