2,907 research outputs found
Bug Searching in Smart Contract
With the frantic development of smart contracts on the Ethereum platform, its
market value has also climbed. In 2016, people were shocked by the loss of
nearly $50 million in cryptocurrencies from the DAO reentrancy attack. Due to
the tremendous amount of money flowing in smart contracts, its security has
attracted much attention of researchers. In this paper, we investigated several
common smart contract vulnerabilities and analyzed their possible scenarios and
how they may be exploited. Furthermore, we survey the smart contract
vulnerability detection tools for the Ethereum platform in recent years. We
found that these tools have similar prototypes in software vulnerability
detection technology. Moreover, for the features of public distribution systems
such as Ethereum, we present the new challenges that these software
vulnerability detection technologies face.Comment: 8 pages, 9 figure
Power spectra and spectral indices of -inflation: high-order corrections
-inflation represents the most general single-field inflation, in which
the perturbations usually obey an equation of motion with a time-dependent
sound speed. In this paper, we study the observational predictions of the
-inflation by using the high-order uniform asymptotic approximation method.
We calculate explicitly the slow-roll expressions of the power spectra,
spectral indices, and running of the spectral indices for both the scalar and
tensor perturbations. These expressions are all written in terms of the Hubble
and sound speed flow parameters. It is shown that the previous results obtained
by using the first-order uniform asymptotic approximation have been
significantly improved by the high-order corrections of the uniform asymptotic
approximations. Furthermore, we also check our results by comparing them with
the ones obtained by other approximation methods, including the Green's
function method, WKB approximation, and improved WKB approximation, and find
the relative errors.Comment: Typos are also corrected. Phys. Rev. D90, 103517 (2014). arXiv admin
note: text overlap with arXiv:1405.530
Inflationary cosmology with nonlinear dispersion relations
We present a technique, {\em the uniform asymptotic approximation}, to
construct accurate analytical solutions of the linear perturbations of
inflation after quantum effects of the early universe are taken into account,
for which the dispersion relations generically become nonlinear. We construct
explicitly the error bounds associated with the approximations and then study
them in detail. With the understanding of the errors and the proper choice of
the Liouville transformations of the differential equations of the
perturbations, we show that the analytical solutions describe the exact
evolution of the linear perturbations extremely well even only in the
first-order approximations. As an application of the approximate analytical
solutions, we calculate the power spectra and indices of scalar and tensor
perturbations in the slow-roll inflation, and find that the amplitudes of the
power spectra get modified due to the quantum effects, while the power spectrum
indices remain the same as in the linear case.Comment: The analysis of power spectra and indices of scalar and tensor
perturbations are enlarged. Two figures added. arXiv admin note: text overlap
with arXiv:1308.110
Pre-inflationary universe in loop quantum cosmology
The evolutions of the flat FLRW universe and its linear perturbations are
studied systematically in the dressed metric approach of LQC. When it is
dominated by the kinetic energy of the inflaton at the quantum bounce, the
evolution of the background can be divided into three different phases prior to
the preheating, {\em bouncing, transition and slow-roll inflation}. During the
bouncing phase, the evolution is independent of not only the initial
conditions, but also the inflationary potentials. In particular, the expansion
factor can be well described by the same exact solution in all the cases
considered. In contrast, in the potential dominated case such a universality is
lost. It is because of this universality that the linear perturbations are also
independent of the inflationary models and obtained exactly. During the
transition phase, the evolutions of the background and its linear perturbations
are found explicitly, and then matched to the ones given in the other two
phases. Hence, once the initial conditions are imposed, the linear scalar and
tensor perturbations will be uniquely determined. Considering two different
sets of initial conditions, one imposed during the contracting phase and the
other at the bounce, we calculate the Bogoliubov coefficients and find that the
two sets yield the same results and all lead to particle creations at the onset
of the inflation. Due to the pre-inflationary dynamics, the scalar and tensor
power spectra become scale-dependent. Comparing with the Planck 2015 data, we
find constraints on the total e-folds that the universe must have expanded
since the bounce, in order to be consistent with current observations.Comment: revtex4, 23 figures, and 5 tables. Some typos were corrected. Phys.
