3,103 research outputs found
Ground state fidelity from tensor network representations
For any D-dimensional quantum lattice system, the fidelity between two ground
state many-body wave functions is mapped onto the partition function of a
D-dimensional classical statistical vertex lattice model with the same lattice
geometry. The fidelity per lattice site, analogous to the free energy per site,
is well-defined in the thermodynamic limit and can be used to characterize the
phase diagram of the model. We explain how to compute the fidelity per site in
the context of tensor network algorithms, and demonstrate the approach by
analyzing the two-dimensional quantum Ising model with transverse and parallel
magnetic fields.Comment: 4 pages, 2 figures. Published version in Physical Review Letter
Causality and Localization Operators
The evolution of the expectation values of one and two points scalar field
operators and of positive localization operators, generated by an istantaneous
point source is non local. Non locality is attributed either to zero point
vacuum fluctuations, or to non local operations or to the microcausality
principle being no satisfied.Comment: 10 pages; submitted to Physics Letters
CO gas inside the protoplanetary disk cavity in HD 142527: disk structure from ALMA
Inner cavities and annular gaps in circumstellar disks are possible signposts
of giant planet formation. The young star HD 142527 hosts a massive
protoplanetary disk with a large cavity that extends up to 140 au from the
central star, as seen in continuum images at infrared and millimeter
wavelengths. Estimates of the survival of gas inside disk cavities are needed
to discriminate between clearing scenarios. We present a spatially and
spectrally resolved carbon monoxide isotopologue observations of the gas-rich
disk HD 142527, in the J=2-1 line of 12CO, 13CO and C18O, obtained with the
Atacama Large Millimeter Array (ALMA). We detect emission coming from inside
the dust-depleted cavity in all three isotopologues. Based on our analysis of
the gas in the dust cavity, the 12CO emission is optically thick, while 13CO
and C18O emission are both optically thin. The total mass of residual gas
inside the cavity is about 1.5-2 Jupiter masses. We model the gas with an
axisymmetric disk model. Our best fit model shows that the cavity radius is
much smaller in CO than it is in millimeter continuum and scattered light
observations, with a gas cavity that does not extend beyond 105 au (at
3-sigma). The gap wall at its outer edge is diffuse and smooth in the gas
distribution, while in dust continuum it is manifestly sharper. The inclination
angle, as estimated from the high velocity channel maps, is 28+/-0.5 degrees,
higher than in previous estimates, assuming a fix central star mass of 2.2
Solar masses.Comment: 13 pages, 10 figures. Accepted for publication in ApJ Main Journa
Turbidity and Other Effects Resulting from Trafalgar Sandbank Dredging and Palmar Beach Nourishment
Beach-nourishment requirements on the southwestern Spanish coast have led to a significant increase in offshore dredging. Following a new research line, assessment of changes recorded in physicochemical and biological parameters due to dredging and dumping operations was performed at the Cape of Trafalgar and Palmar Beach during June and July 2008. Turbidity, salinity, pH, dissolved oxygen, temperature, and suspended-sediment data were collected at 10 stations. At the end of the study, a three-campaign monitoring program was implemented for 1 year to assess the possible effects on biological communities and sediment properties. The relevant results, such as the average extent of the sediment plume (< 400 m) and its persistence in the environment (< 10 min), are discussed in this paper. A precise correlation between turbidity and suspended sediments and the recovery time of ecological balance were also established. Furthermore, minimal and reversible effects caused by dredging and dumping operations in this type of marine environment were identified
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths
We present the Planck Sky Model (PSM), a parametric model for the generation
of all-sky, few arcminute resolution maps of sky emission at submillimetre to
centimetre wavelengths, in both intensity and polarisation. Several options are
implemented to model the cosmic microwave background, Galactic diffuse emission
(synchrotron, free-free, thermal and spinning dust, CO lines), Galactic H-II
regions, extragalactic radio sources, dusty galaxies, and thermal and kinetic
Sunyaev-Zeldovich signals from clusters of galaxies. Each component is
simulated by means of educated interpolations/extrapolations of data sets
available at the time of the launch of the Planck mission, complemented by
state-of-the-art models of the emission. Distinctive features of the
simulations are: spatially varying spectral properties of synchrotron and dust;
different spectral parameters for each point source; modeling of the clustering
properties of extragalactic sources and of the power spectrum of fluctuations
in the cosmic infrared background. The PSM enables the production of random
realizations of the sky emission, constrained to match observational data
within their uncertainties, and is implemented in a software package that is
regularly updated with incoming information from observations. The model is
expected to serve as a useful tool for optimizing planned microwave and
sub-millimetre surveys and to test data processing and analysis pipelines. It
is, in particular, used for the development and validation of data analysis
pipelines within the planck collaboration. A version of the software that can
be used for simulating the observations for a variety of experiments is made
available on a dedicated website.Comment: 35 pages, 31 figure
Renormalized Path Integral for the Two-Dimensional Delta-Function Interaction
A path-integral approach for delta-function potentials is presented.
Particular attention is paid to the two-dimensional case, which illustrates the
realization of a quantum anomaly for a scale invariant problem in quantum
mechanics. Our treatment is based on an infinite summation of perturbation
theory that captures the nonperturbative nature of the delta-function bound
state. The well-known singular character of the two-dimensional delta-function
potential is dealt with by considering the renormalized path integral resulting
from a variety of schemes: dimensional, momentum-cutoff, and real-space
regularization. Moreover, compatibility of the bound-state and scattering
sectors is shown.Comment: 26 pages. The paper was significantly expanded and numerous equations
were added for the sake of clarity; the main results and conclusions are
unchange
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