415 research outputs found
Applications of an exact counting formula in the Bousso-Polchinski Landscape
The Bousso-Polchinski (BP) Landscape is a proposal for solving the
Cosmological Constant Problem. The solution requires counting the states in a
very thin shell in flux space. We find an exact formula for this counting
problem which has two simple asymptotic regime one of them being the method of
counting low states given originally by Bousso and Polchinski. We
finally give some applications of the extended formula: a robust property of
the Landscape which can be identified with an effective occupation number, an
estimator for the minimum cosmological constant and a possible influence on the
KKLT stabilization mechanism.Comment: 43 pages, 11 figures, 2 appendices. We have added a new section (3.4)
on the influence of the fraction of non-vanishing fluxes in the KKLT
mechanism. Other minor changes also mad
Fragmentos de inscripciones monumentales romanas de Sagunto
Unas excavaciones arqueológicas en la ciudad de Sagunto han aportado, entre otros materiales, diversos fragmentos de tres inscripciones monumentales. Su estudio demuestra que estamos ante piezas que reflejan importantes aspectos de la vida romana saguntina de época imperial. AsÃ, en la primera de ellas podrÃa tratarse de una referencia al culto de Mitra, mientras en las otras dos se aludirÃa a algún prominente personaje público.Some archaeological excavations in the city of Saguntum have recovered, among other materials, to different fragments of three monumental inscriptions. Their study shows important aspects of urban life on Roman imperial period. Thus, the first of them could be a reference to the cult of Mithras, while the other two could allude to distinguished public person
Stabilized updated Lagrangian corrected SPH for explicit dynamic problems
This is the pre-peer reviewed version of the following article:Vidal, Y.; Bonet, J.; Huerta, A. Stabilized updated Lagrangian corrected SPH for explicit dynamic problems. "International journal for numerical methods in engineering", Març 2007, vol. 69, núm. 13, p. 2687-2710, which has been published in final form at http://www3.interscience.wiley.com/journal/112777203/abstractSmooth Particle Hydrodynamics with a total Lagrangian formulation are, in general, more robust than nite elements for large distortion problems. Nevertheless, updating the reference con¯guration
may still be necessary in some problems involving extremely large distortions. However, as discussed here a standard updated formulation suffers the presence of zero energy modes that are activated
and may spoil completely the solution. It is important to note that, unlike an Eulerian formulation,the updated Lagrangian does not present tension instability but only zero energy modes. Here an stabilization technique is incorporated to the updated formulation to obtain an improved method
without mechanisms and capable to solve problems with extremely large distortions.Peer ReviewedPostprint (author’s final draft
Exploring a simple sector of the Einstein-Maxwell landscape
We explore the four dimensional Einstein-Maxwell landscape as a toy model in
which we can formulate a sphere compactification stabilized by an
electromagnetic field. Replacing the compactification sphere by J spheres, we
obtain a simple sector of the (2J+2)-dimensional Einstein-Maxwell landscape. In
this toy model, we analyze some properties which are very difficult to uncover
in the string theory landscape, including: complete moduli stabilization,
stability conditions, and state counting. We also show how to construct
anthropic states in this model. A detailed comparison between the main features
of this landscape and the Bousso-Polchinski landscape is given. We finally
speculate on the impact of these phenomena in the string theory landscape.Comment: 69 pages, 16 figures, some references adde
Gaseous time projection chambers for rare event detection: Results from the T-REX project. II. Dark matter
As part of the T-REX project, a number of R&D and prototyping activities have
been carried out during the last years to explore the applicability of
Micromegas-read gaseous TPCs in rare event searches like double beta decay
(DBD), axion research and low-mass WIMP searches. While in the companion paper
we focus on DBD, in this paper we focus on the results regarding the search for
dark matter candidates, both axions and WIMPs. Small ultra-low background
Micromegas detectors are used to image the x-ray signal expected in axion
helioscopes like CAST at CERN. Background levels as low as
c keVcms have already been achieved in CAST while values
down to c keVcms have been obtained in a
test bench placed underground in the Laboratorio Subterr\'aneo de Canfranc.
Prospects to consolidate and further reduce these values down to
c keVcmswill be described. Such detectors, placed at the
focal point of x-ray telescopes in the future IAXO experiment, would allow for
10 better signal-to-noise ratio than CAST, and search for solar axions with
down to few 10 GeV, well into unexplored axion
parameter space. In addition, a scaled-up version of these TPCs, properly
shielded and placed underground, can be competitive in the search for low-mass
WIMPs. The TREX-DM prototype, with 0.300 kg of Ar at 10 bar, or
alternatively 0.160 kg of Ne at 10 bar, and energy threshold well below 1
keV, has been built to test this concept. We will describe the main technical
solutions developed, as well as the results from the commissioning phase on
surface. The anticipated sensitivity of this technique might reach
cm for low mass ( GeV) WIMPs, well beyond current
experimental limits in this mass range.Comment: Published in JCAP. New version with erratum incorporated (new figure
14
Radiopurity of Micromegas readout planes
Micromesh Gas Amplification Structures (Micromegas) are being used in an
increasing number of Particle Physics applications since their conception
fourteen years ago. More recently, they are being used or considered as readout
of Time Projection Chambers (TPCs) in the field of Rare Event searches (dealing
with dark matter, axions or double beta decay). In these experiments, the
radiopurity of the detector components and surrounding materials is measured
and finely controlled in order to keep the experimental background as low as
possible. In the present paper, the first measurement of the radiopurity of
Micromegas planes obtained by high purity germanium spectrometry in the low
background facilities of the Canfranc Underground Laboratory (LSC) is
presented. The obtained results prove that Micromegas readouts of the microbulk
type are currently manufactured with radiopurity levels below 30 microBq/cm2
for Th and U chains and ~60 microBq/cm2 for 40K, already comparable to the
cleanest detector components of the most stringent low background experiments
at present. Taking into account that the studied readouts were manufactured
without any specific control of the radiopurity, it should be possible to
improve these levels after dedicated development.Comment: 15 pages, 2 figure
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