3,557 research outputs found
Flows to Schrodinger Geometries
We construct RG flow solutions interpolating AdS and Schrodinger geometries
in Abelian Higgs models obtained from consistent reductions of type IIB
supergravity and M-theory. We find that z=2 Schrodinger geometries can be
realized at the minima of scalar potentials of these models, where a scalar
charged under U(1) gauge symmetry obtains a nonzero vacuum expectation value.
The RG flows are induced by an operator deformation of the dual CFT. The flows
are captured by fake superpotentials of the theories.Comment: 19 pages, 5 figures, v2: typos corrected, references added, published
version in PR
An astrometric facility for planetary detection on the space station
An Astrometric Telescope Facility (ATF) for planetary detection is being studied as a potential space station initial operating capability payload. The primary science objective of this mission is the detection and study of planetary systems around other stars. In addition, the facility will be capable of other astrometric measurements such as stellar motions of other galaxies and highly precise direct measurement of stellar distance within the Milky Way Galaxy. The results of a recently completed ATF preliminary systems definition study are summarized. Results of this study indicate that the preliminary concept for the facility is fully capable of meeting the science objective without the development of any new technologies. A simple straightforward operations approach was developed for the ATF. A real-time facility control is not normally required, but does maintain a near real-time ground monitoring capability for the facility and science data stream on a full-time basis. Facility observational sequences are normally loaded once a week. In addition, the preliminary system is designed to be fail-safe and single-fault tolerant. Routine interactions by the space station crew with the ATF will not be necessary, but onboard controls are provided for crew override as required for emergencies and maintenance
Nonlinear Evolution of Very Small Scale Cosmological Baryon Perturbations at Recombination
The evolution of baryon density perturbations on very small scales is
investigated. In particular, the nonlinear growth induced by the radiation drag
force from the shear velocity field on larger scales during the recombination
epoch, which is originally proposed by Shaviv in 1998, is studied in detail. It
is found that inclusion of the diffusion term which Shaviv neglected in his
analysis results in rather mild growth whose growth rate is instead
of enormous amplification of Shaviv's original claim since the
diffusion suppresses the growth. The growth factor strongly depends on the
amplitude of the large scale velocity field. The nonlinear growth mechanism is
applied to density perturbations of general adiabatic cold dark matter (CDM)
models. In these models, it has been found in the previous works that the
baryon density perturbations are not completely erased by diffusion damping if
there exists gravitational potential of CDM. With employing the perturbed rate
equation which is derived in this paper, the nonlinear evolution of baryon
density perturbations is investigated. It is found that: (1) The nonlinear
growth is larger for smaller scales. This mechanism only affects the
perturbations whose scales are smaller than , which are
coincident with the stellar scales. (2) The maximum growth factors of baryon
density fluctuations for various COBE normalized CDM models are typically less
than factor 10 for large scale velocity peaks. (3) The growth factor
depends on .Comment: 24 pages, 9 figures, submitted to Ap
Can Geometric Test Probe the Cosmic Equation of State ?
Feasibility of the geometric test as a probe of the cosmic equation of state
of the dark energy is discussed assuming the future 2dF QSO sample. We examine
sensitivity of the QSO two-point correlation functions, which are theoretically
computed incorporating the light-cone effect and the redshift distortions, as
well as the nonlinear effect, to a bias model whose evolution is
phenomenologically parameterized. It is shown that the correlation functions
are sensitive on a mean amplitude of the bias and not to the speed of the
redshift evolution. We will also demonstrate that an optimistic geometric test
could suffer from confusion that a signal from the cosmological model can be
confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ
Near Extremal Black Hole Entropy as Entanglement Entropy via AdS2/CFT1
We point out that the entropy of (near) extremal black holes can be
interpreted as the entanglement entropy of dual conformal quantum mechanics via
AdS2/CFT1. As an explicit example, we study near extremal BTZ black holes and
derive this claim from AdS3/CFT2. We also analytically compute the entanglement
entropy in the two dimensional CFT of a free Dirac fermion compactified on a
circle at finite temperature. From this result, we clarify the relation between
the thermal entropy and entanglement entropy, which is essential for the
entanglement interpretation of black hole entropy.Comment: LaTeX, 32 pages, 7 figures; refinement in the organizatio
The cosmological light-cone effect on the power spectrum of galaxies and quasars in wide-field redshift surveys
We examine observational consequences of the cosmological light-cone effect
on the power spectrum of the distribution of galaxies and quasars from upcoming
redshift surveys. First we derive an expression for the power spectrum of
cosmological objects in real space on a light cone, , which is exact in linear theory of density perturbations. Next we
incorporate corrections for the nonlinear density evolution and redshift-space
distortion in the formula in a phenomenological manner which is consistent with
recent numerical simulations. On the basis of this formula, we predict the
power spectrum of galaxies and quasars on the light cone for future redshift
surveys taking account of the selection function properly. We demonstrate that
this formula provides a reliable and useful method to compute the power
spectrum on the light cone given an evolution model of bias.Comment: 18 pages, 3 figures, to be published in the Astrophysical Journa
High-field magnetization and magnetic phase transition in CeOs2Al10
We have studied the magnetization of CeOs2Al10 in high magnetic fields up to
55 T for H // a and constructed the magnetic phase diagram for H // a. The
magnetization curve shows a concave H dependence below T_max \sim40 K which is
higher than the transition temperature T_0 \sim29 K. The magnetic
susceptibility along the a-axis shows a smooth and continuous decrease down to
\sim20 K below T_max \sim40 K without showing an anomaly at T_0. From these two
results, a Kondo singlet is formed below T_max and coexists with the antiferro
magnetic order below T_0. We also propose that the larger suppression of the
spin degrees of freedom along the a-axis than along the c-axis below T_max is
associated with the origin of the antiferro magnetic component.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B, Rapid Commu
Long-range order and low-energy magnetic excitations in CeRu2Al10
The nature of the unconventional ordered phase occurring in CeRu2Al10 below
T0 = 27 K was investigated by neutron scattering. Powder diffraction patterns
show clear superstructure peaks corresponding to forbidden (h + k)-odd
reflections of the Cmcm space group. Inelastic neutron scattering experiments
further reveal a pronounced magnetic excitation developing in the ordered phase
at an energy of 8 meV.Comment: 5 pages; 4 figure
How to identify sex chromosomes and their turnover
Although sex is a fundamental component of eukaryotic reproduction, the genetic systems that control sex determination are highly variable. In many organisms the presence of sex chromosomes is associated with female or male development. Although certain groups possess stable and conserved sex chromosomes, others exhibit rapid sex chromosome evolution including transitions between male and female heterogamety, and turnover in the chromosome pair recruited to determine sex. These turnover events have important consequences for multiple facets of evolution, as sex chromosomes are predicted to play a central role in adaptation, sexual dimorphism, and speciation. However, our understanding of the processes driving the formation and turnover of new sex chromosome systems is limited, in part because we lack a complete understanding of interâspecific variation in the mechanisms by which sex is determined. New bioinformatic methods are making it possible to identify and characterize sex chromosomes in a diverse array of nonâmodel species, rapidly filling in the numerous gaps in our knowledge of sex chromosome systems across the tree of life. In turn, this growing dataset is facilitating and fueling efforts to address many of the unanswered questions in sex chromosome evolution. Here, we synthesize the available bioinformatic approaches to produce a guide for characterizing sex chromosome system and identity simultaneously across clades of organisms. Furthermore, we survey our current understanding of the processes driving sex chromosome turnover, and highlight important avenues for future research
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