6,421 research outputs found
Exploring Vacuum Structure around Identity-Based Solutions
We explore the vacuum structure in bosonic open string field theory expanded
around an identity-based solution parameterized by . Analyzing the
expanded theory using level truncation approximation up to level 20, we find
that the theory has the tachyon vacuum solution for . We also find
that, at , there exists an unstable vacuum solution in the expanded
theory and the solution is expected to be the perturbative open string vacuum.
These results reasonably support the expectation that the identity-based
solution is a trivial pure gauge configuration for , but it can be
regarded as the tachyon vacuum solution at .Comment: 12 pages, 5 figures; new numerical data up to level (20,60) included;
Contribution to the proceedings of "Second International Conference on String
Field Theory and Related Aspects" (Steklov Mathematical Institute, Moscow,
Russia, April 12-19, 2009
Regularization of identity based solution in string field theory
We demonstrate that an Erler-Schnabl type solution in cubic string field
theory can be naturally interpreted as a gauge invariant regularization of an
identity based solution. We consider a solution which interpolates between an
identity based solution and ordinary Erler-Schnabl one. Two gauge invariant
quantities, the classical action and the closed string tadpole, are evaluated
for finite value of the gauge parameter. It is explicitly checked that both of
them are independent of the gauge parameter.Comment: 9 pages, minor typos corrected and references adde
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
Spin observables in the reaction
The T matrix of the LambdaN-> NN reaction, which is a strangeness changing
weak process, is derived. The explicit formulas of the spin observables are
given for s-wave p-Lambda final states which kinematically corresponds to
inverse reaction of the weak nonmesonic decay of Lambda hypernuclei. One can
study interferences between amplitudes of parity- conserving and violating,
spin- singlet and triplet and isospin- singlet and triplet. Most of them are
not available in the study of the nonmesonic decay. They clarify structure of
the reaction and constrain strongly theoretical models for weak hyperon nucleon
interaction.Comment: 7pages,ReVTeX,no figure
Probing neutrino physics with a self-consistent treatment of the weak decoupling, nucleosynthesis, and photon decoupling epochs
We show that a self-consistent and coupled treatment of the weak decoupling,
big bang nucleosynthesis, and photon decoupling epochs can be used to provide
new insights and constraints on neutrino sector physics from high-precision
measurements of light element abundances and cosmic microwave background
observables. Implications of beyond-standard-model physics in cosmology,
especially within the neutrino sector, are assessed by comparing predictions
against five observables: the baryon energy density, helium abundance,
deuterium abundance, effective number of neutrinos, and sum of the light
neutrino mass eigenstates. We give examples for constraints on dark radiation,
neutrino rest mass, lepton numbers, and scenarios for light and heavy sterile
neutrinos.Comment: 29 pages, 10 figure
The Location of the Nucleus of NGC 1068 and the Three-dimensional Structure of Its Nuclear Region
The HST archival UV imaging polarimetry data of NGC 1068 is re-examined.
Through an extensive estimation of the observational errors, we discuss whether
the distribution of the position angles (PAs) of polarization is simply
centrosymmetric or not. Taking into account the effect of a bad focus at the
time of the observation, we conclude that, within the accuracy of HST/FOC
polarimetry, the PA distribution is completely centrosymmetric. This means that
the UV polarization originates only from scattering of the radiation from a
central point-like source.
However, our analysis shows that the most probable location of the nucleus is
only ~0.''08 (~6pc) south from the brightest cloud called ``cloud B''. The
error circle of 99% confidence level extends to cloud B and to ``cloud A''
which is about 0.''2 south of cloud B. By this FOC observation, Cloud B is only
marginally rejected as the nucleus.
Assuming that the UV flux is dominated by electron-scattered light, we have
also derived a three-dimensional structure of the nuclear region. The inferred
distribution suggests a linear structure which could be related to the radio
jet.Comment: 19 pages, 14 figures, to be published in the Astrophysical Journa
Mid-infrared microlensing of accretion disc and dusty torus in quasars: effects on flux ratio anomalies
Multiply-imaged quasars and AGNs observed in the mid-infrared (MIR) range are
commonly assumed to be unaffected by the microlensing produced by the stars in
their lensing galaxy. In this paper, we investigate the validity domain of this
assumption. Indeed, that premise disregards microlensing of the accretion disc
in the MIR range, and does not account for recent progress in our knowledge of
the dusty torus. To simulate microlensing, we first built a simplified image of
the quasar composed of an accretion disc, and of a larger ring-like torus. The
mock quasars are then microlensed using an inverse ray-shooting code. We
simulated the wavelength and size dependence of microlensing for different
lensed image types and fraction of compact objects projected in the lens. This
allows us to derive magnification probabilities as a function of wavelength, as
well as to calculate the microlensing-induced deformation of the spectral
energy distribution of the lensed images. We find that microlensing variations
as large as 0.1 mag are very common at 11 microns (observer-frame). The main
signal comes from microlensing of the accretion disc, which may be significant
even when the fraction of flux from the disc is as small as 5 % of the total
flux. We also show that the torus of sources with Lbol <~ 10^45 erg/s is
expected to be noticeably microlensed. Microlensing may thus be used to get
insight into the rest near-infrared inner structure of AGNs. Finally, we
investigate whether microlensing in the mid-infrared can alter the so-called
Rcusp relation that links the fluxes of the lensed images triplet produced when
the source lies close to a cusp macro-caustic. This relation is commonly used
to identify massive (dark-matter) substructures in lensing galaxies. We find
that significant deviations from Rcusp may be expected, which means that
microlensing can explain part of the flux ratio problem.Comment: Updated to match the version published in Astronomy and Astrophysics.
12 pages. Abridged version of the abstract. Microlensing maps and source
profiles used in the simulations are available via CDS -
http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/A+A/553/A5
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
Neutrino energy transport in weak decoupling and big bang nucleosynthesis
We calculate the evolution of the early universe through the epochs of weak
decoupling, weak freeze-out and big bang nucleosynthesis (BBN) by
simultaneously coupling a full strong, electromagnetic, and weak nuclear
reaction network with a multi-energy group Boltzmann neutrino energy transport
scheme. The modular structure of our code provides the ability to dissect the
relative contributions of each process responsible for evolving the dynamics of
the early universe in the absence of neutrino flavor oscillations. Such an
approach allows a detailed accounting of the evolution of the ,
, , , , energy
distribution functions alongside and self-consistently with the nuclear
reactions and entropy/heat generation and flow between the neutrino and
photon/electron/positron/baryon plasma components. This calculation reveals
nonlinear feedback in the time evolution of neutrino distribution functions and
plasma thermodynamic conditions (e.g., electron-positron pair densities), with
implications for: the phasing between scale factor and plasma temperature; the
neutron-to-proton ratio; light-element abundance histories; and the
cosmological parameter \neff. We find that our approach of following the time
development of neutrino spectral distortions and concomitant entropy production
and extraction from the plasma results in changes in the computed value of the
BBN deuterium yield. For example, for particular implementations of quantum
corrections in plasma thermodynamics, our calculations show a increase
in deuterium. These changes are potentially significant in the context of
anticipated improvements in observational and nuclear physics uncertainties.Comment: 37 pages, 12 Figures, 6 Table
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