301 research outputs found
Superselection Sectors in Asymptotic Quantization of Gravity
Using the continuity of the scalar (the mass aspect) at null
infinity through we show that the space of radiative solutions of general
relativity can be thought of a fibered space where the value of at
plays the role of the base space. We also show that the restriction of
the available symplectic form to each ``fiber'' is degenerate. By finding the
orbit manifold of this degenerate direction we obtain the reduced phase space
for the radiation data. This reduced phase space posses a global structure,
i.e., it does not distinguishes between future or past null infinity. Thus, it
can be used as the space of quantum gravitons. Moreover, a Hilbert space can be
constructed on each ``fiber'' if an appropriate definition of scalar product is
provided. Since there is no natural correspondence between the Hilbert spaces
of different foliations they define superselection sectors on the space of
asymptotic quantum states.Comment: 22 pages, revtex fil
Heart Angiotensin-Converting Enzyme and Angiotensin-Converting Enzyme 2 Gene Expression Associated With Male Sex and Salt-Sensitive Hypertension in the Dahl Rat
Angiotensin-converting enzyme 2 (ACE 2) in the heart including its sex dependency in the hypertensive heart, has not been much studied compared to ACE. In the present study, we used the Dahl salt-sensitive rat exposed to fructose and salt to model a hypertensive phenotype in males, females, and ovariectomized females. Blood pressure was measured by the tale-cuff technique in the conscious state. Expression of RAS-related genes ACE, ACE2, angiotensin II receptor type 1, Mas1, and CMA1 in the heart were quantified. The results revealed small but significant differences between male and female groups. The main results indicate the presence of a male preponderance for an increase in ACE and ACE2 gene expression. The results are in accordance with the role of androgens or male chromosomal complement in controlling the expression of the two ACE genes
Positive Mass Theorem for Black Holes in Einstein-Maxwell Axion-dilaton Gravity
We presented the proof of the positive mass theorem for black holes in
Einstein-Maxwell axion-dilaton gravity being the low-energy limit of the
heterotic string theory. We show that the total mass of a spacetime containing
a black hole is greater or equal to the square root of the sum of squares of
the adequate dilaton-electric and dilaton-axion charges.Comment: latex file, to appear in Classical Quantum Gravit
On certain quasi-local spin-angular momentum expressions for small spheres
The Ludvigsen-Vickers and two recently suggested quasi-local spin-angular
momentum expressions, based on holomorphic and anti-holomorphic spinor fields,
are calculated for small spheres of radius about a point . It is shown
that, apart from the sign in the case of anti-holomorphic spinors in
non-vacuum, the leading terms of all these expressions coincide. In non-vacuum
spacetimes this common leading term is of order , and it is the product of
the contraction of the energy-momentum tensor and an average of the approximate
boost-rotation Killing vector that vanishes at and of the 3-volume of the
ball of radius . In vacuum spacetimes the leading term is of order ,
and the factor of proportionality is the contraction of the Bel-Robinson tensor
and an other average of the same approximate boost-rotation Killing vector.Comment: 16 pages, Plain Te
Quasi-Local Gravitational Energy
A dynamically preferred quasi-local definition of gravitational energy is
given in terms of the Hamiltonian of a `2+2' formulation of general relativity.
The energy is well-defined for any compact orientable spatial 2-surface, and
depends on the fundamental forms only. The energy is zero for any surface in
flat spacetime, and reduces to the Hawking mass in the absence of shear and
twist. For asymptotically flat spacetimes, the energy tends to the Bondi mass
at null infinity and the \ADM mass at spatial infinity, taking the limit along
a foliation parametrised by area radius. The energy is calculated for the
Schwarzschild, Reissner-Nordstr\"om and Robertson-Walker solutions, and for
plane waves and colliding plane waves. Energy inequalities are discussed, and
for static black holes the irreducible mass is obtained on the horizon.
Criteria for an adequate definition of quasi-local energy are discussed.Comment: 16 page
On the Penrose Inequality for general horizons
For asymptotically flat initial data of Einstein's equations satisfying an
energy condition, we show that the Penrose inequality holds between the ADM
mass and the area of an outermost apparent horizon, if the data are restricted
suitably. We prove this by generalizing Geroch's proof of monotonicity of the
Hawking mass under a smooth inverse mean curvature flow, for data with
non-negative Ricci scalar. Unlike Geroch we need not confine ourselves to
minimal surfaces as horizons. Modulo smoothness issues we also show that our
restrictions on the data can locally be fulfilled by a suitable choice of the
initial surface in a given spacetime.Comment: 4 pages, revtex, no figures. Some comments added. No essential
changes. To be published in Phys. Rev. Let
Two dimensional Sen connections in general relativity
The two dimensional version of the Sen connection for spinors and tensors on
spacelike 2-surfaces is constructed. A complex metric on the spin
spaces is found which characterizes both the algebraic and extrinsic
geometrical properties of the 2-surface . The curvature of the two
dimensional Sen operator is the pull back to of the
anti-self-dual part of the spacetime curvature while its `torsion' is a boost
gauge invariant expression of the extrinsic curvatures of . The difference
of the 2 dimensional Sen and the induced spin connections is the anti-self-dual
part of the `torsion'. The irreducible parts of are shown to be the
familiar 2-surface twistor and the Weyl--Sen--Witten operators. Two Sen--Witten
type identities are derived, the first is an identity between the 2 dimensional
twistor and the Weyl--Sen--Witten operators and the integrand of Penrose's
charge integral, while the second contains the `torsion' as well. For spinor
fields satisfying the 2-surface twistor equation the first reduces to Tod's
formula for the kinematical twistor.Comment: 14 pages, Plain Tex, no report numbe
A Mass Bound for Spherically Symmetric Black Hole Spacetimes
Requiring that the matter fields are subject to the dominant energy
condition, we establish the lower bound for the
total mass of a static, spherically symmetric black hole spacetime. ( and denote the area and the surface gravity of the horizon,
respectively.) Together with the fact that the Komar integral provides a simple
relation between and the strong energy condition,
this enables us to prove that the Schwarzschild metric represents the only
static, spherically symmetric black hole solution of a selfgravitating matter
model satisfying the dominant, but violating the strong energy condition for
the timelike Killing field at every point, that is, .
Applying this result to scalar fields, we recover the fact that the only black
hole configuration of the spherically symmetric Einstein-Higgs model with
arbitrary non-negative potential is the Schwarzschild spacetime with constant
Higgs field. In the presence of electromagnetic fields, we also derive a
stronger bound for the total mass, involving the electromagnetic potentials and
charges. Again, this estimate provides a simple tool to prove a ``no-hair''
theorem for matter fields violating the strong energy condition.Comment: 16 pages, LATEX, no figure
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