2,798 research outputs found
The geometry of antisymplectic involutions, I
We study fixed loci of antisymplectic involutions on projective hyperkahler manifolds of K3([n])-type. When the involution is induced by an ample class of square 2 in the Beauville-Bogomolov-Fujiki lattice, we show that the number of connected components of the fixed locus is equal to the divisibility of the class, which is either 1 or 2
Evolution equation for a model of surface relaxation in complex networks
In this paper we derive analytically the evolution equation of the interface
for a model of surface growth with relaxation to the minimum (SRM) in complex
networks. We were inspired by the disagreement between the scaling results of
the steady state of the fluctuations between the discrete SRM model and the
Edward-Wilkinson process found in scale-free networks with degree distribution
for [Pastore y Piontti {\it et al.},
Phys. Rev. E {\bf 76}, 046117 (2007)]. Even though for Euclidean lattices the
evolution equation is linear, we find that in complex heterogeneous networks
non-linear terms appear due to the heterogeneity and the lack of symmetry of
the network; they produce a logarithmic divergency of the saturation roughness
with the system size as found by Pastore y Piontti {\it et al.} for .Comment: 9 pages, 2 figure
The Cepheid distance to the maser-host galaxy NGC 4258: Studying systematics with the Large Binocular Telescope
We identify and phase a sample of 81 Cepheids in the maser-host galaxy NGC
4258 using the Large Binocular Telescope (LBT), and obtain calibrated mean
magnitudes in up to 4 filters for a subset of 43 Cepheids using archival HST
data. We employ 3 models to study the systematic effects of extinction, the
assumed extinction law, and metallicity on the Cepheid distance to NGC 4258. We
find a correction to the Cepheid colors consistent with a grayer extinction law
in NGC 4258 compared to the Milky Way (), although we believe this is
indicative of other systematic effects. If we combine our Cepheid sample with
previously known Cepheids, we find a significant metallicity adjustment to the
distance modulus of mag/dex, for the Zaritsky et
al. (1994) metallicity scale, as well as a weak trend of Cepheid colors with
metallicity. Conclusions about the absolute effect of metallicity on Cepheid
mean magnitudes appear to be limited by the available data on the metallicity
gradient in NGC 4258, but our Cepheid data require at least some metallicity
adjustment to make the Cepheid distance consistent with independent distances
to the LMC and NGC 4258. From our ensemble of models and the geometric maser
distance of NGC 4258 ( mag), we estimate
mag ( kpc).Comment: Accepted for publication in MNRAS. 28 pages, 13 figures, 11 tables. A
brief video summarizing the key results of this paper can be found at
http://youtu.be/ICTTNyxZ89
Effect of degree correlations above the first shell on the percolation transition
The use of degree-degree correlations to model realistic networks which are
characterized by their Pearson's coefficient, has become widespread. However
the effect on how different correlation algorithms produce different results on
processes on top of them, has not yet been discussed. In this letter, using
different correlation algorithms to generate assortative networks, we show that
for very assortative networks the behavior of the main observables in
percolation processes depends on the algorithm used to build the network. The
different alghoritms used here introduce different inner structures that are
missed in Pearson's coefficient. We explain the different behaviors through a
generalization of Pearson's coefficient that allows to study the correlations
at chemical distances l from a root node. We apply our findings to real
networks.Comment: In press EP
A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder
We report observations of 240 Cepheid variables obtained with the Near
Infrared Camera (NICMOS) through the F160W filter on the Hubble Space Telescope
(HST). The Cepheids are distributed across six recent hosts of Type Ia
supernovae (SNe Ia) and the "maser galaxy" NGC 4258, allowing us to directly
calibrate the peak luminosities of the SNe Ia from the precise, geometric
distance measurements provided by the masers. New features of our measurement
include the use of the same instrument for all Cepheid measurements across the
distance ladder and homogeneity of the Cepheid periods and metallicities thus
necessitating only a differential measurement of Cepheid fluxes and reducing
the largest systematic uncertainties in the determination of the fiducial SN Ia
luminosity. The NICMOS measurements reduce differential extinction in the host
galaxies by a factor of 5 over past optical data. Combined with an expanded of
240 SNe Ia at z<0.1 which define their magnitude-redshift relation, we find
H_0=74.2 +/-3.6, a 4.8% uncertainty including both statistical and systematic
errors. We show that the factor of 2.2 improvement in the precision of H_0 is a
