131 research outputs found
Exact ground states of a staggered supersymmetric model for lattice fermions
We study a supersymmetric model for strongly interacting lattice fermions in
the presence of a staggering parameter. The staggering is introduced as a
tunable parameter in the manifestly supersymmetric Hamiltonian. We obtain
analytic expressions for the ground states in the limit of small and large
staggering for the model on the class of doubly decorated lattices. On this
type of lattice there are two ground states, each with a different density. In
one limit we find these ground states to be a simple Wigner crystal and a
valence bond solid (VBS) state. In the other limit we find two types of quantum
liquids. As a special case, we investigate the quantum liquid state on the one
dimensional chain in detail. It is characterized by a massless kink that
separates two types of order.Comment: 21 pages, 6 figures, v2: largely rewritten version with more emphasis
on physical interpretatio
Quantum phases of supersymmetric lattice models
We review recent results on lattice models for spin-less fermions with strong
repulsive interactions. A judicious tuning of kinetic and interaction terms
leads to a model possessing supersymmetry. In the 1D case, this model displays
critical behavior described by superconformal field theory. On 2D lattices we
generically find superfrustration, characterized by an extensive ground state
entropy. For certain 2D lattices analytical results on the ground state
structure reveal yet another quantum phase, which we tentatively call
'supertopological'.Comment: 5 pages, 1 figure, 1 table, contribution to the proceedings of the
XVI International Congress on Mathematical Physics (2009) in Prague, Czeck
Republi
Detailed analysis of the continuum limit of a supersymmetric lattice model in 1D
We present a full identification of lattice model properties with their field
theoretical counter parts in the continuum limit for a supersymmetric model for
itinerant spinless fermions on a one dimensional chain. The continuum limit of
this model is described by an superconformal field theory
(SCFT) with central charge c=1. We identify states and operators in the lattice
model with fields in the SCFT and we relate boundary conditions on the lattice
to sectors in the field theory. We use the dictionary we develop in this paper,
to give a pedagogical explanation of a powerful tool to study supersymmetric
models based on spectral flow. Finally, we employ the developed machinery to
explain numerically observed properties of the particle density on the open
chain presented in Beccaria et al. PRL 94:100401 (2005).Comment: 28 pages, 7 figures, 3 tables, 1 appendix, this work is based on
chapter 4 of the authors PhD Thesis: L. Huijse, A supersymmetric model for
lattice fermions, University of Amsterdam (2010
A multiplet analysis of spectra in the presence of broken symmetries
We introduce the notion of a generalised symmetry M of a hamiltonian H. It is
a symmetry which has been broken in a very specific manner, involving ladder
operators R and R*. In Theorem 1 these generalised symmetries are characterised
in terms of repeated commutators of H with M. Breaking supersymmetry by adding
a term linear in the supercharges is discussed as a motivating example. The
complex parameter gamma which appears in the definition of a generalised
symmetry is necessarily real when the spectrum of M is discrete. Theorem 2
shows that gamma must also be real when the spectrum of H is fully discrete and
R and R* are bounded operators. Any generalised symmetry induces a partitioning
of the spectrum of H in what we call M-multiplets. The hydrogen atom in the
presence of a symmetry breaking external field is discussed as an example. The
notion of stability of eigenvectors of H relative to the generalised symmetry M
is discussed. A characterisation of stable eigenvectors is given in Theorem 3
Supersymmetric lattice fermions on the triangular lattice: superfrustration and criticality
We study a model for itinerant, strongly interacting fermions where a
judicious tuning of the interactions leads to a supersymmetric Hamiltonian. On
the triangular lattice this model is known to exhibit a property called
superfrustration, which is characterized by an extensive ground state entropy.
Using a combination of numerical and analytical methods we study various ladder
geometries obtained by imposing doubly periodic boundary conditions on the
triangular lattice. We compare our results to various bounds on the ground
state degeneracy obtained in the literature. For all systems we find that the
number of ground states grows exponentially with system size. For two of the
models that we study we obtain the exact number of ground states by solving the
cohomology problem. For one of these, we find that via a sequence of mappings
the entire spectrum can be understood. It exhibits a gapped phase at 1/4
filling and a gapless phase at 1/6 filling and phase separation at intermediate
fillings. The gapless phase separates into an exponential number of sectors,
where the continuum limit of each sector is described by a superconformal field
theory.Comment: 50 pages, 12 figures, 2 appendice
Superfrustration of charge degrees of freedom
We review recent results, obtained with P. Fendley, on frustration of quantum
charges in lattice models for itinerant fermions with strong repulsive
interactions. A judicious tuning of kinetic and interaction terms leads to
models possessing supersymmetry. In such models frustration takes the form of
what we call superfrustration: an extensive degeneracy of supersymmetric ground
states. We present a gallery of examples of superfrustration on a variety of 2D
lattices.Comment: 8 pages, 5 figures, contribution to the proceedings of the XXIII
IUPAP International Conference on Statistical Physics (2007) in Genova, Ital
Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
Context: In the last six years, the VVV survey mapped 562 sq. deg. across the
bulge and southern disk of the Galaxy. However, a detailed study of these
regions, which includes globular clusters (GCs) and thousands of open
clusters is by no means an easy challenge. High differential reddening and
severe crowding along the line of sight makes highly hamper to reliably
distinguish stars belonging to different populations and/or systems. Aims: The
aim of this study is to separate stars that likely belong to the Galactic GC
NGC 6544 from its surrounding field by means of proper motion (PM) techniques.
