9,295 research outputs found
Noncommutative via closed star product
We consider linear star products on of Lie algebra type. First we
derive the closed formula for the polydifferential representation of the
corresponding Lie algebra generators. Using this representation we define the
Weyl star product on the dual of the Lie algebra. Then we construct a gauge
operator relating the Weyl star product with the one which is closed with
respect to some trace functional, . We introduce
the derivative operator on the algebra of the closed star product and show that
the corresponding Leibnitz rule holds true up to a total derivative. As a
particular example we study the space with type
noncommutativity and show that in this case the closed star product is the one
obtained from the Duflo quantization map. As a result a Laplacian can be
defined such that its commutative limit reproduces the ordinary commutative
one. The deformed Leibnitz rule is applied to scalar field theory to derive
conservation laws and the corresponding noncommutative currents.Comment: published versio
The Indirect Search for Dark Matter from the centre of the Galaxy with the Fermi LAT
Dark matter (DM) constitutes around a 25% of the Universe, while baryons only
a 4%. DM can be reasonably assumed to be made of particles, and many theories
(Super-symmetry, Universal Extra Dimensions, etc.) predict Weakly Interacting
Massive Particles (WIMPs) as natural DM candidates at the weak scale.
Self-annihilation (or decay) of WIMPs might produce secondary gamma-rays, via
hadronization or as final state radiation. Since its launch in the 2008, the
Large Area Telescope on-board of the Fermi gamma-ray Space Telescope has
detected the largest amount of gamma-rays to date, in the 20MeV 300GeV energy
range, allowing to perform a very sensitive indirect experimental search for DM
(by means of high-energy gamma-rays). DM forms large gravitationally bounded
structures, the halos, which can host entire galaxies, such as the Milky Way.
The DM distribution in the central part of the halos is not experimentally
know, despite a very large density enhancement might be present. As secondary
gamma rays production is very sensitive to WIMP density, a very effective
search can be performed from the regions where the largest density is expected.
Therefore the information provided by the DM halo N-body simulations are
crucial. The largest gamma-ray signal from DM annihilation is expected from the
centre of the Galaxy. In the same region a large gamma-ray background is
produced by bright discrete sources and the cosmic-rays interacting with the
interstellar gas and the photons fields.
Here we report an update of the indirect search for DM from the Galactic
Center (GC).Comment: 6 pages, 2 figures. Invited talk presented at the Workshop "SciNeGHE
2010", September 8-10, 2010, Trieste, Italy. To appear in Il Nuovo Cimento C
- Colloquia on physic
Conformal Truncation of Chern-Simons Theory at Large
We set up and analyze the lightcone Hamiltonian for an abelian Chern-Simons
field coupled to fermions in the limit of large using conformal
truncation, i.e. with a truncated space of states corresponding to primary
operators with dimension below a maximum cutoff . In both the
Chern-Simons theory, and in the model at infinite , we compute the
current spectral functions analytically as a function of and
reproduce previous results in the limit that the truncation
is taken to . Along the way, we determine how to preserve gauge
invariance and how to choose an optimal discrete basis for the momenta of
states in the truncation space.Comment: 32+25 pages, 8 figures. v2: updated ref
Factors controlling the formation of mineral precipitates lining the channel in Rabbit Creek Yellowstone National Park Wyoming
A robust hierarchical clustering for georeferenced data
The detection of spatially contiguous clusters is a relevant task in geostatistics since near located observations might have similar features than distant ones. Spatially compact groups can also improve clustering results interpretation according to the different detected subregions. In this paper, we propose a robust metric approach to neutralize the effect of possible outliers, i.e. an exponential transformation of a dissimilarity measure between each pair of locations based on non-parametric kernel estimator of the direct and cross variograms (Fouedjio, 2016) and on a different bandwidth identification, suitable for agglomerative hierarchical clustering techniques applied to data indexed by geographical coordinates. Simulation results are very promising showing very good performances of our proposed metric with respect to the baseline ones. Finally, the new clustering approach is applied to two real-word data sets, both giving locations and top soil heavy metal concentrations
Search for Dark Matter with Fermi Large Area Telescope: The Galactic Center
Dark Matter (DM) as a weakly interacting massive particle could annihilate or decay and give rise to high energy gamma-rays. Then an indirect search for Dark Matter is possible by means of the Large Area Telescope on board the Fermi satellite. A relatively large signal is expected from the regions where the Dark Matter is expected to have the greatest density, such as the central region of the Milky Way. This region also hosts many high-energy gamma ray sources, of many different classes. Furthermore diffuse gamma-ray emission due to cosmic-ray interactions with interstellar gas and radiation is detected from the same direction. A greatly improved understanding of the gamma ray emission from the Galactic Center region is going to be obtained with the Fermi LAT first-year data. The data along with refined modelling of the diffuse emission and a careful evaluation of the discrete sources will improve our ability to disentangle a potential dark matter signal from the astrophysical background and to place new limits on the mass and annihilation rate (or lifetime) of Dark Matter particle
