1,331 research outputs found
Supersolid of Hardcore Bosons on the Face Centered Cubic Lattice
We investigate a supersolid state in hardcore boson models on the
face-centered-cubic (FCC) lattice. The supersolid state is characterized by a
coexistence of crystalline order and superfluidity. Using a quantum Monte Carlo
method based on the directed-loop algorithm, we calculate static structure
factors and superfluid density at finite temperature, from which we obtain the
phase diagram. The supersolid phase exists at intermediate fillings between a
three-quarter-filled solid phase and a half-filled solid phase. We also discuss
the mechanism of the supersolid state on the FCC lattice.Comment: 5pages, 6figure
Ground-State Phase Diagram of the Two-Dimensional Extended Bose-Hubbard Model
We investigate the ground-state phase diagram of the soft-core Bose-Hubbard
model with the nearest-neighbor repulsion on a square lattice by using an
unbiased quantum Monte Carlo method. In contrast to the previous study[P.
Sengupta {\it et. al.}, Phys. Rev. Lett. {\bf 94}, 207202 (2005)], we present
the ground-state phase diagrams up to large hopping parameters. As a result, in
addition to the known supersolid above half-filling, we find supersolid even
below and at half-filling for large hopping parameters. Furthermore, for the
strong nearest-neighbor repulsion, we show that the supersolid phase occupies a
remarkably broad region in the phase diagram. The results are in qualitative
agreement with that obtained by the Gutzwiller mean-field approximation[M.
Iskin, Phys. Rev. A {\bf 83}, 051606(R) (2011) and T. Kimura, Phys. Rev. A {\bf
84}, 063630 (2011)]
Correlation analysis of stochastic gravitational wave background around 0.1-1Hz
We discuss prospects for direct measurement of stochastic gravitational wave
background around 0.1-1Hz with future space missions. It is assumed to use
correlation analysis technique with the optimal TDI variables for two sets of
LISA-type interferometers. The signal to noise for detection of the background
and the estimation errors for its basic parameters (amplitude, spectral index)
are evaluated for proposed missions.Comment: 11 pages, 7 figures, revised version, to appear in PR
LISA Measurement of Gravitational Wave Background Anisotropy: Hexadecapole Moment via a Correlation Analysis
We discuss spatial fluctuations in the gravitational wave background arising
from unresolved Galactic binary sources, such as close white dwarf binaries,
due to the fact the galactic binary source distribution is anisotropic. We
introduce a correlation analysis of the two data streams of the Laser
Interferometer Space Antenna (LISA) to extract spherical harmonic coefficients,
in an independent manner, of the hexadecapole moment () related to the
projected two-dimensional density distribution of the binary source population.
The proposed technique complements and improves over previous suggestions in
the literature to measure the gravitational wave background anisotropy based on
the time modulation of data as LISA orbits around the Sun. Such techniques,
however, are restricted only to certain combinations of spherical harmonic
coefficients of the galaxy with no ability to separate them individually. With
LISA, and 4 coefficients of the hexadecapole () can be measured
with signal-to-noise ratios at the level of 10 and above in a certain
coordinate system. In addition to the hexadecapole coefficients, when combined
with the time modulation analysis, the correlation study can also be used, in
principle, to measure quadrupole coefficients of the binary distribution.Comment: 8 pages, 2 figure
Chiral Lagrangian and spectral sum rules for dense two-color QCD
We analytically study two-color QCD with an even number of flavors at high
baryon density. This theory is free from the fermion sign problem. Chiral
symmetry is broken spontaneously by the diquark condensate. Based on the
symmetry breaking pattern we construct the low-energy effective Lagrangian for
the Nambu-Goldstone bosons. We identify a new epsilon-regime at high baryon
density in which the quark mass dependence of the partition function can be
determined exactly. We also derive Leutwyler-Smilga-type spectral sum rules for
the complex eigenvalues of the Dirac operator in terms of the fermion gap. Our
results can in principle be tested in lattice QCD simulations.Comment: 24 pages, 1 table, no figur
Can we distinguish between black holes and wormholes by their Einstein-ring systems?
For the last decade, the gravitational lensing in the strong gravitational
field has been studied eagerly. It is well known that, for the lensing by a
black hole, infinite number of Einstein rings are formed by the light rays
which wind around the black hole nearly on the photon sphere, which are called
relativistic Einstein rings. This is also the case for the lensing by a
wormhole. In this paper, we study the Einstein ring and relativistic Einstein
rings for the Schwarzschild black hole and the Ellis wormhole, the latter of
which is an example of traversable wormholes of the Morris-Thorne class. Given
the configuration of the gravitational lensing and the radii of the Einstein
ring and relativistic Einstein rings, we can distinguish between a black hole
and a wormhole in principle. We conclude that we can detect the relativistic
Einstein rings by wormholes which have the radii of the throat pc
at a galactic center with the distance 10Mpc and which have AU in
our galaxy using by the most powerful modern instruments which have the
resolution of arcsecond such as a 10-meter optical-infrared telescope.
