166 research outputs found
Courant-Dorfman algebras and their cohomology
We introduce a new type of algebra, the Courant-Dorfman algebra. These are to
Courant algebroids what Lie-Rinehart algebras are to Lie algebroids, or Poisson
algebras to Poisson manifolds. We work with arbitrary rings and modules,
without any regularity, finiteness or non-degeneracy assumptions. To each
Courant-Dorfman algebra (\R,\E) we associate a differential graded algebra
\C(\E,\R) in a functorial way by means of explicit formulas. We describe two
canonical filtrations on \C(\E,\R), and derive an analogue of the Cartan
relations for derivations of \C(\E,\R); we classify central extensions of
\E in terms of H^2(\E,\R) and study the canonical cocycle
\Theta\in\C^3(\E,\R) whose class obstructs re-scalings of the
Courant-Dorfman structure. In the nondegenerate case, we also explicitly
describe the Poisson bracket on \C(\E,\R); for Courant-Dorfman algebras
associated to Courant algebroids over finite-dimensional smooth manifolds, we
prove that the Poisson dg algebra \C(\E,\R) is isomorphic to the one
constructed in \cite{Roy4-GrSymp} using graded manifolds.Comment: Corrected formulas for the brackets in Examples 2.27, 2.28 and 2.29.
The corrections do not affect the exposition in any wa
Towards a Resolution of the Cosmological Singularity in Non-local Higher Derivative Theories of Gravity
One of the greatest problems of standard cosmology is the Big Bang
singularity. Previously it has been shown that non-local ghostfree
higher-derivative modifications of Einstein gravity in the ultra-violet regime
can admit non-singular bouncing solutions. In this paper we study in more
details the dynamical properties of the equations of motion for these theories
of gravity in presence of positive and negative cosmological constants and
radiation. We find stable inflationary attractor solutions in the presence of a
positive cosmological constant which renders inflation {\it geodesically
complete}, while in the presence of a negative cosmological constant a cyclic
universe emerges. We also provide an algorithm for tracking the super-Hubble
perturbations during the bounce and show that the bouncing solutions are free
from any perturbative instability.Comment: 38 pages, 6 figures. V2: Added: a word to the title, clarifications,
an appendix, many references. To appear in JCA
Pseudo-supersymmetry and a Tale of Alternate Realities
We discuss how all variant 10d and 11d maximal supergravities, including star
supergravities and supergravities in different signatures, can be obtained as
different real slices of three complex actions. As an application we study the
recently introduced domain-wall/cosmology correspondence in this approach. We
give an example in 9d and 10d where the domain-wall and corresponding cosmology
can be viewed as different real slices of the same complex solution. We argue
how in this case the pseudo-supersymmetry of the cosmological solutions can be
understood as the invariance under supersymmetry of a variant supergravity.Comment: 32 page
Super Yang-Mills Operators from the D3-brane Action in a Curved Background
A consistent truncation of IIB on S^5 has been obtained in the sector of the
metric and the 4-form potential. The ansatz contains 20 scalars and all 15
gauge fields of gauged supergravity in five dimensions. With this
fully non-linear ansatz, the calculations for n-point correlators of super
Yang-Mills (SYM) theory via AdS/CFT are simpler than those in the literature
that use {\em linear} ansatz followed by non-linear field redefinitions. We
work out the SYM operators that couple to the scalars by expanding the
Dirac-Born-Infeld (DBI) action plus Wess-Zumino (WZ) terms around an
AdS_5\timesS^5 background with the metric fluctuations. The resulting
operators agree with those based on a superconformal symmetry argument. We
discuss the significance of our results.Comment: one author's name correcte
General structure of the photon self-energy in non-commutative QED
We study the behavior of the photon two point function, in non-commutative
QED, in a general covariant gauge and in arbitrary space-time dimensions. We
show, to all orders, that the photon self-energy is transverse. Using an
appropriate extension of the dimensional regularization method, we evaluate the
one-loop corrections, which show that the theory is renormalizable. We also
prove, to all orders, that the poles of the photon propagator are gauge
independent and briefly discuss some other related aspects.Comment: 16 pages, revtex4. This is the final version to be published in Phys.
