4,563 research outputs found
Fractional Branes and N=1 Gauge Theories
We discuss fractional D3-branes on the orbifold C^3/Z_2*Z_2. We study the
open and the closed string spectrum on this orbifold. The corresponding N=1
theory on the brane has, generically, a U(N_1)*U(N_2)*U(N_3)*U(N_4) gauge group
with matter in the bifundamental. In particular, when only one type of brane is
present, one obtains pure N=1 Yang-Mills. We study the coupling of the branes
to the bulk fields and present the corresponding supergravity solution, valid
at large distances. By using a probe analysis, we are able to obtain the
Wilsonian beta-function for those gauge theories that possess some chiral
multiplet. Although, due to the lack of moduli, the probe technique is not
directly applicable to the case of pure N=1 Yang-Mills, we point out that the
same formula gives the correct result also for this case.Comment: 21 pages, AMS-LaTeX, v2: references added and typos correcte
Direct CP violation in K->3pi decays induced by SUSY chromomagnetic penguins
An analysis of the CP violating asymmetry in decays in
the Standard Model and, by means of the mass insertion approximation, in a wide
class of possible supersymmetric extensions, is presented. We find that the
natural order of magnitude for this asymmetry is \cO(10^{-5}) in both cases.
Within supersymmetric models effects as large as \cO(10^{-4}) are possible,
but only in a restricted range of the relevant parameters.Comment: Latex, 11 pages, 1 figur
D-branes, Orientifolds and K-theory
The complete D-brane spectrum in ZZ[squared] orientifolds is computed. Stable non-BPS D-branes with both integral and torsion charges are found. The relation to K-theory is discussed and a new K-theory relevant to orientifolds is suggested
Aerial inventory of surficial geological effects induced by the recent Emilia earthquake (Italy): preliminary report.
As a consequence of the two main shocks that recently
struck the central alluvial Po Plain (May 20, 2012, ML 5.9, and
May 29, 2012, ML 5.8), a great number of surficial geologic
disturbances appeared over a wide area (ca. 500 km2), which
extended up to 20 km from the epicenters. The affected area
includes Mirabello, San Carlo, Sant'Agostino (Province of
Ferrara), San Felice, Cavezzo, Concordia (Modena), Moglia
and Quistello (Mantova).
Most of the surficial effects that were observed during
this study were clearly induced (directly or indirectly) by sand
liquefaction phenomena, such as sand volcanoes, burst of
water and sand from domestic wells, tension cracks, lateral
spreading and associated deformation, graben-like fracturing,
and sink-holes. Other effects can probably be ascribed
simply to the shaking of the ground (e.g., small collapses of
irrigation canal walls). Lastly, there were also some features
of dubious origin, such as two 'yellow crop spots' that are
cited here with reservations.
All of these data were surveyed by means of a small airplane
that was especially adapted for this purpose.
The aim of this study was to furnish a wide-ranging
image of the surface deformation over the whole area impacted
by these recent earthquakes, as an instrument towards
more exhaustive research, both at the scientific and
technical levels (e.g., seismic microzonation)
Quark-Squark Alignment Revisited
We re-examine the possibility that the solution to the supersymmetric flavor
problem is related to small mixing angles in gaugino couplings induced by
approximate horizontal Abelian symmetries. We prove that, for a large class of
models, there is a single viable structure for the down quark mass matrix with
four holomorphic zeros. Consequently, we are able to obtain both lower and
upper bounds on the supersymmetric mixing angles and predict the contributions
to various flavor changing neutral current processes. We find that the most
likely signals for alignment are close to the present bound,
significant CP violation in mixing, and shifts of order a few
percent in various CP asymmetries in and decays. In contrast, the
modifications to radiative B decays, to and to
decays are small. We further investigate a new class of
alignment models, where supersymmetric contributions to flavor changing
processes are suppressed by both alignment and RGE-induced degeneracy.Comment: 20 pages, 3 figure
Anomalies and Tadpoles in Open/Closed String Duality
We discuss the role played by the divergences appearing in the interaction
between a fractional D3 brane dressed with an SU(N) gauge field and a stack of
N fractional D3 branes on the orbifolds C^2/Z_2 and C^3/(Z_2 x Z_2). In
particular we show that the logarithmic divergences in the closed string
channel, interpreted as due to twisted massless tadpoles, are mapped, under
open/closed string duality, in the logarithmic ones in the open string channel,
due to the massless states circulating in the annulus diagram and corresponding
to the one-loop divergences that one finds in the gauge theory living in the
world volume of the brane. This result provides a quantitative evidence of why
the chiral and scale anomalies of the supersymmetric and non conformal gauge
theories supported by the world volume of the branes can be inferred from
supergravity calculations.Comment: LaTeX, 8 pages. Contribution to the proceedings of the workshop of
the RTN Network "The quantum structure of space-time and the geometric nature
of fundamental interactions", Copenhagen, September 200
Learning from a well-documented geotechnical cold case : the Two Towers of Bologna, Italy.
The Garisenda Tower and the Asinelli Tower, also widely known as the Two Towers, are the best preserved and famous medieval towers in the city of Bologna (Northern Italy). Standing one close to the other, right in the heart of the city centre, the Two Towers are delicate remains of the old towered city, which counted more than 75 towers in the 12th century.
The foundations of historic towers and the surrounding soil often hide major hazards for the long-term preservation of these heritage structures. The initial fundamental step to this aim is indeed a deep understanding of their original conception, foundations and subsoil. However, the idea that also such elements are an integral part of the overall structure, and thus subjected to the same conservation rules, is relatively new. The present paper outlines the investigation criteria applied to the soil-foundation systems of the Two Towers of Bologna and describes the authenticity of their characteristics, through the interpretation of new experimental data and the analysis of historical documents. A geotechnical perspective on this type of monuments turns out to be crucial in order to effectively understand the soil-structure interaction mechanisms, which govern their safety conditions over time. This study also aims to better understand the reasons why the Two Towers of Bologna, despite their numerous similarities, have reached completely different structural configurations.
The methodology described to investigate this case study, which required the integration of several aspects, can be usefully applied to any historic tower
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