49 research outputs found
Late-time vacuum phase transitions: Connecting sub-eV scale physics with cosmological structure formation
We show that a particular class of postrecombination phase transitions in the
vacuum can lead to localized overdense regions on relatively small scales,
roughly 10^6 to 10^10 M_sun, potentially interesting for the origin of large
black hole seeds and for dwarf galaxy evolution. Our study suggests that this
mechanism could operate over a range of conditions which are consistent with
current cosmological and laboratory bounds. One byproduct of phase transition
bubble-wall decay may be extra radiation energy density. This could provide an
avenue for constraint, but it could also help reconcile the discordant values
of the present Hubble parameter (H_0) and sigma_8 obtained by cosmic microwave
background (CMB) fits and direct observational estimates. We also suggest ways
in which future probes, including CMB considerations (e.g., early dark energy
limits), 21-cm observations, and gravitational radiation limits, could provide
more stringent constraints on this mechanism and the sub-eV scale
beyond-standard-model physics, perhaps in the neutrino sector, on which it
could be based. Late phase transitions associated with sterile neutrino mass
and mixing may provide a way to reconcile cosmological limits and laboratory
data, should a future disagreement arise.Comment: 17 pages, 18 figures. v2: includes additional references and minor
corrections/clarifications. v3: includes additional text, figures, and
references (matches published version
Neutrino Flavor Evolution in Neutron Star Mergers
We examine the flavor evolution of neutrinos emitted from the disk-like
remnant (hereafter called \lq\lq neutrino disk\rq\rq) of a binary neutron star
(BNS) merger. We specifically follow the neutrinos emitted from the center of
the disk, along the polar axis perpendicular to the equatorial plane. We
carried out two-flavor simulations using a variety of different possible
initial neutrino luminosities and energy spectra, and for comparison,
three-flavor simulations in specific cases. In all simulations, the normal
neutrino mass hierarchy was used. The flavor evolution was found to be highly
dependent on the initial neutrino luminosities and energy spectra; in
particular, we found two broad classes of results depending on the sign of the
initial net electron neutrino lepton number (i.e., the number of neutrinos
minus the number of antineutrinos). In the antineutrino dominated case, we
found that the Matter-Neutrino Resonance (MNR) effect dominates, consistent
with previous results, whereas in the neutrino dominated case, a bipolar
spectral swap develops. The neutrino dominated conditions required for this
latter result have been realized, e.g, in a BNS merger simulation that employs
the \lq\lq DD2\rq\rq\ equation of state for neutron star matter[Phys. Rev. D
93, 044019 (2016)]. For this case, in addition to the swap at low energies, a
collective Mikheyev-Smirnov-Wolfenstein (MSW) mechanism generates a high-energy
electron neutrino tail. The enhanced population of high-energy electron
neutrinos in this scenario could have implications for the prospects of
-process nucleosynthesis in the material ejected outside the plane of the
neutrino disk.Comment: Version published in Physical Review D. 22 pages, 16 figures, 9
tables. For movies see Ancillary files in version
Treatment of trigeminal ganglion neurons in vitro with NGF, GDNF or BDNF: effects on neuronal survival, neurochemical properties and TRPV1-mediated neuropeptide secretion
BACKGROUND: Nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) all play important roles in the development of the peripheral sensory nervous system. Additionally, these growth factors are proposed to modulate the properties of the sensory system in the adult under pathological conditions brought about by nerve injury or inflammation. We have examined the effects of NGF, GDNF and BDNF on adult rat trigeminal ganglion (TG) neurons in culture to gain a better understanding of how these growth factors alter the cytochemical and functional phenotype of these neurons, with special attention to properties associated with nociception. RESULTS: Compared with no growth factor controls, GDNF, at 1 and 100 ng/ml, significantly increased by nearly 100% the number of neurons in culture at 5 days post-plating. A significant, positive, linear trend of increasing neuron number as a function of BDNF concentration was observed, also peaking at nearly 100%. NGF treatment was without effect. Chronic treatment with NGF and GDNF significantly and concentration-dependently increased 100 nM capsaicin (CAP)-evoked calcitonin gene-related peptide (CGRP) release, reaching approximately 300% at the highest concentration tested (100 ng/ml). Also, NGF and GDNF each augmented anandamide (AEA)- and arachidonyl-2-chloroethylamide (ACEA)-evoked CGRP release, while BDNF was without effect. Utilizing immunohistochemistry to account for the proportions of TRPV1- or CGRP-positive neurons under each growth factor treatment condition and then standardizing evoked CGRP release to these proportions, we observed that NGF was much more effective in enhancing CAP- and 50 mM K(+)-evoked CGRP release than was GDNF. Furthermore, NGF and GDNF each altered the concentration-response function for CAP- and AEA-evoked CGRP release, increasing the E(max )without altering the EC(50 )for either compound. CONCLUSIONS: Taken together, our results illustrate that NGF, GDNF and BDNF differentially alter TG sensory neuron survival, neurochemical properties and TRPV1-mediated neuropeptide release in culture. In particular, our findings suggest that GDNF and NGF differentially modulate TRPV1-mediated neuropeptide secretion sensitivity, with NGF having a much greater effect on a per neuron basis than GDNF. These findings are discussed in relation to possible therapeutic roles for growth factors or their modulators in pathological pain states, especially as these relate to the trigeminal system
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