Rev.
Phantom Divide Crossing with General Non-minimal Kinetic Coupling
We propose a model of dark energy consists of a single scalar field with a
general non-minimal kinetic couplings to itself and to the curvature. We study
the cosmological dynamics of the equation of state in this setup. The coupling
terms have the form and
where
and are coupling parameters and their dimensions depend on the type
of function . We obtain the conditions required for phantom divide
crossing and show numerically that a cosmological model with general
non-minimal derivative coupling to the scalar and Ricci curvatures can realize
such a crossing.Comment: 12 pages, 4 figures. Accepted for publication in Gen. Rel. Grav.
arXiv admin note: substantial text overlap with arXiv:1105.4967,
arXiv:1201.1627, and with arXiv:astro-ph/0610092 by other author
S-matrix elements and off-shell tachyon action with non-abelian gauge symmetry
We propose that there is a unique expansion for the string theory S-matrix
elements of tachyons that corresponds to non-abelian tachyon action. For those
S-matrix elements which, in their expansion, there are the Feynman amplitudes
resulting from the non-abelian kinetic term, we give a prescription on how to
find the expansion. The gauge invariant action is an expanded action,
and the tachyon mass which appears as coefficient of many different
couplings, is arbitrary. We then analyze in details the S-matrix element of
four tachyons and the S-matrix element of two tachyons and two gauge fields, in
both bosonic and superstring theories, in favor of this proposal. In the
superstring theory, the leading terms of the non-abelian gauge invariant
couplings are in agreement with the symmetrised trace of the direct non-abelian
generalization of the tachyonic Born-Infeld action in which the tachyon
potential is consistent with . In the bosonic
theory, on the other hand, the leading terms are those appear in superstring
case as well as some other gauge invariant couplings which spoils the
symmetrised trace prescription. These latter terms are zero in the abelian
case.Comment: Latex, 27 pages, no figures,v4:change the introduction section, add
some notes to clarify the idea, add reference
Abelian and nonabelian vector field effective actions from string field theory
The leading terms in the tree-level effective action for the massless fields
of the bosonic open string are calculated by integrating out all massive fields
in Witten's cubic string field theory. In both the abelian and nonabelian
theories, field redefinitions make it possible to express the effective action
in terms of the conventional field strength. The resulting actions reproduce
the leading terms in the abelian and nonabelian Born-Infeld theories, and
include (covariant) derivative corrections.Comment: 49 pages, 1 eps figur
Fragmentation and Multifragmentation of 10.6A GeV Gold Nuclei
We present the results of a study performed on the interactions of 10.6A GeV
gold nuclei in nuclear emulsions. In a minimum bias sample of 1311 interac-
tions, 5260 helium nuclei and 2622 heavy fragments were observed as Au projec-
tile fragments. The experimental data are analyzed with particular emphasis of
target separation interactions in emulsions and study of criticalexponents.
Multiplicity distributions of the fast-moving projectile fragments are inves-
tigated. Charged fragment moments, conditional moments as well as two and three
-body asymmetries of the fast moving projectile particles are determined in
terms of the total charge remaining bound in the multiply charged projectile
fragments. Some differences in the average yields of helium nuclei and heavier
fragments are observed, which may be attributed to a target effect. However,
two and three-body asymmetries and conditional moments indicate that the
breakup mechanism of the projectile seems to be independent of target mass. We
looked for evidence of critical point observable in finite nuclei by study the
resulting charged fragments distributions. We have obtained the values for the
critical exponents gamma, beta and tau and compare our results with those at
lower energy experiment (1.0A GeV data). The values suggest that a phase
transition like behavior, is observed.Comment: latex, revtex, 28 pages, 12 figures, 3tables, submitted to Europysics
Journal
Biocerâmicas aditivadas com nióbio (V): avaliação da rota hidrotérmica modificada com ácido cítrico e ureia para obtenção de hidroxiapatitas modificadas
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