2,472 research outputs found
The rp-Process in Neutrino-driven Winds
Recent hydrodynamic simulations of core-collapse supernovae with accurate
neutrino transport suggest that the bulk of the early neutrino-heated ejecta is
proton rich, in which the production of some interesting proton-rich nuclei is
expected. As suggested in recent nucleosynthesis studies, the rapid
proton-capture (rp) process takes place in such proton-rich environments by
bypassing the waiting point nuclei with the beta-lives of a few minutes via the
faster capture of neutrons continuously supplied from the neutrino absorption
by protons. In this study, the nucleosynthesis calculations are performed with
the wide ranges of the neutrino luminosities and the electron fractions (Ye),
using the semi-analytic models of proto-neutron star winds. The masses of
proto-neutron stars are taken to be 1.4 Msolar and 2.0 Msolar, where the latter
is regarded as the test for somewhat high entropy winds (about a factor of
two). For Ye > 0.52, the neutrino-induced rp-process takes place in many wind
trajectories, and the p-nuclei up to A ~ 130 are synthesized with interesting
amounts. However, 92Mo is somewhat underproduced compared to those with similar
mass numbers. For 0.46 < Ye < 0.49, on the other hand, 92Mo is significantly
enhanced by the nuclear flows in the vicinity of the abundant 90Zr that
originates from the alpha-process at higher temperature. The nucleosynthetic
yields are averaged over the ejected masses of winds, and further the Ye
distribution predicted by the recent hydrodynamic simulation of a core-collapse
supernova. Comparison of the mass-Ye-averaged yields to the solar compositions
implies that the neutrino-driven winds can be potentially the origin of light
p-nuclei up to A ~ 110, including 92,94Mo and 96,98Ru that cannot be explained
by other astrophysical sites.Comment: 29 pages, 18 figures, accepted for publication in Ap
The retina visual cycle is driven by cis retinol oxidation in the outer segments of cones
Vertebrate rod and cone photoreceptors require continuous supply of chromophore for regenerating their visual pigments after photoactivation. Cones, which mediate our daytime vision, demand a particularly rapid supply of 11-cis retinal chromophore in order to maintain their function in bright light. An important contribution to this process is thought to be the chromophore precursor 11-cis retinol, which is supplied to cones from Müller cells in the retina and subsequently oxidized to 11-cis retinal as part of the retina visual cycle. However, the molecular identity of the cis retinol oxidase in cones remains unclear. Here, as a first step in characterizing this enzymatic reaction, we sought to determine the subcellular localization of this activity in salamander red cones. We found that the onset of dark adaptation of isolated salamander red cones was substantially faster when exposing directly their outer vs. their inner segment to 9-cis retinol, an analogue of 11-cis retinol. In contrast, this difference was not observed when treating the outer vs. inner segment with 9-cis retinal, a chromophore analogue which can directly support pigment regeneration. These results suggest, surprisingly, that the cis-retinol oxidation occurs in the outer segments of cone photoreceptors. Confirming this notion, pigment regeneration with exogenously added 9-cis retinol was directly observed in the truncated outer segments of cones, but not in rods. We conclude that the enzymatic machinery required for the oxidation of recycled cis retinol as part of the retina visual cycle is present in the outer segments of cones
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Spectral cues are necessary to encode azimuthal auditory space in the mouse superior colliculus.
Sound localization plays a critical role in animal survival. Three cues can be used to compute sound direction: interaural timing differences (ITDs), interaural level differences (ILDs) and the direction-dependent spectral filtering by the head and pinnae (spectral cues). Little is known about how spectral cues contribute to the neural encoding of auditory space. Here we report on auditory space encoding in the mouse superior colliculus (SC). We show that the mouse SC contains neurons with spatially-restricted receptive fields (RFs) that form an azimuthal topographic map. We found that frontal RFs require spectral cues and lateral RFs require ILDs. The neurons with frontal RFs have frequency tunings that match the spectral structure of the specific head and pinna filter for sound coming from the front. These results demonstrate that patterned spectral cues in combination with ILDs give rise to the topographic map of azimuthal auditory space
Coherent versus non-coherent decode-and-forward relaying aided cooperative space-time shift keying
Motivated by the recent concept of Space-Time Shift Keying (STSK), we propose a novel cooperative STSK family, which is capable of achieving a flexible rate-diversity tradeoff, in the context of cooperative space-time transmissions. More specifically, we first propose a Coherent cooperative STSK (CSTSK) scheme, where each Relay Node (RN) activates Decode-and-Forward (DF) transmissions, depending on the success or failure of Cyclic Redundancy Checking (CRC). We invoke a bitto- STSK mapping rule, where according to the input bits, one of the Q pre-assigned dispersion vectors is activated to implicitly convey log2(Q) bits, which are transmitted in combination with the classic log2(L)-bit modulated symbol. Additionally, we introduce a beneficial dispersion vector design, which enables us to dispense with symbol-level Inter-Relay Synchronization (IRS). Furthermore, the Destination Node (DN) is capable of jointly detecting the signals received from the source-destination and relay-destination links, using a low-complexity single-stream-based Maximum Likelihood (ML) detector, which is an explicit benefit of our Inter-Element Interference (IEI)-free system model. More importantly, as a benefit of its design flexibility, our cooperative CSTSK arrangement enables us to adapt the number of the RNs, the transmission rate as well as the achievable diversity order. Moreover, we also propose a Differentially-encoded cooperative STSK (DSTSK) arrangement, which dispenses with CSI estimation at any of the nodes, while retaining the fundamental benefits of the cooperative CSTSK scheme
Holographic QCD Integrated back to Hidden Local Symmetry
We develop a previously proposed gauge-invariant method to integrate out
infinite tower of Kaluza-Klein (KK) modes of vector and axialvector mesons in a
class of models of holographic QCD (HQCD). The HQCD is reduced by our method to
the chiral perturbation theory with the hidden local symmetry (HLS) having only
the lowest KK mode identified as the HLS gauge boson. We take the
Sakai-Sugimoto model as a concrete HQCD, and completely determine the terms as well as the terms from the DBI part and the
anomaly-related (intrinsic parity odd) gauge-invariant terms from the CS part.
