11,437 research outputs found
On N=8 attractors
We derive and solve the black hole attractor conditions of N=8 supergravity
by finding the critical points of the corresponding black hole potential. This
is achieved by a simple generalization of the symplectic structure of the
special geometry to all extended supergravities with .
There are two solutions for regular black holes, one for 1/8 BPS ones and one
for the non-BPS. We discuss the solutions of the moduli at the horizon for BPS
attractors using N=2 language. An interpretation of some of these results in
N=2 STU black hole context helps to clarify the general features of the black
hole attractors.Comment: 15 page
Further Evidence for a Merger Origin for the Thick Disk: Galactic Stars Along Lines-of-sight to Dwarf Spheroidal Galaxies
The history of the Milky Way Galaxy is written in the properties of its
stellar populations. Here we analyse stars observed as part of surveys of local
dwarf spheroidal galaxies, but which from their kinematics are highly probable
to be non-members. The selection function -- designed to target metal-poor
giants in the dwarf galaxies, at distances of ~100kpc -- includes F-M dwarfs in
the Milky Way, at distances of up to several kpc. Thestars whose motions are
analysed here lie in the cardinal directions of Galactic longitude l ~ 270 and
l ~ 90, where the radial velocity is sensitive to the orbital rotational
velocity. We demonstrate that the faint F/G stars contain a significant
population with V_phi ~ 100km/s, similar to that found by a targeted, but
limited in areal coverage, survey of thick-disk/halo stars by Gilmore, Wyse &
Norris (2002). This value of mean orbital rotation does not match either the
canonical thick disk or the stellar halo. We argue that this population,
detected at both l ~ 270 and l ~ 90, has the expected properties of `satellite
debris' in the thick-disk/halo interface, which we interpret as remnants of the
merger that heated a pre-existing thin disk to form the thick disk.Comment: Accepted, Astrophysical Journal Letter
Generalized coherent states are unique Bell states of quantum systems with Lie group symmetries
We consider quantum systems, whose dynamical symmetry groups are semisimple
Lie groups, which can be split or decay into two subsystems of the same
symmetry. We prove that the only states of such a system that factorize upon
splitting are the generalized coherent states. Since Bell's inequality is never
violated by the direct product state, when the system prepared in the
generalized coherent state is split, no quantum correlations are created.
Therefore, the generalized coherent states are the unique Bell states, i.e.,
the pure quantum states preserving the fundamental classical property of
satisfying Bell's inequality upon splitting.Comment: 4 pages, REVTeX, amssymb style. More information on
http://www.technion.ac.il/~brif/science.htm
Quantum-to-Classical Correspondence and Hubbard-Stratonovich Dynamical Systems, a Lie-Algebraic Approach
We propose a Lie-algebraic duality approach to analyze non-equilibrium
evolution of closed dynamical systems and thermodynamics of interacting quantum
lattice models (formulated in terms of Hubbard-Stratonovich dynamical systems).
The first part of the paper utilizes a geometric Hilbert-space-invariant
formulation of unitary time-evolution, where a quantum Hamiltonian is viewed as
a trajectory in an abstract Lie algebra, while the sought-after evolution
operator is a trajectory in a dynamic group, generated by the algebra via
exponentiation. The evolution operator is uniquely determined by the
time-dependent dual generators that satisfy a system of differential equations,
dubbed here dual Schrodinger-Bloch equations, which represent a viable
alternative to the conventional Schrodinger formulation. These dual
Schrodinger-Bloch equations are derived and analyzed on a number of specific
examples. It is shown that deterministic dynamics of a closed classical
dynamical system occurs as action of a symmetry group on a classical manifold
and is driven by the same dual generators as in the corresponding quantum
problem. This represents quantum-to-classical correspondence. In the second
part of the paper, we further extend the Lie algebraic approach to a wide class
of interacting many-particle lattice models. A generalized Hubbard-Stratonovich
transform is proposed and it is used to show that the thermodynamic partition
function of a generic many-body quantum lattice model can be expressed in terms
of traces of single-particle evolution operators governed by the dynamic
Hubbard-Stratonovich fields. Finally, we derive Hubbard-Stratonovich dynamical
systems for the Bose-Hubbard model and a quantum spin model and use the
Lie-algebraic approach to obtain new non-perturbative dual descriptions of
these theories.Comment: 25 pages, 1 figure; v2: citations adde
LSST optical beam simulator
We describe a camera beam simulator for the LSST which is capable of
illuminating a 60mm field at f/1.2 with realistic astronomical scenes, enabling
studies of CCD astrometric and photometric performance. The goal is to fully
simulate LSST observing, in order to characterize charge transport and other
features in the thick fully depleted CCDs and to probe low level systematics
under realistic conditions. The automated system simulates the centrally
obscured LSST beam and sky scenes, including the spectral shape of the night
sky. The doubly telecentric design uses a nearly unit magnification design
consisting of a spherical mirror, three BK7 lenses, and one beam-splitter
window. To achieve the relatively large field the beam-splitter window is used
twice. The motivation for this LSST beam test facility was driven by the need
to fully characterize a new generation of thick fully-depleted CCDs, and assess
their suitability for the broad range of science which is planned for LSST. Due
to the fast beam illumination and the thick silicon design [each pixel is 10
microns wide and over 100 microns deep] at long wavelengths there can be
effects of photon transport and charge transport in the high purity silicon.
