27,671 research outputs found
Physical state representations and gauge fixing in string theory
We re-examine physical state representations in the covariant quantization of
bosonic string. We especially consider one parameter family of gauge fixing
conditions for the residual gauge symmetry due to null states (or BRST exact
states), and obtain explicit representations of observable Hilbert space which
include those of the DDF states. This analysis is aimed at giving a necessary
ingredient for the complete gauge fixing procedures of covariant string field
theory such as temporal or light-cone gauge.Comment: 16 page
Secondary Photons from High-energy Protons Accelerated in Hypernovae
Recent observations show that hypernovae may deposit some fraction of their
kinetic energy in mildly relativistic ejecta. In the dissipation process of
such ejecta in a stellar wind, cosmic ray protons can be accelerated up to
eV. We discuss the TeV to MeV gamma-ray and the X-ray photon
signatures of cosmic rays accelerated in hypernovae. Secondary X-ray photons,
emitted by electron-positron pairs produced via cascade processes due to
high-energy protons, are the most promising targets for X-ray telescopes.
Synchrotron photons emitted by protons can appear in the GeV band, requiring
nearby ( Mpc) hypernovae for detection with GLAST. In addition, air
Cherenkov telescopes may be able to detect regenerated TeV photons emitted by
electron-positron pairs generated by CMB attenuation of decay photons.Comment: Accepted by ApJ
Delayed Onset of High-Energy Emissions in Leptonic and Hadronic Models of Gamma-Ray Bursts
The temporal--spectral evolution of the prompt emission of gamma-ray bursts
(GRBs) is simulated numerically for both leptonic and hadronic models. For weak
enough magnetic fields, leptonic models can reproduce the few seconds delay of
the onset of GeV photon emission observed by Fermi-LAT, due to the slow growth
of the target photon field for inverse Compton scattering. However, even for
stronger magnetic fields, the GeV delay can be explained with hadronic models,
due to the long acceleration timescale of protons and the continuous photopion
production after the end of the particle injection. While the FWHMs of the MeV
and GeV lightcurves are almost the same in one-zone leptonic models, the FWHM
of the 1--30 GeV lightcurves in hadronic models are significantly wider than
those of the 0.1--1 MeV lightcurves. The amount of the GeV delay depends on the
importance of the Klein--Nishina effect in both the leptonic and hadronic
models. In our examples of hadronic models the energies of the escaped neutrons
are comparable to the gamma-ray energy, although their contribution to the
ultra high-energy cosmic rays is still subdominant. The resulting neutrino
spectra are hard enough to avoid the flux limit constraint from IceCube. The
delay of the neutrino emission onset is up to several times longer than the
corresponding delay of the GeV photon emission onset. The quantitative
differences in the lightcurves for various models may be further tested with
future atmospheric Cherenkov telescopes whose effective area is larger than
that of Fermi-LAT, such as CTA.Comment: Accepted for publication in ApJ; 35 pages, 17 figure
Hadronic Models for the Extra Spectral Component in the short GRB 090510
A short gamma-ray burst GRB 090510 detected by {\it Fermi} shows an extra
spectral component between 10 MeV and 30 GeV, an addition to a more usual
low-energy ( MeV) Band component. In general, such an extra component
could originate from accelerated protons. In particular, inverse Compton
emission from secondary electron-positron pairs and proton synchrotron emission
are competitive models for reproducing the hard spectrum of the extra component
in GRB 090510. Here, using Monte Carlo simulations, we test the hadronic
scenarios against the observed properties. To reproduce the extra component
around GeV with these models, the proton injection isotropic-equivalent
luminosity is required to be larger than erg/s. Such large proton
luminosities are a challenge for the hadronic models.Comment: 12pages, 4 figures. Accepted for publication in ApJ
Very High Energy Neutrinos Originating from Kaons in Gamma-Ray Bursts
We simulate neutrino production in a gamma-ray burst (GRB) with the most
detailed method to date. We show that the highest energy neutrinos from GRBs
mainly come from kaons. Although there is little chance to detect such
neutrinos, attempts of detection are very important to prove physical
conditions in GRBs.Comment: 4 figures. Accepted for publication in ApJ
Boltzmann Equation with a Large Potential in a Periodic Box
The stability of the Maxwellian of the Boltzmann equation with a large
amplitude external potential has been an important open problem. In this
paper, we resolve this problem with a large potential in a periodic box
, . We use [1] in framework to
establish the well-posedness and the stability of the Maxwellian
Prompt X-ray and Optical Excess Emission due to Hadronic Cascades in Gamma-Ray Bursts
A fraction of gamma-ray bursts exhibit distinct spectral features in their
prompt emission below few 10s of keV that exceed simple extrapolations of the
low-energy power-law portion of the Band spectral model. This is also true for
the prompt optical emission observed in several bursts. Through Monte Carlo
simulations, we model such low-energy spectral excess components as hadronic
cascade emission initiated by photomeson interactions of ultra-high-energy
protons accelerated within GRB outflows. Synchrotron radiation from the
cascading, secondary electron-positron pairs can naturally reproduce the
observed soft spectra in the X-ray band, and in some cases the optical spectra
as well. These components can be directly related to the higher energy
radiation at GeV energies due to the hadronic cascades. Depending on the
spectral shape, the total energy in protons is required to be comparable to or
appreciably larger than the observed total photon energy. In particular, we
apply our model to the excess X-ray and GeV emission of GRB 090902B, and the
bright optical emission of the "naked-eye" GRB 080319B. Besides the hard GeV
components detected by {\it Fermi}, such X-ray or optical spectral excesses are
further potential signatures of ultra-high-energy cosmic ray production in
gamma-ray bursts.Comment: 12 pages, 2 figure
Josephson Spin Current in Triplet Superconductor Junctions
This paper theoretically discusses the spin current in spin-triplet
superconductor / insulator / spin-triplet superconductor junctions. At low
temperatures, a midgap Andreev resonant state anomalously enhances not only the
charge current but also the spin current. The coupling between the Cooper pairs
and the electromagnetic fields leads to the Frounhofer pattern in the direct
current spin flow in magnetic fields and the alternative spin current under
applied bias-voltages.Comment: 4 pages, 2 figure
On a class of topological quantum field theories in three-dimensions
We investigate the Chung-Fukuma-Shapere theory, or Kuperberg theory, of
three-dimensional lattice topological field theory. We construct a functor
which satisfies the Atiyah's axioms of topological quantum field theory by
reformulating the theory as Turaev-Viro type state-sum theory on a triangulated
manifold. The theory can also be extended to give a topological invariant of
manifolds with boundary.Comment: 22 pages, LaTeX, 9 ps figures include
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