193 research outputs found
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
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
Neutrino masses from operator mixing
We show that in theories that reduce, at the Fermi scale, to an extension of
the standard model with two doublets, there can be additional dimension five
operators giving rise to neutrino masses. In particular there exists a singlet
operator which can not generate neutrino masses at tree level but generates
them through operator mixing. Under the assumption that only this operator
appears at tree level we calculate the neutrino mass matrix. It has the Zee
mass matrix structure and leads naturally to bimaximal mixing. However, the
maximal mixing prediction for solar neutrinos is very sharp even when higher
order corrections are considered. To allow for deviations from maximal mixing a
fine tuning is needed in the neutrino mass matrix parameters. However, this
fine tuning relates the departure from maximal mixing in solar neutrino
oscillations with the neutrinoless double beta decay rate.Comment: 11 pages, 1 figure, revte
Neutrino Masses and Lepton Flavour Violation in Thick Brane Scenarios
We address the issue of lepton flavour violation and neutrino masses in the
``fat-brane'' paradigm, where flavour changing processes are suppressed by
localising different fermion field wave-functions at different positions (in
the extra dimensions) in a thick brane. We study the consequences of
suppressing lepton number violating charged lepton decays within this scenario
for lepton masses and mixing angles. In particular, we find that charged lepton
mass matrices are constrained to be quasi-diagonal. We further consider whether
the same paradigm can be used to naturally explain small Dirac neutrino masses
by considering the existence of three right-handed neutrinos in the brane, and
discuss the requirements to obtain phenomenologically viable neutrino masses
and mixing angles. Finally, we examine models where neutrinos obtain a small
Majorana mass by breaking lepton number in a far away brane and show that, if
the fat-brane paradigm is the solution to the absence of lepton number
violating charged lepton decays, such models predict, in the absence of flavour
symmetries, that charged lepton flavour violation will be observed in the next
round of rare muon/tau decay experiments.Comment: 33 pages, 9 eps figure
Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters
Empirical evidence for both stellar mass black holes M_bh<10^2 M_sun) and
supermassive black holes (SMBHs, M_bh>10^5 M_sun) is well established.
Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is
correlated with the bulge mass, and even more strongly with the central stellar
velocity dispersion sigma_c, the `M-sigma' relation. On the other hand,
evidence for "intermediate-mass" black holes (IMBHs, with masses in the range
1^2 - 10^5 M_sun) is relatively sparse, with only a few mass measurements
reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We
explore the question of whether globular clusters extend the M-sigma
relationship for galaxies to lower black hole masses and find that available
data for globular clusters are consistent with the extrapolation of this
relationship. We use this extrapolated M-sigma relationship to predict the
putative black hole masses of those globular clusters where existence of
central IMBH was proposed. We discuss how globular clusters can be used as a
constraint on theories making specific predictions for the low-mass end of the
M-sigma relation.Comment: 14 pages, 3 figures, accepted for publication in Astrophysics and
Space Science; fixed typos and a quote in Sec.
Recent Progress on Anomalous X-ray Pulsars
I review recent observational progress on Anomalous X-ray Pulsars, with an
emphasis on timing, variability, and spectra. Highlighted results include the
recent timing and flux stabilization of the notoriously unstable AXP 1E
1048.1-5937, the remarkable glitches seen in two AXPs, the newly recognized
variety of AXP variability types, including outbursts, bursts, flares, and
pulse profile changes, as well as recent discoveries regarding AXP spectra,
including their surprising hard X-ray and far-infrared emission, as well as the
pulsed radio emission seen in one source. Much has been learned about these
enigmatic objects over the past few years, with the pace of discoveries
remaining steady. However additional work on both observational and theoretical
fronts is needed before we have a comprehensive understanding of AXPs and their
place in the zoo of manifestations of young neutron stars.Comment: 10 pages, 6 figures; to appear in proceedings of the conference
"Isolated Neutron Stars: From the Interior to the Surface" eds. S. Zane, R.
Turolla, D. Page; Astrophysics & Space Science in pres
Neutrinoless Double Beta Decay from Singlet Neutrinos in Extra Dimensions
We study the model-building conditions under which a sizeable
-decay signal to the recently reported level of~0.4 eV is due
to Kaluza--Klein singlet neutrinos in theories with large extra dimensions. Our
analysis is based on 5-dimensional singlet-neutrino models compactified on an
orbifold, where the Standard--Model fields are localized on a
3-brane. We show that a successful interpretation of a positive signal within
the above minimal 5-dimensional framework would require a non-vanishing shift
of the 3-brane from the orbifold fixed points by an amount smaller than the
typical scale (100 MeV) characterizing the Fermi nuclear momentum. The
resulting 5-dimensional models predict a sizeable effective Majorana-neutrino
mass that could be several orders of magnitude larger than the light neutrino
masses. Most interestingly, the brane-shifted models with only one bulk sterile
neutrino also predict novel trigonometric textures leading to mass scenarios
with hierarchical active neutrinos and large - and
- mixings that can fully explain the current atmospheric and
solar neutrino data.Comment: 33 pages, LaTeX, minor rewordings, references adde
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
Gamma-Ray Pulsar Bonanza
Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but were first detected at other wavelengths (see the Perspective by
Halpern
). Using the Fermi Gamma-Ray Space Telescope,
Abdo
et al.
(p.
840
, published online 2 July; see the cover) report the detection of 16 previously unknown pulsars based on their gamma-ray emission alone. Thirteen of these coincide with previously unidentified gamma-ray sources, solving the 30-year-old mystery of their identities. Pulsars are fast-rotating neutron stars. With time they slow down and cease to radiate; however, if they are in a binary system, they can have their spin rates increased by mass transfer from their companion stars, starting a new life as millisecond pulsars. In another study,
Abdo
et al.
(p.
845
) report the detection of gamma-ray emission from the globular cluster 47 Tucanae, which is coming from an ensemble of millisecond pulsars in the cluster's core. The data imply that there are up to 60 millisecond pulsars in 47 Tucanae, twice as many as predicted by radio observations. In a further companion study,
Abdo
et al.
(p.
848
, published online 2 July) searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars outside of stellar clusters, finding gamma-ray pulsations for eight of them. Their properties resemble those of other gamma-ray pulsars, suggesting that they share the same basic emission mechanism. Indeed, both sets of pulsars favor emission models in which the gamma rays are produced in the outer magnetosphere of the neutron star
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