13,440 research outputs found
Brane world corrections to scalar vacuum force in RSII-p
Vacuum force is an interesting low energy test for brane worlds due to its
dependence on field's modes and its role in submillimeter gravity experiments.
In this work we generalize a previous model example: the scalar field vacuum
force between two parallel plates lying in the brane of a Randall-Sundrum
scenario extended by compact dimensions (RSII-). Upon use of Green's
function technique, for the massless scalar field, the 4D force is obtained
from a zero mode while corrections turn out attractive and depend on the
separation between plates as . For the massive scalar field a
quasilocalized mode yields the 4D force with attractive corrections behaving
like . Corrections are negligible w.r.t. 4D force for
radius less than m. Although the case is not
physically viable due to the different behavior in regard to localization for
the massless scalar and electromagnetic fields it yields an useful comparison
between the dimensional regularization and Green's function techniques as we
describe in the discussion.Comment: 14 pages, v2: discussion clarified, reference adde
Self-Dual Action for Fermionic Fields and Gravitation
This paper studies the self-dual Einstein-Dirac theory. A generalization is
obtained of the Jacobson-Smolin proof of the equivalence between the self-dual
and Palatini purely gravitational actions. Hence one proves equivalence of
self-dual Einstein-Dirac theory to the Einstein-Cartan-Sciama-Kibble-Dirac
theory. The Bianchi symmetry of the curvature, core of the proof, now contains
a non-vanishing torsion. Thus, in the self-dual framework, the extra terms
entering the equations of motion with respect to the standard Einstein-Dirac
field equations, are neatly associated with torsion.Comment: 13 pages, plain-tex, recently appearing in Nuovo Cimento B, volume
109, pages 973-982, September 199
Quantum Gravity Hamiltonian for Manifolds with Boundary
In canonical quantum gravity, when space is a compact manifold with boundary
there is a Hamiltonian given by an integral over the boundary. Here we compute
the action of this `boundary Hamiltonian' on observables corresponding to open
Wilson lines in the new variables formulation of quantum gravity. In cases
where the boundary conditions fix the metric on the boundary (e.g., in the
asymptotically Minkowskian case) one can obtain a finite result, given by a
`shift operator' generating translations of the Wilson line in the direction of
its tangent vector. A similar shift operator serves as the Hamiltonian
constraint in Morales-T\'ecotl and Rovelli's work on quantum gravity coupled to
Weyl spinors. This suggests the appearance of an induced field theory of Weyl
spinors on the boundary, analogous to that considered in Carlip's work on the
statistical mechanics of the 2+1-dimensional black hole.Comment: 17 pages in LaTeX format, vastly improved versio
Casimir force in brane worlds: coinciding results from Green's and Zeta function approaches
Casimir force encodes the structure of the field modes as vacuum fluctuations
and so it is sensitive to the extra dimensions of brane worlds. Now, in flat
spacetimes of arbitrary dimension the two standard approaches to the Casimir
force, Green's function and zeta function, yield the same result, but for brane
world models this was only assumed. In this work we show both approaches yield
the same Casimir force in the case of Universal Extra Dimensions and
Randall-Sundrum scenarios with one and two branes added by p compact
dimensions. Essentially, the details of the mode eigenfunctions that enter the
Casimir force in the Green's function approach get removed due to their
orthogonality relations with a measure involving the right hyper-volume of the
plates and this leaves just the contribution coming from the Zeta function
approach. The present analysis corrects previous results showing a difference
between the two approaches for the single brane Randall-Sundrum; this was due
to an erroneous hyper-volume of the plates introduced by the authors when using
the Green's function. For all the models we discuss here, the resulting Casimir
force can be neatly expressed in terms of two four dimensional Casimir force
contributions: one for the massless mode and the other for a tower of massive
modes associated with the extra dimensions.Comment: 30 pages, title, abstract and discussion have change
Delocalization and the semiclassical description of molecular rotation
We discuss phase-space delocalization for the rigid rotator within a
semiclassical context by recourse to the Husimi distributions of both the
linear and the anisotropic instances. Our treatment is based upon the
concomitant Fisher information measures. The pertinent Wehrl entropy is also
investigated in the linear case.Comment: 6 pages, 3 figure
The Matrix Theory S-Matrix
The technology required for eikonal scattering amplitude calculations in
Matrix theory is developed. Using the entire supersymmetric completion of the
v^4/r^7 Matrix theory potential we compute the graviton-graviton scattering
amplitude and find agreement with eleven dimensional supergravity at tree
level.Comment: 10 pages, RevTeX, no figure
The Role of Mesotocin on Social Bonding in Pinyon Jays
The neuropeptide oxytocin influences mammalian social bonding by facilitating the building and maintenance of parental, sexual, and same‐sex social relationships. However, we do not know whether the function of the avian homologue mesotocin is evolutionarily conserved across birds. While it does influence avian prosocial behavior, mesotocin\u27s role in avian social bonding remains unclear. Here, we investigated whether mesotocin regulates the formation and maintenance of same‐sex social bonding in pinyon jays (Gymnorhinus cyanocephalus), a member of the crow family. We formed squads of four individually housed birds. In the first, “pair‐formation” phase of the experiment, we repeatedly placed pairs of birds from within the squad together in a cage for short periods of time. Prior to entering the cage, we intranasally administered one of three hormone solutions to both members of the pair: mesotocin, oxytocin antagonist, or saline. Pairs received repeated sessions with administration of the same hormone. In the second, “pair‐maintenance” phase of the experiment, all four members of the squad were placed together in a large cage, and no hormones were administered. For both phases, we measured the physical proximity between pairs as our proxy for social bonding. We found that, compared with saline, administering mesotocin or oxytocin antagonist did not result in different proximities in either the pair‐formation or pair‐maintenance phase of the experiment. Therefore, at the dosages and time frames used here, exogenously introduced mesotocin did not influence same‐sex social bond formation or maintenance. Like oxytocin in mammals, mesotocin regulates avian prosocial behavior; however, unlike oxytocin, we do not have evidence that mesotocin regulates social bonds in birds
Entropy Function for Non-Extremal Black Holes in String Theory
We generalize the entropy function formalism to five-dimensional and
four-dimensional non-extremal black holes in string theory. In the near horizon
limit, these black holes have BTZ metric as part of the spacetime geometry. It
is shown that the entropy function formalism also works very well for these
non-extremal black holes and it can reproduce the Bekenstein-Hawking entropy of
these black holes in ten dimensions and lower dimensions.Comment: 19 pages, no figure, JHEP3 style, to appear in JHE
Degenerate Configurations, Singularities and the Non-Abelian Nature of Loop Quantum Gravity
Degenerate geometrical configurations in quantum gravity are important to
understand if the fate of classical singularities is to be revealed. However,
not all degenerate configurations arise on an equal footing, and one must take
into account dynamical aspects when interpreting results: While there are many
degenerate spatial metrics, not all of them are approached along the dynamical
evolution of general relativity or a candidate theory for quantum gravity. For
loop quantum gravity, relevant properties and steps in an analysis are
summarized and evaluated critically with the currently available information,
also elucidating the role of degrees of freedom captured in the sector provided
by loop quantum cosmology. This allows an outlook on how singularity removal
might be analyzed in a general setting and also in the full theory. The general
mechanism of loop quantum cosmology will be shown to be insensitive to recently
observed unbounded behavior of inverse volume in the full theory. Moreover,
significant features of this unboundedness are not a consequence of
inhomogeneities but of non-Abelian effects which can also be included in
homogeneous models.Comment: 28 pages, 1 figure; v2: extended discussion of singularity removal
and summar
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