5,568 research outputs found
Cosmological tests of gravity with latest observations
We perform observational tests of modified gravity on cosmological scales
following model-dependent and model-independent approaches using the latest
astronomical observations, including measurements of the local Hubble constant,
cosmic microwave background, the baryonic acoustic oscillations and redshift
space distortions derived from galaxy surveys including the SDSS BOSS and
eBOSS, as well as the weak lensing observations performed by the CFHTLenS team.
Using all data combined, we find a deviation from the prediction of general
relativity in both the effective Newton's constant, , and in the
gravitational slip, . The deviation is at a level in the
joint space using a two-parameter phenomenological
model for and , and it reaches a level if a general
parametrisation is used. This signal, which may be subject to unknown
observational systematics, or a sign of new physics, is worth further
investigating with forthcoming observations.Comment: 12 pages, 8 figures; ApJ accepte
QCD corrections to double J/\psi production in e+e- annihilation at \sqrt{s}=10.6 GeV
Next-to-Leading-Order(NLO) QCD corrections to double J/psi production in
e^+e^- annihilation at sqrt{s}=10.6 GeV are calculated. We find that they
greatly decrease the cross section, with a K factor (NLO/LO) ranging from -0.31
to 0.25 depending on the renormalization scale. Although the renormalization
scale dependence indicates a large uncertainty, when combined with the NLO QCD
corrections to J/psi + eta_c production, it can explain why the double J/psi$
production could not be found at B factories while the J/psi + eta_c production
could, despite the fact that cross section of the former is larger than that of
the latter at LO by a factor of 1.8.Comment: 4 pages, 4 figures, use revtex
QCD corrections to J/psi plus eta_c production in e+e- annihilation at sqrt{s}=10.6 GeV
Next-to-Leading-Order(NLO) QCD corrections to J/jpsi plus eta_c production in
e+e- annihilation at sqrt{s}=10.6 GeV is calculated in this paper, and an
analytic result is obtained. By choosing proper physical parameters, a K factor
(ratio of NLO to LO) of about 2, which is in agreement with the result in
Ref.\cite{Zhang:2005ch}, is obtained. Our results show that the
Next-Next-to-Leading-Order(NNLO) corrections might be quite large. The plot of
the K-factor vs the center-of-mass energy sqrt{s} shows that it is more
difficult to obtain a convergent result from the perturbative QCD without
resummation of ln(s/m_c) terms as the sqrt{s} becomes larger.Comment: 8 pages, 6 figures, two column
The Independent Monetary Policy under the Fixed Exchange Regime
Using a macro-econometric model that is specified for the current Chinese economy, we investigate the performance of monetary policy in China with the assumption (which anyway will occur in the near future) that capital market was opened. Our purpose is to find how the monetary authority should response to a variety of external shocks by applying different policy tools (including required reserve ratio, buying and selling foreign exchange, the open market operation, the discount rate among others) while keeping the exchange rate within a designed regime. The Monte Carlo simulation will be used to evaluate the effectiveness of such policy reactions.
Evolutionary Game Dynamics for Two Interacting Populations under Environmental Feedback
We study the evolutionary dynamics of games under environmental feedback
using replicator equations for two interacting populations. One key feature is
to consider jointly the co-evolution of the dynamic payoff matrices and the
state of the environment: the payoff matrix varies with the changing
environment and at the same time, the state of the environment is affected
indirectly by the changing payoff matrix through the evolving population
profiles. For such co-evolutionary dynamics, we investigate whether convergence
will take place, and if so, how. In particular, we identify the scenarios where
oscillation offers the best predictions of long-run behavior by using
reversible system theory. The obtained results are useful to describe the
evolution of multi-community societies in which individuals' payoffs and
societal feedback interact.Comment: 7 pages, submitted to a conferenc
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