Rev. D 96, 083520 (2017
High-order Primordial Perturbations with Quantum Gravitational Effects
In this paper, we provide a systematic investigation of high-order primordial
perturbations with nonlinear dispersion relations due to quantum gravitational
effects in the framework of {\em uniform asymptotic approximations}. Because of
these effects, the equation of motion of the mode function in general has
multiple-turning points. After obtaining analytically approximated solutions to
any order in different regions, associated with different types of turning
points, we match them to the third one. To this order the errors are less than
. General expressions of the power spectra of the primordial tensor and
scalar perturbations are derived explicitly. We also investigate effects of
back-reactions of the quantum gravitational corrections, and make sure that
inflation lasts long enough in order to solve the underlying problems, such as
flatness, horizon and monopole. Then, we study various features of the spectra
that are observationally relevant. In particular, under a moderate assumption
about the energy scale of the underlying theory of quantum gravity, we have
shown that the quantum gravitational effects may alter significantly the ratio
between the tensor and scalar power spectra, thereby providing a natural
mechanism to alleviate the tension between observations and certain
inflationary models, including the one with a quadratic potential.Comment: revtex4, 9 figures, no tables. Typos are corrected, and sections are
rearranged. Version to appear in PR
Primordial non-Gaussianity and power asymmetry with quantum gravitational effects in loop quantum cosmology
Loop quantum cosmology (LQC) provides a resolution of the classical big bang
singularity in the deep Planck era. The evolution, prior to the usual slow-roll
inflation, naturally generates excited states at the onset of the slow-roll
inflation. It is expected that these quantum gravitational effects could leave
its fingerprints on the primordial perturbation spectrum and non-Gaussianity,
and lead to some observational evidences in the cosmic microwave background
(CMB). While the impact of the quantum effects on the primordial perturbation
spectrum has been already studied and constrained by current data, in this
paper we continue studying such effects on the non-Gaussianity of the
primordial curvature perturbations. In this paper, we present detailed and
analytical calculations of the non-Gaussianity and show explicitly that the
corrections due to quantum effects are in the same magnitude of the slow-roll
parameters in the observable scales and thus are well within current
observational constraints. Despite this, we show that the non-Gaussianity in
the squeezed limit can be enhanced at superhorizon scales and further, these
effects may yield a large statistical anisotropy on the power spectrum through
the Erickcek-Kamionkowski-Carroll mechanism.Comment: revtex4, one figure and no table
Energy loss of heavy and light quarks in holographic magnetized background
We systematically study holographic effects on the magnetic field dependence
of the drag force, diffusion coefficient, jet quenching parameter of heavy
quarks and the shooting string energy loss of light quarks in the RHIC and LHC
energy regions by using the AdS/CFT correspondence in this paper. This study is
motivated by the phenomena of strong magnetic field and jet quenching, which
have been found in relativistic heavy ion collisions. The probe's direction of
motion is perpendicular and parallel to the direction of magnetic field .
The effects of magnetic field on energy loss when moving perpendicular to the
magnetic field direction are larger than moving parallel to the magnetic field
direction, which implies that the magnetic field tends to suppress more quarks
and jets when moving in the transverse direction than in the parallel
direction. It is found that the diffusion coefficient decreases with the
magnetic field in the transverse direction, but increases with the magnetic
field in the parallel direction, which indicates that the quark may diffuse
farther when moving parallel to the magnetic field direction. We also find that
the magnetic field will enhance the energy loss of the light quarks when moving
in the transverse direction than in the parallel direction.Comment: 26 pages, 8 figure
Scalar and tensor perturbations in loop quantum cosmology: High-order corrections
Loop quantum cosmology (LQC) provides promising resolutions to the
trans-Planckian issue and initial singularity arising in the inflationary
models of general relativity. In general, due to different quantization
approaches, LQC involves two types of quantum corrections, the holonomy and
inverse-volume, to both of the cosmological background evolution and
perturbations. In this paper, using {\em the third-order uniform asymptotic
approximations}, we derive explicitly the observational quantities of the
slow-roll inflation in the framework of LQC with these quantum corrections. We
calculate the power spectra, spectral indices, and running of the spectral
indices for both scalar and tensor perturbations, whereby the tensor-to-scalar
ratio is obtained. We expand all the observables at the time when the
inflationary mode crosses the Hubble horizon. As the upper error bounds for the
uniform asymptotic approximation at the third-order are ,
these results represent the most accurate results obtained so far in the
literature. It is also shown that with the inverse-volume corrections, both
scalar and tensor spectra exhibit a deviation from the usual shape at large
scales. Then, using the Planck, BAO and SN data we obtain new constraints on
quantum gravitational effects from LQC corrections, and find that such effects
could be within the detection of the forthcoming experiments.Comment: revtex4, one figure. JCAP10 (2015) 05
Detecting quantum gravitational effects of loop quantum cosmology in the early universe?
We derive the primordial power spectra and spectral indexes of the density
fluctuations and gravitational waves in the framework of loop quantum cosmology
(LQC) with holonomy and inverse-volume corrections, by using the uniform
asymptotic approximation method to its third-order, at which the upper error
bounds are , and accurate enough for the current and
forthcoming cosmological observations. Then, using the Planck, BAO and SN data
we obtain the tightest constraints on quantum gravitational effects from LQC
corrections, and find that such effects could be well within the detection of
the current and forthcoming cosmological observations.Comment: revtex4, 2 figutes and 1 table. ApJL 807 (2015) L1
Preinflationary perturbations from the closed algebra approach in loop quantum cosmology
In this paper, the scalar and tensor perturbations in the closed algebra
approach of loop quantum cosmology are studied. Instead of the distant past in
the contracting phase, we choose the moment at which the initial conditions are
imposed to be the silent point, which circumvents the problem due to the
signature change in the super-inflationary phase and results in a well-defined
Cauchy problem. For the ultraviolet and infrared modes, different approaches
are applied in order to obtain analytical solutions with high accuracy. While
previous numerical simulations reveal an exponentially divergent power spectrum
in the ultraviolet regime, when the initial conditions are imposed in the
remote contracting phase, we find a special set of initial conditions at the
silent point, which can reproduce results that are consistent with current
observations.Comment: Corrected some typos. Phys. Rev. D99, 103536 (2019
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