27,038 research outputs found
Long-term X-ray emission from Swift J1644+57
The X-ray emission from Swift J1644+57 is not steadily decreasing instead it
shows multiple pulses with declining amplitudes. We model the pulses as reverse
shocks from collisions between the late ejected shells and the externally
shocked material, which is decelerated while sweeping the ambient medium. The
peak of each pulse is taken as the maximum emission of each reverse shock. With
a proper set of parameters, the envelope of peaks in the light curve as well as
the spectrum can be modelled nicely.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Constraining the bulk Lorentz factor from the photosphere emission
We propose a direct and model-independent method to constrain the Lorentz
factor of a relativistically expanding object, like gamma-ray bursts. Only the
measurements, such as thermal component of the emission, the distance and the
variable time scale of the light curve, are used. If the uncertainties are
considered, we will obtain lower limits of the Lorentz factor instead. We apply
this method to GRB 090618 and get a lower limit of the Lorentz factor to be 22.
The method can be used to any relativistically moving object, such as gamma-ray
bursts, blazars, and soft gamma-ray repeaters, providing the thermal component
of the emission being observed.Comment: 10 pages, 1 figur
A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China
Cosmic rays interact with the Earth's atmosphere to produce C, which
can be absorbed by trees. Therefore, rapid increases of C in tree rings
can be used to probe previous cosmic-ray events. By this method, three C
rapidly increasing events have been found. Plausible causes of these events
include large solar proton events, supernovae or short gamma-ray bursts.
However, due to the lack of measurements of C by year, the occurrence
frequency of such C rapidly increasing events is poorly known. In
addition, rapid increases may be hidden in the IntCal13 data with five-year
resolution. Here we report the result of C measurements using an ancient
buried tree during the period between BC 3388 and 3358. We find a rapid
increase of about 9\textperthousand~ in the C content from BC 3372 to BC
3371. We suggest that this event could originate from a large solar proton
event.Comment: 23 pages, 3 figures, 2 tables, published in Nature Communication
Nonleptonic two-body charmless B decays involving a tensor meson in the Perturbative QCD Approach
Two-body charmless hadronic B decays involving a light tensor meson in the
final states are studied in the perturbative QCD approach based on
factorization. From our calculations, we find that the decay branching ratios
for color allowed tree-dominated decays and modes are of order and , respectively.
While other color suppressed tree-dominated decays have very small branching
ratios. In general, the branching ratios of most decays are in the range of
to , which are bigger by one or two orders of magnitude than
those predictions obtained in Isgur-Scora-Grinstein-Wise II model and in the
covariant light-front approach, but consistent with the recent experimental
measurements and the QCD factorization calculations. Since the decays with a
tensor meson emitted from vacuum are prohibited in naive factorization, the
contributions of nonfactorizable and annihilation diagrams are very important
to these decays, which are calculable in our perturbative QCD approach. We also
give predictions to the direct CP asymmetries, some of which are large enough
for the future experiments to measure. Because we considered the mixing between
and , the decay rates are enhanced significantly for some
decays involving meson, even with a small mixing angle.Comment: 26 pages, 2 figure
Sigma_c Dbar and Lambda_c Dbar states in a chiral quark model
The S-wave Sigma_c Dbar and Lambda_c Dbar states with isospin I=1/2 and spin
S=1/2 are dynamically investigated within the framework of a chiral constituent
quark model by solving a resonating group method (RGM) equation. The results
show that the interaction between Sigma_c and Dbar is attractive, which
consequently results in a Sigma_c Dbar bound state with the binding energy of
about 5-42 MeV, unlike the case of Lambda_c Dbar state, which has a repulsive
interaction and thus is unbound. The channel coupling effect of Sigma_c Dbar
and Lambda_c Dbar is found to be negligible due to the fact that the gap
between the Sigma_c Dbar and Lambda_c Dbar thresholds is relatively large and
the Sigma_c Dbar and Lambda_c Dbar transition interaction is weak.Comment: 7 pages,2 figures. arXiv admin note: text overlap with
arXiv:nucl-th/0606056 by other author
Progress towards quantum simulating the classical O(2) model
We connect explicitly the classical model in 1+1 dimensions, a model
sharing important features with lattice gauge theory, to physical models
potentially implementable on optical lattices and evolving at physical time.
Using the tensor renormalization group formulation, we take the time continuum
limit and check that finite dimensional projections used in recent proposals
for quantum simulators provide controllable approximations of the original
model. We propose two-species Bose-Hubbard models corresponding to these finite
dimensional projections at strong coupling and discuss their possible
implementations on optical lattices using a Rb and K Bose-Bose
mixture.Comment: 7 pages, 6 figures, uses revtex, new material and one author added,
as to appear in Phys. Rev.
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