2,096 research outputs found
The WFCAM Multi-wavelength Variable Star Catalog
Stellar variability in the near-infrared (NIR) remains largely unexplored.
The exploitation of public science archives with data-mining methods offers a
perspective for the time-domain exploration of the NIR sky. We perform a
comprehensive search for stellar variability using the optical-NIR multi-band
photometric data in the public Calibration Database of the WFCAM Science
Archive (WSA), with the aim of contributing to the general census of variable
stars, and to extend the current scarce inventory of accurate NIR light curves
for a number of variable star classes. We introduce new variability indices
designed for multi-band data with correlated sampling, and apply them for
pre-selecting variable star candidates, i.e., light curves that are dominated
by correlated variations, from noise-dominated ones. Pre-selection criteria are
established by robust numerical tests for evaluating the response of
variability indices to colored noise characteristic to the data. We find 275
periodic variable stars and an additional 44 objects with suspected variability
with uncertain periods or apparently aperiodic variation. Only 44 of these
objects had been previously known, including 11 RR~Lyrae stars in the outskirts
of the globular cluster M3 (NGC~5272). We provide a preliminary classification
of the new variable stars that have well-measured light curves, but the
variability types of a large number of objects remain ambiguous. We classify
most of the new variables as contact binary stars, but we also find several
pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are
likely Cepheids. We also identify 32 highly reddened variable objects close to
previously known dark nebulae, suggesting that these are embedded young stellar
objects. We publish our results and all light-curve data as the WFCAM Variable
Star Catalog.Comment: 21 pages, 11 figure
Caracterização morfológica comparativa de Jatropha curcas L., Jatropha mollissima (Pohl.)Baill. e Jatropha gossypiifolia L.
(Z_2)^3 Symmetry of the Tripartite Model
We derive in a simple way the symmetry which characterizes uniquely
the phenomenologically successful tripartite form leading to the tribimaximal
mixing in the neutrino mass matrix. We impose this symmetry in a setup
including the charged leptons and find that it can accommodate all the possible
patterns of lepton masses in the framework of type-I and type-II seesaw
mechanisms. We also discuss the possibility of generating enough baryon
asymmetry through lepton-lepton asymmetry.Comment: Substantial changes: enlarging the paper and changing the title. 11
page
Caracterização de genótipos de pinhão manso do banco ativo de germoplasma da embrapa algodão.
On zooplankton of the coastal waters of Rio Grande Do Norte sampled from oil producing platform
Lack of a comprehensive knowledge of zooplankton of the coastal waters of the northeast region of Brazil prompted the present study. Seasonal and diurnal collections were made from an oil producing platform located off Ouamari, Rio Grande do Norte, %azi! during the period of one year from March 1987 to February 1988. A pneliminary analysis of the samples showed a discernible seasonal fluctu* atioD and a clear pattern of diurnal changes in the composition of zooplankton
Lepton Mixing and Cancellation of the Dirac Mass Hierarchy in SO(10) GUTs with Flavor Symmetries T7 and Sigma(81)
In SO(10) grand unified theories (GUTs) the hierarchy which is present in the
Dirac mass term of the neutrinos is generically as strong as the one in the
up-type quark mass term. We propose a mechanism to partially or completely
cancel this hierarchy in the light neutrino mass matrix in the seesaw context.
The two main ingredients of the cancellation mechanism are the existence of
three fermionic gauge singlets and of a discrete flavor symmetry G_f which is
broken at a higher scale than SO(10). Two realizations of the cancellation
mechanism are presented. The realization based on the Frobenius group T7 = Z7 x
Z3 leads to a partial cancellation of the hierarchy and relates maximal 2-3
lepton mixing with the geometric hierarchy of the up-quark masses. In the
realization with the group Sigma(81) the cancellation is complete and
tri-bimaximal lepton mixing is reproduced at the lowest order. In both cases,
to fully accommodate the leptonic data we take into account additional effects
such as effects of higher-dimensional operators involving more than one flavon.
The heavy neutral fermion mass spectra are considered. For both realizations we
analyze the flavon potential at the renormalizable level as well as ways to
generate the Cabibbo angle.Comment: 31 page
Patterns in the Fermion Mixing Matrix, a bottom-up approach
We first obtain the most general and compact parametrization of the unitary
transformation diagonalizing any 3 by 3 hermitian matrix H, as a function of
its elements and eigenvalues. We then study a special class of fermion mass
matrices, defined by the requirement that all of the diagonalizing unitary
matrices (in the up, down, charged lepton and neutrino sectors) contain at
least one mixing angle much smaller than the other two. Our new parametrization
allows us to quickly extract information on the patterns and predictions
emerging from this scheme. In particular we find that the phase difference
between two elements of the two mass matrices (of the sector in question)
controls the generic size of one of the observable fermion mixing angles: i.e.
just fixing that particular phase difference will "predict" the generic value
of one of the mixing angles, irrespective of the value of anything else.Comment: 29 pages, 3 figures, references added, to appear in PR
Specific heat of heavy fermion CePd2Si2 in high magnetic fields
We report specific heat measurements on the heavy fermion compound CePd2Si2
in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp
peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3
K in zero field. The transition is found to shift to lower temperatures when a
magnetic field is applied along the crystallographic a-axis, while a field
applied parallel to the tetragonal c-axis does not affect the transition. The
magnetic contribution to the specific heat below T_N is well described by a sum
of a linear electronic term and an antiferromagnetic spin wave contribution.
Just below T_N, an additional positive curvature, especially at high fields,
arises most probably due to thermal fluctuations. The field dependence of the
coefficient of the low temperature linear term, gamma_0, extracted from the
fits shows a maximum at about 6 T, at the point where an anomaly was detected
in susceptibility measurements. The relative field dependence of both T_N and
the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the
disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of
the antiferromagnetic transition temperature to zero makes the existence of a
magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte
On the relation between local and geometric Lagrangians for higher spins
Equations of motion for free higher-spin gauge fields of any symmetry can be
formulated in terms of linearised curvatures. On the other hand, gauge
invariance alone does not fix the form of the corresponding actions which, in
addition, either contain higher derivatives or involve inverse powers of the
d'Alembertian operator, thus introducing possible subtleties in degrees of
freedom count. We suggest a path to avoid ambiguities, starting from local,
unconstrained Lagrangians previously proposed, and integrating out the
auxiliary fields from the functional integral, thus generating a unique
non-local theory expressed in terms of curvatures.Comment: 14 pages. Contribution to the proceedings of the 1st Mediterranean
Conference on Classical and Quantum Gravity, Kolymbary (Crete, Greece)
September 14-18 200
On the spectrum of AdS/CFT beyond supergravity
We test the spectrum of string theory on AdS_5 x S^5 derived in
hep-th/0305052 against that of single-trace gauge invariant operators in free
N=4 super Yang-Mills theory. Masses of string excitations at critical tension
are derived by extrapolating plane-wave frequencies at g_{YM}=0 down to finite
J. On the SYM side, we present a systematic description of the spectrum of
single-trace operators and its reduction to PSU(2,2|4) superconformal primaries
via a refined Eratostenes' supersieve. We perform the comparison of the
resulting SYM/string spectra of charges and multiplicities order by order in
the conformal dimension \Delta up to \Delta=10 and find perfect agreement.
Interestingly, the SYM/string massive spectrum exhibits a hidden symmetry
structure larger than expected, with bosonic subgroup SO(10,2) and thirty-two
supercharges.Comment: 28 pages, LaTeX2
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