significant aid to the determination of the equation-of-state of dark energy, w
= P/(rho c^2). Combined with the WMAP 5-year measurement of Omega_M h^2, we
find w= -1.12 +/- 0.12 independent of high-redshift SNe Ia or baryon acoustic
oscillations (BAO). This result is also consistent with analyses based on the
combination of high-z SNe Ia and BAO. The constraints on w(z) now with high-z
SNe Ia and BAO are consistent with a cosmological constant and improved by a
factor of 3 from the refinement in H_0 alone. We show future improvements in
H_0 are likely and will further contribute to multi-technique studies of dark
energy.Comment: 60 pages, 15 figures Accepted for Publication, ApJ. This is the
second of two papers reporting results from a program to determine the Hubble
constant to 5% precision from a refurbished distance ladder based on
extensive use of differential measurement
Charge-coupled devices with fast timing for astrophysics and space physics research
A charge coupled device is under development with fast timing capability (15 millisecond full frame readout, 30 microsecond resolution for measuring the time of individual pixel hits). The fast timing CCD will be used in conjunction with a CsI microfiber array or segmented scintillator matrix detector to detect x rays and gamma rays with submillimeter position resolution. The initial application will be in conjunction with a coded aperture hard x ray/gamma ray astronomy instrument. We describe the concept and the readout architecture of the device
A First Look at Cepheids in a SN Ia Host with JWST
We report the first look at extragalactic Cepheid variables with the James
Webb Space Telescope, obtained from a serendipitous (to this purpose)
observation of NGC 1365, host of an SN Ia (SN 2012fr), a calibration path used
to measure the Hubble constant. As expected, the high-resolution observations
with NIRCam through F200W show better source separation from line-of-sight
companions than HST images at similar near-infrared wavelengths, the spectral
region that has been used to mitigate the impact of host dust on distance
measurements. Using the standard star P330E as a zeropoint and PSF reference,
we photometered 31 previously-known Cepheids in the JWST field, spanning 1.15 <
log P < 1.75 including 24 Cepheids in the longer period interval of 1.35 < log
P < 1.75. We compared the resultant Period-Luminosity relations to that of 49
Cepheids in the full period range including 38 in the longer period range
observed with WFC3/IR on HST and transformed to the JWST photometric system
(F200W, Vega). The P-L relations measured with the two space telescopes are in
good agreement, with intercepts (at log P=1) of 25.74+/-0.04 and 25.72+\-0.05
for HST and JWST, respectively. Our baseline result comes from the longer
period range where the Cepheids have higher signal-to-noise ratios where we
find 25.75+\-0.05 and 25.75+\-0.06 mag for HST and JWST, respectively. We find
good consistency between this first JWST measurement and HST, and no evidence
that HST Cepheid photometry is "biased bright" at the ~0.2 mag level that would
be needed to mitigate the Hubble Tension, though comparisons from more SN hosts
are warranted and anticipated. We expect future JWST observations to surpass
these in quality as they will be optimized for measuring Cepheids.Comment: 11 pages, 4 figure
Bound state dynamics in the long-range spin- ½ XXZ model
Experimental platforms based on trapped ions, cold molecules, and Rydberg atoms have made possible the investigation of highly nonlocal spin-1/2 Hamiltonians with long-range couplings. Here, we study the effects of such nonlocal couplings in the long-range spin-1/2 XXZ Heisenberg Hamiltonian. We calculate explicitly the two-spin energy spectrum, which describes all possible energetic configurations of two spins pointing in a specific direction embedded in a background of spins with opposite orientation. For fast decay of the spin-spin couplings, we find that the two-spin energy spectrum is characterized by well-defined discrete values, corresponding to bound states, separated by a set of continuum states describing the scattering region. In the deep long-range regime instead, the bound states disappear as they get incorporated by the scattering region. The presence of two-spin bound states results to be crucial to determine both two- and many-spin dynamics. On one hand, radically different two-spin spreadings can be observed by tuning the decay of the spin couplings. On the other hand, two-spin bound states enable the dynamical stabilization of effective antiferromagnetic states in the presence of ferromagnetic couplings. Finally, we propose a novel scheme based on a trapped-ion quantum simulator to experimentally realize the long-range XXZ model and to study its out-of-equilibrium properties
Data analysis of the COMPTEL instrument on the NASA gamma ray observatory
The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied
- …