The black holes which make the Einstein rings of the same size as the ones by
the wormholes are galactic supermassive black holes and the relativistic
Einstein rings by the black holes are too small to measure at this moment. We
may test some hypotheses of astrophysical wormholes by using the Einstein ring
and relativistic Einstein rings in the future.Comment: 13 pages, 2 figures, minor changes from v
Constitutional Rights of Infants and Toddlers to Have Opportunities to Form Secure Attachment with Incarcerated Mothers: Importance of Prison Nurseries
While the number of women is increasing among the prison population, so too is the need to accommodate those who are pregnant and with children. Instead of examining the diminished rights of incarcerated mothers, this paper examines the rights of babies (infants and toddlers) to have opportunities to form a secure attachment with their incarcerated mother. This paper argues this right triggers the government’s affirmative duty to provide prison nurseries. This paper also seeks several aims that include an examination of the issue of prison nurseries, the need for such programs, their history, the constitutional rights of infants and toddlers to have opportunities to form secure attachment with their long-term caregiver, and the policy implications for women or female prisons
The Dynamics of Exploitation and Class in Accumulation Economies
This paper analyses the equilibrium dynamics of exploitation and class in general accumulation economies with population growth, technical change, and bargaining by adopting a novel computational approach. First, the determinants of the emergence and persistence of exploitation and class are investigated, and the role of labour-saving technical change and, even more importantly, power is highlighted. Second, it is shown that the concept of exploitation provides the foundations for a logically coherent and empirically relevant analysis of inequalities and class relations in advanced capitalist economies. An index that identifies the exploitation level, or intensity of each individual can be defined and its empirical distribution studied using the standard tools developed in the theory of inequality measurement
Disk Galaxy Formation in a LambdaCDM Universe
We describe hydrodynamical simulations of galaxy formation in a Lambda cold
dark matter (CDM) cosmology performed using a subresolution model for star
formation and feedback in a multiphase interstellar medium (ISM). In
particular, we demonstrate the formation of a well-resolved disk galaxy. The
surface brightness profile of the galaxy is exponential, with a B-band central
surface brightness of 21.0 mag arcsec^-2 and a scale-length of R_d = 2.0 h^-1
kpc. We find no evidence for a significant bulge component. The simulated
galaxy falls within the I-band Tully-Fisher relation, with an absolute
magnitude of I = -21.2 and a peak stellar rotation velocity of V_rot=121.3 km
s^-1. While the total specific angular momentum of the stars in the galaxy
agrees with observations, the angular momentum in the inner regions appears to
be low by a factor of ~2. The star formation rate of the galaxy peaks at ~7
M_sun yr^-1 between redshifts z=2-4, with the mean stellar age decreasing from
\~10 Gyrs in the outer regions of the disk to ~7.5 Gyrs in the center,
indicating that the disk did not simply form inside-out. The stars exhibit a
metallicity gradient from 0.7 Z_sun at the edge of the disk to 1.3 Z_sun in the
center. Using a suite of idealized galaxy formation simulations with different
models for the ISM, we show that the effective pressure support provided by
star formation and feedback in our multiphase model is instrumental in allowing
the formation of large, stable disk galaxies. If ISM gas is instead modeled
with an isothermal equation of state, or if star formation is suppressed
entirely, growing gaseous disks quickly violate the Toomre stability criterion
and undergo catastrophic fragmentation.Comment: 14 pages, 12 figures, LaTex (emulateapj.cls), submitted to ApJ, high
resolution images available at
http://www-cfa.harvard.edu/~brobertson/papers/galaxy
Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling
We study evolution of various statistical quantities of smoothed cosmic
density and velocity fields using N-body simulations. The parameter
characterizes nonlinear coupling of
these two fields and determines behavior of bulk velocity dispersion as a
function of local density contrast.
It is found that this parameter depends strongly on the smoothing scale even
in quasi-linear regimes where the skewness parameter
is nearly constant and close to the predicted value by the second-order
perturbation theory. We also analyze weakly nonlinear effects caused by an
adaptive smoothing known as the gather approach.Comment: 22 pages, 4 figures, to appear in ApJ (558, Sep 10
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