AbstractBinary black hole systems are among the most important sources for gravitational wave detection. They are also good objects for theoretical research for general relativity. A gravitational waveform template is important to data analysis. An effective-one-body-numerical-relativity (EOBNR) model has played an essential role in the LIGO data analysis. For future space-based gravitational wave detection, many binary systems will admit a somewhat orbit eccentricity. At the same time, the eccentric binary is also an interesting topic for theoretical study in general relativity. In this paper, we construct the first eccentric binary waveform model based on an effective-one-body-numerical-relativity framework. Our basic assumption in the model construction is that the involved eccentricity is small. We have compared our eccentric EOBNR model to the circular one used in the LIGO data analysis. We have also tested our eccentric EOBNR model against another recently proposed eccentric binary waveform model; against numerical relativity simulation results; and against perturbation approximation results for extreme mass ratio binary systems. Compared to numerical relativity simulations with an eccentricity as large as about 0.2, the overlap factor for our eccentric EOBNR model is better than 0.98 for all tested cases, including spinless binary and spinning binary, equal mass binary, and unequal mass binary. Hopefully, our eccentric model can be the starting point to develop a faithful template for future space-based gravitational wave detectors.DOI:10.1103/PhysRevD.96.044028https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.044028
AbstractWith aLIGO’s discovery of the gravitational wave (GW) sources, we were ushered into the age of observational GW astronomy. The success of LISA Pathfinder in demonstrating the LISA drag-free requirement paved the road of using space missions for detecting low-frequency and middle-frequency GWs. The new LISA GW mission proposes to use arm length of 2.5 Gm (1Gm = 106 km). The TAIJI GW mission proposes to use arm length of 3 Gm. In order to attain the requisite sensitivity, laser frequency noise must be suppressed to below the secondary noises such as the optical path noise, acceleration noise etc. In previous papers, we have performed the numerical simulation of the time delay interferometry (TDI) for original LISA, ASTROD-GW and eLISA together with a LISA-type mission with a nominal arm length of 2 Gm using the CGC2.7/CGC2.7.1 ephemeris framework. In this paper, we follow the same procedure to simulate the time delay interferometry numerically for the new LISA mission and the TAIJI mission together with LISA-like missions of arm length 1 Gm, 2 Gm, 4 Gm, 5 Gm and 6 Gm. To do this, we work out a set of 2200-day (6-year) optimized mission orbits of each mission starting at March 22, 2028 using the CGC 2.7.1 ephemeris framework. We then use numerical method to calculate the residual optical path differences of the first-generation TDI configurations --- Michelson X, Y & Z; Sagnac α, β & γ; Relay U, V & W; Beacon P, Q & R; Monitor E, F & G --- and the second generation TDI configurations --- 2-arm type, [ab, ba]’s (a, optical path from S/C 1 to S/C 2 and back to S/C 1; b, optical path from S/C 1 to S/C 3 and back to S/C 1); [aabb, bbaa]’s; [abab, baba]’s; [abba, baab]’s; Sagnac-type α2, β2 & γ2. The resulting optical path differences of the second-generation TDI calculated for new LISA, TAIJI, and LISA-like missions or arm length 1, 2, 4, 5 & 6 Gm are well below their respective limits which the laser frequency noise is required to be suppressed. However, for of the first generation X, Y, and Z TDI configurations, the original requirements need to be relaxed by 3 to 30 fold to be satisfied. For the new LISA and TAIJI, about one order of magnitude relaxation would be good and recommended; this could be borne on the laser stability requirement in view of recent progress in laser stability. Compared with X, Y and Z, the X+Y+Z configuration does have a good cancellation of path length differences and could serve as a null string detection check. We compile and compare the resulting differences of various TDI configurations due to the different arm lengths for various LISA-like mission proposals and for the ASTROD-GW mission proposal.https://arxiv.org/ftp/arxiv/papers/1707/1707.09127.pdf
AbstractWe investigate constraints on Lorentz invariance violation in the neutrino sector from a joint analysis of big bang nucleosynthesis and the cosmic microwave background. The effect of Lorentz invariance violation during the epoch of big bang nucleosynthesis changes the predicted helium-4 abundance, which influences the power spectrum of the cosmic microwave background at the recombination epoch. In combination with the latest measurement of the primordial helium-4 abundance, the Planck 2015 data of the cosmic microwave background anisotropies give a strong constraint on the deformation parameter since adding the primordial helium measurement breaks the degeneracy between the deformation parameter and the physical dark matter density. DOI:10.1140/epjc/s10052-017-4959-6https://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-017-4959-6.pdf
AbstractThe direct detection of gravitational wave by Laser Interferometer Gravitational Wave Observatory indicates the coming of the era of gravitational-wave astronomy and gravitational-wave cosmology. It is expected that more and more gravitational-wave events will be detected by currently existing and planned gravitational-wave detectors. The gravitational waves open a new window to explore the Universe and various mysteries will be disclosed through the gravitational-wave detection, combined with other cosmological probes. The gravitational-wave physics is not only related to gravitation theory, but also is closely tied to fundamental physics, cosmology and astrophysics. In this review article, three kinds of sources of gravitational waves and relevant physics will be discussed, namely gravitational waves produced during the inflflation and preheating phases of the Universe, the gravitational waves produced during the fifirst-order phase transition as the Universe cools down and the gravitational waves from the three phases: inspiral, merger and ring down of a compact binary system, respectively. We will also discuss the gravitational waves as a standard siren to explore the evolution of the Universe. DOI:10.1093/nsr/nwx029https://arxiv.org/pdf/1703.00187.pdf
AbstractBig Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, 3He, 4He, and 7Li produced in the early universe. The primordial abundances of D and 4He inferred from observational data are in good agreement with predictions, however, BBN theory overestimates the primordial 7Li abundance by about a factor of three. This is the so-called “cosmological lithium problem.” Solutions to this problem using conventional astrophysics and nuclear physics have not been successful over the past few decades, probably indicating the presence of new physics during the era of BBN. We have investigated the impact on BBN predictions of adopting a generalized distribution to describe the velocities of nucleons in the framework of Tsallis non-extensive statistics. This generalized velocity distribution is characterized by a parameter q, and reduces to the usually assumed Maxwell–Boltzmann distribution for q = 1. We find excellent agreement between predicted and observed primordial abundances of D, 4He, and 7Li for 1.069≤q≤1.082, suggesting a possible new solution to the cosmological lithium problem.DOI:10.3847/1538-4357/834/2/165 https://iopscience.iop.org/article/10.3847/1538-4357/834/2/165
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.
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