1,520 research outputs found
Comparison of Stemness and Gene Expression between Gingiva and Dental Follicles in Children
published_or_final_versio
Classification of non-Riemannian doubled-yet-gauged spacetime
Assuming covariant fields as the `fundamental' variables,
Double Field Theory can accommodate novel geometries where a Riemannian metric
cannot be defined, even locally. Here we present a complete classification of
such non-Riemannian spacetimes in terms of two non-negative integers,
, . Upon these backgrounds, strings become
chiral and anti-chiral over and directions respectively, while
particles and strings are frozen over the directions. In
particular, we identify as Riemannian manifolds, as
non-relativistic spacetime, as Gomis-Ooguri non-relativistic string,
as ultra-relativistic Carroll geometry, and as Siegel's
chiral string. Combined with a covariant Kaluza-Klein ansatz which we further
spell, leads to Newton-Cartan gravity. Alternative to the conventional
string compactifications on small manifolds, non-Riemannian spacetime such as
, may open a new scheme of the dimensional reduction from ten to
four.Comment: 1+41 pages; v2) Refs added; v3) Published version; v4) Sign error in
(2.51) correcte
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
Thermophilic anaerobic digestion of model organic wastes: Evaluation of biomethane production and multiple kinetic models analysis
© 2019 Elsevier Ltd The main aim of this work was to test various organic wastes, i.e. from a livestock farm, a cattle slaughterhouse and agricultural waste streams, for its ability to produce methane under thermophilic anaerobic digestion (AD) conditions. The stability of the digestion, potential biomethane production and biomethane production rate for each waste were assessed. The highest methane yield (110.83 mL CH4/g VSadded day) was found in the AD of crushed animal carcasses on day 4. The experimental results were analyzed using four kinetic models and it was observed that the Cone model described the biomethane yield as well as the methane production rate of each substrate. The results from this study showed the good potential of model organic wastes to produce biomethane
Double Field Theory for Double D-branes
We consider Hull's doubled formalism for open strings on D-branes in flat
space and construct the corresponding effective double field theory. We show
that the worldsheet boundary conditions of the doubled formalism describe in a
unified way a T-dual pair of D-branes, which we call double D-branes. We
evaluate the one-loop beta function for the boundary gauge coupling and then
obtain the effective field theory for the double D-branes. The effective field
theory is described by a DBI action of double fields. The T-duality covariant
form of this DBI action is thus a kind of "master" action, which describes all
the double D-brane configurations related by T-duality transformations. We
discuss a number of aspects of this effective theory.Comment: Latex, 1+33 pages. v2 with minor corrections, a new reference added.
v3 a typo correcte
Double Field Theory Formulation of Heterotic Strings
We extend the recently constructed double field theory formulation of the
low-energy theory of the closed bosonic string to the heterotic string. The
action can be written in terms of a generalized metric that is a covariant
tensor under O(D,D+n), where n denotes the number of gauge vectors, and n
additional coordinates are introduced together with a covariant constraint that
locally removes these new coordinates. For the abelian subsector, the action
takes the same structural form as for the bosonic string, but based on the
enlarged generalized metric, thereby featuring a global O(D,D+n) symmetry.
After turning on non-abelian gauge couplings, this global symmetry is broken,
but the action can still be written in a fully O(D,D+n) covariant fashion, in
analogy to similar constructions in gauged supergravities.Comment: 28 pages, v2: minor changes, version published in JHE
Double field theory of type II strings
We use double field theory to give a unified description of the low energy limits of type IIA and type IIB superstrings. The Ramond-Ramond potentials fit into spinor representations of the duality group O(D, D) and field-strengths are obtained by acting with the Dirac operator on the potentials. The action, supplemented by a Spin+ (D, D)-covariant self-duality condition on field strengths, reduces to the IIA and IIB theories in different frames. As usual, the NS-NS gravitational variables are described through the generalized metric. Our work suggests that the fundamental gravitational variable is a hermitian element of the group Spin(D, D) whose natural projection to O(D, D) gives the generalized metric.United States. Dept. of Energy (cooperative research agreement DE-FG02-05ER41360)
Incorporation of fermions into double field theory
Based on the stringy differential geometry we proposed earlier, we
incorporate fermions such as gravitino and dilatino into double field theory in
a manifestly covariant manner with regard to O(D,D) T-duality, diffeomorphism,
one-form gauge symmetry for B-field and a pair of local Lorentz symmetries. We
note that there are two kinds of fermions in double field theory: O(D,D)
singlet and non-singlet which may be identified, respectively as the common and
the non-common fermionic sectors in type IIA and IIB supergravities. For each
kind, we construct corresponding covariant Dirac operators. Further, we derive
a simple criterion for an O(D,D) rotation to flip the chirality of the O(D,D)
non-singlet chiral fermions, which implies the exchange of type IIA and IIB
supergravities.Comment: (v1) 1+21 pages, no figure; (v2) Refs. added, to appear in JHEP; (v3)
minor change, a comment in the last section removed and Eq.(3.22) correcte
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