Effects of higher KK modes are fully included in these terms. To demonstrate
power of our method, we compute momentum-dependences of several form factors
such as the pion electromagnetic form factors, the - and
- transition form factors compared with experiment, which was
not achieved before due to complication to handle infinite sums. We also study
other anomaly-related quantities like --- and
--- vertex functions.Comment: 4 eps figures, 37 pages, latex, typos fixed; some discussions and
references added; fig.4 replace
Dimension-six top-Higgs interaction and its effect in collider phenomenology
Measurement of the Yukawa interaction between the top quark and the Higgs
boson should be useful to clarify the mechanism of fermion mass generation.
We discuss the impact of non-standard interactions characterized by
dimension-six operators on the effective top Yukawa coupling.
The cross section of the process is calculated including these operators, and possible deviation
from the standard model prediction is evaluated under the constraint from
perturbative unitarity and current experimental data.
We find that if the new physics scale is in a TeV region, the cross section
can be significantly enhanced due to the non-standard interactions.
Such a large effect should be detectable at the International Linear
Collider.Comment: 22 pages, RevTex4, 20 eps figure
A light Higgs scenario based on the TeV-scale supersymmetric strong dynamics
We consider a model based on the supersymmetric QCD theory with N_c=2 and
N_f=3. The theory is strongly coupled at the infrared scale \Lambda_H. Its low
energy effective theory below \Lambda_H is described by the supersymmetric
standard model with the Higgs sector that contains four iso-spin doublets, two
neutral iso-spin singlets and two charged iso-spin singlets. If \Lambda_H is at
the multi-TeV to 10 TeV, coupling constants for the F-terms of these composite
fields are relatively large at the electroweak scale. Nevertheless, the SM-like
Higgs boson is predicted to be as light as 125 GeV because these F-terms
contribute to the mass of the SM-like Higgs boson not at the tree level but at
the one-loop level. A large non-decoupling effect due to these F-terms appears
in the one-loop correction to the triple Higgs boson coupling, which amounts to
a few tens percent. Such a non-decoupling property in the Higgs potential
realizes the strong first order phase transition, which is required for a
successful scenario of electroweak baryogenesis
Off-diagonal Gluon Mass Generation and Infrared Abelian Dominance in Maximally Abelian Gauge in SU(3) Lattice QCD
In SU(3) lattice QCD formalism, we propose a method to extract gauge fields
from link-variables analytically. With this method, we perform the first study
on effective mass generation of off-diagonal gluons and infrared Abelian
dominance in the maximally Abelian (MA) gauge in the SU(3) case. Using SU(3)
lattice QCD, we investigate the propagator and the effective mass of the gluon
fields in the MA gauge with U(1)_3 \timesU(1)_8 Landau gauge fixing. The
Monte Carlo simulation is performed on at =5.7, 5.8 and 6.0 at
the quenched level. The off-diagonal gluons behave as massive vector bosons
with the approximate effective mass in the region of fm, and the propagation is
limited within a short range, while the propagation of diagonal gluons remains
even in a large range. In this way, infrared Abelian dominance is shown in
terms of short-range propagation of off-diagonal gluons. Furthermore, we
investigate the functional form of the off-diagonal gluon propagator. The
functional form is well described by the four-dimensional Euclidean Yukawa-type
function with
for fm. This also indicates that the spectral function of
off-diagonal gluons has the negative-value region
Triviality and vacuum stability bounds in the three-loop neutrino mass model
We study theoretical constraints on the parameter space under the conditions
from vacuum stability and triviality in the three-loop radiative seesaw model
with TeV-scale right-handed neutrinos which are odd under the parity. In
this model, some of the neutrino Yukawa coupling constants can be of the order
of one. Requirement of strongly first order phase transition for successful
electroweak baryogenes is also prefers order-one coupling constants in the
scalar sector. Hence, it is important to clarify whether this model satisfies
those theoretical conditions up to a given cutoff scale. It is found that the
model can be consistent up to the scale above 10 TeV in the parameter region
where the neutrino data, the lepton flavor violation data, the thermal relic
abundance of dark matter as well as the requirement from the strongly first
order phase transition are satisfied.Comment: 22 pages, 14 figure
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