AbstractWe consider the process of magnetogenesis in the context of nonsingular bounce cosmology. We show that large primordial magnetic fields can be generated during contraction without encountering strong coupling and backreaction issues. The fields may seed large-scale magnetic fields with observationally interesting strengths. This result leads to a theoretical constraint on the relation of the energy scale of the bounce cosmology to the number of effective e-folding of the contracting phase in the case of scale invariance for the power spectrum of primordial magnetic fields. We show that this constraint can be satisfied in a sizable region of the parameter space for the nonsingular bounce cosmology. DOI:10.1103/PhysRevD.94.083524https://arxiv.org/pdf/1607.06578.pdf
Abstract We develop a new model-independent method to probe the constancy of the speed of light c. In our method, the degeneracy between the cosmic curvature and the speed of light can be eliminated, which makes the test more natural and general. Combining the independent observations of Hubble paramete H(z) and luminosity distanc dL(z), we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and then detect variation of the speed of light. We find no signal of deviation from the present value of the speed of light c0. Moreover, to demonstrate the improvement in probing the constancy of the speed of light from future experiments, we produce a series of simulated data. The Dark Energy Survey will be able to detect Δc/c0~1% at ~1.5σ confidence level and Δc/c0~2% at ~3σ confidence level. If the errors are reduced to one-tenth of the expected DES ones, it can detect a Δc/c0~0.1% variation at ~2σ confidence level.DOI:10.1088/1475-7516/2016/08/016https://arxiv.org/pdf/1601.05497.pdf
AbstractWe introduce a model-independent approach to the null test of the cosmic curvature which is geometrically related to the Hubble parameter H(z) and luminosity distance dL(z). Combining the independent observations of H(z) and dL(z), we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and determine the cosmic curvature ΩK(0) in the null test relation. The null test is totally geometrical and does not assume any cosmological model. We show that the cosmic curvature ΩK(0)=0 is consistent with current observational data sets, falling within the 1σ limit. To demonstrate the effect on the precision of the null test, we produce a series of simulated data of the models with different ΩK(0). Future observations in better quality can provide a greater improvement to constrain or refute the flat universe with ΩK(0)=0.DOI:10.1103/PhysRevD.93.043517https://arxiv.org/pdf/1509.06283.pdf
AbstractThe Moon–solar wind interaction results in the formation of a complicated lunar space plasma environment. Here, we investigate the solar wind turbulence around the Moon using the magnetic field observed by the dual-probe mission Acceleration, Reconnection,Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS). Structure functions in a time range on kinetic scales are computed to measure the scaling index ζ, the spatial distribution of which reveals the global aspects of the lunar space plasma and shows the dependence on the local instability. On the lunar nightside, in the plasma void, the dominating magnetic pressure over the thermal pressure restrains the turbulence, and a quiet zone is built with , where is the scaling index in the ambient solar wind. Downstream in the lunar wake, ζ is elevated gradually and goes above at a radial distance of (lunar radius), which implies that the plasma refilling process in the lunar wake begins to generate the local turbulence. On the dayside around the subsolar point, ζ is enhanced at a low altitude of ~200 km, where the solar wind turbulence might be strengthened due to interaction with the lunar source plasma. The largest scaling indices lie around the day–night terminator with , and the observed dawn–dusk asymmetry could be an effect of the magnetic field not being parallel with the solar wind. The correspondence between the enhanced scaling index and the local instability also raises new questions about the description of solar wind turbulence. DOI: 10.3847/2041-8205/816/1/L3 https://iopscience.iop.org/article/10.3847/2041-8205/816/1/L3This research work was supported by projects such as the Key Laboratory of Planetary Sciences of the Chinese Academy of Sciences, the Strategic Pilot Science and Technology Special Project of the Chinese Academy of Sciences (Class B), the National Natural Science Foundation of China, and the Special Research Fund of the National Key Laboratory.
AbstractThe accuracy of Einstein's equivalence principle (EEP) can be tested with the observed time delays between correlated particles or photons that are emitted from astronomical sources. Assuming as a lower limit that the time delays are caused mainly by the gravitational potential of the Milky Way, we prove that fast radio bursts (FRBs) of cosmological origin can be used to constrain the EEP with high accuracy. Taking FRB 110220 and two possible FRB/gamma-ray burst (GRB) association systems (FRB/GRB 101011A and FRB/GRB 100704A) as examples, we obtain a strict upper limit on the differences of the parametrized post-Newtonian parameter γ values as low as [γ(1.23  GHz)-γ(1.45  GHz)]<4.36×10(-9). This provides the most stringent limit up to date on the EEP through the relative differential variations of the γ parameter at radio energies, improving by 1 to 2 orders of magnitude the previous results at other energies based on supernova 1987A and GRBs. DOI: 10.1103/PhysRevLett.115.261101https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.261101The reviewers of "Physical Review Letters" gave high evaluation,the work presented in the manuscript represents a novel, innovative method to test Einstein's Equivalence principle, and provides the most stringent upper limits to date at radio energies.
AbstractIncreasing total electron content (TEC) measurements from the low Earth orbiting satellites to Global Positioning System satellites flourish the exploration of the ionosphere and plasmasphere for decades. This paper indicates a method that 3‐D Var is applied to assimilate precise orbit determination antenna TEC measurements of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites into the background global core plasma model (GCPM). The slant TEC data archived in the COSMIC Data Analysis and Archive Center from 500 km to 20,200 km are used to reconstruct a new electron density model. This model has a temporal resolution of 2 h and spatial resolutions of 2.5° in geomagnetic latitude, 5° in longitude, 50 km in the upper ionosphere, and several hundred kilometers in the plasmasphere. Preliminary results show that the data assimilation modifies the initial GCPM forecast to be better coincident with actual COSMIC measurements in internal quality check. Furthermore, independent validation with upper ionosphere‐retrieved electron density and TEC of global ionosphere maps implies a reasonable improvement in the estimation of plasmaspheric electron density after the assimilation. DOI: 10.1002/2015RS005732 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015RS005732
AbstractIn this paper, we report radio observations of the Galactic Center magnetar PSR J1745-2900 at six epochs between 2014 June and October. These observations were carried out using the new Shanghai Tian Ma Radio Telescope at a frequency of 8.6 GHz. Both the flux density and integrated profile of PSR J1745-2900 show dramatic changes from epoch to epoch, showing that the pulsar was in its “erratic” phase. On MJD 56836, the flux density of this magnetar was about 8.7 mJy, which was 10 times larger than that reported at the time of discovery, enabling a single-pulse analysis. The emission is dominated by narrow “spiky” pulses that follow a log-normal distribution in peak flux density. From 1913 pulses, we detected 53 pulses whose peak flux densities are 10 times greater than that of the integrated profile. They are concentrated in pulse phase at the peaks of the integrated profile. The pulse widths at the 50% level of these bright pulses were between 0.°2 and 0.°9, much narrower than that of the integrated profile (∼12°). The observed pulse widths may be limited by interstellar scattering. No clear correlation was found between the widths and peak flux density of these pulses and no evidence was found for subpulse drifting. Relatively strong spiky pulses are also detected in the other five epochs of observation, showing the same properties as those detected in MJD 56836. These strong spiky pulses cannot be classified as “giant” pulses but are more closely related to normal pulse emission. DOI: 10.1088/0004-637X/814/1/5https://arxiv.org/pdf/1510.00183.pdf