1,498 research outputs found
Bosonized noncommutative bi-fundamental fermion and S-duality
We perform the path-integral bosonization of the recently proposed
noncommutative massive Thirring model (NCMT) [JHEP0503(2005)037]. This
model presents two types of current-current interaction terms related to the
bi-fundamental representation of the group U(1). Firstly, we address the
bosonization of a bi-fundamental free Dirac fermion defined on a noncommutative
(NC) Euclidean plane \IR_{\theta}^{2}. In this case we show that the fermion
system is dual to two copies of the NC Wess-Zumino-Novikov-Witten model. Next,
we apply the bosonization prescription to the NCMT model living on
\IR_{\theta}^{2} and show that this model is equivalent to two-copies of the
WZNW model and a two-field potential defined for scalar fields corresponding to
the global symmetry plus additional bosonized terms for the
four fermion interactions. The bosonic sector resembles to the one proposed by
Lechtenfeld et al. [Nucl. Phys. B705(2005)477] as the noncommutative
sine-Gordon for a {\sl pair} of scalar fields. The bosonic and fermionic
couplings are related by a strong-weak duality. We show that the couplings of
the both sectors for some representations satisfy similar relationships up to
relevant re-scalings, thus the NC bi-fundamental couplings are two times the
corresponding ones of the NC fundamental (anti-fundamental) and eight times the
couplings of the ordinary massive Thirring and sine-Gordon models.Comment: 18 pages, LaTex. References added. A general product has been considered in the conclusion section . Version to appear in
JHE
Bigravity and Lorentz-violating Massive Gravity
Bigravity is a natural arena where a non-linear theory of massive gravity can
be formulated. If the interaction between the metrics and is
non-derivative, spherically symmetric exact solutions can be found. At large
distances from the origin, these are generically Lorentz-breaking bi-flat
solutions (provided that the corresponding vacuum energies are adjusted
appropriately). The spectrum of linearized perturbations around such
backgrounds contains a massless as well as a massive graviton, with {\em two}
physical polarizations each. There are no propagating vectors or scalars, and
the theory is ghost free (as happens with certain massive gravities with
explicit breaking of Lorentz invariance). At the linearized level, corrections
to GR are proportional to the square of the graviton mass, and so there is no
vDVZ discontinuity. Surprisingly, the solution of linear theory for a static
spherically symmetric source does {\em not} agree with the linearization of any
of the known exact solutions. The latter coincide with the standard
Schwarzschild-(A)dS solutions of General Relativity, with no corrections at
all. Another interesting class of solutions is obtained where and are
proportional to each other. The case of bi-de Sitter solutions is analyzed in
some detail.Comment: 25 pages. v3 Typos corrected, references added. v4 Introduction
extende
Testing Lorentz invariance of dark matter
We study the possibility to constrain deviations from Lorentz invariance in
dark matter (DM) with cosmological observations. Breaking of Lorentz invariance
generically introduces new light gravitational degrees of freedom, which we
represent through a dynamical timelike vector field. If DM does not obey
Lorentz invariance, it couples to this vector field. We find that this coupling
affects the inertial mass of small DM halos which no longer satisfy the
equivalence principle. For large enough lumps of DM we identify a (chameleon)
mechanism that restores the inertial mass to its standard value. As a
consequence, the dynamics of gravitational clustering are modified. Two
prominent effects are a scale dependent enhancement in the growth of large
scale structure and a scale dependent bias between DM and baryon density
perturbations. The comparison with the measured linear matter power spectrum in
principle allows to bound the departure from Lorentz invariance of DM at the
per cent level.Comment: 42 pages, 9 figure
Análisis de los nidos de algunas Osmia (Hymenoptera, Megachilidae) nidificantes en cavidades preestablecidas
Nests of some cavity-nesting Osmia (Hymenoptera, Megachilidae). Nests of seven Osmia species (0. cornuta, 0 . rufa, O. tricornis, 0. coerulescens, 0. fulviventris, 0. latreillei, and 0 . submicans) nesting in preestablished holes were obtained through placement of trap-nests in the field. Analyses of nests provided data on nest architecture (number of cells per nest, materials used for nest construction), structure of provisions (including types of pollens collected), structure of cocoons and faeces, and parasites and predators. Over-wintering stages, number of generations per year, and flying seasons for each Osmia species are also given.Mitjançant la col·locació de niadors-trampa al camp s'han obtingut nius de set espècies d'Osmia (0. cornuta, 0. rufa, O. tricornis, 0. coerulescens, 0.fulviventris, 0 . latreillei, i 0 . subrnicans) nidificants en cavitats preestablertes. S'inclou una descripció dels nius obtinguts, i s'aporten dades sobre la seva estructura (nombre de cel·les, materials utilitzats per a la construcció del niu), aspecte de les provisions i tipus de pol·lens recol·lectats, aspecte dels capolls, aspecte i distribució de les femtes, presència de parà sits i depredadors, època de vol, nombre de generacions per any, i estadi d'hivernació
Metric-scalar gravity with torsion and the measurability of the non-minimal coupling
The "measurability" of the non-minimal coupling is discussed by considering
the correction to the Newtonian static potential in the semi-classical
approach. The coefficient of the "gravitational Darwin term" (GDT) gets
redefined by the non-minimal torsion-scalar couplings. Based on a similar
analysis of the GDT in the effective field theory approach to non-minimal
scalar we conclude that for reasonable values of the couplings the correction
is very small.Comment: 10 pages, LaTex. Accepted for publication in Mod. Phys. Lett.
