33 research outputs found
Quantum Coherence of Relic Neutrinos
We argue that in at least a portion of the history of the universe the relic
background neutrinos are spatially-extended, coherent superpositions of mass
states. We show that an appropriate quantum mechanical treatment affects the
neutrino mass values derived from cosmological data. The coherence scale of
these neutrino flavor wavepackets can be an appreciable fraction of the causal
horizon size, raising the possibility of spacetime curvature-induced
decoherence.Comment: 4 pages, 4 figures; matches publication in PR
Neutrino Burst-Generated Gravitational Radiation From Collapsing Supermassive Stars
We estimate the gravitational radiation signature of the electron/positron
annihilation-driven neutrino burst accompanying the asymmetric collapse of an
initially hydrostatic, radiation-dominated supermassive object suffering the
Feynman-Chandrasekhar instability. An object with a mass
, with primordial metallicity, is
an optimal case with respect to the fraction of its rest mass emitted in
neutrinos as it collapses to a black hole: lower initial mass objects will be
subject to scattering-induced neutrino trapping and consequently lower
efficiency in this mode of gravitational radiation generation; while higher
masses will not get hot enough to radiate significant neutrino energy before
producing a black hole. The optimal case collapse will radiate several percent
of the star's rest mass in neutrinos and, with an assumed small asymmetry in
temperature at peak neutrino production, produces a characteristic linear
memory gravitational wave burst signature. The timescale for this signature,
depending on redshift, is to , optimal for proposed
gravitational wave observatories like DECIGO. Using the response of that
detector, and requiring a signal-to-noise ratio SNR 5, we estimate that
collapse of a supermassive star could produce a
neutrino burst-generated gravitational radiation signature detectable to
redshift . With the envisioned ultimate DECIGO design sensitivity,
we estimate that the linear memory signal from these events could be detectable
with SNR to .Comment: 15 pages, 8 figure
Neutrino-Accelerated Hot Hydrogen Burning
We examine the effects of significant electron anti-neutrino fluxes on
hydrogen burning. Specifically, we find that the bottleneck weak nuclear
reactions in the traditional pp-chain and the hot CNO cycle can be accelerated
by anti-neutrino capture, increasing the energy generation rate. We also
discuss how anti-neutrino capture reactions can alter the conditions for break
out into the rp-process. We speculate on the impact of these considerations for
the evolution and dynamics of collapsing very- and super- massive compact
objects.Comment: 14 pages, 6 figures, submitted to ApJ; minor content chang
Heavy sterile neutrinos, entropy and relativistic energy production, and the relic neutrino background
We explore the implications of the existence of heavy neutral fermions (i.e.,
sterile neutrinos) for the thermal history of the early universe. In
particular, we consider sterile neutrinos with rest masses in the 100 MeV to
500 MeV range, with couplings to ordinary active neutrinos large enough to
guarantee thermal and chemical equilibrium at epochs in the early universe with
temperatures T > 1 GeV, but in a range to give decay lifetimes from seconds to
minutes. Such neutrinos would decouple early, with relic densities comparable
to those of photons, but decay out of equilibrium, with consequent prodigious
entropy generation prior to, or during, Big Bang Nucleosynthesis (BBN). Most of
the ranges of sterile neutrino rest mass and lifetime considered are at odds
with Cosmic Microwave Background (CMB) limits on the relativistic particle
contribution to energy density (e.g., as parameterized by N_eff). However, some
sterile neutrino parameters can lead to an acceptable N_eff. These parameter
ranges are accompanied by considerable dilution of the ordinary background
relic neutrinos, possibly an adverse effect on BBN, but sometimes fall in a
range which can explain measured neutrino masses in some particle physics
models. A robust signature of these sterile neutrinos would be a measured N_eff
not equal to 3 coupled with no cosmological signal for neutrino rest mass when
the detection thresholds for these probes are below laboratory-established
neutrino mass values, either as established by the atmospheric neutrino
oscillation scale or direct measurements with, e.g., KATRIN or neutrino-less
double beta decay experiments.Comment: 18 pages, 12 figure
Lepton Number-Driven Sterile Neutrino Production in the Early Universe
We examine medium-enhanced, neutrino scattering-induced decoherent production
of dark matter candidate sterile neutrinos in the early universe. In cases with
a significant net lepton number we find two resonances, where the effective
in-medium mixing angles are large. We calculate the lepton number
depletion-driven evolution of these resonances. We describe the dependence of
this evolution on lepton numbers, sterile neutrino rest mass, and the
active-sterile vacuum mixing angle. We find that this resonance evolution can
result in relic sterile neutrino energy spectra with a generic form which is
sharply peaked in energy. We compare our complete quantum kinetic equation
treatment with the widely-used quantum Zeno ansatz.Comment: 15 pages, 7 figures; matches published versio
Exploring resonantly produced mixed sterile neutrino dark matter models
An unidentified 3.55 keV X-ray line in stacked spectra of galaxies and
clusters raises the interesting possibility that it originates from the decay
of sterile neutrino dark matter. In this work, we explore mixed sterile
neutrino dark matter models that combine cold dark matter and warmer sterile
neutrino dark matter produced through lepton number-driven active-to-sterile
neutrino transformation. We analyze the sensitivity of the sterile neutrino
spectra on active-sterile mixing and on initial neutrino lepton numbers.
Furthermore, we assess the viability of these models with estimates of the
number of subhalos formed as the host sites of satellite galaxies.Comment: 10 pages, 12 figure
Coherent Active-Sterile Neutrino Flavor Transformation in the Early Universe
We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein (MSW) resonant
active-to-sterile neutrino flavor conversion driven by an initial lepton number
in the early universe. We find incomplete destruction of lepton number in this
process and a sterile neutrino energy distribution with a distinctive cusp and
high energy tail. These features imply alteration of the non-zero lepton number
primordial nucleosynthesis paradigm when there exist sterile neutrinos with
rest masses ~ 1 eV. This could result in better light element probes of
(constraints on) these particles.Comment: 4 pages, 3 figures, matches version printed in PR
Diluted equilibrium sterile neutrino dark matter
We present a model where sterile neutrinos with rest masses in the range ~
keV to ~ MeV can be the dark matter and be consistent with all laboratory,
cosmological, large-scale structure, as well as x-ray constraints. These
sterile neutrinos are assumed to freeze out of thermal and chemical equilibrium
with matter and radiation in the very early Universe, prior to an epoch of
prodigious entropy generation ("dilution") from out-of-equilibrium decay of
heavy particles. In this work, we consider heavy, entropy-producing particles
in the ~ TeV to ~ EeV rest-mass range, possibly associated with new physics at
high-energy scales. The process of dilution can give the sterile neutrinos the
appropriate relic densities, but it also alters their energy spectra so that
they could act like cold dark matter, despite relatively low rest masses as
compared to conventional dark matter candidates. Moreover, since the model does
not rely on active-sterile mixing for producing the relic density, the mixing
angles can be small enough to evade current x-ray or lifetime constraints.
Nevertheless, we discuss how future x-ray observations, future lepton number
constraints, and future observations and sophisticated simulations of
large-scale structure could, in conjunction, provide evidence for this model
and/or constrain and probe its parameters.Comment: 15 pages, 6 figures. v2: changes in text and figures; matches
published versio