On The Origin Of The Gamma Rays From The Galactic Center
The region surrounding the center of the Milky Way is both astrophysically
rich and complex, and is predicted to contain very high densities of dark
matter. Utilizing three years of data from the Fermi Gamma Ray Space Telescope
(and the recently available Pass 7 ultraclean event class), we study the
morphology and spectrum of the gamma ray emission from this region and find
evidence of a spatially extended component which peaks at energies between 300
MeV and 10 GeV. We compare our results to those reported by other groups and
find good agreement. The extended emission could potentially originate from
either the annihilations of dark matter particles in the inner galaxy, or from
the collisions of high energy protons that are accelerated by the Milky Way's
supermassive black hole with gas. If interpreted as dark matter annihilation
products, the emission spectrum favors dark matter particles with a mass in the
range of 7-12 GeV (if annihilating dominantly to leptons) or 25-45 GeV (if
annihilating dominantly to hadronic final states). The intensity of the
emission corresponds to a dark matter annihilation cross section consistent
with that required to generate the observed cosmological abundance in the early
universe (sigma v ~ 3 x 10^-26 cm^3/s). We also present conservative limits on
the dark matter annihilation cross section which are at least as stringent as
those derived from other observations.Comment: 13 pages, 11 figure
Imperforate hymen causing congenital hydrometrocolpos.
A 3-day-old girl in good health was referred to our department for the evaluation of an abdominal mass detected at birth. Prenatal ultrasound (US) examinations had shown no anomaly. US examination revealed the presence of a hypoechoic and corpusculated cystic formation of about 8 × 5 × 4 cm located in the mid region of the abdomen. The uterus was not visible and the kidneys were normal with no sign of hydronephrosis. The ovaries were normal. Physical examination confirmed US findings revealing the presence of a curved membrane which covered the vaginal opening. Based on these findings, the patient was diagnosed to have hydrometrocolpos. Hymenectomy was performed and about 100 ml of milky fluid was subsequently removed by aspiration. The patient presented no other congenital anomalies and US follow-up showed a normal structure of the uterus
Sun-photometric measurements of atmospheric turbidity variations caused by the Pinatubo aerosol cloud in the Himalayan region during the summer periods of 1991 and 1992
Measurements of direct solar irradiance were taken episodically on two days of September 1990 and regularly in the summer periods from July to October 1991 and from
mid-July to mid-August 1992 at the Pyramid Laboratory (5050 m a.m.s.l.) situated at the foot of Mt. Everest (Nepal), using two examples of the Volz multispectral sunphotometer, model A. These sun-photometric measurements were analysed in terms of the Bouguer-Lambert-Beer law in order to
determine the values of aerosol optical thickness at the three sun-photometric window-wavelengths. Examining these spectral series in terms of the well-known Ångström formula, the best-fit values of turbidity parameters a and b were calculated with great accuracy. From the measurements taken in September 1990, we found values of the aerosol optical thickness in good agreement with the mean values of the background aerosol optical depth measured at the Mauna Loa Observatory (Hawaii) during the four-year period from 1988 to 1991. The spectral values of the aerosol optical thickness determined during the summer of 1991 show that the mean daily values of parameter b increased abruptly from about 0.06 to more than 0.16 from July 26 to 28, 1991, and then varied between 0.09 and 0.16 during the rest of the measurement period. Simultaneously, parameter a was found to decrease from more than 1.25 to 0.39 towards the end of July and to vary between 0.40 and 0.78 during September. These large variations of both atmospheric turbidity parameters have been attributed to the growth of the aerosol particles and to the consequent
changes in the size distribution curve of the Pinatubo aerosol particles. Analysing the variations of the stratospheric aerosol optical depth in terms of particle polydispersions consisting of a linear combination of a background aerosol monomodal model and a bimodal model representing the Pinatubo fresh aerosol particle size
distribution, the vertical mass loading of stratospheric aerosol particles was estimated to vary between 0.037 and 0.047 g m22 from July 24 to 27 and to increase to values ranging between 0.048 and 0.074 g m22 during the rest of summer 1991, presenting a mean value of (0.063 6 0.009) g m22 for the two-month period. The measurements taken in summer 1992 show that parameter b ranged between 0.08 and 0.12, while parameter a was found to vary between 0.23 and 0.73. The stratospheric aerosol depth values were analysed through a best-fit procedure based on a linear combination of a background model of small aerosol particles and a trimodal model consisting of aged volcanic aerosol particles. Following this procedure, the vertical mass loading of Pinatubo aerosol particles was found to vary between 0.043 and 0.057 g m22 during summer 1992, the mean value being evaluated as equal to (0.047 6 0.004) g m22
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