γ Heavy Chain Disease in Man: cDNA Sequence Supports Partial Gene Deletion Model
Human gamma heavy chain disease (HCD) is characterized by the presence in serum of a short monoclonal Ig gamma chain unattached to light chains. Although most HCD proteins have internal deletions, in some the defect is NH2-terminal. The OMM gamma 3 HCD serum protein is of the latter type, having undergone an extensive NH2-terminal deletion with a sequence starting within the hinge. A cell line synthesizing the OMM protein has enabled us to study the biogenesis of the abnormal molecule. In vitro translation of isolated mRNA yields a protein containing a hydrophobic NH2-terminal leader sequence. In the intact cell, the precursor molecule is processed normally to yield a protein with an NH2-terminal sequence homologous to the beginning of the variable (V) region. The nucleotide sequence of cDNA prepared from the OMM mRNA encodes a 19-amino acid leader followed by the first 15 residues of the V region. An extensive internal deletion encompasses the remainder of the V and the entire CHl domain. Immediately following the short V region, there is information in the cDNA for the entire normal hinge. The primary synthetic product is thus an internally deleted molecule that undergoes postsynthetic degradation to yield the NH2-terminally deleted serum protein. The structure of the OMM mRNA suggests that the protein abnormality results from a partial gene deletion rather than defective splicing
Factors Influencing Chat-Based Cultural Discussions for Learning History in a 3D Virtual World
In a fast-changing world, there is an increasingly felt need to bring
what we teach and how we teach it intothe 21st Century. Learning@Europe is an attempt in this direction: a shared online virtual world where students from different European countries meet to play and learn about European history.
Chat-based discussions of study material, research homework to prepare in col-laboration with remote peers on online forums, team games and a cultural com-petition are the main ingredients of this innovative experience, already tested by over 6000 high-school students and teachers from 18 European countries. This paper focuses on a particular Learning@Europe activity – chat-based cultural discussions about history – and analyzes the elements that are essential to its success. Basing on evaluation data and our 3-years experience, we describe strategies deal with the different elements to be taken into account: Technology; Content; Interaction Design; and – mostimportant of all – Social Behavior
Families of stable and metastable solitons in coupled system of scalar fields
In this paper, we obtain stable and metastable soliton solutions of a coupled
system of two real scalar fields with five five discrete points of vacua. These
solutions have definite topological charges and rest energies and show
classical dynamical stability. From a quantum point of view, however, the
V-type solutions are expected to be unstable and decay to D-type solutions. The
induced decay of a V-type soliton into two D-type ones is calculated
numerically, and shown to be chiral, in the sense that the decay products do
not respect left-right symmetry.Comment: 9 pages and 5 figure
Technically natural dark energy from Lorentz breaking
We construct a model of dark energy with a technically natural small
contribution to cosmic acceleration, i.e. this contribution does not receive
corrections from other scales in the theory. The proposed acceleration
mechanism appears generically in the low-energy limit of gravity theories with
violation of Lorentz invariance that contain a derivatively coupled scalar
field Theta. The latter may be the Goldstone field of a broken global symmetry.
The model, that we call Theta-CDM, is a valid effective field theory up to a
high cutoff just a few orders of magnitude below the Planck scale. Furthermore,
it can be ultraviolet-completed in the context of Horava gravity. We discuss
the observational predictions of the model. Even in the absence of a
cosmological constant term, the expansion history of the Universe is
essentially indistinguishable from that of Lambda-CDM. The difference between
the two theories appears at the level of cosmological perturbations. We find
that in Theta-CDM the matter power spectrum is enhanced at subhorizon scales
compared to Lambda-CDM. This property can be used to discriminate the model
from Lambda-CDM with current cosmological data.Comment: A few equations in the Appendix correcte
Beyond Findability: Search-Enhanced Information Architecture for Content-Intensive Rich Internet Applications
This paper details a way to extend classic information architecture for web-based applications. The goal is to enhance traditional user experiences, mainly based on navigation or search, to new ones (also relevant for stakeholders’ requirements).
Examples are sense making, at a glance understanding, playful exploration, serendipitous browsing, and brand communication. These new experiences are often unmet by current information architecture solutions, which may be stiff and difficult to scale, especially in the case of large or very large websites. A heavy
reliance upon search engines seems not to offer a viable solution: it supports, in fact, a limited range of user experiences. We propose to transform (parts of) websites into Rich Internet Applications (RIAs), based, beside other features, upon interaction-rich interfaces and semantic browsing across content. We introduce SEE-IA (SEarch-Enhanced Information Architecture), a coherent set of information architecture design strategies, which innovatively blend and extend IA and search
paradigms. The key ingredients of SEE-IA are a seamless combination of structured hypertext-based information architectures, faceted search paradigms, and RIA-enabled visualization techniques. The paper elucidates and codifies these
design strategies and their underlying principles, identifying also how they support a set of requirements which are often neglected by most current design approaches. A real case study of a complex RIA designed for a major institutional client in Italy is used to vividly showcase the design strategies and to provide
ready-to-use examples that can be transferred to other IA contexts and domains
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