The focal surface covers a field more than sufficient for a 40x40 mm LSST CCD.
Delivered optical quality meets design goals, with 50% energy within a 5 micron
circle. The tests of CCD performance are briefly described.Comment: 9 pages, 9 figure
Phase diagram for a Cubic Consistent-Q Interacting Boson Model Hamiltonian: signs of triaxiality
An extension of the Consistent-Q formalism for the Interacting Boson Model
that includes the cubic QxQxQ term is proposed. The potential energy surface
for the cubic quadrupole interaction is explicitly calculated within the
coherent state formalism using the complete chi-dependent expression for the
quadrupole operator. The Q-cubic term is found to depend on the asymmetry
deformation parameter gamma as a linear combination of cos(3gamma) and
cos^2(3\gamma) terms, thereby allowing for triaxiality. The phase diagram of
the model in the large N limit is explored, it is described the order of the
phase transition surfaces that define the phase diagram, and moreover, the
possible nuclear equilibrium shapes are established. It is found that, contrary
to expectations, there is only a very tiny region of triaxiality in the model,
and that the transition from prolate to oblate shapes is so fast that, in most
cases, the onset of triaxiality might go unnoticed.Comment: 18 pages, 19 figure
A new low mass for the Hercules dSph: the end of a common mass scale for the dwarfs?
We present a new mass estimate for the Hercules dwarf spheroidal galaxy
(dSph), based on the revised velocity dispersion obtained by Aden et al. (2009,
arXiv:0908.3489).
The removal of a significant foreground contamination using newly acquired
Stromgren photometry has resulted in a reduced velocity dispersion. Using this
new velocity dispersion of 3.72 +/- 0.91 km/s, we find a mass of
M_300=1.9^{+1.1}_{-0.8} 10^6 M_sun within the central 300 pc, which is also the
half-light radius, and a mass of M_433=3.7_{-1.6}^{+2.2} 10^6 M_sun within the
reach of our data to 433 pc, significantly lower than previous estimates. We
derive an overall mass-to-light ratio of M_433/L=103^{+83}_{-48} M_sun/L_sun.
Our mass estimate calls into question recent claims of a common mass scale for
dSph galaxies.
Additionally, we find tentative evidence for a velocity gradient in our
kinematic data of 16 +/- 3 km/s/kpc, and evidence of an asymmetric extension in
the light distribution at about 0.5 kpc. We explore the possibility that these
features are due to tidal interactions with the Milky Way. We show that there
is a self-consistent model in which Hercules has an assumed tidal radius of r_t
= 485 pc, an orbital pericentre of r_p = 18.5 +/- 5 kpc, and a mass within r_t
of M_{tid,r_t}=5.2 +/- 2.7 10^6 M_sun. Proper motions are required to test this
model. Although we cannot exclude models in which Hercules contains no dark
matter, we argue that Hercules is more likely to be a dark matter dominated
system which is currently experiencing some tidal disturbance of its outer
parts.Comment: 10 pages, 3 figures, Accepted for publication by ApJ
Quantum reflection of ultracold atoms from thin films, graphene, and semiconductor heterostructures
We show that thin dielectric films can be used to enhance the performance of
passive atomic mirrors by enabling quantum reflection probabilities of over 90%
for atoms incident at velocities ~1 mm/s, achieved in recent experiments. This
enhancement is brought about by weakening the Casimir-Polder attraction between
the atom and the surface, which induces the quantum reflection. We show that
suspended graphene membranes also produce higher quantum reflection
probabilities than bulk matter. Temporal changes in the electrical resistance
of such membranes, produced as atoms stick to the surface, can be used to
monitor the reflection process, non-invasively and in real time. The resistance
change allows the reflection probability to be determined purely from
electrical measurements without needing to image the reflected atom cloud
optically. Finally, we show how perfect atom mirrors may be manufactured from
semiconductor heterostructures, which employ an embedded two-dimensional
electron gas to tailor the atom-surface interaction and so enhance the
reflection by classical means.Comment: 8 pages, 4 figure
- …