Quantum optomechanics of a Bose-Einstein Antiferromagnet

We investigate the cavity optomechanical properties of an antiferromagnetic Bose-Einstein con- densate, where the role of the mechanical element is played by spin-wave excitations. We show how this system can be described by a single rotor that can be prepared deep in the quantum regime under realizable experimental conditions. This system provides a bottom-up realization of dispersive rotational optomechanics, and opens the door to the direct observation of quantum spin fluctuations.Comment: 4 pages, 1 figure, accepted for publication in Physical Review Letters (2011

Confinement induced by fermion damping in three-dimensional QED

The three-dimensional non-compact QED is known to exhibit weak confinement when fermions acquire a finite mass via the mechanism of dynamical chiral symmetry breaking. In this paper, we study the effect of fermion damping caused by elastic scattering on the classical potential between fermions. By calculating the vacuum polarization function that incorporates the fermion damping effect, we show that fermion damping can induce a weak confinement even when the fermions are massless and the chiral symmetry is not broken.Comment: 4 pages, no figur

Abundance of moderate-redshift clusters in the Cold + Hot dark matter model

Using a set of \pppm simulation which accurately treats the density evolution of two components of dark matter, we study the evolution of clusters in the Cold + Hot dark matter (CHDM) model. The mass function, the velocity dispersion function and the temperature function of clusters are calculated for four different epochs of $z\le 0.5$. We also use the simulation data to test the Press-Schechter expression of the halo abundance as a function of the velocity dispersion $\sigma_v$. The model predictions are in good agreement with the observational data of local cluster abundances ($z=0$). We also tentatively compare the model with the Gunn and his collaborators' observation of rich clusters at $z\approx 0.8$ and with the x-ray luminous clusters at $z\approx 0.5$ of the {\it Einstein} Extended Medium Sensitivity Survey. The important feature of the model is the rapid formation of clusters in the near past: the abundances of clusters of \sigma_v\ge 700\kms and of \sigma_v\ge 1200 \kms at $z=0.5$ are only 1/4 and 1/10 respectively of the present values ($z=0$). Ongoing ROSAT and AXAF surveys of distant clusters will provide sensitive tests to the model. The abundance of clusters at $z\approx 0.5$ would also be a good discriminator between the CHDM model and a low-density flat CDM model both of which show very similar clustering properties at $z=0$.Comment: 21 pages + 6 figures (uuencoded version of the PS files), Steward Preprints No. 118

The shapes, orientation, and alignment of Galactic dark matter subhalos

We present a study of the shapes, orientations, and alignments of Galactic dark matter subhalos in the ``Via Lactea'' simulation of a Milky Way-size LCDM host halo. Whereas isolated dark matter halos tend to be prolate, subhalos are predominantly triaxial. Overall subhalos are more spherical than the host halo, with minor to major and intermediate to major axis ratios of 0.68 and 0.83, respectively. Like isolated halos, subhalos tend to be less spherical in their central regions. The principal axis ratios are independent of subhalo mass, when the shapes are measured within a physical scale like r_Vmax, the radius of the peak of the circular velocity curve. Subhalos tend to be slightly more spherical closer to the host halo center. The spatial distribution of the subhalos traces the prolate shape of the host halo when they are selected by the largest V_max they ever had, i.e. before they experienced strong tidal mass loss. The subhalos' orientation is not random: the major axis tends to align with the direction towards the host halo center. This alignment disappears for halos beyond 3 r_200 and is more pronounced when the shapes are measured in the outer regions of the subhalos. The radial alignment is preserved during a subhalo's orbit and they become elongated during pericenter passage, indicating that the alignment is likely caused by the host halo's tidal forces. These tidal interactions with the host halo act to make subhalos rounder over time.Comment: 12 pages, 11 figures, submitted to ApJ, v2: corrected typo in abstract ("[...] subhalos tend be less spherical in their central regions."), added a few reference

Wave spectra of 2D dusty plasma solids and liquids

Brownian dynamics simulations were carried out to study wave spectra of two-dimensional dusty plasma liquids and solids for a wide range of wavelengths. The existence of a longitudinal dust thermal mode was confirmed in simulations, and a cutoff wavenumber in the transverse mode was measured. Dispersion relations, resulting from simulations, were compared with those from analytical theories, such as the random-phase approximation (RPA), quasi-localized charged approximation (QLCA), and harmonic approximation (HA). An overall good agreement between the QLCA and simulations was found for wide ranges of states and wavelengths after taking into account the direct thermal effect in the QLCA, while for the RPA and HA good agreement with simulations were found in the high and low temperature limits, respectively.Comment: 26 pages, 9 figure

The influence of baryons on the mass distribution of dark matter halos

Using a set of high-resolution N-body/SPH cosmological simulations with identical initial conditions but run with different numerical setups, we investigate the influence of baryonic matter on the mass distribution of dark halos when radiative cooling is NOT included. We compare the concentration parameters of about 400 massive halos with virial mass from $10^{13}$ \Msun to $7.1 \times 10^{14}$ \Msun. We find that the concentration parameters for the total mass and dark matter distributions in non radiative simulations are on average larger by ~3% and 10% than those in a pure dark matter simulation. Our results indicate that the total mass density profile is little affected by a hot gas component in the simulations. After carefully excluding the effects of resolutions and spurious two-body heating between dark matter and gas particles, we conclude that the increase of the dark matter concentration parameters is due to interactions between baryons and dark matter. We demonstrate this with the aid of idealized simulations of two-body mergers. The results of individual halos simulated with different mass resolutions show that the gas profiles of densities, temperature and entropy are subjects of mass resolution of SPH particles. In particular, we find that in the inner parts of halos, as the SPH resolution increases the gas density becomes higher but both the entropy and temperature decrease.Comment: 8 pages, 6 figures, 1 table, ApJ in press (v652n1); updated to match with the being published versio

Implication of Omega_m through the Morphological Analysis of Weak Lensing Fields

We apply the morphological descriptions of two-dimensional contour map, the so-called Minkowski functionals (the area fraction, circumference, and Euler characteristics), to the convergence field $\kappa(\bm{\theta})$ of the large-scale structure reconstructed from the shear map produced by the ray-tracing simulations. The perturbation theory of structure formation has suggested that the non-Gaussian features on the Minkowski functionals with respect to the threshold in the weakly nonlinear regime are induced by the three skewness parameters of $\kappa$ that are sensitive to the density parameter of matter, $\Omega_{\rm m}$. We show that, in the absence of noise due to the intrinsic ellipticities of source galaxies with which the perturbation theory results can be recovered, the accuracy of $\Omega_{\rm m}$ determination is improved by $\sim 20$ using the Minkowski functionals compared to the conventional method of using the direct measure of skewness.Comment: 4 pages, 3 figures, to appear in ApJ Lette

Asymptotic tails of massive scalar fields in a stationary axisymmetric EMDA black hole geometry

The late-time tail behavior of massive scalar fields is studied analytically in a stationary axisymmetric EMDA black hole geometry. It is shown that the asymptotic behavior of massive perturbations is dominated by the oscillatory inverse power-law decaying tail $t^{-(l+3/2)}\sin(\mu t)$ at the intermediate late times, and by the asymptotic tail $t^{-5/6}\sin(\mu t)$ at asymptotically late times. Our result seems to suggest that the intermediate tails $t^{-(l+3/2)}\sin(\mu t)$ and the asymptotically tails $t^{-5/6} \sin(\mu t)$ may be quite general features for evolution of massive scalar fields in any four dimensional asymptotically flat rotating black hole backgrounds.Comment: 6 page