87 research outputs found
Astrophysical Implications of the Induced Neutrino Magnetic Moment from Large Extra Dimensions
Theories involving extra dimensions, a low (TeV) string scale and bulk
singlet neutrinos will produce an effective neutrino magnetic moment which may
be large (< 10^{-11} mu_B). The effective magnetic moment increases with
neutrino energy, and therefore high energy reactions are most useful for
limiting the allowed number of extra dimensions. We examine constraints from
both neutrino-electron scattering and also astrophysical environments. We find
that supernova energy loss considerations require a number of extra dimensions,
n > 1, for an electron neutrino-bulk neutrino Yukawa coupling of order 1.Comment: 12 pages, 3 figures, figure added, references adde
A Study of the Charged Scalar in the Zee Model
An extension of the Zee model involving a light right handed neutrino, nu_R
is considered. We update constraints on couplings between the bilepton scalar,
the active neutrinos, nu_R and the charged leptons. We find that the most
stringent constraint currently comes from measurements limiting the width of
the decay mu -> e gamma. These are used to predict the upper bound on violation
of lepton universality in leptonic W boson decays and rare Z decays, such as Z
-> e mu.Comment: 18 pages, 4 figure
Prospects for obtaining an r-process from Gamma Ray Burst Disk Winds
We discuss the possibility that r-process nucleosynthesis may occur in the
winds from gamma ray burst accretion disks. This can happen if the temperature
of the disk is sufficiently high that electron antineutrinos are trapped as
well as neutrinos. This implies accretion disks with greater than a solar mass
per second accretion rate, although lower accretion rates with higher black
hole spin parameters may provide viable environments as well. Additionally, the
outflow from the disk must either have relatively low entropy, e.g. around s =
10, or the initial acceleration of the wind must be slow enough that it is
neutrino and antineutrino capture as opposed to electron and positron capture
that sets the electron fraction.Comment: 8 pages, submitted to Nucl. Phys. A as part of the Nuclei in Cosmos 8
proceeding
Prospects for Detecting a Neutrino Magnetic Moment with a Tritium Source and Beta-beams
We compare the prospects for detecting a neutrino magnetic moment by the
measurement of neutrinos from a tritium source, reactors and low-energy
beta-beams. In all cases the neutrinos or antineutrinos are detected by
scattering of electrons. We find that a large (20 MCurie) tritium source could
improve the limit on the neutrino magnetic moment significantly, down to the
level of a few while low-energy beta-beams with sufficiently
rapid production of ions could improve the limits to the level of a few . The latter would require ion production at the rate of at least
s.Comment: 6 pages, 3 figure
Two new species of Cyperus (Cyperaceae) from Brazil
Abstract Two new species of Cyperus L. (Cyperaceae), both from Brazil, are described and compared to near relatives. Cyperus hooperae is described from two collections from the Chapada do Veadeiros in the State of Goiás; it is most similar to C. refractus of the southeastern U.S. Cyperus thomasii is described from a single collection from the municipality of Caruaru in Pernambuco; it is most similar to C. granatensis of Colombia. Following IUCN standards, both are considered threatened
Neutrino capture by r-process waiting-point nuclei
We use the Quasiparticle Random Phase Approximation to include the effects of
low-lying Gamow-Teller and first forbidden strength in neutrino capture by very
neutron-rich nuclei with N = 50, 82, or 126. For electron neutrinos in what is
currently considered the most likely r-process site the capture cross sections
are two or more times previous estimates. We briefly discuss the reliability of
our calculations and their implications for nucleosynthesis.Comment: 9 pages, 4 figure
Collective Flavor Oscillations Of Supernova Neutrinos and r-Process Nucleosynthesis
Neutrino-neutrino interactions inside core-collapse supernovae may give rise
to collective flavor oscillations resulting in swap between flavors. These
oscillations depend on the initial energy spectra, and relative fluxes or
relative luminosities of the neutrinos. It has been observed that departure
from energy equipartition among different flavors can give rise to one or more
sharp spectral swap over energy, termed as splits. We study the occurrence of
splits in the neutrino and antineutrino spectra, varying the initial relative
