The production of heavy sterile neutrinos from π − , K − decay at rest yields charged leptons with negative helicity (positive for π + , K + ). We obtain the branching ratio for this process and argue that a Stern-Gerlach filter with a magnetic field gradient leads to spatially separated domains of both helicity components with abundances determined by the branching ratio. Complemented with a search of the monochromatic peak, this setup can yield both the mass and mixing angles for sterile neutrinos with masses in the range 3 MeV m s 414 MeV in next generation high intensity experiments. We also study oscillations of light Dirac and Majorana sterile neutrinos with m s ≃ eV produced in meson decays including decoherence aspects arising from lifetime effects of the decaying mesons and the stopping distance of the charged lepton in short baseline experiments. We obtain the transition probability from production to detection via charged current interactions including these decoherence effects for 3 + 1 and 3 + 2 scenarios, also studying |∆L| = 2 transitions from ν ↔ ν oscillations for Majorana neutrinos and the impact of these effects on the determination of CP-violating amplitudes. We argue that decoherence effects are important in current short baseline accelerator experiments, leading to an underestimate of masses, mixing and CP-violating angles. At MiniBooNE/SciBooNE we estimate that these effects lead to an ∼ 15% underestimate for sterile neutrino masses m s 3 eV. We argue that reactor and current short baseline accelerator experiments are fundamentally different and suggest that in future high intensity experiments with neutrinos produced from π, K decay at rest, stopping the charged leptons on distances much smaller than the decay length of the parent meson suppresses considerably these decoherence effects.

The decay of a parent particle into two or more daughter particles results in an entangled quantum state as a consequence of conservation laws in the decay process. Recent experiments at Belle and BaBar take advantage of quantum entanglement and the correlations in the time evolution of the product particles to study CP and T violations. If one (or more) of the product particles are not observed, their degrees of freedom are traced out of the pure state density matrix resulting from the decay, leading to a mixed state density matrix and an entanglement entropy. This entropy is a measure of the loss of information present in the original quantum correlations of the entangled state. We use the Wigner-Weisskopf method to construct an approximation to this state that evolves in time in a {\em manifestly unitary} way. We then obtain the entanglement entropy from the reduced density matrix of one of the daughter particles obtained by tracing out the unobserved states, and follow its time evolution. We find that it grows over a time scale determined by the lifetime of the parent particle to a maximum, which when the width of the parent particle is narrow, describes the phase space distribution of maximally entangled Bell-like states. The method is generalized to the case in which the parent particle is described by a wave packet localized in space. Possible experimental avenues to measure the entanglement entropy in the decay of mesons at rest are discussed.Comment: Discussion on wavepackets and experimental measurement. 20 pages, 2 fig

We study the production of sterile neutrinos in the early universe from π → lν s shortly after the QCD phase transition in the absence of a lepton asymmetry while including finite temperature corrections to the π mass and decay constant f π . Sterile neutrinos with masses 1M eV produced via this mechanism freeze-out at T f ≃ 10M eV with a distribution function that is highly nonthermal and features a sharp enhancement at low momentum thereby making this species cold even for very light masses. Dark matter abundance constraints from the CMB and phase space density constraints from the most dark matter dominated dwarf spheroidal galaxies provide upper and lower bounds respectively on combinations of mass and mixing angles. For π → µν s , the bounds lead to a narrow region of compatibility with the latest results from the 3.55KeV line. The non-thermal distribution function leads to free-streaming lengths (today) in the range of ∼ few kpc consistent with the observation of cores in dwarf galaxies. For sterile neutrinos with mass 1eV that are produced by this reaction, the most recent accelerator and astrophysical bounds on U ls combined with the non-thermal distribution function suggests a substantial contribution from these sterile neutrinos to N ef f .

If the large scale anomalies in the temperature power spectrum of the cosmic microwave background are of primordial origin, they may herald modifications to the slow roll inflationary paradigm on the largest scales. We study the possibility that the origin of the large scale power suppression is a modification of initial conditions during slow roll as a result of a pre-slow roll phase during which the inflaton evolves rapidly. This stage is manifest in a potential in the equations for the Gaussian fluctuations during slow roll and modify the power spectra of scalar perturbations via an initial condition transfer function T (k). We provide a general analytical study of its large and small scale properties and analyze the impact of these initial conditions on the infrared aspects of typical test scalar fields. The infrared behavior of massless minimally coupled test scalar field theories leads to the dynamical generation of mass and anomalous dimensions, both depend non-analytically on T (0). During inflation all quanta decay into many quanta even of the same field because of the lack of kinematic thresholds. The decay leads to a quantum entangled state of sub and superhorizon quanta with correlations across the horizon. We find the modifications of the decay width and the entanglement entropy from the initial conditions. In all cases, initial conditions from a "fast-roll" stage that lead to a suppression in the scalar power spectrum at large scales also result in a suppression of the dynamically generated masses, anomalous dimensions and decay widths.

We study non-perturbatively the time evolution of cascade decay for generic fields π ϕϕ ϕ χχ → → 1 2 1 2 2 1 2 . In the opposite limit the population of resonances (ϕ 1 ) does not build up substantially and the cascade decay proceeds almost directly from the initial parent to the final state without resulting in a large amplitude of the resonant state. An alternative but equivalent non-perturbative method useful in cosmology is presented. Possible phenomenological implications for heavy sterile neutrinos as resonant states and consequences of quantum entanglement and correlations in the final state are discussed.