Methods: This work was based upon a new astrometric reduction method optimized
for images of the VVV survey. Results: Photometry over the six years baseline
of the survey allowed us to obtain a mean precision of mas/yr, in
each PM coordinate, for stars with Ks < 15 mag. In the area studied here,
cluster stars separate very well from field stars, down to the main sequence
turnoff and below, allowing us to derive for the first time the absolute PM of
NGC 6544. Isochrone fitting on the clean and differential reddening corrected
cluster color magnitude diagram yields an age of 11-13 Gyr, and
metallicity [Fe/H] = -1.5 dex, in agreement with previous studies restricted to
the cluster core. We were able to derive the cluster orbit assuming an
axisymmetric model of the Galaxy and conclude that NGC 6544 is likely a halo
GC. We have not detected tidal tail signatures associated to the cluster, but a
remarkable elongation in the galactic center direction has been found. The
precision achieved in the PM determination also allows us to separate bulge
stars from foreground disk stars, enabling the kinematical selection of bona
fide bulge stars across the whole survey area. Our results show that VVV data
is perfectly suitable for this kind of analysis.Comment: 13 pages, 12 figures, accepted in A&
Spin chains with dynamical lattice supersymmetry
Spin chains with exact supersymmetry on finite one-dimensional lattices are
considered. The supercharges are nilpotent operators on the lattice of
dynamical nature: they change the number of sites. A local criterion for the
nilpotency on periodic lattices is formulated. Any of its solutions leads to a
supersymmetric spin chain. It is shown that a class of special solutions at
arbitrary spin gives the lattice equivalents of the N=(2,2) superconformal
minimal models. The case of spin one is investigated in detail: in particular,
it is shown that the Fateev-Zamolodchikov chain and its off-critical extension
admits a lattice supersymmetry for all its coupling constants. Its
supersymmetry singlets are thoroughly analysed, and a relation between their
components and the weighted enumeration of alternating sign matrices is
conjectured.Comment: Revised version, 52 pages, 2 figure
The High Cadence Transit Survey (HiTS): Compilation and Characterization of Light-curve Catalogs
Indexación: Scopus.J.M. acknowledges support from CONICYT-Chile through CONICYT-PCHA/Doctorado-Nacional/2014-21140892. J.M., F.F., G.C.V., and G.M. acknowledge support from the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS). F.F. acknowledges support from Conicyt through the Fondecyt Initiation into Research project No. 11130228. J.M., F.F., J.S.M., G.C.V., and S.G. acknowledge support from Basal Project PFB-03, Centro de Modelamiento Matemáico (CMM), Universidad de Chile. P.L. acknowledges support by Fondecyt through project #1161184. G.C.V. gratefully acknowledges financial support from CON-ICYT-Chile through FONDECYT postdoctoral grant number 3160747 and CONICYT-Chile and NSF through the Programme of International Cooperation project DPI201400090. P.H. acknowledges support from FONDECYT through grant 1170305. L.G. was supported in part by the US National Science Foundation under grant AST-1311862. G.M. acknowledges support from Conicyt through CONICYT-PCHA/Magís-terNacional/2016-22162353. Support for T.d.J. has been provided by US NSF grant AST-1211916, the TABASGO Foundation, and Gary and Cynthia Bengier. R.R.M. acknowledges partial support from BASAL Project PFB-06, as well as FONDECYT project N◦1170364. Powered@NLHPC: this research was supported by the High Performance Computing infrastructure of the National Laboratory for High Performance Computing (NLHPC), PIA ECM-02, CONICYT. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaborating institutions: Argonne National Lab, the University of California Santa Cruz, the University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologi-cas-Madrid, the University of Chicago, University College London, the DES-Brazil consortium, the University of Edinburgh, ETH-Zurich, the University of Illinois at Urbana-Champaign, Institut de Ciencies de l’Espai, Institut de Fisica d’Altes Energies, Lawrence Berkeley National Lab, Ludwig-Maximilians Universitat, the University of Michigan, the National Optical Astronomy Observatory, the University of Nottingham, Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Lab, Stanford University, the University of Sussex, and Texas A&M University. Funding for DES, including DECam, has been provided by the U.S. Department of Energy, National Science Foundation, Ministry of Education and Science (Spain), Science and Technology Facilities Council (UK), Higher Education Funding Council (England), National Center for Supercomputing Applications, Kavli Institute for Cosmological Physics, Financia-dora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo a Pesquisa, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia (Brazil), the German Research Foundation-sponsored cluster of excellence “Origin and Structure of the universe,” and the DES collaborating institutions. Facility: CTIO:1.5 m (DECam).The High Cadence Transient Survey (HiTS) aims to discover and study transient objects with characteristic timescales between hours and days, such as pulsating, eclipsing, and exploding stars. This survey represents a unique laboratory to explore large etendue observations from cadences of about 0.1 days and test new computational tools for the analysis of large data. This work follows a fully data science approach, from the raw data to the analysis and classification of variable sources. We compile a catalog of ∼15 million object detections and a catalog of ∼2.5 million light curves classified by variability. The typical depth of the survey is 24.2, 24.3, 24.1, and 23.8 in the u, g, r, and i bands, respectively. We classified all point-like nonmoving sources by first extracting features from their light curves and then applying a random forest classifier. For the classification, we used a training set constructed using a combination of cross-matched catalogs, visual inspection, transfer/active learning, and data augmentation. The classification model consists of several random forest classifiers organized in a hierarchical scheme. The classifier accuracy estimated on a test set is approximately 97%. In the unlabeled data, 3485 sources were classified as variables, of which 1321 were classified as periodic. Among the periodic classes, we discovered with high confidence one δ Scuti, 39 eclipsing binaries, 48 rotational variables, and 90 RR Lyrae, and for the nonperiodic classes, we discovered one cataclysmic variable, 630 QSOs, and one supernova candidate. The first data release can be accessed in the project archive of HiTS (http://astro.cmm.uchile.cl/HiTS/). © 2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/1538-3881/aadfd
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