2,490 research outputs found
Fixing the Solar Neutrino Parameters with Sterile Neutrinos
Neutrino mixing matrix appears to be close to bimaximal mixing, but for the
solar mixing angle which is definitively smaller than forty five degrees.
Whereas it seems quite easy to understand bimaximal mixing with the use of new
global symmetries, as in models using , understanding the
about to eleven degrees of deviation in the observed solar angle seems less
simple. We suggest that such a deviation could be due to a light sterile
neutrino that mixes with the active sector. The mass scale needed to produce
the effect has to be smaller than atmospheric scale, and it would introduce a
new mass squared difference which should be smaller than the solar scale. We
present a toy model that exemplifies these features.Comment: 19 pages, two figures. Discussion extended. References adde
FRW Universe in Ho\~rava Gravity
Recently, a field theoretic model for a UV complete theory of gravity has
been proposed by Ho\~{r}ava. This theory is a non-relativistic renormalizable
gravity theory which coincides with Einstein's general relativity at large
distances. Subsequently L\"{u} et al have formulated the modified Friedmann
equations and have presented a solution in vacuum. In the present work, we
rewrite the modified FRW equations in the form of usual FRW equations in
Einstein gravity and consequences has been analyzed. Also the thermodynamics of
the FRW universe has been studied
Scalar and tensorial topological matter coupled to (2+1)-dimensional gravity:A.Classical theory and global charges
We consider the coupling of scalar topological matter to (2+1)-dimensional
gravity. The matter fields consist of a 0-form scalar field and a 2-form tensor
field. We carry out a canonical analysis of the classical theory, investigating
its sectors and solutions. We show that the model admits both BTZ-like
black-hole solutions and homogeneous/inhomogeneous FRW cosmological
solutions.We also investigate the global charges associated with the model and
show that the algebra of charges is the extension of the Kac-Moody algebra for
the field-rigid gauge charges, and the Virasoro algebrafor the diffeomorphism
charges. Finally, we show that the model can be written as a generalized
Chern-Simons theory, opening the perspective for its formulation as a
generalized higher gauge theory.Comment: 40 page
A Review of the "Digital Turn" in the New Literacy Studies
Digital communication has transformed literacy practices and assumed great importance in the functioning of workplace, recreational, and community contexts. This article reviews a decade of empirical work of the New Literacy Studies, identifying the shift toward research of digital literacy applications. The article engages with the central theoretical, methodological, and pragmatic challenges in the tradition of New Literacy Studies, while highlighting the distinctive trends in the digital strand. It identifies common patterns across new literacy practices through cross-comparisons of ethnographic research in digital media environments. It examines ways in which this research is taking into account power and pedagogy in normative contexts of literacy learning using the new media. Recommendations are given to strengthen the links between New Literacy Studies research and literacy curriculum, assessment, and accountability in the 21st century
Bogomolnyi Bound with a Cosmological Constant
Bogomolnyi-type bound is constructed for the topological solitons in O(3)
nonlinear model coupled to gravity with a negative cosmological
constant. Spacetimes made by self-dual solutions form a class of G\"{o}del-type
universe. In the limit of a spinless massive point particle, the obtained
stationary metric does not violate the causality and it is a new point particle
solution different from the known static hyperboloid and black hole. We also
showed that static Nielsen-Olesen vortices saturate Bogomolnyi-type bound only
when the cosmological constant vanishes.Comment: 11 pages, RevTe
Exploring the vicinity of the Bogomol'nyi-Prasad-Sommerfield bound
We investigate systems of real scalar fields in bidimensional spacetime,
dealing with potentials that are small modifications of potentials that admit
supersymmetric extensions. The modifications are controlled by a real
parameter, which allows implementing a perturbation procedure when such
parameter is small. The approach allows obtaining the energy and topological
charge in closed forms, up to first order in the parameter. We illustrate the
procedure with some examples. In particular, we show how to remove the
degeneracy in energy for the one-field and the two-field solutions that appear
in a model of two real scalar fields.Comment: Revtex, 9 pages, To be published in J. Phys.
G-Structures, Fluxes and Calibrations in M-Theory
We study the most general supersymmetric warped M-theory backgrounds with
non-trivial G-flux of the type R^{1,2} x M_8 and AdS_3 x M_8. We give a set of
necessary and sufficient conditions for preservation of supersymmetry which are
phrased in terms of G-structures and their intrinsic torsion. These equations
may be interpreted as calibration conditions for a static ``dyonic'' M-brane,
that is, an M5-brane with self-dual three-form turned on. When the electric
flux is turned off we obtain the supersymmetry conditions and non-linear PDEs
describing M5-branes wrapped on associative and special Lagrangian three-cycles
in manifolds with G_2 and SU(3) structures, respectively. As an illustration of
our formalism, we recover the 1/2-BPS dyonic M-brane, and also construct some
new examples.Comment: 40 pages; v2: one reference added, typos correcte
Extensions, expansions, Lie algebra cohomology and enlarged superspaces
After briefly reviewing the methods that allow us to derive consistently new
Lie (super)algebras from given ones, we consider enlarged superspaces and
superalgebras, their relevance and some possible applications.Comment: 9 pages. Invited talk delivered at the EU RTN Workshop, Copenhagen,
Sep. 15-19 and at the Argonne Workshop on Branes and Generalized Dynamics,
Oct. 20-24, 2003. Only change: wrong number of a reference correcte
Making sense of the bizarre behaviour of horizons in the McVittie spacetime
The bizarre behaviour of the apparent (black hole and cosmological) horizons
of the McVittie spacetime is discussed using, as an analogy, the
Schwarzschild-de Sitter-Kottler spacetime (which is a special case of McVittie
anyway). For a dust-dominated "background" universe, a black hole cannot exist
at early times because its (apparent) horizon would be larger than the
cosmological(apparent) horizon. A phantom-dominated "background" universe
causes this situation, and the horizon behaviour, to be time-reversed.Comment: 8 pages, 3 figure
Supersymmetric black holes in 2D dilaton supergravity: baldness and extremality
We present a systematic discussion of supersymmetric solutions of 2D dilaton
supergravity. In particular those solutions which retain at least half of the
supersymmetries are ground states with respect to the bosonic Casimir function
(essentially the ADM mass). Nevertheless, by tuning the prepotential
appropriately, black hole solutions may emerge with an arbitrary number of
Killing horizons. The absence of dilatino and gravitino hair is proven.
Moreover, the impossibility of supersymmetric dS ground states and of
nonextremal black holes is confirmed, even in the presence of a dilaton. In
these derivations the knowledge of the general analytic solution of 2D dilaton
supergravity plays an important role. The latter result is addressed in the
more general context of gPSMs which have no supergravity interpretation.
Finally it is demonstrated that the inclusion of non-minimally coupled
matter, a step which is already nontrivial by itself, does not change these
features in an essential way.Comment: 30 pages, LaTeX, v2: mayor revision (rearranged title, shortened
abstract, revised introduction, inserted section from appendix to main text,
added subsection with new material on non-SUGRA gPSMs, added clarifying
remarks at some places, updated references); v3: corrected minor misprints,
added note with a new referenc
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