118924830
Can Quintessence Be The Rolling Tachyon?
In light of the recent work by Sen and Gibbons, we present a phase-plane analysis on the cosmology containing a rolling tachyon field in a potential resulted from string theory. We show that there is no stable point on the phase-plane, which indicated that there is a coincidence problem if one consider tachyon as a candidate of quintessence. Furthermore, we also analyze the phase-plane of the cosmology containing a rolling tachyon field for an exactly solvable toy potential in which the critical point is stable. Therefore, it is possible for rolling tachyon to be quintessence if one give up the strict constraint on the potential or find a more appropriate effective potential for the tachyon from M/string theory.
119458029
O(N) Quintessence with a Cosine-Type Potential
We propose a quintessence model with a cosine-type potential, in which the scalar field Φa possesses an O(N) internal symmetry. The most prominent feature of this model is that it will not reduce to a cosmological constant even when |Φa| is spatially uniform and time-independent. Since different values of the potential parameter will lead to different cosmic microwave background anisotropies, which may be detectable in future satellite experiments, one can decide by observations whether the cosine-type quintessence consists of one scalar field or many fields with a symmetry constraint.
121863790
A New Exactly Solvable Inflation Model and Its Power Spectrum
We present a new exactly solvable inflation model in which inflation can stop automatically, and in the approximately de Sitter limit, we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.
199673346
Generalized quartessence cosmic dynamics: phantom or quintessence with de Sitter attractor
7857108
Cosmological dynamics of scalar fields with O(N) symmetry
In this paper, we study the cosmological dynamics of scalar fields with O(N) symmetry in general potentials. We compare the phase space of the dynamical systems of the quintessence and phantom and give the conditions for the existence of various attractors as well as their cosmological implications. We also show that the existence of a tracking attractor in O(N) phantom models requires the potential with Γ < 1/2, which makes the model with exponential potential possess no tracking attractor.
198140971
Charged D stars
We describe charged soliton stars with a solid angular deficit (charged boson D stars), and find the approximate solution in the external space. Besides, we discuss the stability of charged D stars and find when the number of bosons is less than certain value, charged D stars are quantum mechanically stable.
119202826
Sunyaev-Zel’dovich signal of the maxBCG SDSS galaxy clusters in WMAP
The Planck Collaboration measured the Sunyaev-Zel'dovich (SZ) decrement of optically selected clusters from the Sloan Digital Sky Survey, finding that it falls significantly below expectations based on existing mass calibration of the maxBCG galaxy clusters. Resolving this tension requires either the data to go up, or the theoretical expectations to come down. Here, we use data from the Wilkinson Microwave Anisotropy Probe (WMAP) to perform an independent estimate of the SZ decrement of maxBCG clusters. The recovered signal is consistent with that obtained using Planck, though with larger error bars due to WMAP's larger beam size and smaller frequency range. Nevertheless, this detection serves as an independent confirmation of the magnitude of the effect, and demonstrates that the observed discrepancy must be theoretical in origin.
14496803
LARGE-SCALE CAVITIES SURROUNDING MICROQUASARS INFERRED FROM EVOLUTION OF THEIR RELATIVISTIC JETS
The black hole (BH) X-ray transient XTE J1550-564 has undergone a strong outburst in 1998 and two relativistic X-ray jets have been detected years later with the Chandra X-ray observatory; the eastern jet was found previously to have decelerated after its first detection. Here, we report a full analysis of the evolution of the western jet; significant deceleration is also detected in the western side. Our analysis indicates that there is a cavity outside the central source and the jets first traveled with constant velocity and then were slowed down by the interactions between the jets and the interstellar medium. The best-fitted radius of the cavity is similar to 0.31 pc on the eastern side and similar to 0.44 pc on the western side, and the densities also show asymmetry, of similar to 0.034 cm(-3) on the east to similar to 0.12 cm(-3) on the west. The best-fitted magnetic fields on both sides are similar to 0.5 mG. Similar analysis is also applied to another microquasar system, H 1743-322, and a large-scale low-density region is also found. Based on these results and the comparison with other microquasar systems, we suggest a generic scenario for microquasar jets, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them. We also suggest that either continuous jets or accretion disk winds, or both may be responsible for creating these cavities. Therefore X-ray jets from microquasars provide us with a promising method of probing the environment of accreting BHs.
16218923
Evolution of relativistic jets from XTE J1550‐564 and the environment of microquasars
Two relativistic X‐ray jets have been detected with the Chandra X‐ray observatory in the black hole X‐ray transient XTE J1550‐564. We report a full analysis of the evolution of the two jets with a gamma‐ray burst external shock model. A plausible scenario suggests a cavity outside the central source and the jets first travelled with constant velocity and then are slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is ∼0.36 pc on the eastern side and ∼0.46 pc on the western side, and the densities also show asymmetry, of ∼0.015 cm−3 on the east to ∼0.21 cm−3 on the west. Large scale low density region is also found in another microquasar system, H 1743‐322. These results are consistent with previous suggestions that the environment of microquasars should be rather vacuous, compared to the normal Galactic environment. A generic scenario for microquasar jets is proposed, classifying the observed jets into three main categories, with differe...
118439902
Jets and environment of microquasars
Two relativistic X-ray jets have been detected with the Chandra X-ray observatory from the black hole X-ray transient XTE J1550-564. We report a full analysis of the evolution of the two jets with a gamma-ray burst external shock model. A plausible scenario suggests a cavity outside the central source and the jets first travelled with constant velocity and then are slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is $\sim$0.36 pc on the eastern side and $\sim$0.46 pc on the western side, and the densities also show asymmetry, of $\sim$0.015 cm$^{-3}$ on the east to $\sim$0.21 cm$^{-3}$ on the west. A large scale low density region is also found in another microquasar system, H 1743-322. These results are consistent with previous suggestions that the environment of microquasars should be rather vacuous, compared to the normal Galactic environment. A generic scenario for microquasar jets is proposed, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them.