fluxes for different models of initial energy spectrum, in both normal and
inverted hierarchy. These initial relative flux variations give rise to several
possible split patterns whereas variation over different models of energy
spectra give similar results. We explore the effect of these spectral splits on
the electron fraction, , that governs r-process nucleosynthesis inside
supernovae. Since spectral splits modify the electron neutrino and antineutrino
spectra in the region where r-process is postulated to happen, and since the
pattern of spectral splits depends on the initial conditions of the spectra and
the neutrino mass hierarchy, we show that the condition required
for successful r-process nucleosynthesis will lead to constraints on the
initial spectral conditions, for a given neutrino mass hierarchy.Comment: 25 pages, 10 figures, added figure and improved discussion, result
unchanged. Version matches to published version of JCA
Constraints on Large Extra Dimensions with Bulk Neutrinos
We consider right-handed neutrinos propagating in (large) extra
dimensions, whose only coupling to Standard Model fields is the Yukawa coupling
to the left-handed neutrino and the Higgs boson. These theories are attractive
as they can explain the smallness of the neutrino mass, as has already been
shown. We show that if is bigger than two, there are strong
constraints on the radius of the extra dimensions, resulting from the
experimental limit on the probability of an active state to mix into the large
number of sterile Kaluza-Klein states of the bulk neutrino. We also calculate
the bounds on the radius resulting from requiring that perturbative unitarity
be valid in the theory, in an imagined Higgs-Higgs scattering channel.Comment: 24 pages, 4 figures, revtex4. v2: Minor typos corrected, references
adde
Possible Z-width probe of a "brane-world" scenario for neutrino masses
The possibility that the accurately known value of the Z width might furnish
information about the coupling of two neutrinos to the Majoron (Nambu-Goldstone
boson of spontaneous lepton number violation) is proposed and investigated in
detail. Both the "ordinary" case and the case in which one adopts a "brane"
world picture with the Majoron free to travel in extra dimensions are studied.
Bounds on the dimensionless coupling constants are obtained, allowing for any
number of extra dimensions and any intrinsic mass scale. These bounds may be
applied to a variety of different Majoron models. If a technically natural
see-saw model is adopted, the predicted coupling constants are far below these
upper bounds. In addition, for this natural model, the effect of extra
dimensions is to decrease the predicted partial Z width, the increase due to
many Kaluza-Klein excitations being compensated by the decrease of their common
coupling constant.Comment: RevTeX, 12 pages, 3 figure
Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows
Motivated by recent hints for sterile neutrinos from the reactor anomaly, we
study active-sterile conversions in a three-flavor scenario (2 active + 1
sterile families) for three different representative times during the
neutrino-cooling evolution of the proto-neutron star born in an
electron-capture supernova. In our "early model" (0.5 s post bounce), the
nu_e-nu_s MSW effect driven by Delta m^2=2.35 eV^2 is dominated by ordinary
matter and leads to a complete nu_e-nu_s swap with little or no trace of
collective flavor oscillations. In our "intermediate" (2.9 s p.b.) and "late
models" (6.5 s p.b.), neutrinos themselves significantly modify the nu_e-nu_s
matter effect, and, in particular in the late model, nu-nu refraction strongly
reduces the matter effect, largely suppressing the overall nu_e-nu_s MSW
conversion. This phenomenon has not been reported in previous studies of
active-sterile supernova neutrino oscillations. We always include the feedback
effect on the electron fraction Y_e due to neutrino oscillations. In all
examples, Y_e is reduced and therefore the presence of sterile neutrinos can
affect the conditions for heavy-element formation in the supernova ejecta, even
if probably not enabling the r-process in the investigated outflows of an
electron-capture supernova. The impact of neutrino-neutrino refraction is
strong but complicated, leaving open the possibility that with a more complete
treatment, or for other supernova models, active-sterile neutrino oscillations
could generate conditions suitable for the r-process.Comment: 23 pages, including 14 figures and 2 tables (minor changes in the
text). Matches published version in JCA
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