195378147
Effects of cosmological constant on motion of UHECR particles
Recent astronomical observations manifest that about two-thirds of the whole energy in the Universe is contributed by a small positive cosmological constant Λ (>0). Then, an asymptotically de Sitter spacetime is premised naturally. However, physics in the de Sitter spacetime is very different from that in the Minkowski spacetime. As the first step, a covariant formalism of the kinematics in the de Sitter spacetime is presented here. By solving exactly the equations of motion for a field, we obtain the dispersion relation of a free particle. It is noticed that the dispersion relation is dependent on the degree of freedom of angular momentum of the particle. We show the threshold anomaly of the ultra high energy cosmic ray disappears naturally in the framework of the de Sitter kinematics.
120446208
Construction and commissioning of the first wiggler at BEPC
Abstract The SRW1 at BEPC is under normal operation now. This article describes the construction and commissioning of the wiggler. Some experimental results are reported and suggestions for improvement are discussed.
119109295
Collision of two general geodesic particles around a Kerr-Newman black hole
We study collision of two general geodesic particles around the Kerr-Newman (KN) black hole and get the center-of-mass (CM) energy of the non-marginally and marginally bound critical particles in the direct collision and LSO collision scenarios. We find the constraint conditions that arbitrarily high CM energy can be obtained for the near-horizon collision of two general geodesic particles in the extremal KN black hole, and note that the charge decreases the value of the latitude in which arbitrarily high CM energy can occurs. We also interpret why the high-velocity collision belt centers to the equator with the increase of the charge.
118505725
Quasinormal modes of charged squashed Kaluza-Klein black holes in the Gödel universe
We study the quasinormal modes of scalar perturbation in the background of five-dimensional charged Kaluza-Klein black holes with squashed horizons immersed in the G\"odel universe. Besides the influence due to the compactness of the extra dimension, we disclose the cosmological rotational effect in the wave dynamics. The wave behavior affected by the G\"odel parameter provides an interesting insight into the G\"odel universe.
32703258
Quasinormal modes of a black hole surrounded by quintessence
Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless scalar field perturbation around a black hole which is surrounded by static and spherically symmetric quintessence. Our result shows that due to the presence of quintessence, the scalar field damps more rapidly. Moreover, we also note that the quintessential state parameter (the ratio of pressure pq to the energy density ρq) plays an important role for the quasinormal frequencies. As the state parameter increases, so does the real part and the absolute value of the imaginary part decreases. This means that the scalar field decays more slowly in the larger quintessence case.
119299977
Dynamical evolution of a scalar field coupling to Einstein’s tensor in the Reissner-Nordström black hole spacetime
We study the dynamical evolution of a scalar field coupling to Einstein's tensor in the background of a Reissner-Nordstrom black hole. Our results show that the coupling constant η imprints in the wave dynamics of a scalar perturbation. In the weak coupling, we find that with the increase of the coupling constant η the real parts of the fundamental quasinormal frequencies decrease and the absolute values of imaginary parts increase for fixed charge q and multipole number l. In the strong coupling, we find that for l ≠ 0 the instability occurs when η is larger than a certain threshold value η c which deceases with the multipole number l and charge q. However, for the lowest l = 0, we find that there does not exist such a threshold value and the scalar field always decays for arbitrary coupling constant.
119099273
Improved parametrization of the growth index for dark energy and DGP models
Abstract We propose two improved parameterized form for the growth index of the linear matter perturbations: (I) γ ( z ) = γ 0 + ( γ ∞ − γ 0 ) z z + 1 and (II) γ ( z ) = γ 0 + γ 1 z z + 1 + ( γ ∞ − γ 1 − γ 0 ) ( z z + 1 ) α . With these forms of γ ( z ) , we analyze the accuracy of the approximation the growth factor f by Ω m γ ( z ) for both the w CDM model and the DGP model. For the first improved parameterized form, we find that the approximation accuracy is enhanced at the high redshifts for both kinds of models, but it is not at the low redshifts. For the second improved parameterized form, it is found that Ω m γ ( z ) approximates the growth factor f very well for all redshifts. For chosen α , the relative error is below 0.003% for the Λ CDM model and 0.028% for the DGP model when Ω m = 0.27 . Thus, the second improved parameterized form of γ ( z ) should be useful for the high precision constraint on the growth index of different models with the observational data. Moreover, we also show that α depends on the equation of state w and the fractional energy density of matter Ω m 0 , which may help us learn more information about dark energy and DGP models.