Gabriela Barenboim

Theory of neutrinos: a white paper

This paper is a review of the present status of neutrino mass physics, which grew out of an APS sponsored study of neutrinos in 2004. After a discussion of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, it summarizes what can be learned about neutrino interactions as well as the nature of new physics beyond the Standard Model from the various proposed neutrino experiments. The intriguing possibility that neutrino mass physics may be at the heart of our understanding of a long standing puzzle of cosmology, i.e. the origin of matter?antimatter asymmetry is also discussed.

Neutrinos as the messengers of CPT violation

CPT violation has the potential to explain all three existing neutrino anomalies without enlarging the neutrino sector. CPT violation in the Dirac mass terms of the three neutrino flavors preserves on-shell Lorentz invariance, but generates independent masses for neutrinos and antineutrinos. This specific signature is strongly motivated by braneworld scenarios with extra dimensions, where neutrinos are the natural messengers for Standard Model physics of CPT violation in the bulk. A simple model of maximal CPT violation is sufficient to explain the existing neutrino data quite neatly, while making dramatic predictions for the KamLAND and MiniBooNE experiments. We obtain a promising and economical new mechanism for electroweak baryogenesis.

Non-decoupling of heavy neutrinos and lepton flavour violation

We consider a class of models predicting new heavy neutral fermionic states, whose mixing with the light neutrinos can be naturally significant and produce observable effects below the threshold for their production. We update the indirect limits on the flavour non-diagonal mixing parameters that can be derived from unitarity, and show that significant rates are in general expected for one-loop-induced rare processes due to the exchange of virtual heavy neutrinos, involving the violation of the muon and electron lepton numbers. In particular, the amplitudes for μ-e conversion in nuclei and for μ → ee+e− show a non-decoupling quadratic dependence on the heavy neutrino mass M, while μ → eγ is almost independent of the heavy scale above the electroweak scale. These three processes are then used to set stringent constraints on the flavour-violating mixing angles. In all the cases considered, we point out explicitly that the non-decoupling behaviour is strictly related to the spontaneous breaking of the SU(2) symmetry.

A model of CPT violation for neutrinos

Abstract Any local relativistic quantum field theory of Dirac–Weyl fermions conserves CPT. Here we examine whether a simple nonlocal field theory can violate CPT. We construct a new relativistic field theory of fermions, which we call “homeotic”, which is nonlocal but causal and Lorentz invariant. The free homeotic theory is in fact equivalent to free Dirac theory. We show that a homeotic theory with a suitable nonlocal four-fermion interaction is causal and as a result has a well-defined perturbative S -matrix. By coupling a right-handed homeotic fermion to a left-handed Dirac–Weyl fermion, we obtain a causal theory of CPT-violating neutrino oscillations.

Neutrino observatories can characterize cosmic sources and neutrino properties

Neutrino telescopes that measure relative fluxes of ultrahigh-energy

Neutrinos that violate CPT, and the experiments that love them

\nu_{e}, \nu_{\mu}, \nu_{\tau}

CPT violation and the nature of neutrinos

can give information about the location and characteristics of sources, about neutrino mixing, and can test for neutrino instability and for departures from CPT invariance in the neutrino sector. We investigate consequences of neutrino mixing for the neutrino flux arriving at Earth, and consider how terrestrial measurements can characterize distant sources. We contrast mixtures that arise from neutrino oscillations with those signaling neutrino decays. We stress the importance of measuring

CPT violating decoherence and LSND: a possible window to planck scale physics

\nu_{e}, \nu_{\mu}, \nu_{\tau}

Prospects for constraining the shape of non-Gaussianity with the scale-dependent bias

fluxes in neutrino observatories.

Decoherent neutrino mixing, dark energy, and matter-antimatter asymmetry

Recently we proposed a framework for explaining the observed evidence for neutrino oscillations without enlarging the neutrino sector, by introducing CPT violating Dirac masses for the neutrinos. In this paper we continue the exploration of the phenomenology of CPT violation in the neutrino sector. We show that our CPT violating model fits the existing SuperKamiokande data at least as well as the standard atmospheric neutrino oscillation models. We discuss the challenge of measuring CP violation in a neutrino sector that also violates CPT. We point out that the proposed off-axis extension of MINOS looks especially promising in this regard. Finally, we describe a method to compute CPT violating neutrino effects by mocking them up with analog matter effects.Abstract Recently we proposed a framework for explaining the observed evidence for neutrino oscillations without enlarging the neutrino sector, by introducing CPT -violating Dirac masses for the neutrinos. In this Letter we continue the exploration of the phenomenology of CPT violation in the neutrino sector. We show that our CPT -violating model fits the existing SuperKamiokande data at least as well as the standard atmospheric neutrino oscillation models. We discuss the challenge of measuring CP violation in a neutrino sector that also violates CPT . We point out that the proposed off-axis extension of MINOS looks especially promising in this regard. Finally, we describe a method to compute CPT -violating neutrino effects by mocking them up with analog matter effects.